程序升温-气相色谱-同位素比值质谱法分析多环芳烃单体碳同位素组成

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

环境样品中PAHs的单体碳同位素比值在迁移转化过程中能基本保持稳定,是重要的溯源指标,可通过气相色谱-同位素比值质谱(GC-IRMS)分析获得。对于低PAHs含量的样品,满足GC-IRMS检出限是高精度、准确分析单体碳同位素比值的前提。本文优化了一种程序升温汽化进样(PTV)方法,通过对PTV进样模式及进样口参数进行优化调整,提高目标物谱峰强度,进而提高GC-IRMS碳同位素分析的灵敏度。实验对比研究了恒温不分流、PTV不分流和溶剂分流进样模式,并对PTV进样口参数包括进样口压力梯度、传输温度和时间、蒸发温度和时间、进样口不分流时间进行了对比优化,以选出最优的PAHs单体碳同位素分析条件。结果表明:在PTV不分流进样、进样口压力40psi—60psi—70psi梯度升高、传输温度320℃、传输时间1.0min、蒸发温度55℃、蒸发时间2.5min、不分流时间1.5min条件下,PAHs的单体碳同位素结果最优。增加预柱可以提高峰强,尤其5环PAHs的峰强度提高达50%~100%。单体碳同位素分析精度(1σ)在0.5‰以内,系统性碳同位素分馏可以采用双标法校正。优化后的PTV-GC-IRMS方法可以实现低含量PAHs单体碳同位素的高精度、准确分析,扩大了同位素溯源在环境研究中的适用性。

BACKGROUND: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.OBJECTIVES:To establish a PTV injection method with stronger intensity of PAHs,thereby improving the sensitivity of GC-IRMS carbon isotope analysis.METHODS: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.RESULTS:The optimized parameters were PTV splitless,transfer temperature of 320℃,transfer time of 1.0 min,injection pressure operating in a gradient of 40—60—70 psi,evaporation temperature of 55℃,evaporation time of 2.5 min,and splitless time of 1.5 min.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 ofδ13C 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.CONCLUSIONS: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.