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TOC analyser · Calibration procedure

System suitability (sucrose / benzoquinone)

Compares the response to an easy-to-oxidise compound (sucrose) with a hard-to-oxidise compound (1,4-benzoquinone) at the same carbon level to prove the analyser oxidises organics efficiently.

PURPOSE

Why this is checked

USP <643> and Ph. Eur. 2.2.44 require evidence that the analyser fully oxidises organic compounds of different kinds. If benzoquinone gives a much lower response than sucrose, the analyser would under-report hard-to-oxidise contaminants.

Frequency

At the interval required by the chapter and your SOP, for example before use, after calibration and after major maintenance.

Learn how the TOC analyser works
YOU WILL NEED

Standards & tools

  • Reagent water with low TOC (not more than 0.10 mg/L carbon is typical)
  • Sucrose reference standard solution: about 1.19 mg/L sucrose, equal to 0.50 mg/L carbon
  • 1,4-Benzoquinone solution: about 0.75 mg/L, equal to 0.50 mg/L carbon
BEFORE YOU START

Prerequisites

  • Analyser calibrated
  • Standards prepared fresh in low-TOC reagent water, in TOC-clean glassware or vials
PROCEDURE

Step by step

  1. 1Analyse the reagent water used to prepare the standards and record its response (Rw).
  2. 2Analyse the sucrose standard (0.50 mg/L C) and record the response (Rs).
  3. 3Analyse the 1,4-benzoquinone solution (0.50 mg/L C) and record the response (Rss).
  4. 4Calculate the response efficiency and the limit response.
RECORD

Example observation table

SolutionSymbolResponse (mg/L C, as reported)
Reagent waterRw0.08
Sucrose standard (0.50 mg/L C)Rs0.55
1,4-Benzoquinone (0.50 mg/L C)Rss0.53
CALCULATION

How to calculate the result

Response efficiency (%) = (Rss − Rw) ÷ (Rs − Rw) × 100; Limit response = Rs − Rw
  1. Sucrose carbon fraction = 144.13 ÷ 342.30 = 0.421, so 0.50 mg/L C needs 0.50 ÷ 0.421 = 1.19 mg/L sucrose
  2. Benzoquinone carbon fraction = 72.07 ÷ 108.10 = 0.667, so 0.50 mg/L C needs 0.75 mg/L benzoquinone
  3. Response efficiency = (0.53 − 0.08) ÷ (0.55 − 0.08) × 100 = 0.45 ÷ 0.47 × 100 = 95.7%
  4. Limit response = 0.55 − 0.08 = 0.47 (used to judge samples)
ACCEPTANCE CRITERIA

Pass if

  • Response efficiency typically 85–115% (see the current USP <643> / Ph. Eur. 2.2.44).
  • Reagent water response low, as defined in your SOP.
IF IT FAILS

What to do

  • Prepare fresh standards and repeat, checking calculations and the reagent water.
  • Check the oxidiser reagent, UV lamp or combustion catalyst.
  • Recalibrate the analyser, then repeat system suitability.
  • Do not release water results until system suitability passes.
MORE

Other TOC analyser 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