Analysis of Compound-specific Carbon Isotopic Composition of Polycyclic Aromatic Hydrocarbons by PTV-GC-IRMS

The carbon isotope ratio of PAHs is stable in the migration and transformation, which is an important traceability index and can be analyzed by gas chromatography-isotope ratio mass spectrometry (GC-IRMS). For samples with low PAH content, meeting the detection limit of GC-IRMS is the premise for high-precision and accurate analysis of the carbon isotope ratio.

To establish a PTV injection method with stronger intensity of PAHs, thereby improving the sensitivity of GC-IRMS carbon isotope analysis.

Parameters of the programmed temperature vaporization (PTV) injector were optimized, including injection mode (constant temperature splitless, PTV splitless and solvent split), pressure process, sample transfer temperature and time, evaporation temperature and time, and splitless time.

The optimized parameters were PTV splitless, transfer temperature of 320℃, transfer time of 1.0min, injection pressure operating in a gradient of 40—60—70psi, evaporation temperature of 55℃, evaporation time of 2.5min, and splitless time of 1.5min. Pre-columns reduced the peak width and increased the peak intensity, especially high boiling point PAHs as benzo(a)pyrene, indeno(1, 2, 3-cd)pyrene, dibenzo(a, h)anthracene and benzo(g, h, i)perylene increased by 50%-100%. The precision of δ¹³C of 16 PAHs determined by the optimized PTV-GC-IRMS were within 0.5‰. The fractionation within the system can be corrected by two PAH references.

The optimized PTV-GC-IRMS can adjust the precision and accuracy of compound-specific carbon isotope analysis of PAHs at low concentrations, and expand the applicability of isotope tracing in environmental studies.