Isotope dilution studies: Determination of carbon-13, nitrogen-15 and deuterium-enriched compounds using capillary gas chromatography—chemical reaction interface/mass spectrometry

Abstract

In addition to the ability of a capillary gas chromatographic-chemical reaction interface/mass spectrometric technique (CRIMS) to detect the presence of 13C, 15N and 2H (D) it can also quantify the level of the enriched substance. The microwave-powered chemical reaction interface converts materials from their original forms into small molecules whose mass spectra serve to identify and quantify the nuclides which make up each analyte. The presence of enrichment of each element is followed by monitoring the isotopic variants of CO2, NO or H2 which are produced in the chemical reaction interface. Chromatograms showing only enriched 13C and 15N are produced by subtracting the abundance of naturally occurring isotopes from the observed M + 1 signal. A selective chromatogram of 2H (D) is obtained by measuring HD at m/z 3.0219 with a resolution of 2000. Enrichment of 13C and 15N is quantified by measuring the ratio of excess 13CO2 to total 12CO2 or excess 15NO to total 14NO. To evaluate linearity and detection limits, we have used phenytoin as an example of an unlabeled substance and added various labeled phenytoin analogs. Atom enrichments of 0.3% were detectable for (2,4,5-13C3) phenytoin and 0.06% for (1,3-15N2)labeled phenytoin, each in the presence of 500 ng of unlabeled phenytoin, respectively. For deuterium, enrichment could not be directly determined. However, 1 ng of (ring D10) phenytoin was determined in the presence of 500 ng of unlabeled diethylated phenytoin. We have found CRIMS capable of quantifying 13C-, 15N- and D-enriched substances.

Liquid Chromatography/Chemical Reaction Interface Mass Spectrometry as an Alternative to Radioisotopes for Quantitative Drug Metabolism Studies

“…The CRIMS technique is thus useful for detecting compounds containing multiple intrinsic and extrinsic labels. It should be noted that no compound dependence has been reported for microwave combustion and mass spectral detection in CRIMS although successful implementation of LC/CRIMS methodology has lagged behind GC.…”

Implementation of the chemical reaction interface mass spectrometry technique on a Hewlett-Packard mass-selective detector

“…CRIM5 combines selective detection of elements and their isotopes and conventional mass spectrometry in a single system involving few modifications to the instrumentation. Selective detection of 2H , 13 C, 14 C, 15N, S, and CI has been reported [2][3][4][5][6][7][8][9][10][11][12]. The range of analytes includes drugs and drug metabolites, environmentally important substances, and endogenous compounds.…”

“…The useful species are CO 2, NO, and HCl. These three products show sensitive, selective, and linear detection characteristics and provide good isotopic information [2,3,5,[7][8][9][10][11][12]. Water is not a good analytical species because of adsorption, reactivity, and exchange.…”

Selective detection of sulfur-containing compounds by gas chromatography/chemical reaction interface mass spectrometry

“…For a giv en rea ctant gas the array of molecules formed reflects the elem en tal composition of the original analyte. Recently , applications of th is system for selective detection of BC, 15N , 2 H, and 14C [3][4][5][6] were published. Isotopic nitrogen detection by emission and mass sp ectrometry was previously reviewed [7].…”