%

% torque (viscometer): The torque a rotational viscometer measures, as a percentage of its maximum. Readings near the bottom of the range have large relative errors, so methods set a minimum torque.

2

2θ (two-theta): The angle between the incident and diffracted X-ray beams; the x-axis of an XRPD pattern, in degrees.

A

Absorbance (A): A measure of how much light a sample absorbs: A = log₁₀ (I₀ / I). It has no units and is proportional to concentration within the linear range.
Accelerated stability study: A stability study at raised temperature and humidity (typically 40 °C/75% RH for 6 months) designed to speed up chemical and physical change and help predict shelf life.
Acceptance value (AV): The statistic used in the uniformity of dosage units test: AV = |M − X̄| + k·s. At stage 1 (10 units, k = 2.4) it must not exceed L1 = 15.0.
Accuracy: How close a result is to the true or accepted value. In method validation it is usually shown by recovering known amounts of analyte spiked into placebo or sample.
Air-displacement pipette: A piston pipette in which an air cushion separates the piston from the liquid. Suited to aqueous liquids; affected by viscosity, volatility and temperature.
ALCOA+: The principles of good data: attributable, legible, contemporaneous, original and accurate, plus complete, consistent, enduring and available.
Alert and action limits: Levels for monitoring results. An alert limit gives early warning of a possible drift and prompts closer review; an action limit, when exceeded, requires investigation and corrective action.
Amorphous halo: The broad hump seen in an XRPD pattern from material without long-range order. Its presence indicates amorphous content.
Analytical method transfer: The documented process that shows a receiving laboratory can run a validated method and get results equivalent to the transferring laboratory.
Analytical target profile: A statement, introduced in ICH Q14, of what an analytical procedure must measure and the performance it must achieve, used to guide development and later changes.
Anolyte and catholyte: The reagent solutions in the anode and cathode compartments of a coulometric KF cell. The anolyte contains iodide and receives the sample; both have a limited water capacity.
Apparent viscosity: The viscosity of a non-Newtonian sample measured under one set of conditions (spindle, speed, temperature and time). It is only comparable with results taken under the same conditions.
Assignable cause: A specific, documented and scientifically supported reason why a result is wrong. Only an assignable cause can justify invalidating an OOS result.
Assigned potency: The purity or content value given to a reference or working standard, on a stated basis (as is, dried or anhydrous), that analysts use in assay calculations.
ATR (attenuated total reflectance): An IR sampling technique in which the sample is pressed against a crystal and probed by an evanescent wave a few micrometres deep. Needs little or no sample preparation.
Audit trail: A secure, computer-generated, time-stamped record of who created, changed or deleted electronic data, when, and why. It must not be editable or able to be switched off by ordinary users.
Automatic temperature compensation (ATC): A meter function that uses a temperature sensor to correct the reading for temperature: the electrode slope for pH, or a reference-temperature conversion for conductivity.
Average weight: The total weight of a set of tablets or capsules (usually 20) divided by their number. Used in assay calculations and weight variation tests.

B

Background spectrum: A spectrum recorded without the sample (empty beam or clean ATR crystal) and ratioed against the sample spectrum to remove atmospheric and instrument contributions.
Bacterial endotoxin: Lipopolysaccharide from the outer membrane of Gram-negative bacteria. Even after the bacteria are killed it can cause fever and shock if injected, so parenteral products are tested for it.
Band application: In HPTLC, applying the sample as a narrow band by spraying, rather than as a spot. It gives sharper zones and better resolution and quantitation.
Beer–Lambert law: Absorbance equals molar absorptivity × path length × concentration (A = εbc). The basis of quantitative UV-Vis analysis.
Bile-tolerant Gram-negative bacteria: Gram-negative bacteria that grow in the presence of bile salts, mainly Enterobacteriaceae. They are tested as an indicator of hygiene in non-sterile products.
Biological indicator (BI): A carrier holding a known number of highly resistant spores, such as Geobacillus stearothermophilus for steam, used to show that a sterilisation cycle kills them.
Biosafety cabinet classes (I, II, III): Groups of microbiological safety cabinets by the protection they give. Class I protects the operator and room; Class II protects operator, product and room; Class III is a sealed glove box for the highest-risk work.
Birefringence: The splitting of polarised light by crystalline material. Under crossed polarisers birefringent crystals appear bright against a dark background, which is used to show crystallinity.
Bivoltametric indication: Endpoint detection using a constant small current between two platinum electrodes. The voltage drops sharply when excess iodine appears, marking the KF endpoint.
Blank titration: A titration carried out without the sample, using the same solvent and reagents. The blank volume is subtracted from the sample titration volume.
Bowie-Dick test: A daily test for pre-vacuum steam sterilisers using a standard pack with an indicator sheet that changes colour uniformly only if air removal and steam penetration are complete.
Bracketing and matrixing: Reduced stability designs from ICH Q1D. Bracketing tests only the extremes (such as highest and lowest strength); matrixing tests a subset of samples at each time point.
Bragg's law: nλ = 2d sin θ: X-rays reflected by lattice planes of spacing d reinforce each other only at angles θ that satisfy this equation.
Breaking force (tablet hardness): The force, normally in newtons, needed to break a tablet by diametral compression between two platens. 1 kP ≈ 9.81 N.
Brimful capacity: The volume a container holds when filled to the brim. Glass container tests fill to a fixed percentage of it, for example 90%.
Bulk density: Mass of a powder divided by its untapped volume, including the air spaces between particles. Expressed in g/mL.
Buoyancy effect (TGA): The apparent mass gain of a TGA pan as the surrounding gas warms and becomes less dense. It is corrected by subtracting a blank run.

