IMS Spectrum, Measurement and Calibration for Airborne Molecular Contamination (AMC)

IMS Spectrum, Measurement and Calibration for Airborne Molecular Contamination (AMC)

Calibration and Spectrum Troubleshooting

(Series Part 1 of 4)

The AirSentry® II AMC Analyzer detects airborne molecular contamination (AMCs) in cleanroom manufacturing environments. AMCs cause defect loss and product degradation and its reduction is critical for manufacturers to stay competitive.

Airborne Molecular Contamination Monitor AMC from Particle Measuring Systems PMS

AMC measurement techniques must allow for accurate, reliable event detection in real-time. The AirSentry II analyzer uses Ion Mobility Spectrometry (IMS) to facilitate sub-ppb concentration detection in as little as 5 seconds per reading. The software has built-in diagnostic tools for the evaluation of  analyzer performance and to rule out any inaccurate readings. Functionality is assessed both visually with the Ion Mobility Spectrum curve, and quantitatively with key operating parameters.


All ionically-charged molecular species are measured once they reach an ion collector plate inside the IMS drift chamber. However, only properly functionally drift chambers will attenuate detection to both:

  1. Ionized dopant or “reactant” molecules
  2. Ionized AMC or “target” molecules

AMC Monitor AirSentry II Mobile System from Particle Measuring SystemsThese two types of molecules appear as two defined peaks on the IMS spectrum. They also add a current charge to the ion collector plate. The software first measures the location and height of these two peaks. Then, it uses the data for the calculation of AMC abundance in sampled air in real-time.


It is critical to perform calibrations of any AMC analyzer at the location of the final point of use. This ensures accurate and stable AMC concentration detection. This includes zero and span calibrations:

  • Zero calibrations: Performed to ensure that when zero AMCs are present, the only peak in the IMS spectrum is from the dopant.
  • Span calibrations: Performed to ensure there is a second peak that results from the presence of 25 ppb of a calibrant AMC span gas.

Zero and span calibration factors depend on local atmospheric conditions. The software continuously uses these factors to tune the ASII AMC algorithm calculation for all subsequent real-time AMC measurements.

Look forward to our next blog covering how to perform zero calibrations. You can also download the full paper here to learn more about what the AirSentry II analyzers can do to improve your yield through accurate detection of AMC.


Click here to learn more about innovative AMC monitoring solutions to help you quickly identify problems and their location before your product is contaminated: AirSentry II Point-of-Use Ion Mobility Spectrometer


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