LimsPulse
GC · Calibration procedure

Detector linearity

Checks that FID response is proportional to the amount of analyte across the range used by your methods.

Photo of a GC
Photo: Sarka Na kopci, CC BY-SA 4.0 (cropped), via Wikimedia Commons
PURPOSE

Why this is checked

Quantitation against a single standard, and impurity limits at low levels, assume a linear detector response. The FID is linear over a very wide range but a dirty jet or wrong gas flows can reduce it.

Frequency

Typically every 6 or 12 months, and after major repair or relocation, as defined in your calibration SOP.

Learn how the GC works
YOU WILL NEED

Standards & tools

  • At least five solutions of a stable compound (e.g. n-dodecane in hexane) covering the working range, prepared with calibrated volumetric glassware
BEFORE YOU START

Prerequisites

  • Injector precision already passed
  • FID gas flows set to the manufacturer's recommended values
  • System equilibrated with a stable baseline
PROCEDURE

Step by step

  1. 1Prepare at least five concentrations, for example 10, 50, 100, 250 and 500 µg/mL.
  2. 2Inject each solution (in duplicate if your SOP requires) under identical conditions.
  3. 3Plot mean peak area against concentration.
  4. 4Calculate the regression line and correlation coefficient, and check residuals for any trend.
RECORD

Example observation table

Concentration (µg/mL)Mean peak area (pA·s)
1020,480
50101,950
100204,310
250509,870
5001,021,560
CALCULATION

How to calculate the result

Linear regression y = mx + c; report the correlation coefficient r
  1. Using the five points above
  2. Slope m = 2,042.9 pA·s per µg/mL, intercept c = −165
  3. r = 0.99999 (passes r ≥ 0.999)
Use the Standard curve (linear regression) calculator
ACCEPTANCE CRITERIA

Pass if

  • Typically correlation coefficient r not less than 0.999 over the tested range, or the limit in your SOP.
IF IT FAILS

What to do

  • Check hydrogen, air and make-up flows.
  • Clean or replace the FID jet and collector.
  • Repeat with freshly prepared solutions.
  • Service the detector if it still fails.
MORE

Other GC 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