C

Calibration: Comparing an instrument's readings with a traceable standard to establish and document its accuracy.
Capillary column: A long, narrow fused-silica GC column (typically 15–60 m × 0.25–0.53 mm) with the stationary phase coated as a thin film on its inner wall.
Carr's index: 100 × (V0 − Vf) ÷ V0, where V0 is the untapped and Vf the tapped volume. A flow indicator: values up to about 10% mean excellent flow and above about 25% poor flow.
Carrier gas: The inert gas (helium, nitrogen or hydrogen) that carries vaporised sample through a GC column. It is the mobile phase in gas chromatography.
Cavitation: The formation and violent collapse of tiny bubbles in a liquid exposed to ultrasound. It provides the cleaning, dispersing and dissolving action of an ultrasonic bath.
Cell constant (DSC): The factor that converts the measured DSC signal into true heat flow, set by melting a standard of known enthalpy such as indium.
Cell constant (K): The ratio of the distance between the electrodes of a conductivity cell to their area, in cm⁻¹. Conductivity = cell constant × measured conductance.
Chamber saturation: Filling a closed TLC tank with mobile-phase vapour, usually with a filter-paper lining, before placing the plate in it, to give even development and reproducible Rf values.
Characteristic concentration: In AAS, the concentration of an element that gives an absorbance of 0.0044 (1% absorption). Used to check instrument sensitivity against the manufacturer's value.
Chemical indicator: A strip, tape or sheet that changes colour on exposure to sterilisation conditions. It shows that an item was processed but does not prove sterility.
Chemical shift (δ): The position of an NMR signal relative to a reference such as TMS, in parts per million. It reflects the electronic environment of the nucleus.
Chemometrics: The use of mathematical and statistical methods, such as PCA and PLS, to extract chemical information from complex data like NIR spectra.
Chromophore: The part of a molecule, such as an aromatic ring or a conjugated double-bond system, that absorbs UV or visible light.
Clark electrode: An electrochemical oxygen sensor in which oxygen diffuses through a membrane and is reduced at a cathode, producing a current proportional to its partial pressure.
Class A glassware: Volumetric glassware made to the tightest tolerance class. Class B tolerances are about twice as wide.
Cleanroom grades (A, B, C, D): The four levels of cleanliness defined in EU GMP Annex 1, from Grade A (critical aseptic zone) to Grade D (least critical), each with particle and microbial limits.
Clear point: The temperature at which a sample in a capillary becomes completely liquid. It marks the end of the melting range.
Climatic zones: Regions grouped by climate (I temperate to IVb hot and very humid). The zone of the intended market decides the long-term stability storage condition.
Closed-vessel microwave digestion: Dissolving a sample in acids inside sealed vessels heated by microwaves. High temperature and pressure destroy the matrix quickly without losing volatile elements.
Coincidence limit: The particle concentration above which two or more particles may cross a counter's sensor together and be counted as one larger particle.
Cold chain: The unbroken series of controlled-temperature storage and transport steps that keeps temperature-sensitive products within their labelled range from manufacture to use.
Cold spot: The location in a steriliser chamber or load that heats most slowly. Cycles are validated so that the cold spot receives the required lethality.
Collision/reaction cell: A gas-filled cell before the ICP-MS mass analyser. Helium collisions (kinetic energy discrimination) or reactive gases remove polyatomic interferences.
Colony-forming unit (cfu): A viable microorganism, or cluster of organisms, that grows into one visible colony on agar. Microbial counts are reported as cfu per gram, mL, plate or m³.
Conductivity (κ): The ability of a solution to conduct electric current, caused by dissolved ions. Reported in µS/cm and strongly dependent on temperature.
Coning: A cone of undissolved powder that collects under the paddle in the low-flow zone at the bottom of a dissolution vessel, often giving low and variable results.
Constant weight: The state reached when two consecutive weighings, with a further period of drying or ignition between them, differ by no more than the small amount stated in the pharmacopoeia.
Contact plate: A plate with a raised agar surface pressed onto a flat surface or glove to sample surface microorganisms, usually about 25 cm².
Container closure integrity (CCI): The ability of a container and its closure to keep the product in and contaminants (microbes, gases, moisture) out throughout its shelf life.
Content uniformity: Assay of the drug content of individual dosage units to show that each contains close to the labelled amount.
Control standard endotoxin (CSE): An endotoxin preparation calibrated against the reference standard endotoxin (RSE) for a given lysate lot, used to make standard curves and spikes.
Control threshold (ICH Q3D): 30% of the PDE of an element in the drug product. If levels are consistently below it, additional controls are generally not needed; above it, controls are put in place.
Corrective and preventive action (CAPA): Actions that remove the root cause of a problem (corrective) and reduce the chance of similar problems happening elsewhere (preventive), with a later check that they worked.
Coulometric titration: A titration in which the titrant (for example iodine) is generated electrically inside the cell. The amount of analyte is calculated from the electric charge passed.
Counting efficiency (particle counter): The fraction of particles of a given size that a particle counter detects compared with a reference instrument. ISO 21501-4 sets typical expectations at and above the minimum detectable size.
Critical angle: The angle of incidence above which light is totally reflected at the boundary between a dense medium (the refractometer prism) and the sample. It depends on the sample's refractive index.
Crucible: A heat-resistant cup of porcelain, silica or platinum used to hold samples during ignition.
Curie point: The temperature at which a ferromagnetic material loses its magnetism. Certified Curie point standards are used to calibrate TGA temperature.
Cuvette: A small transparent container of fixed path length (usually 10 mm) that holds the solution in a spectrophotometer. Quartz is required below about 320 nm.

D

D-value: The time at a stated temperature needed to reduce a microbial population by 90% (one log). Used to describe the heat resistance of biological indicator spores.
D10, D50, D90: Percentile sizes from a cumulative particle size distribution: 10%, 50% and 90% of the sample volume lies below each size. D50 is the volume median diameter.
d50 cut-off: The particle size that an air sampler collects with 50% efficiency. A lower d50 means smaller particles are captured.
Data integrity: The extent to which data are complete, consistent and accurate throughout their life cycle, from generation and processing to review, archiving and destruction.
Deaeration: Removal of dissolved air from a dissolution medium, for example by warming, vacuum filtration and stirring under vacuum, so bubbles do not form on the dosage unit or apparatus during the test.
Degrees Brix (°Brix): A refractive-index scale for sucrose solutions. 1 °Brix is about 1 g of sucrose in 100 g of solution.
Densitometry (TLC / HPTLC): Measuring the absorbance or fluorescence of each zone on a developed plate by scanning it with a light beam, giving a chromatogram for each track.
Depyrogenation: Removal or destruction of endotoxin, usually by dry heat (e.g. 250 °C for at least 30 minutes, or a validated cycle). Validation typically shows at least a 3-log reduction of endotoxin.
Deterministic leak test: A leak test that measures a physical quantity with an objective, predictable result, such as vacuum decay, pressure decay or laser headspace analysis. Preferred by USP <1207>.
Deuterated solvent: A solvent in which hydrogen is replaced by deuterium. It gives no large ¹H signal and provides the lock signal for NMR.
Dextrorotatory (+): Turning plane-polarised light clockwise, seen by an observer looking towards the light source. Given a plus sign.
Diffuse reflectance: Light that enters a powder, is scattered and partly absorbed, and comes back out. NIR measures it as log(1/R), which behaves like absorbance.
Direct inoculation: A sterility test technique in which the product is added straight into the culture media, used when the product cannot be filtered.
Disintegration: The break-up of a tablet or capsule into particles in a liquid under standard agitation. Complete disintegration leaves no firm core on the mesh, only a soft mass or insoluble coating or shell fragments.
Dispersity (Mw/Mn): Weight-average molecular weight divided by number-average molecular weight. It describes how broad a polymer's molecular-weight distribution is; 1.0 means all molecules are the same size.
Dissolution: The process by which drug leaves a dosage form and goes into solution. The dissolution test measures the % of label claim dissolved in a stated medium and time under standardised conditions.
Dissolution profile: % dissolved measured at several time points. Profiles of two products or batches are often compared with the f2 similarity factor, where a value of 50–100 is usually taken as similar.
Dissolution stages (S1, S2, S3): Staged acceptance for dissolution: S1 tests 6 units (each ≥ Q + 5%), S2 adds 6 (mean of 12 ≥ Q, none < Q − 15%), S3 adds 12 (mean of 24 ≥ Q, not more than 2 < Q − 15%, none < Q − 25%).
Dissolved oxygen (DO): Oxygen gas dissolved in a liquid, reported in mg/L or as % of air saturation. It depends on temperature, pressure and salinity.
DOP / PAO test: A HEPA filter integrity test that introduces an oil aerosol upstream and scans the downstream face with a photometer for leaks.
Downflow velocity: The speed of HEPA-filtered air moving down over the work surface of a biosafety cabinet, typically 0.25–0.50 m/s. It protects the work from contamination.
Drift (Karl Fischer): The rate at which background moisture enters a conditioned KF cell, in µg/min. It is checked before analysis and subtracted from results as drift × titration time.
DTG curve: The first derivative of a TGA mass curve. Its peaks mark the temperatures of fastest mass loss.
Dwell volume: The volume between the point where gradient solvents are mixed and the column inlet. It delays the gradient reaching the column and differs between instruments, so it matters when transferring gradient methods.
Dye ingress test: A probabilistic leak test in which packs are immersed in a coloured solution under vacuum; after pressure is restored, dye found inside a pack shows a leak.
Dynamic viscosity (η): A liquid's resistance to flow: shear stress divided by shear rate. Measured in Pa·s; in practice mPa·s, where 1 mPa·s = 1 centipoise (cP).

