KF titrator (volumetric) · Calibration procedure
Burette accuracy
Checks that the motorised burette delivers the volume it reports, by weighing dispensed water and converting mass to volume.
PURPOSE
Why this is checked
The titrator converts burette volume directly to water content. A biased burette gives biased results for every sample and titre, so its delivery is verified gravimetrically.
Frequency
Typically every 6 or 12 months and after repair, as defined in your calibration SOP.
Learn how the KF titrator (volumetric) worksYOU WILL NEED
Standards & tools
- Calibrated analytical balance (readability 0.1 mg or better)
- Degassed purified water
- Calibrated thermometer
- Z factor table (mL/g) for water at the test temperature, for example from ISO 8655-6
BEFORE YOU START
Prerequisites
- Burette unit filled with water instead of KF reagent (use a spare unit or flush the reagent out first)
- Water, balance and burette equilibrated to room temperature
PROCEDURE
Step by step
- 1Fill the burette with degassed purified water and run several prepare / flush cycles to remove air bubbles.
- 2Record the water temperature and note the matching Z factor (mL/g) from the table in your SOP (about 1.0033 mL/g at 22 °C).
- 3Place a weighing vessel with a little water (to reduce evaporation) on the balance and tare it.
- 4Dispense the first test volume from the burette into the vessel, touching the tip to the wall to remove the last drop, and record the mass.
- 5Repeat for each test volume and replicate required by the SOP (for example 10%, 50% and 100% of the burette volume).
- 6Convert each mass to volume with the Z factor and compare it with the nominal volume.
RECORD
Example observation table
| Nominal (mL) | Mass (g) | Z (mL/g, 22 °C) | Volume (mL) | Error (mL) | Error (%) |
|---|---|---|---|---|---|
| 1.000 | 0.9958 | 1.0033 | 0.9991 | −0.0009 | −0.09 |
| 2.000 | 1.9921 | 1.0033 | 1.9987 | −0.0013 | −0.07 |
| 5.000 | 4.9802 | 1.0033 | 4.9966 | −0.0034 | −0.07 |
| 10.000 | 9.9614 | 1.0033 | 9.9943 | −0.0057 | −0.06 |
CALCULATION
How to calculate the result
Delivered volume V = m × Z; Error % = (V − Nominal) ÷ Nominal × 100
- Nominal 10.000 mL, mass 9.9614 g, water at 22 °C (Z = 1.0033 mL/g)
- V = 9.9614 × 1.0033 = 9.9943 mL
- Error = (9.9943 − 10.000) ÷ 10.000 × 100 = −0.06%
ACCEPTANCE CRITERIA
Pass if
- Systematic error within the limits in your SOP, commonly about ±0.3% of nominal for a 10 mL burette, based on ISO 8655-3 or the manufacturer's specification.
- Random error (CV of replicates) within the SOP limit, commonly not more than 0.1%.
IF IT FAILS
What to do
- Check for air bubbles, leaks and a worn piston seal; repeat the test.
- Label the titrator 'Out of calibration' and have the burette serviced if it still fails.
- Assess the impact on results since the last passing check.
MORE
Other KF titrator (volumetric) calibrations
In LimsPulse · Calibration Management
LimsPulse schedules this calibration, records the result against limits, and blocks the instrument everywhere if it fails or goes overdue.