A new apparatus for laser micropyrolysis-gas chromatography/mass spectrometry

A new instrumental configuration for laser micropyrolysis - gas chromatography/mass spectrometric analysis is reported. The principal devices are a high powered continuous wave Nd:YAG laser; a commercial reflected light/fluorescence microscope (slightly modified to accommodate laser radiation), a pyrolysis chamber, a gas inlet system, a gas chromatograph (modified to accommodate the inlet system) and a hybrid (double focusing-quad) mass spectrometer. The mass spectrometer offers very high sensitivity (max^m = 5 × 10^-7 C μg^-1) and mass resolution (max^m = 80 000). A Sydney Basin torbanite sample was analysed to test the efficiency and potency of the instrument. High concentrations of pyrolysis products were obtained from the sample with mild laser conditions. The dominant products are homologous series of straight chain aliphatic hydrocarbons ranging from C₆ to greater than C₃₀. Secondary contaminant products from sample charring were minimal with laser energies in the region of 0.5-3 W, even for continuous exposure of up to 300 s duration. To make comparison with more conventional techniques used for the pyrolysis of organic sediments, the Sydney Basin torbanite sample was also subjected to gas chromatography/mass spectrometric analysis with the following pyrolysis methods: (i) a pyroprobe; (ii) a pyrojector; and (iii) a quantum microscale sealed vessel (MSSV-1) pyrolysis unit. A comparison reveals similar aliphatic dominated product distributions from each pyrolysis method. The consistency of these results proves the capability of the new laser apparatus to perform analytical pyrolysis at a microscopic level, rather than on bulk samples as required by more traditional techniques.