E

Eccentricity: The change in a balance reading when the same load is placed away from the centre of the pan.
Electrode offset: The voltage a pH electrode gives in pH 7 buffer. Ideally 0 mV; typically accepted within about ±30 mV.
Electrode slope: The change in electrode voltage per pH unit, often shown as a percentage of the theoretical Nernst value (59.16 mV/pH at 25 °C). Typically 95–105% for a healthy electrode.
Electrode slope (Nernst slope): The change in electrode potential per unit change in pH. The theoretical value is about 59.16 mV/pH at 25 °C; the measured slope is reported as a percentage of it.
Electrodeionisation (EDI): A water purification process that combines ion-exchange resins and membranes with an electric field, so the resins are regenerated continuously without chemicals.
Electron ionisation (EI): The standard GC-MS ionisation method: molecules are bombarded with 70 eV electrons, forming a molecular ion and reproducible fragments that can be searched against spectral libraries.
Electronic signature: A computer-based signature, unique to one person, that is linked to an electronic record and shows the signer's name, date and time, and the meaning of the signature.
Electrospray ionisation (ESI): A soft ionisation method for LC-MS. The column effluent is sprayed through a charged needle; as droplets evaporate, ions such as [M+H]⁺ or [M−H]⁻ are released into the gas phase.
Electrostatic weighing error: Drift or wrong readings on a sensitive balance caused by electric charge on the sample or container, which is attracted to or repelled by the balance housing. Removed with an ioniser or anti-static container.
Elemental impurities: Trace elements in drug products that give no therapeutic benefit, coming from catalysts, equipment, excipients, water or packaging. Controlled by risk assessment against PDEs under ICH Q3D and USP <232>.
Endothermic and exothermic: An endothermic event absorbs heat (for example melting); an exothermic event releases heat (for example crystallisation or decomposition).
Endotoxin limit: The maximum endotoxin allowed in a product, calculated as K ÷ M, where K is the threshold pyrogenic dose (5 EU/kg for most parenteral routes) and M is the maximum dose per kg per hour.
Endotoxin unit (EU): The unit of endotoxin activity, defined against the reference standard endotoxin. Results and limits are given in EU/mL, EU/mg or EU per device.
Endpoint (titration): The point in a titration at which the indicator or electrode signals that the reaction is complete. Ideally it coincides with the equivalence point.
Enteric coating: A coating that resists stomach acid and dissolves in the higher pH of the small intestine. Enteric products are tested first in acid and then in buffer.
Enthalpy of fusion (ΔHf): The heat absorbed per gram when a solid melts, measured from the area of the DSC melting peak, in J/g.
Equivalence point: The point at which the amount of titrant added is chemically equivalent to the amount of analyte. In potentiometric titration it is the inflection point of the curve.
Equivalent spherical diameter: The diameter of a sphere that would give the same measured response (scattering, light blocking or volume) as the real, irregular particle.
Exclusion limit: The molecular size above which molecules cannot enter the pores of an SEC packing; they all elute together at the void (interstitial) volume.
Extra-column volume: All the volume in the flow path outside the column (injector, tubing, fittings, detector cell). It broadens peaks and is especially important in UHPLC.

F

F0 value: The lethality of a moist heat cycle expressed as equivalent minutes at 121.1 °C, calculated with a z-value of 10 °C. Used to compare cycles and load positions.
Face velocity: The speed of air entering the front opening of a fume hood, typically around 0.4–0.6 m/s depending on the site standard.
Factor of a volumetric solution: The ratio of the actual concentration of a volumetric solution to its nominal concentration, for example 0.10043 M ÷ 0.1 M = 1.0043.
Faraday's law of electrolysis: The amount of substance produced at an electrode is proportional to the charge passed. One mole of electrons carries about 96 485 coulombs.
Fingerprint region: The part of the mid-IR spectrum below about 1500 cm⁻¹, where complex vibrations give a band pattern characteristic of the whole molecule.
First derivative (dE/dV): The change in electrode potential per unit volume of titrant. Its maximum locates the equivalence point in a potentiometric titration.
Flame ionisation detector (FID): A GC detector that burns the column effluent in a hydrogen–air flame and measures the ion current produced by organic compounds. Robust, sensitive and linear over a wide range.
Fluid Thioglycollate Medium (FTM): A sterility test medium with a reducing agent and a redox indicator that supports anaerobic and aerobic bacteria; incubated at 30–35 °C.
Fluorescence quantum yield (Φ): The fraction of absorbed photons that a molecule re-emits as fluorescence, between 0 and 1.
Fluorescence quenching: Any process that reduces fluorescence intensity, such as collisions with oxygen or halide ions, complex formation, or self-quenching at high concentration.
Forced degradation: Deliberately degrading a drug or product with acid, base, oxidant, heat and light to find likely degradation products and prove that an analytical method is stability-indicating.
Formazin: A polymer suspension made from hydrazine sulphate and hexamethylenetetramine, used as the primary standard for turbidity. The concentrated stock is defined as 4000 NTU.
Freezing point depression: The lowering of a solvent's freezing point by dissolved particles. For water it is about 1.86 °C per osmol/kg and is the basis of freezing-point osmometers.
Friability: The tendency of tablets to chip and abrade during handling, measured as the % weight lost after 100 revolutions in a rotating drum at 25 rpm.

G

Generator electrode (KF): The electrode in a coulometric KF cell where iodine is produced from iodide by electrolysis. It may have a diaphragm separating anolyte and catholyte, or be diaphragm-free.
Glass transition (Tg): The temperature range in which an amorphous solid changes from a hard, glassy state to a softer, rubbery state. It shows as a baseline step on a DSC curve.
Glass types I, II and III: Pharmacopoeial classes of glass containers: Type I borosilicate glass (high hydrolytic resistance), Type II surface-treated soda-lime glass and Type III soda-lime glass (moderate resistance).
Good documentation practice (GDP): The rules for recording GMP information so records are permanent, readable, contemporaneous and complete, for example using indelible ink and single-line corrections with initials, date and reason.
Grade A (cleanroom): The cleanest zone in the EU GMP Annex 1 grading system, used for high-risk aseptic operations. Particles ≥0.5 µm are limited to 3,520 per m³ and no viable microorganisms are expected.
Gradient elution: Elution in which the mobile-phase composition changes during the run, usually increasing in solvent strength.
Growth promotion: A test that shows a batch of culture medium can support growth of a low inoculum (not more than 100 cfu) of specified organisms.

