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Effects of GC temperature and carrier gas flow rate on on‐line oxygen isotope measurement as studied by on‐column CO injection
Author(s) -
Chen ZhiGang,
Yin XiJie,
Zhou Youping
Publication year - 2015
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.3617
Subject(s) - chemistry , analytical chemistry (journal) , volumetric flow rate , volume (thermodynamics) , oxygen , injection port , two dimensional gas , chromatography , gas chromatography , thermodynamics , organic chemistry , physics , medicine , surgery
Although deemed important to δ 18 O measurement by on‐line high‐temperature conversion techniques, how the GC conditions affect δ 18 O measurement is rarely examined adequately. We therefore directly injected different volumes of CO or CO–N 2 mix onto the GC column by a six‐port valve and examined the CO yield, CO peak shape, CO–N 2 separation, and δ 18 O value under different GC temperatures and carrier gas flow rates. The results show the CO peak area decreases when the carrier gas flow rate increases. The GC temperature has no effect on peak area. The peak width increases with the increase of CO injection volume but decreases with the increase of GC temperature and carrier gas flow rate. The peak intensity increases with the increase of GC temperature and CO injection volume but decreases with the increase of carrier gas flow rate. The peak separation time between N 2 and CO decreases with an increase of GC temperature and carrier gas flow rate. δ 18 O value decreases with the increase of CO injection volume (when half m / z 28 intensity is <3 V) and GC temperature but is insensitive to carrier gas flow rate. On average, the δ 18 O value of the injected CO is about 1‰ higher than that of identical reference CO. The δ 18 O distribution pattern of the injected CO is probably a combined result of ion source nonlinearity and preferential loss of C 16 O or oxygen isotopic exchange between zeolite and CO. For practical application, a lower carrier gas flow rate is therefore recommended as it has the combined advantages of higher CO yield, better N 2 –CO separation, lower He consumption, and insignificant effect on δ 18 O value, while a higher‐than‐60 °C GC temperature and a larger‐than‐100 µl CO volume is also recommended. When no N 2 peak is expected, a higher GC temperature is recommended, and vice versa. Copyright © 2015 John Wiley & Sons, Ltd.