LimsPulse
ICP-MS · Calibration procedure

Detection limit check

Converts the noise of repeated blank measurements into the lowest concentration the ICP-MS can detect for key elements such as Pb, Cd, As and Hg.

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

Why this is checked

ICP-MS is chosen for elemental impurities because of its very low detection limits. A rising detection limit shows contamination, a high background or lost sensitivity before it affects results near the control threshold.

Frequency

Typically tuning check each day of use; full mass calibration and detection limit calibration every 6 or 12 months and after cone, lens or detector service, as defined in your calibration SOP.

Learn how the ICP-MS works
YOU WILL NEED

Standards & tools

  • 2% nitric acid blank (ultrapure acid and Type 1 water)
  • Calibration standards of the test elements at µg/L levels, with internal standard
BEFORE YOU START

Prerequisites

  • Tuning passed
  • Calibration of test elements completed in the mode used for routine work
PROCEDURE

Step by step

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

Example observation table

Replicate²⁰⁸Pb blank (cps)
1118
2131
3109
4125
5122
6114
7137
8119
9126
10121
CALCULATION

How to calculate the result

Detection limit (µg/L) = 3 × SD of blank (cps) ÷ Sensitivity (cps per µg/L)
  1. Mean blank = 122.2 cps; SD of blank = 8.09 cps
  2. Sensitivity for ²⁰⁸Pb = 25,000 cps per µg/L
  3. Detection limit = 3 × 8.09 ÷ 25,000 = 0.00097 µg/L (about 1 ng/L)
ACCEPTANCE CRITERIA

Pass if

  • Detection limit for each test element not more than the manufacturer's specification or the limit in your SOP (often in the ng/L range).
IF IT FAILS

What to do

  • Check acids, water and vessels for contamination; prepare a fresh blank.
  • Clean cones and sample introduction system; check the tune.
  • Repeat; label 'Out of calibration' and call service if it still fails.
MORE

Other ICP-MS 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