The reactor is modeled as a linear series of discrete gas parcels moving past and interacting with a single, stationary box representing surface adsorption sites in graphitic carbon (Fig. S-1). Each gas parcel equilibrates with the graphite surface for one residence time (τ, typically 0.5 s), after which the gas parcels shift sequentially and the next gas parcel equilibrates. The molar amount a...

RATIONALE: Organic nitrogen (N) greatly exceeds inorganic N in soils, but the complexity and heterogeneity of this important soil N pool make investigations into the fate of N-containing additions and soil organic N cycling challenging. This paper details a novel approach to investigate the fate of applied N in soils, generating quantitative measures of microbial assimilation and of newly synth...

Popularity of gamma-hydroxybutyric acid (GHB) is fairly stable among drug users, while the consumption of its chemical precursor, gamma-butyrolactone (GBL), is a growing phenomenon. Although conventional analytical methods allow to detect this substance in various matrices, linking a trace and a source is still a difficult challenge. However, as several synthesis pathways and chemical precursor...

A survey of the multi-stable isotopic composition of an active pharmaceutical ingredient (API), naproxen, was performed to assess the potential of Isotope Ratio Mass Spectrometry (IRMS) to distinguish the provenance of APIs. Twenty-six lots of naproxen from six manufacturers representing four countries (Italy, India, Ireland, and the USA) were analyzed for three isotope ratios (13C/12C, 18O/16O...

A study was conducted to differentiate lard, chicken fat, beef fat and mutton fat using Gas Chromatography Mass Spectrometry (GC-MS) and Elemental Analyzer-Isotope Ratio Mass Spectrometry (EA-IRMS). The comparison of overall fatty acid data showed that lard and chicken fat share common characteristics by having palmitic, oleic and linoleic acid as major fatty acids while beef and mutton fats sh...

Compound-specific analyses of lipid D/H ratios often encounter ranges of 300 per thousand or more, and experiments using D-enriched water to study fractionations often extend the range up to 1000 per thousand. Here we show that for such large dynamic ranges in D/H ratio, isotopic "memory" between adjacent peaks can be significant. Memory effects have not been previously reported for GC/P/IRMS s...

Nondispersive infrared spectrometry (NDIRS) was used to detect Helicobacter pylori infection with the 13C-urea breath test. The results were compared with those of standard isotope ratio mass spectrometry (IRMS). Both methods accurately distinguished between H. pylori-positive and H. pylori-negative individuals. The results demonstrate that NDIRS technology is accurate and therefore of equal va...

The isotopic composition, e.g. 14C/12C, 13C/12C, 2H/1H, 15N/14N and 18O/16O, of matter elements is heterogeneous. It is ruled by physical, chemical and biological mechanisms. Isotopes thus be enable to follow the fate of mineral and organic compounds during biogeochemical transformations. The determination of the isotopic composition of organic substances occurring at trace level into very comp...