Pyrolysis-GC-MS analysis

What is pyrolysis GC-MS used for?

Py-GC-MS is used in various fields of chemical analysis to test for the presence of chemical species and determine their respective concentrations. It can be used for quality control across the pharmaceutical and consumer goods industries, where it is especially useful when screening samples for polymers and plastics, which are notoriously difficult to detect through conventional means. The method can also be used to characterize polymeric materials and estimate the molecular composition of lignin samples.

The ability of py-GC-MS to detect plastic contaminants is also highly useful in environmental analysis, particularly when analyzing the presence of microplastics in drinking water, wastewater, sediment, soil, and sludge. The procedure for screening clean water samples for microplastics with py-GC-MS is outlined in ISO 16094-3, which is one of the first international standards for microplastic analysis (along with ISO 24187 and ISO 4484).

How does pyrolysis GC-MS work?

The key principle of py-GC-MS is that the sample is first pyrolyzed, which means that it is broken down with heat. The pyrolysis is conducted under an inert atmosphere, as this prevents the sample from reacting or oxidizing further, instead causing it to separate into smaller constituent parts.

The fragmented sample is then passed through a gas chromatography column, which will separate the components based on their size and chemical properties. Finally, the fragments pass through a mass spectrometer, which separates them further and detects them as they reach the end of the chamber, recording their respective mass/charge ratio. These ratios can be used to determine the chemical composition of the individual fragments, their concentrations, and subsequently the composition of the original sample.

Suitable samples and sample preparation

Unlike conventional GC-MS, there are fewer restrictions on what can be tested through py GC-MS, simply because the pyrolysis step helps to break down complex sample types to make them suitable for testing without much preparation. This means that py-GC-MS can be effectively carried out on small amounts of powdered solid samples. It can also be carried out on solutions, as well as dispersions of insoluble materials. Both clean and wastewater are also suitable sample materials.

Advantages and limitations of pyrolysis GC-MS

The key advantage of py-GC-MS is the ability to detect components in solutions that are non-volatile and therefore would not usually appear in conventional GC-MS analysis. Furthermore, it can be conducted on a greater range of sample types than other similar methods. Pyrolysis-GC/MS can also detect very small quantities of contaminants, down to microliters or micrograms within liters of sample material.

One key disadvantage of py-GC-MS in microplastics analysis is that it can only quantify polymers in micrograms per liter, thus not providing information on the number of particles that belong to different size ranges (Raman and FTIR spectroscopy are the recommended methods for obtaining particle size information). Furthermore, it is incapable of detecting certain inorganic substances, and non-homogeneous samples may produce slightly varying results, sometimes needing to be tested multiple times to reach reliable conclusions.