Effects of GC temperature and carrier gas flow rate on on-line oxygen isotope measurement as studied by on-column CO injection

Simple software solution for N2 diversion when measuring δ18O values of nitrogen-rich samples materials using a Thermo Scientific EA-IRMS System

This method is a simple, cost-free, and reliable approach for the removal of N2 interference on a CO analyte when analysing nitrogen-rich (>0.5% w/w) samples by Elemental Analysis Isotope Ratio Mass Spectrometry. Specifically, the isobaric interference on m/z 30 is eliminated using only the open split of the Thermo Scientific ConFlo IV Universal Interface Device, improving the analytical workflow when using a static temperature Gas Chromatography (GC) column. It simplifies the N2 diversion methods described in recent decades. When applied, the method described here:•Provides sufficient baseline resolution between the N2 and CO analytes, to permit quantitative N2 diversion, using an extended length packed GC column;•Quantitatively eliminates all N2 analyte from the analytical gas stream ensuring that no N2 enters the ion source and therefore no isobaric interference is produced on m/z 30 ion trace of the CO analyte;•Allows reproducible measurement of δ18O values from nitrogen-rich sample materials without a N2 isobaric interference, where the CO analyte is measured on the analytical baseline that it was produced on in the reactor (i.e., no addition make-up helium or new baseline of pure helium for the CO analyte).

Phosphate distribution and sources in the waters of Huangbai River, China: using oxygen isotope composition of phosphate as a tracer

We investigated the distributions of phosphate (PO₄-P) and used the oxygen isotope composition of phosphate (δ¹⁸O_P) to quantify PO₄-P sources in the waters of Huangbai River. According to the environmental characteristics of Huangbai River basin, the sampling stations in the Huangbai River were divided into three groups: sampling stations in the phosphate mining area, in the outcrop area of phosphate rock, and in the residential/agricultural area. The average PO₄-P concentration was highest (2.34 ± 1.00 μmol/L) in the outcrop area of phosphate ore, intermediate in the residential/agricultural area (1.06 ± 1.21 μmol/L), and lowest in the phosphate mining area (0.58 ± 0.31 μmol/L). The δ¹⁸O_P measured in the Huangbai River waters ranged from 6.0 to 20.9‰, with the highest average value in the outcrop area of phosphate rock (average: 14.6‰ ± 3.1‰). The majority of the measured δ¹⁸O_P values in the Huangbai River deviated greatly from the expected equilibrium values, indicating that δ¹⁸O_P in this area could be used to trace PO₄-P sources. We used two end-member mixing models to quantify the contribution of PO₄-P from different sources. In the phosphate mining area, the average fractions of PO₄-P from phosphate ore and sewage were 49.5% ± 23.8% and 50.5% ± 23.8%, respectively. In the outcrop area of phosphate rock, the average fractions of PO₄-P from phosphate ore and sewage were 60.1% ± 21.7% and 39.9% ± 21.7%, respectively. In the residential/agricultural area, the average fractions of PO4-P from fertilizer and sewage were 49.2% ± 23.2% and 50.8% ± 23.2%, respectively. These results indicate that phosphate mining activities was not an important source for PO₄-P in the waters of Huangbai River. The natural weathering of phosphate rock, fertilization, and domestic sewage contributed more to the high PO₄-P concentrations in the Huangbai River waters.