Total Organic Carbon (TOC) Analyser
Oxidises organic compounds in water to carbon dioxide and measures the CO₂ formed to give the total organic carbon content. The standard test for organic contamination in purified water and water for injections.
- Pharmaceutical
- Biotech
- Semiconductors
- Power generation
- Environmental
- Drinking water
How TOC analyser works
Total carbon in water is made up of inorganic carbon (IC) and organic carbon. The analyser either removes IC first and measures what remains, or measures total carbon and IC separately and subtracts them (TOC = TC − IC). Organic compounds are oxidised to CO₂, and the CO₂ is measured by a conductivity cell or a non-dispersive infrared (NDIR) detector.
The path of a sample
- 01
Sample intake
Water is drawn from a vial or directly from the water loop.
- 02
Inorganic carbon
IC is removed by acidifying and sparging, or measured separately.
- 03
Oxidation
Organic carbon is oxidised to CO₂ by UV/persulphate or high-temperature combustion.
- 04
CO₂ detection
CO₂ is measured by conductivity (often through a membrane) or NDIR.
- 05
Result
The signal is converted to mg/L or µg/L of carbon using the calibration.
Main parts and what they do
Sample inlet / autosampler
Takes up grab samples from vials, or the online sample line from the loop.
Acid and oxidiser reagent supply
Adds acid to convert IC to CO₂ and persulphate for oxidation (in UV/persulphate models).
Oxidation reactor
UV lamp reactor or high-temperature combustion furnace that converts organics to CO₂.
CO₂ detector
Conductivity cell (often with a gas-permeable membrane) or NDIR detector.
Carrier gas supply (combustion models)
Moves CO₂ from the reactor to the detector.
Control software
Runs calibration, system suitability, sample sequences, data storage and audit trail.
Terms every analyst should know
TOC = TC − IC
Total carbon minus inorganic carbon gives total organic carbon. In very pure water the IC is small, but it must still be removed or subtracted.
Oxidation methods
UV with persulphate works well at low levels in pure water. High-temperature catalytic combustion (around 680 °C or higher) oxidises tougher compounds and suits higher or particle-containing samples.
Detection methods
Conductivity detection measures the rise in conductivity as CO₂ dissolves in clean water. NDIR measures CO₂ absorbance in a gas stream.
System suitability
Sucrose is easy to oxidise and 1,4-benzoquinone is hard to oxidise. Comparing their responses at the same carbon level (0.50 mg/L) shows the analyser oxidises both well.
Limit response
USP <643> compares the sample response with the response of a 0.50 mg/L carbon sucrose standard minus the water blank, rather than relying only on a printed number.
Keep every TOC analyser in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.