Continuous-Flow Isotope Ratio Mass Spectrometry Using the Chemical Reaction Interface with Either Gas or Liquid Chromatographic Introduction

Abstract

A novel method of sample introduction into an isotope ratio mass spectrometer (IRMS) is described. The technique uses the chemical reaction interface (CRI) to convert samples coming from a gas chromatograph (GC) or high-performance liquid chromatograph (HPLC) into CO2 using a microwave-induced helium plasma. Optimization parameters for both GC/CRI/IRMS and HPLC/CRI/IRMS are described. In both modes of operation, it was possible to obtain 13CO2/12CO2 ratios with standard deviations less than 1%. Investigation of HPLC/CRI/IRMS performance at low and high concentrations (0.5-10 micrograms) resulted in no significant deviations of the isotope ratios. The ability to differentiate samples of different biological origins was illustrated using chlorophyll a from spinach and algae, where a large difference was observed but good precision was maintained (SD < 0.60%).

Peer Reviewed: Measuring DNA Synthesis Rates with Stable Isotopes.

“…We hypothesize that the salvage pathway predominates under most conditions. Certainly, the low precursorproduct relationship we found in cells given [1][2][3][4][5][6][7][8][9][10][11][12][13] C]glycine supports that suggestion (2). However, when G-CSF triggers a surge in white blood cell production with its attendant increase in DNA synthesis, the availability of preformed nucleosides is not sufficient to meet the body's needs, and the de novo pathway becomes more important.…”

“…The trick is finding a labeled DNA precursor that has meaningful bioavailability. To address this question, single intravenous and oral doses of [1,[2][3][4][5][6][7][8][9][10][11][12][13] C 2 ]glycine, [U-13 C]glucose, and [U-13 C, 15 N]thymidine were administered to rabbits. The bioavailability of glycine at 3 mg/kg in one rabbit was 21%, and the bioavailability of glucose at 10 mg/kg in another rabbit was 43%, showing that both glycine and glucose would allow oral dosing.…”

Flow injection with chemical reaction interface-isotope ratio mass spectrometry: an alternative to off-line combustion for detecting low levels of enriched 13C in mass balance studies

“…The general configuration of the instrument used in these experiments has been described before [4]. It consists of a HPLC pumping system coupled to an IRMS with a unique interface.…”

“…Changes in the 45/44 ratios between samples will correctly represent changes in the 13 C content. To be formal, our calculations use the notation PDB*, where the asterisk denotes the absence of this correction [4]. In each calculation, the isotope ratio of our standard (dCMP that we determined had a 13 C PDB* of Ϫ25.19‰ Ϯ 1.13 via a chain of measurements ultimately linked to PDB) was used as R STD , and the isotope ratio of each unknown peak was calculated from that known value.…”

“…The system used the chemical reaction interface mass spectrometry (CRIMS) technique that we recently adapted to an IRMS [4]. Following flow injection, CO 2 will be produced and transmitted to the IRMS in a steady stream of helium for the duration of the injection period.…”