Effects of GC temperature and carrier gas flow rate on on-line oxygen isotope measurement as studied by on-column CO injection.
Although deemed important to δ18O measurement by on-line high-temperature conversion techniques, how the GC conditions affect δ18O measurement is rarely examined adequately. We therefore directly injected different volumes of CO or CO-N2mix onto the GC column by a six-port valve and examined the CO yield, CO peak shape, CO-N2separation, and δ18O 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 N2and CO decreases with an increase of GC temperature and carrier gas flow rate. δ18O 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 δ18O value of the injected CO is about 1‰ higher than that of identical reference CO. The δ18O distribution pattern of the injected CO is probably a combined result of ion source nonlinearity and preferential loss of C16O 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 N2-CO separation, lower He consumption, and insignificant effect on δ18O value, while a higher-than-60 °C GC temperature and a larger-than-100 µl CO volume is also recommended. When no N2peak is expected, a higher GC temperature is recommended, and vice versa. Copyright © 2015 John Wiley & Sons, Ltd.
College of Ocean and Earth Sciences, Xiamen University, Xiamen, 361102, China.|Key Laboratory of Coastal and Wetland Ecosystems, Ministry of Education, Xiamen University, Xiamen, 361102, China.
Zhi-Gang
ZG
Chen
The Third Institute of Oceanography, State Oceanic Administration, Xiamen, 361005, China.
Xi-Jie
XJ
Yin
Institute for Landscape Biogeochemistry, ZALF, Müncheberg, Germany.|Leibniz Institute of Freshwater Ecology and Inland Fisheries, Neuglobsow, Germany.
Youping
Y
Zhou
GC temperature; N2-CO separation; carrier gas flow rate; high-temperature conversion; on-line continuous flow; oxygen isotope