BACKGROUND Epitestosterone is prohibited by sport authorities because its administration will lower the urinary testosterone/epitestosterone ratio, a marker of testosterone administration. A definitive method for detecting epitestosterone administration is needed. METHODS We developed a gas chromatography-combustion-isotope ratio mass spectrometry method for measuring the delta(13)C values fo...

Stable isotope labeling is a standard technique for tracing material transfer in molecular, ecological and biogeochemical studies. The main assumption in this approach is that the enrichment with a heavy isotope has no effect on the organism metabolism and growth, which is not consistent with current theoretical and empirical knowledge on kinetic isotope effects. Here, we demonstrate profound c...

it is very important to determine the stable nitrogen isotope ratio for the nitrogenous substances in aerosols and the geochemistry behavior of stable nitrate ion isotopes in aerosols in order to elucidate the chemical and physical functions of clouds. hence, aerosol field sampling was conducted in the skies offshore from malibu beach and santa barbara, california, u.s.a. on 16 and 18 july 2009...

The recent development of multidimensional liquid chromatographic methods combined with tandem mass spectrometry (LC-LC-MS/MS) has permitted sensitive detection of thousands of low abundance proteins, membrane proteins and proteins with extreme isoelectric points (pI) from highly complex protein mixtures. The ability to perform global relative quantitative proteomics has been significantly enha...

Accumulating evidence suggests that cellular metabolites and nutrition levels control epigenetic modifications, including histone methylation. However, it is not currently possible to measure the metabolic control of histone methylation. Here we report a novel detection method to monitor methyl transfer from serine to histones through the one-carbon metabolic pathway, using stable-isotope label...

The development of an enzyme-linked immunosorbent assay (ELISA) for the detection of heat-labile Escherichia coli enterotoxin is described. The assay, which is based on the immunological similarity between Vibrio cholerae toxin and heat-labile E. coli enterotoxin, is similar in design to a radioimmunoassay but utilizes enzyme-labeled rather than radioactive isotope-labeled reagents. The ELISA s...

The second point makes the matrix matching of standards to samples for direct analysis impossible and, in order to normalize all samples to a similar matrix, the analysis of a diluted (or digested) solution is preferable. High instrumental sensitivity is then required to reliably measure the resulting single digit pg g-1 uranium concentrations. While the quantification of uranium is therefore d...

The commercial availability of inductively coupled plasma-mass spectrometry technology (ICP-MS) has presented the opportunity to measure the boron concentrations and isotope ratios in a large number of samples with minimal sample preparation. A typical analytical sequence for fecal samples consists of 25 acid blanks, 1 digestion blank, 5 calibration solutions, 4 standard reference material solu...

Combined capillary gas-liquid chromatography-electron capture negative chemical ionization mass spectrometry of pentafluorobenzyl ester-TMSi ether derivatives of bile acids and isotope dilution using deuterated internal standards are introduced as a sensitive and selective analysis technique for plasma bile acids. As a result of the high ionization efficiency of pentafluorobenzyl derivatives un...

Introduction Accelerator mass spectrometry (AMS) is an ultrasensitive analytical technique for measuring rare nuclides. Single atoms of one isotope can be counted in the presence of 1015 atoms of a neighboring isotope. AMS is used mainly for measuring radionuclides since stable nuclides are usually sufficiently abundant to measure with smaller instruments. The potential for AMS to make possible...