SPME-GC-CIMS (Solid-Phase Microextraction – Gas Chromatography – Chemical Ionization Mass Spectroscopy)

In mass spectrometry, it is essential to ionize the molecules of the analyte. The most common method for the generation is electron shock ionization (EI). This form of "hard" ionization leads to a high fragmentation of the molecules, which leads to complex spectra and an increasing chemical background.

A “soft” method for ionization of the sample is represented by chemical ionization (CI) with reactive gases. The advanced method presented here is a modified mass spectrometer, which makes water vapor usable for chemical ionization by protonation with hydronium ions. This allows the low-fractioning ionization of numerous compounds in the mass range of 25 to 650 g/mol. This special GC-MS process is coupled with an upstream solid-phase microextraction (SPME), providing an extremely high degree of selectivity and detection sensitivity for volatile organic substances.

Our Services

• Organic screening and analysis of volatile single substances in the smallest sample quantities found
  • in gases
  • in liquids
  • on surfaces down to the trace level
• Identification of unknown mixtures of organic substances
• Quantification of key substances (e.g. odor carriers)

Applications

• Monitoring of outgassing substances in cleanrooms
• Analysis of gas composition in reaction chambers, mini-environments, facilities
• Outgassing of parts, components, auxiliary materials, and finished products
• Analysis of organic surface layers
• Analysis of the tiniest amounts of liquid (e.g. condensate droplets)
• Analysis of odors in cosmetics, packaging, indoor air, interior materials, etc.
• Determination of food ingredients and foreign substances in food chemistry
• Organic screening and quantification of relevant key substances:
  • in clinical chemistry
  • after accidents and damage cases
  • in material manufacturing

Sampling / Requirements

Sampling can be carried out easily and quickly using vials:

• Installation of a vial at the point of collection, e.g. in the cleanroom or in a machine
• Leave it open for 30–60 minutes, seal it and send it to the laboratory
• Sample amount:
  Gases: 40 ml (1 vial)
  Liquids: from 5 to 10 µl

Specifications / Detection Limits / Special Features

• Ion trap of the mass spectrometer (Paul trap)
  • Reactive gas is H₂O for protonation of analytes by H₃O+
  • Gentle ionization at 12 eV:
    Molecules remain largely intact, no thermal decomposition of the analytes
  • No residue or background noise due to additional chemicals
  • Self-cleaning effect of sensitive device parts due to OH* radicals
• Sensitivity / Selectivity
  • Extremely high sensitivity
  • 100 times better than CI-MS with conventional reactive gases
  • 20,000 times better than EI-MS (quadrupole)
  • Signal-to-noise ratio:
  • 1 nanogram sample = 1 : 10,000,000
  • 1 Femto-gram sample = 1 : 10
• Analytes
  • Molar mass range of 26 to approx. 400
  • Very volatile substances (VVOC) possible: ethyne, methanol, hydrogen cyanide, formaldehyde, ethanol, H₂S, PH₃, AsH₃, etc.
  • Siloxanes up to a molar mass of 650 possible
  • Organics in aqueous bulk are directly measurable
  • Must enter the gas phase ("evaporable")

Case Examples

- Comparative analysis of room air with cleanroom air in an ISO-class cleanroom 4

Air samples were collected from a clean room and from a lab. More than 400 organic substances were detected and summarized in groups. The detected signals are presented in the diagram as intensities.

Results:

The organic load on the cleanroom air is lower by several orders of magnitude than on the laboratory room.

Advantage:

Regular repeat measurements of cleanroom air can be used for detecting deviations and their causes. Furthermore, specifications for cleanroom air quality can also be determined.

- Outgassing of packaging

In the semiconductor industry, so-called FOUPs (Front Opening Unified Pod) are used for the transport of wafers. They are made of plastic and must not release any substances onto the wafers by outgassing or sublimation.

Task:

During an inspection, a strange smell was detected in a FOUP which was due to a possible incident. The root cause had to be evaluated.

Results:

After evaluating several 100 individual substances, three odor-intensive VOC candidates were shortlisted for comparison with the ambient air: Acetaldehyde was identified as the key substance for the odor in question.

Root Cause:

• Outgassing substances from the plastic that may have their origin in the manufacturing process of the FOUP
  or:
• The plastic surface of the FOUP had absorbed reaction gases from an environment where thermal processes took place.

Contact

SGS INSTITUT FRESENIUS GmbH
Königsbrücker Landstr. 161
01109 Dresden

t +49 351 8841-200
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