H

Hausner ratio: Untapped volume divided by tapped volume (V0 ÷ Vf), or tapped density divided by bulk density. Values close to 1.0 mean good flow; above about 1.35 mean poor flow.
Headspace (static): A sampling technique where a sealed vial is heated so volatile compounds pass into the gas above the sample, and a portion of that gas is injected into the GC.
HEPA filter: A high-efficiency air filter that removes at least 99.97% of particles at about 0.3 µm (H14 grade: at least 99.995% at the most penetrating particle size). Used in LAF units and clean rooms.
Hit quality index (HQI): A number, usually derived from the correlation between a test spectrum and a library spectrum, that expresses how well they match. Identity passes if it exceeds a validated threshold.
Hollow cathode lamp (HCL): The light source in AAS. Its cathode is made of the analyte element, so it emits that element's sharp resonance lines.
Holmium oxide standard: A solution or glass filter with sharp absorption bands at certified wavelengths, used to check the wavelength accuracy of UV-Vis spectrophotometers.
HPTLC fingerprint: The characteristic pattern of zones (positions, colours and intensities) given by a herbal drug or extract, compared with a reference for identification.
Hydrodynamic volume: The effective volume a molecule occupies in solution, depending on its molecular weight, shape and the solvent. It is what size-exclusion chromatography separates by.
Hydrolytic resistance: The resistance of glass to releasing soluble substances, mainly alkali, into water under defined conditions. Measured by titrating the extract with dilute acid.

I

ICH Q3C solvent classes: Class 1: solvents to be avoided (known or suspected carcinogens or environmental hazards). Class 2: solvents to be limited, with limits based on a permitted daily exposure. Class 3: solvents of low toxic potential, acceptable up to 5000 ppm without justification.
ICH Q3D element classes: ICH Q3D groups elements by toxicity and likelihood of occurrence: Class 1 (As, Cd, Hg, Pb); Class 2A (Co, Ni, V); Class 2B (e.g. Ag, Au, Ir, Os, Pd, Pt, Rh, Ru, Se, Tl) assessed when intentionally added; Class 3 (e.g. Ba, Cr, Cu, Li, Mo, Sb, Sn) of low oral toxicity.
ICH storage conditions: The temperature and humidity conditions for stability studies set out in ICH Q1A(R2): long-term 25 °C/60% RH or 30 °C/65% RH, intermediate 30 °C/65% RH and accelerated 40 °C/75% RH, with typical tolerances of ±2 °C and ±5% RH.
Ignition to constant mass: Repeated ignition, cooling and weighing until two consecutive weighings agree within the limit set in the chapter or SOP.
In vitro release test (IVRT): A test that measures the rate of drug release from a semi-solid product through an inert synthetic membrane, usually in a Franz (vertical diffusion) cell at about 32 °C.
Inductively coupled plasma (ICP): A very hot (about 6000–10,000 K) argon plasma sustained by a radio-frequency field. It atomises, excites and ionises samples for ICP-OES and ICP-MS.
Inflow velocity: The average speed of room air entering the front opening of a biosafety cabinet. It forms the air curtain that protects the operator and is checked at every certification.
Inner-filter effect: Loss of measured fluorescence at high absorbance because the solution absorbs the excitation light, or its own emission, before it is detected. Makes calibration curves bend downwards.
Inorganic carbon (IC): Carbon present as dissolved carbon dioxide, bicarbonate and carbonate. It is removed or subtracted when measuring TOC (TOC = TC − IC).
Instrument qualification (DQ/IQ/OQ/PQ): Documented evidence that an instrument is designed, installed, operates and performs as required for its intended use.
Instrument status label: A label on an instrument showing whether it is in use, calibrated (with due date), under maintenance or out of service, so analysts can see at a glance whether it may be used.
Interferogram: The raw signal recorded by an FTIR: detector response against moving-mirror position. A Fourier transform converts it into a spectrum.
Ion suppression: A reduction (or increase) of analyte signal in LC-MS caused by co-eluting matrix components competing in the ion source. Controlled by sample clean-up, better separation or isotope-labelled internal standards.
Ion-exchange chromatography: Chromatography in which ions in the sample compete with eluent ions for fixed charged sites on a resin. Anion exchangers retain anions; cation exchangers retain cations.
Ionisation buffer: An excess of an easily ionised element (e.g. caesium or potassium) added in flame AAS to stop the analyte from ionising, keeping it as absorbing atoms.
Isobaric interference: In ICP-MS, overlap of isotopes of different elements with the same mass, e.g. ²⁰⁴Hg and ²⁰⁴Pb. Avoided by choosing another isotope or by mathematical correction.
Isocratic elution: Elution with a mobile phase whose composition stays constant throughout the run.
Isokinetic sampling: Taking an air sample at the same velocity as the surrounding air stream, so that large particles are neither over- nor under-collected.
Isolator: A sealed enclosure with glove ports, decontaminated (often with hydrogen peroxide vapour) and supplied with HEPA-filtered air, giving a Grade A environment separated from the operator.
Isotonic: Having about the same osmotic pressure as body fluids, typically around 280–300 mOsm/kg. Hypotonic solutions are lower and hypertonic solutions higher.

J

J value: In USP <233>, the concentration of an element at its target limit after sample preparation and dilution, expressed in the measured solution. Standards and spikes are set relative to J.

K

Karl Fischer reaction: The reaction of water with iodine and sulphur dioxide in the presence of a base and an alcohol, in which one mole of iodine is consumed per mole of water. It is the basis of KF water determination.
KBr disc: A transparent disc made by pressing a small amount of sample ground with dry potassium bromide. A classic transmission technique for IR spectra of solids.
Kinematic viscosity (ν): Dynamic viscosity divided by density, in mm²/s. Measured directly by capillary viscometers.

