Elemental quantitation of carbon via production of polyatomic anions in gas chromatography-plasma assisted reaction chemical ionization mass spectrometry.

Elemental mass spectrometry offers quantitation and isotopic analysis without the need for compound-specific standards. We have recently introduced plasma assisted reaction chemical ionization (PARCI) as an efficient elemental ionization method for halogens. Here, we report a new ionization chemistry in PARCI for facile quantitation of elemental carbon in gas chromatography eluates. We demonstrate that in-plasma reactions of organic compounds followed by afterglow ionization lead to formation of polyatomic anions (CN, OCN, and CO), among which CN offers the best analytical sensitivity with a detection limit of ~25 pg (21 pg/s) carbon on column. Using a mixture of pesticides with wide variations in structures and heteroatom content, we demonstrate that CN ion response is quantitatively correlated with the carbon concentration over two orders of magnitude (r  = 0.985). We show that the novel GC-PARCI-MS method provides recoveries within 80-120% using a single standard for all analytes, highlighting the strength of elemental quantitation. Further, the ability of GC-PARCI-MS to identify C-tagged molecules without a priori knowledge of chemical formulas of analytes is demonstrated. Graphical abstract ᅟ.