Potentiometric titrator · Calibration procedure
Burette accuracy
Checks the delivered volume of the titrator's burette gravimetrically with water, corrected for temperature using the Z factor.
PURPOSE
Why this is checked
The titrant volume at the equivalence point drives every assay result. A burette that delivers too much or too little gives a proportional error in the result.
Frequency
Typically every 6 or 12 months and after repair, as defined in your calibration SOP.
Learn how the Potentiometric titrator 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
BEFORE YOU START
Prerequisites
- Burette unit flushed and filled with water
- Water, balance and burette at 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 (%) |
|---|---|---|---|---|---|
| 5.000 | 4.9861 | 1.0033 | 5.0026 | +0.0026 | +0.05 |
| 10.000 | 9.9688 | 1.0033 | 10.0017 | +0.0017 | +0.02 |
| 15.000 | 14.9547 | 1.0033 | 15.0041 | +0.0041 | +0.03 |
| 20.000 | 19.9402 | 1.0033 | 20.0060 | +0.0060 | +0.03 |
CALCULATION
How to calculate the result
Delivered volume V = m × Z; Error % = (V − Nominal) ÷ Nominal × 100
- Nominal 20.000 mL, mass 19.9402 g, water at 22 °C (Z = 1.0033 mL/g)
- V = 19.9402 × 1.0033 = 20.0060 mL
- Error = (20.0060 − 20.000) ÷ 20.000 × 100 = +0.03%
ACCEPTANCE CRITERIA
Pass if
- Systematic error within the limits in your SOP, commonly about ±0.2% of nominal for a 20 mL burette, based on ISO 8655-3 or the manufacturer's specification.
- Random error (CV of replicates) commonly not more than 0.1%.
IF IT FAILS
What to do
- Check for air bubbles, leaks at the valve and tubing, and a worn piston seal.
- Repeat the test after correction; if it still fails, label the titrator 'Out of calibration' and have the burette serviced.
- Assess the impact on results generated since the last passing check.
MORE
Other Potentiometric titrator 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.