L

Label claim: The amount of active ingredient stated on the product label, for example 500 mg per tablet.
Laevorotatory (−): Turning plane-polarised light anticlockwise, seen by an observer looking towards the light source. Given a minus sign.
LAL reagent water (LRW): Water with endotoxin below the detection limit of the test, used for dilutions and negative controls in the bacterial endotoxins test.
Light obscuration: A particle counting technique in which each particle crossing a light beam in a narrow sensor blocks part of the light; the size of the signal drop gives the particle's equivalent size.
Limit response (TOC): The response of a 0.50 mg/L carbon sucrose standard minus the response of the reagent water used to make it. A water sample complies if its response is not more than this.
Limit test: A semi-quantitative test showing whether an impurity is above or below a set limit by comparing the sample with a standard, rather than measuring the exact amount.
Limulus amebocyte lysate (LAL): A reagent made from horseshoe crab blood cells that reacts with bacterial endotoxin through an enzyme cascade. It is the basis of the bacterial endotoxins test.
Linearity: The ability of a method to give results directly proportional to analyte concentration within a given range.
Liquid junction: The porous contact through which the reference electrolyte of a pH electrode meets the sample. A blocked junction causes slow, drifting readings.
LOD / LOQ: The lowest amount of analyte that can be detected (LOD) or quantified with acceptable precision and accuracy (LOQ).
Loss on drying (LOD): The percentage loss in mass of a sample after drying under specified conditions. It includes water and any other volatile matter.
Lysate sensitivity (λ): In gel-clot, the lowest endotoxin concentration that forms a firm gel; in kinetic methods, the lowest concentration on the standard curve. Used to calculate the MVD.

M

Mass accuracy (ppm): The difference between measured and theoretical m/z, divided by the theoretical m/z and multiplied by one million. High-resolution instruments typically achieve a few ppm.
Mass balance (stability): In stress or stability studies, adding the remaining assay value and the total degradation products to see whether they account for the initial amount of drug, typically within about 95–105%.
Mass variation: A way of showing uniformity of dosage units by weighing individual units and estimating each one's content from a pooled assay. Allowed only when the pharmacopoeia's dose and ratio conditions are met.
Mass-to-charge ratio (m/z): The quantity a mass spectrometer measures: the mass of an ion divided by its charge number. For singly charged ions it equals the ion mass.
Maximum valid dilution (MVD): The greatest dilution of a sample at which the endotoxin limit can still be detected: MVD = (endotoxin limit × concentration of test solution) ÷ λ.
Mean kinetic temperature (MKT): A single calculated temperature that has the same overall effect on degradation as the fluctuating temperatures actually recorded. It gives more weight to higher temperatures than a simple average.
Mechanical calibration (dissolution): Measurement of the physical set-up of each dissolution position: shaft wobble, shaft and vessel verticality, centring, paddle or basket height, speed and temperature.
Melting point depression: The lowering and broadening of a melting range caused by impurities. It is the basis of using melting range as a purity check.
Melting range: The temperature interval from the start of melting (collapse of the column or first liquid) to the clear point, when the sample is completely liquid.
Meniscus: The curved surface of a liquid in a narrow tube. Clear liquids are read at the bottom of the meniscus with the eye level with the mark to avoid parallax error.
Metadata: Data that describe other data and give them meaning, for example who acquired a result, when, on which instrument, with which method and processing settings.
Method suitability (microbiology): Demonstration that a microbiological test method recovers test organisms in the presence of the product, usually within a factor of 2 of a control.
Method verification: Showing that an already validated pharmacopoeial method works in your laboratory, with your analysts, equipment and sample matrix.
Metrological traceability: An unbroken chain of calibrations linking a measurement to national or international standards.
Mie theory: The full optical theory of light scattering by spheres, which uses the refractive indices of particle and medium. Laser diffraction software uses it to turn a scattering pattern into a size distribution; the simpler Fraunhofer approximation ignores refractive index and suits larger particles.
Minimum weight: The smallest net sample mass that can be weighed on a balance while keeping the weighing error within the required limit (0.10% under USP <41>). Calculated as 2000 × the repeatability standard deviation.
Mixed melting point: The melting range of a 1 : 1 mixture of sample and reference standard. No depression supports identity; a lower, wider range shows the materials differ.
Mobile phase: The liquid (or gas, in GC) that carries the sample through the column.
Molar absorptivity (ε): The absorbance of a 1 mol/L solution in a 1 cm cell at a given wavelength, in L mol⁻¹ cm⁻¹. A constant for a substance under fixed conditions.
Multiple reaction monitoring (MRM): A tandem-MS mode in which the first quadrupole selects a precursor ion, it is fragmented, and the third quadrupole monitors a specific product ion. Very selective and sensitive for quantitation.
Mutarotation: The gradual change in optical rotation of a freshly prepared solution, for example of a sugar, as its forms interconvert until they reach equilibrium.

N

Nephelometry: Measurement of the light scattered by particles in a liquid, usually at 90° to the incident beam.
Nernst equation: Relates electrode potential to ion activity. For a pH electrode the potential changes by 0.19841 × absolute temperature mV per pH unit (59.16 mV at 25 °C).
Nessler cylinder: A flat-bottomed glass tube of standard size used in matched pairs to compare colour or opalescence of a sample and a standard by eye.
Newtonian liquid: A liquid whose viscosity does not change with shear rate, such as water, glycerol or simple syrups. Viscosity standards are Newtonian.
NTU (nephelometric turbidity unit): The unit of turbidity measured by light scattered at 90°, based on formazin standards. FNU is the equivalent unit for 860 nm instruments under ISO 7027.

O

Obscuration (laser diffraction): The percentage of laser light blocked by the sample in a laser diffraction measurement. It must stay within the method range to avoid a weak signal or multiple scattering.
Onset temperature: The temperature where the tangent to the leading edge of a thermal peak or step meets the extrapolated baseline. It is the usual reported transition temperature.
Onset time: In kinetic LAL methods, the time taken for the reaction to reach a set absorbance or turbidity. Higher endotoxin gives a shorter onset time.
Opalescence: A milky or cloudy appearance caused by a fine suspended precipitate, such as silver chloride or barium sulphate in limit tests.
Operator protection factor: The ratio of aerosol released inside a safety cabinet to the amount escaping to the operator's breathing zone, measured with a potassium iodide or microbiological challenge (EN 12469).
Optical (luminescent) DO sensor: An oxygen sensor whose dye luminescence is quenched by oxygen. The change in luminescence lifetime gives the oxygen level; it does not consume oxygen.
Optical rotation (α): The angle, in degrees, through which a solution of a chiral substance turns the plane of polarised light, measured with a polarimeter.
Oscillating U-tube: The measuring cell of a digital density meter: a glass U-tube whose natural period of vibration increases with the density of the sample filling it.
Osmolality: The number of osmoles of dissolved particles per kilogram of water, in mOsm/kg. Measured by an osmometer.
Osmolarity: The number of osmoles of dissolved particles per litre of solution, in mOsm/L. Usually calculated from the formula; close to, but not the same as, osmolality.
Out of calibration: An instrument that has failed calibration or is past its calibration due date and must not be used.
Out of specification (OOS): A test result that falls outside the approved specification limits and must be investigated.
Out of trend (OOT): A result that is within specification but does not follow the pattern expected from earlier results, such as an unusually large change between stability time points.
Overtone and combination bands: Weak absorptions at roughly two or three times (overtones) or at sums (combinations) of fundamental vibration frequencies. They make up the near-infrared spectrum.
Oxide ratio (CeO⁺/Ce⁺): The ratio of cerium oxide ions to cerium ions in an ICP-MS tune. A low value (typically a few percent or less) shows the plasma is forming few oxide interferences.

