Gas chromatography – mass spectrometry (GC-MS)
The analytical method GC-MS is used to identify and quantify volatile substances within a test sample.
It combines the features of gas-chromatography which separates substances in a mixture primarily based on the boiling point but also on the affinity of the column used for the separation. The mass spectrometer breaks each molecule into ionized fragments and sorts the ions based on their mass-to-charge ratio.
Using both GC and MS gives more certainty when identifying substances. Using a column coated with an appropriate stationary phase causes the substances within the sample to elute at different times, known as the retention time. In some cases, substances may travel through the column using the same amount of time, which results in two or more substances that co-elute. When using MS as the detector, these substances may be identified by the mass spectra. Two different substances may also have a similar pattern of ionized fragments when using a mass spectrometer, as shown in the mass spectra of Diethyleneglycol dimethacrylate and Triethyleneglycoldimethacrylate, but often have different retention times.
With the use of GC-MS we are able to identify substances often used in dental materials e.g. composites, sealants and denture base materials.
NIOM has extensive experience with the use of gas chromatography and have made our own library of substances over the years, which helps us to identify unknowns based on retention time. For identification we also use Safety data sheets, manufacturer’s instruction, a NIST MS Search program, and reference solutions.
When substances are identified they may also be quantified using GC-MS. The detection/quantification limits are set for each substance.
NIOM is experienced in quantification of residual methyl methacrylate according to the two standards of ISO 20795 — Dentistry — Base polymers Part 1 and 2.