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KF titrator (coulometric) · Calibration procedure

Drift check

Records the background drift of the conditioned coulometric cell and checks it is low and stable before analysis.

Illustration of KF titrator (coulometric)
PURPOSE

Why this is checked

Coulometric samples often contain only a few hundred micrograms of water, so even a small leak is a large error. The drift must be low and stable so that the drift correction (drift × determination time) is reliable.

Frequency

Before each series of determinations, and continuously monitored during use.

Learn how the KF titrator (coulometric) works
YOU WILL NEED

Standards & tools

  • No external standard; the instrument's own drift measurement is used
  • Timer or the instrument's drift log
BEFORE YOU START

Prerequisites

  • Cell filled with fresh reagent and conditioned
  • Septum and drying tubes in good condition
PROCEDURE

Step by step

  1. 1Start conditioning and wait until the instrument reports a stable state.
  2. 2Record the drift at regular intervals, for example every 2 minutes for 10 minutes.
  3. 3Calculate the mean drift and the range of readings.
  4. 4Compare with the limits in your SOP and record the result in the logbook.
RECORD

Example observation table

Time (min)Drift (µg/min)
04.1
23.8
43.9
63.7
83.8
103.8
CALCULATION

How to calculate the result

Drift correction (µg) = Drift (µg/min) × Determination time (min); Net water = Gross water − Drift correction
  1. Mean drift = (4.1 + 3.8 + 3.9 + 3.7 + 3.8 + 3.8) ÷ 6 = 3.85 µg/min; range 3.7–4.1 µg/min (stable)
  2. A sample determination takes 3.0 min with a drift of 3.8 µg/min: correction = 3.8 × 3.0 = 11.4 µg
  3. Gross water 245.6 µg − 11.4 µg = 234.2 µg net
ACCEPTANCE CRITERIA

Pass if

  • Drift typically not more than about 10 µg/min (many labs aim for below 5 µg/min), or the limit in your SOP.
  • Drift stable, with no steady upward trend over the observation period.
IF IT FAILS

What to do

  • Replace the septum and check all joints and drying tubes.
  • Replace exhausted reagent.
  • Dry the cell and electrodes if they were recently cleaned.
  • Repeat the drift check; do not run samples until it passes.
MORE

Other KF titrator (coulometric) 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.

See how