P

Partial least squares (PLS) regression: A chemometric regression method that relates spectra to reference values, such as Karl Fischer water content, so the property can be predicted from new spectra.
Partition coefficient (K): The ratio of an analyte's concentration in one phase to its concentration in another at equilibrium. In headspace, K = concentration in liquid ÷ concentration in gas; a low K gives a larger peak.
Peak purity: A check, usually with a photodiode-array detector, that the spectrum is the same across a peak, suggesting no other compound is co-eluting. Mass spectrometry gives a more definitive check.
Performance verification test (PVT): A dissolution test run with pharmacopoeial reference tablets and compared with lot-specific acceptance ranges, to check the whole dissolution system performs as expected.
Permitted daily exposure (PDE): The maximum acceptable intake per day of a residual solvent or impurity. ICH Q3C converts the PDE into a ppm limit assuming a 10 g daily dose (Option 1).
PFTBA (perfluorotributylamine): A volatile reference compound used to tune and mass-calibrate GC-MS instruments. Its main EI ions are at m/z 69, 219 and 502.
pH: Minus the logarithm (base 10) of the hydrogen-ion activity of a solution. pH 7 is neutral at 25 °C; each unit is a tenfold change in acidity.
pH buffer: A solution that resists change in pH and has a certified pH value at a stated temperature, used to calibrate and check pH meters.
Phase ratio (β): In a headspace vial, the volume of gas divided by the volume of liquid. In a GC column, the gas volume divided by the stationary-phase volume.
Platinum resistance thermometer (PRT): A temperature sensor whose platinum element's resistance rises with temperature; a Pt100 has 100 Ω at 0 °C. Stable and accurate, so often used as a reference.
Polarisability: How easily the electron cloud of a molecule is distorted by an electric field. A vibration that changes polarisability is Raman-active.
Polyatomic interference: In ICP-MS, an ion formed from argon, acids or the matrix that has the same nominal mass as the analyte, e.g. ⁴⁰Ar³⁵Cl⁺ at m/z 75 (arsenic).
Polymorph screen: A study that crystallises an API under many conditions and analyses the solids (mainly by XRPD) to find all accessible polymorphs, solvates and hydrates.
Polymorphism: The ability of a substance to exist in more than one crystal arrangement. Polymorphs share a chemical formula but can differ in solubility, stability and bioavailability.
Polystyrene reference film: A thin certified polystyrene film whose IR bands at known wavenumbers are used to check the wavenumber accuracy and resolution of IR spectrometers.
Positive product control (PPC): A sample spiked with a known amount of endotoxin. Recovery of 50–200% shows the product does not inhibit or enhance the LAL reaction.
Positive-displacement pipette: A pipette whose piston is in direct contact with the liquid, in a disposable capillary tip. Suited to viscous, dense or volatile liquids.
Positive-hole correction: A statistical correction applied to sieve impactor counts because more than one organism passing through the same hole forms only one colony.
Precision: How close repeated measurements of the same sample are to each other, usually expressed as %RSD. Studied as repeatability (same conditions), intermediate precision (different days, analysts or instruments in one lab) and reproducibility (between labs).
Preferred orientation: Non-random alignment of plate- or needle-shaped crystals in a powder sample. It changes relative XRPD peak intensities but not peak positions.
Primary standard: A highly pure, stable, non-hygroscopic substance of known composition, such as potassium hydrogen phthalate, used to standardise volumetric solutions.
Principal component analysis (PCA): A chemometric method that reduces many correlated variables (e.g. absorbances at every wavelength) to a few principal components that capture most of the variation. Used to classify spectra and detect outliers.
Probabilistic leak test: A leak test whose outcome depends on chance events and inspection, such as dye ingress, bubble emission or microbial challenge. Usually less sensitive and less repeatable than deterministic methods.
Process analytical technology (PAT): A framework for designing, analysing and controlling manufacturing by timely measurement of critical quality attributes during processing, often with in-line NIR or Raman.
PSL spheres: Uniform polystyrene latex particles of certified size, used to calibrate the size channels of particle counters.
Purge gas: Gas, usually dry nitrogen, flowed through a DSC or TGA cell to keep the atmosphere controlled and carry away volatiles.
Purified water (PW): Pharmacopoeial water for making medicines that are not required to be sterile. It is produced by a validated system and tested for conductivity, TOC and microbial quality.

Q

Q value: The amount of drug dissolved, as a percentage of the label claim, specified in the monograph at a stated time. For many immediate-release tablets Q is 75–80%.
Quantitative NMR (qNMR): Use of NMR signal areas, with a certified internal standard, to determine purity or content. It does not need a reference standard of the analyte itself.
Quartz control plate: A certified quartz plate with a known optical rotation, used to calibrate and check the angle scale of a polarimeter.

R

R2A agar: A low-nutrient agar used with longer incubation to recover stressed bacteria from pharmaceutical water.
Raman shift: The difference in wavenumber (cm⁻¹) between the laser line and the Raman-scattered light. It equals the vibrational frequency and does not depend on the laser wavelength.
Random error: The scatter of repeated measurements around their mean, expressed as a standard deviation or coefficient of variation.
Raw data: The original record of an activity in the form in which it was first captured, such as a balance printout or the electronic data file from a chromatography data system.
Rayleigh scattering: Scattering of light with no change in energy. It is about a million times stronger than Raman scattering and is blocked by a notch or edge filter.
Readability (d): The smallest difference in mass a balance display shows, for example 0.1 mg on an analytical balance. It is not the same as accuracy.
Recombinant factor C (rFC): An animal-free reagent made by recombinant technology that reproduces the first enzyme of the LAL cascade and detects endotoxin by fluorescence.
Reference standard: A highly characterised substance of known purity used as the basis for quantitative comparison.
Refractive index (n): The ratio of the speed of light in air or vacuum to its speed in the sample. Reported at a stated temperature and wavelength, for example nD at 20 °C. Water is about 1.3330.
Relative centrifugal force (RCF): The force acting on a sample in a centrifuge, expressed as a multiple of gravity. RCF = 1.118 × 10⁻⁵ × r (cm) × rpm².
Relative density: The density of a substance divided by the density of water at stated temperatures, for example d 20/20. It has no unit.
Relative humidity (RH): The amount of water vapour in air as a percentage of the maximum the air could hold at the same temperature.
Relative response factor (RRF): The detector response of an impurity per unit concentration divided by that of the drug. Used to correct impurity results when they are calculated against a diluted standard of the drug; the correction factor is 1/RRF.
Relative retention time (RRT): The retention time of a peak divided by the retention time of a reference peak (usually the main drug). Used to identify impurity peaks in related-substances tests.
Relative standard deviation (%RSD): Standard deviation divided by the mean, expressed as a percentage. Used to express precision.
Releasing agent: A substance such as lanthanum or strontium added in flame AAS to bind interfering anions (e.g. phosphate) so the analyte is released as free atoms.
Repeatability (balance): How closely repeated weighings of the same object agree, expressed as a standard deviation. It decides the balance's minimum weight.
Reporting, identification and qualification thresholds: ICH Q3B(R2) levels, set by maximum daily dose, above which a degradation product must be reported, identified (structure determined) and qualified (shown to be safe). For doses above 2 g/day they are 0.05%, 0.10% and 0.15%.
Residual solvents: Organic volatile chemicals used or produced in manufacturing a drug substance, excipient or product that are not completely removed. Controlled under ICH Q3C and USP <467>.
Resistivity: The reciprocal of conductivity, in MΩ·cm. Ultrapure water at 25 °C is about 18.2 MΩ·cm.
Resolution (Rs): A measure of how well two adjacent peaks are separated. Rs ≥ 1.5 indicates baseline separation.
Response efficiency (TOC): In TOC system suitability, the response to 1,4-benzoquinone compared with sucrose at the same carbon level, after subtracting the water blank. Typically required to be 85–115%.
Retention sample: A portion of a batch of starting material or finished product kept under defined conditions for a defined period, so the batch can be re-examined later if needed.
Retention time (tR): The time between injection and the maximum of a chromatographic peak. Under fixed conditions it identifies a compound.
Retest and resample: A retest is a repeat analysis of the original homogeneous sample; a resample is a new sample taken from the batch, allowed only when the original sample is shown to be unrepresentative or compromised.
Retest date: The date by which a material or in-house standard must be re-examined to confirm it is still suitable for use. It is not the same as an expiry date.
Reverse osmosis (RO): A purification process in which pressure forces water through a semi-permeable membrane that holds back most dissolved ions, organics and microbes.
Reverse pipetting: Aspirating to the second (blow-out) stop and dispensing only to the first stop, leaving a small remainder in the tip. Improves accuracy with viscous or foaming liquids.
Reversed-phase chromatography: Chromatography with a non-polar stationary phase (e.g. C18) and a polar mobile phase. The most common HPLC mode.
Rf value: In TLC, the distance moved by a spot divided by the distance moved by the solvent front, both measured from the origin. Always between 0 and 1.
Robustness: The ability of a method to stay unaffected by small, deliberate changes in its parameters, such as mobile phase pH, column temperature or flow rate.

