THE USE OF TWO-DIMENSIONAL GC-MS FOR THE IDENTIFICATION AND QUANTIFICATION OF LOW MOLECULAR WEIGHT COMPOUNDS FROM HIGH PERFORMANCE ELASTOMERS

摘要

A full characterisation of the low molecular weight compounds present in rubber compounds is becoming increasing necessary due to the requirements of the food and pharmaceutical industry. It is important that manufacturers of medical devices, such as metered dose inhalers (MDI) and food contact rubber products, can provide information on the types and levels of compounds, including breakdown products, that may have the potential to migrate into drugs and foodstuffs. This knowledge is also of use in others areas, such as in occupational health or environmental areas, where the knowledge gained can form part of effective risk management strategies for workplace fume or external emissions. Better characterisation data on these low molecular weight components is also vital in reverse engineering work, where an improved knowledge of, for example, the breakdown products of a cure system can enable the analyst to provide the client with a more accurate formulation. The range of low molecular weight components present in rubber is complex and will include monomers and oligomers, manufacturing impurities and artefacts within compound additives, the additives (eg process aids, antidegradants and cure system species) themselves, as well as breakdown products. These breakdown products can originate from a number of sources, for example reaction products from components of the base polymer as a result of the thermal history of the compound, or products of additives such as curatives and antidegradants formed as a direct or indirect product of them performing their primary function in the compound. Gas-chromatography-mass spectroscopy (GC-MS) has been the analytical tool of choice for this type of investigative work for over thirty years due to it's ability to separate the components that are present in a complex mixture and then identify them via their mass spectra. The recent advent of two-dimensional gas chromatography (GCxGC) associated with mass spectroscopy (referred to as GCxGC to ToF-MS) has provided the rubber analyst with a quantum step improvement as the use of a non-polar and polar GC column in series greatly enhances the resolving power available and it is now possible to identify and quantify compounds that were masked by other, more abundant compounds or by multiple compounds having similar retention times. Analysis work has been carried out on five high performance elastomer formulations to illustrate how the use of the two-dimensional GC-MS technique can provide a more complete characterisation of the low molecular weight fraction within such materials.