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ICP-OES · Calibration procedure

Detection limit check

Measures the noise of repeated blank readings and converts it into the lowest concentration the instrument can reliably detect for selected elements.

Photo of a ICP-OES
Photo: Cyberwork 95, CC BY-SA 4.0 (cropped), via Wikimedia Commons
PURPOSE

Why this is checked

Elemental impurity methods need the instrument to see well below the target limit. A rising detection limit warns of a dirty torch, weak plasma or worn sample introduction parts.

Frequency

Typically wavelength calibration daily or per manufacturer recommendation, and detection limits every 6 or 12 months and after major repair, as defined in your calibration SOP.

Learn how the ICP-OES works
YOU WILL NEED

Standards & tools

  • Dilute nitric acid blank (the same acid as the standards)
  • Calibration standards of the test elements (e.g. Pb, Cd, As at known µg/L concentrations)
BEFORE YOU START

Prerequisites

  • Plasma stable, wavelength calibration passed
  • Calibration for the test elements just completed
PROCEDURE

Step by step

  1. 1Calibrate the test elements with a blank and at least one standard to obtain the slope (cps per µg/L).
  2. 2Aspirate the blank and record ten replicate readings for each element.
  3. 3Calculate the standard deviation of the blank intensities.
  4. 4Calculate the detection limit (3 × SD ÷ slope) and compare with the specification.
RECORD

Example observation table

ReplicatePb 220.353 nm blank intensity (cps)
1412
2398
3405
4421
5393
6409
7401
8417
9396
10408
CALCULATION

How to calculate the result

Detection limit (µg/L) = 3 × SD of blank (cps) ÷ Slope (cps per µg/L)
  1. Mean blank = 406 cps; SD of blank = 9.15 cps
  2. Slope for Pb 220.353 nm = 15.0 cps per µg/L
  3. Detection limit = 3 × 9.15 ÷ 15.0 = 1.83 µg/L
ACCEPTANCE CRITERIA

Pass if

  • Detection limit for each test element not more than the manufacturer's specification or the limit in your SOP (low single-digit µg/L is typical for Pb in axial view).
IF IT FAILS

What to do

  • Clean the torch, nebuliser and spray chamber; replace pump tubing.
  • Check the blank and acids for contamination.
  • Re-optimise plasma conditions and repeat.
  • Label 'Out of calibration' if it still fails.
MORE

Other ICP-OES 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