S

Safety factor (weighing): A multiplier, often 2 or 3, applied to the minimum weight to give a working minimum that allows for changes in environment and operator.
Sampling thief: A long probe with a closable chamber that is pushed into a powder blend to remove a small sample from a chosen location and depth.
Sash: The movable transparent front window of a fume hood. It shields the user and sets the size of the opening, and so the face velocity.
Saturated steam: Steam in equilibrium with liquid water, with a fixed temperature for each pressure. It is the sterilising agent in autoclaves.
Selected ion monitoring (SIM): A mass spectrometer mode that monitors only a few chosen m/z values instead of scanning a full range, giving much higher sensitivity for target compounds.
Selective medium: A culture medium with ingredients that suppress most organisms while allowing the target to grow, often with an indicator that gives the target a typical colony appearance.
Septum bleed: Siloxane compounds released from a heated GC inlet septum that appear as ghost peaks or a rising baseline. Reduced by low-bleed septa and regular replacement.
Settle plate: An open agar plate exposed for a set time (up to 4 hours) to collect microorganisms settling from the air. Results are reported as cfu per plate per 4 hours.
Shear-thinning: Behaviour in which viscosity falls as shear rate rises. Common in suspensions, gels and creams.
Shelf life: The time during which a medicine, stored as stated on the label, is expected to stay within its specification. Set from stability data and evaluated as described in ICH Q1E.
Sieve aperture: The nominal width of the square openings in a test sieve, e.g. 250 µm. Actual openings must stay within the tolerances in ISO 3310-1 or ASTM E11.
Sieve blinding: Clogging of sieve openings by particles, which reduces open area and makes sieving results appear coarser.
Significant change (stability): A change in a stability sample defined in ICH Q1A(R2) — for example a 5% loss of assay or a degradant over its limit. At accelerated conditions it triggers testing at the intermediate condition.
Silicon powder standard: Certified silicon powder with a precisely known lattice parameter (about 5.4311 Å), used to check the 2θ angle scale of powder diffractometers.
Sink conditions: A medium volume large enough (commonly at least three times the volume needed to saturate it with the dose) that the dissolved drug does not slow further dissolution. The result then reflects the formulation, not the drug's solubility limit.
Sinker: A small wire coil or cage that holds a floating capsule or tablet at the bottom of a dissolution vessel. Used only when the method specifies or permits it.
Soybean-Casein Digest Medium (SCDM): A general-purpose broth that supports aerobic bacteria and fungi. In the sterility test it is incubated at 20–25 °C; it is also the pre-enrichment broth in tests for specified microorganisms.
Span (particle size distribution): A measure of how wide a size distribution is: (D90 − D10) ÷ D50. Smaller values mean a narrower, more uniform distribution.
Specific absorbance A(1%, 1 cm): The absorbance of a 1% w/v solution (1 g in 100 mL) in a 1 cm cell. Calculated as A ÷ (c × b) with c in g/100 mL; used in monographs for identification and assay.
Specific optical rotation [α]: Optical rotation corrected for tube length and concentration: [α] = 100 × α ÷ (l × c), with l in dm and c in g/100 mL. Stated with temperature and wavelength, for example at 20 °C and 589 nm.
Specificity: The ability of a method to measure the analyte unequivocally in the presence of other components such as impurities, degradants and excipients.
Specified impurity: An impurity individually listed with its own limit in a specification; it may be identified or unidentified. Unspecified impurities are controlled by a general limit, usually the identification threshold.
Specified microorganism: A named organism whose absence is required in a non-sterile product, such as E. coli, Salmonella, P. aeruginosa, S. aureus or C. albicans, tested as per USP <62> / Ph. Eur. 2.6.13.
Spectral bandwidth (SBW): The width of the band of wavelengths that passes through the sample, set by the monochromator slit. Narrower bandwidth gives better spectral resolution.
Spectral library: A validated collection of reference spectra of authentic materials, against which a test spectrum is compared to confirm identity.
Spike recovery: The percentage of a known added amount of analyte that is measured back: (spiked result − unspiked result) ÷ amount added × 100. Used to show accuracy in the sample matrix.
Spin–spin coupling (J): Splitting of an NMR signal by neighbouring nuclei into doublets, triplets and so on. The spacing J, in Hz, shows which atoms are connected.
Split ratio: In a split inlet, the ratio of gas vented through the split line to gas entering the column, for example 1:50. It controls how much of the injected sample reaches the column.
Stability-indicating method: A validated analytical procedure that measures the active ingredient accurately without interference from degradation products, impurities or excipients, and can also quantify the degradants.
Stage micrometer: A microscope slide with an accurately ruled scale, used to calibrate the eyepiece graticule at each magnification.
Standard normal variate (SNV): A spectral pre-treatment that centres and scales each spectrum individually, reducing baseline offsets and particle-size scatter effects in NIR data.
Standardisation: Determining the exact concentration of a volumetric solution by titrating it against a primary standard or a solution of known concentration.
Stationary phase: The material packed inside the column that retains sample components to different degrees, causing separation.
Sterility assurance level (SAL): The probability of a single viable microorganism surviving on an item after sterilisation. Terminal sterilisation usually targets 10^-6 or better.
Sterility test invalidation: Declaring a sterility test invalid, allowed only when a fault in the facility, procedure or negative controls, or a clear link of the growth to the test itself, is shown. An invalid test is repeated with the same number of units.
Stokes shift: The difference between the excitation and emission maxima in fluorescence. Emission is at a longer wavelength because some energy is lost before light is emitted.
Stratified sampling: Sampling dosage units at planned points throughout compression or filling, including likely weak points, to show uniformity across a batch.
Stray light: Light of wavelengths outside the selected band that reaches the detector. It makes high absorbances read too low and is checked with cut-off solutions such as potassium chloride at 198 nm.
Sub-visible particles: Particles in injections too small to see by eye, roughly 1–100 µm. Pharmacopoeias limit counts at ≥ 10 µm and ≥ 25 µm.
Sulphated ash: The residue left after a substance is treated with sulphuric acid and ignited, usually at 600 ± 50 °C, to constant mass. It measures inorganic impurities.
Superficially porous particles: Column packing particles with a solid core and a thin porous outer shell. They give efficiency close to sub-2 µm particles at lower back-pressure.
Suppressor (ion chromatography): A device after the IC column that removes eluent conductivity (e.g. converts hydroxide to water) and converts analyte ions to a more conductive form, so the conductivity detector can see low-level ions.
Switch-off criterion: The rule a moisture analyser uses to end a test, for example when the mass loss is less than a set amount over a set time.
System suitability: Checks performed before and during an analysis to confirm the analytical system is fit for use on that day.
Systematic error: The difference between the mean of repeated measurements and the true or nominal value. It shows a consistent bias in one direction.

