Topic of the Month: February 2015 - Relevant details for laboratory work on the application

Analysis of microplastic

System for the pyrolysis analysis of microplastic. Image: GERSTEL

The scientists used a GC 7890 (Agilent Technologies) equipped with a cooled injection system (CIS) for their analytical method. A thermal desorption system (TDS) was fitted on this, equipped with a precisely co-ordinated TDS module for pyrolysis (PM1). This combination is suitable for manual procedure in the thermal desorption of volatile compounds, including pyrolysis of one and the same sample. If, on the other hand, the intention is to process larger numbers of samples, automation of the process is advisable and is possible using an autosampler in connection with the thermal desorption unit (TDU) and a special pyrolysis module.

Fries et al. adopted the following procedure in their tests: one microparticle was in each case put in a pyrolysis test tube and was heated up in the TDS, initially from 40°C to 350°C (10 min.) at 10°C/min.; the volatile compounds escaped from the matrix during this process. Cryofocussing of the analytes was carried out in the CIS at –50°C; they were then transferred to the GC column in the context of a temperature programme [-50°C – 12°C/min. – 280°C (3 min.)]. The GC column was a 30 m HP-5MS with a 250 µ ID and a film thickness of 0.25 µ. The GC furnace was heated up via a temperature programme [40°C – 15°C/min. – 180°C – 5°C – 300°C (12 min.)]. The carrier gas was helium.

After the chromatogram of the volatile and non-volatile compounds had been produced, pyrolysis of one and the same sample was carried out. The TDS was heated up from 60°C (1 min.) to 350°C at 180°C/min. in preparation for this. Pyrolysis was then carried out in the PM1 module at 700°C (1 min.). The resulting fragments were transferred to the CIS (which had been cooled with liquid nitrogen) with the flow of carrier gas, were cryofocussed and were then transferred to the GC after heating. A MS 5975C from Agilent Technologies was used for mass selective detection: the chromatogram of the volatile compounds was recorded in the first stage and this was followed immediately afterwards – in the second stage – by the pyrogram of the pyrolysis products.
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