TOC analyser · Calibration procedure
Calibration standards
Calibrates the analyser's response against standards of known carbon concentration (for example potassium hydrogen phthalate or sucrose) and checks it with an independent standard.
PURPOSE
Why this is checked
The analyser converts its detector signal into mg/L of carbon using a calibration. A multi-point calibration covering the working range, followed by an independent check, shows that reported TOC values are accurate around the 0.50 mg/L limit.
Frequency
Typically every 6–12 months, after replacing the lamp, catalyst or detector parts, and when check standards fail, as defined in your SOP or by the supplier.
Learn how the TOC analyser worksYOU WILL NEED
Standards & tools
- Potassium hydrogen phthalate (KHP) or sucrose, of known purity
- Low-TOC reagent water
- Class A volumetric glassware or TOC-clean vials
BEFORE YOU START
Prerequisites
- Stock solution prepared fresh: 2.125 g of KHP in 1 L gives 1000 mg/L carbon (KHP is 47.05% carbon)
- Working standards made by dilution of the stock in reagent water
PROCEDURE
Step by step
- 1Prepare standards at, for example, 0 (reagent water), 0.25, 0.50, 1.00 and 2.00 mg/L added carbon.
- 2Analyse each standard in replicate as set by the analyser method.
- 3Fit a straight line of response against added carbon and record the slope, intercept and r².
- 4Analyse an independent check standard (for example 0.50 mg/L C prepared from a different weighing or source) and calculate the recovery.
RECORD
Example observation table
| Added carbon (mg/L) | Response (area counts) | Back-calculated (mg/L) |
|---|---|---|
| 0.00 | 152 | 0.002 |
| 0.25 | 1398 | 0.249 |
| 0.50 | 2671 | 0.501 |
| 1.00 | 5180 | 0.997 |
| 2.00 | 10260 | 2.002 |
CALCULATION
How to calculate the result
Response = slope × concentration + intercept; Check standard found = (Response − intercept) ÷ slope; Recovery % = found ÷ nominal × 100
- Linear fit: slope = 5055.7 counts per mg/L, intercept = 140.4 counts, r² = 0.99999
- Check standard 0.50 mg/L C gives 2640 counts
- Found = (2640 − 140.4) ÷ 5055.7 = 0.494 mg/L
- Recovery = 0.494 ÷ 0.50 × 100 = 98.9%
ACCEPTANCE CRITERIA
Pass if
- Correlation coefficient r typically not less than 0.995 (r² not less than 0.990), or the supplier's / SOP limit.
- Check standard recovery typically within 90–110% (some SOPs use ±15% near the limit).
IF IT FAILS
What to do
- Check standard preparation, reagent water and vials, then repeat.
- Check reagents, lamp or catalyst, and detector condition.
- Call service if the calibration still fails; label the analyser out of calibration.
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.