T

T1 (spin–lattice relaxation time): The time constant for nuclei to return to equilibrium after a pulse. qNMR uses a delay of at least about 5 × T1 between scans so signals are fully quantitative.
Tachometer: An instrument that measures rotational speed in revolutions per minute. Non-contact optical tachometers read a reflective mark on a rotating part.
Tailing factor (T): A measure of peak symmetry. 1.0 is perfectly symmetrical; values above 1 indicate tailing.
TAMC: Total aerobic microbial count: the number of cfu found on Soybean-Casein Digest Agar after incubation at 30–35 °C, including any fungi that grow.
Tapped density: Mass of a powder divided by its volume after mechanical tapping has packed it down to a near-constant volume. Equal to or higher than bulk density.
Temperature excursion: A period during which storage temperature (or humidity) is outside its allowed range. Excursions are recorded, investigated and assessed for impact on the stored material.
Temperature mapping: A study in which calibrated loggers are placed at many positions in a chamber, fridge or room to find hot and cold spots and prove that the whole storage zone stays within its limits.
Temperature programming: Raising the GC oven temperature at a set rate during a run so compounds with a wide range of boiling points elute as sharp peaks in a reasonable time.
Tensile strength (tablet): Breaking force converted to a stress using the tablet's diameter and thickness, which allows tablets of different sizes to be compared.
Test weight: A calibrated mass standard of a defined accuracy class (for example OIML class E2 or F1) used to check or calibrate a balance.
Testing into compliance: Repeating a test, or running unofficial trial analyses, until a passing result is obtained and then reporting only that result. It is not acceptable under GMP.
Theoretical plates (N): A measure of column efficiency; the higher the number, the narrower the peaks for a given retention time.
Thermogram: A plot of a measured property, such as heat flow (DSC) or mass (TGA), against temperature or time.
Three-stage conductivity test: The USP <645> approach to water conductivity: Stage 1 temperature-dependent limit, Stage 2 stirred at 25 °C, Stage 3 pH-dependent limit.
Titre: The strength of a titrant. For KF reagents it is the mass of water (mg) that 1 mL reacts with; for volumetric solutions it is often expressed as the actual molarity or as a factor relative to nominal.
To contain (TC) / to deliver (TD): Markings showing whether glassware is calibrated to hold the stated volume (flasks) or to deliver it (pipettes and burettes).
Total ion chromatogram (TIC): A chromatogram made by summing the intensities of all ions detected at each time point. Extracted ion chromatograms (EIC) show one chosen m/z only.
Total organic carbon (TOC): The amount of carbon bound in organic compounds in water, usually in mg/L or µg/L of carbon. A non-specific measure of organic contamination.
Transmittance (T): The fraction of incident light that passes through a sample, T = I / I₀, often given as a percentage. Absorbance = −log₁₀ T.
True copy: A copy of an original record, verified by a documented process, that keeps the full content and meaning of the original including relevant metadata.
Turbidity: The cloudiness of a liquid caused by suspended particles that scatter light. Measured with a turbidity meter in NTU or FNU.
TYMC: Total combined yeasts and moulds count: the number of cfu found on Sabouraud Dextrose Agar after incubation at 20–25 °C, including any bacteria that grow.

U

Ultrapure water (Type 1): Laboratory water of the highest purity, with resistivity close to 18.2 MΩ·cm at 25 °C and very low TOC. Used for HPLC, trace analysis and sensitive tests.
Unidirectional airflow: Filtered air moving in parallel streams at a uniform speed in one direction across a work zone, sweeping particles away.
Uniformity of weight: A test in which 20 dosage units are weighed individually and each one's deviation from the average weight is compared with a limit based on the average weight.

V

Vacuum decay: A deterministic, non-destructive leak test: the container sits in an evacuated, isolated chamber and a leak is shown by a pressure rise above a validated limit.
Van Deemter equation: Describes how plate height (H) depends on mobile-phase velocity (u) through eddy diffusion (A), longitudinal diffusion (B/u) and mass-transfer resistance (Cu). The minimum of the curve is the optimum flow velocity.
Visualisation reagent: A chemical sprayed or dipped onto a developed TLC plate to make colourless spots visible, for example iodine, ninhydrin or anisaldehyde–sulphuric acid.
Volumetric solution: A solution of accurately known concentration used as a titrant, for example 0.1 M sodium hydroxide.

W

Water equivalence factor: The titre of a Karl Fischer reagent, in mg of water per mL, determined against a water standard such as sodium tartrate dihydrate.
Water Raman band: Inelastic light scatter from water, shifted about 3400 cm⁻¹ from the excitation (near 397 nm for 350 nm excitation). Used to test fluorimeter sensitivity as a signal-to-noise ratio.
Wavenumber (cm⁻¹): The number of waves per centimetre, equal to 10,000 ÷ wavelength in µm. The usual x-axis unit for IR spectra.
Weighing by difference: Finding the mass transferred by weighing a container before and after removing sample; the difference is the amount transferred.
Working standard: An in-house standard qualified against a primary reference standard and used for routine analysis.

Z

Z factor: The factor (mL/g) used to convert the mass of water dispensed in a gravimetric volume check into volume, allowing for water density and air buoyancy at the test temperature.
z-value: The temperature change needed to change the D-value tenfold. For steam sterilisation of spores it is usually taken as 10 °C.

Λ

λmax (wavelength of maximum absorbance): The wavelength at which a substance absorbs most strongly under stated conditions. Used for identification and chosen for measurement because sensitivity is highest there.

Lab terms, in plain language.

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J

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Λ