Large-volume injection combined with gas chromatography/isotope ratio mass spectrometry for the analysis of polycyclic aromatic hydrocarbons.

Rationale: Compound-specific stable isotope analyses of carbon require relatively large amounts of sample for reliable analyses. Commonly applied injections of 1 μL may thus be insufficient for samples with low concentrations of pollutants (e.g. air particulate matter) or when the amount of a sample is limited.

Methods: A Large-Volume Injection (LVI) method for carbon stable isotope ratio analysis of Polycyclic Aromatic Hydrocarbons (PAHs) was optimized in this study. Gas chromatography/combustion/isotope ratio mass spectrometry (GCCIRMS) and ion trap mass spectrometry (ITMS) were used for the determination of stable carbon isotope ratios and quantification of compounds, respectively.

Results: The optimized method resulted in very good reproducibility, even for the most volatile PAH, naphthalene, when a small amount of higher boiling co-solvent was used. No significant fractionation of isotope ratios could be seen and the recoveries of analytes were similar to or better than that of a splitless cold injection.

Conclusions: Injection of 100 μL, instead of the commonly used 1 μL, increases the detection limit for PAHs significantly and/or simplifies the sample preparation step. Using our optimized method, stable carbon isotope ratios can be reliably measured in samples with concentrations of PAHs down to 0.05-0.1 ng μL(-1).