Nitrogen isotope ratios, instrumental

CF-IRMS Continuous flow-isotope ratio mass spectrometry. A procedure that uses an instrument that is capable of repeatedly and rapidly measuring the masses of selected gases (e.g., carbon dioxide, hydrogen, nitrogen) delivered in a continuous gas stream from another instrument, such as an elemental analyzer or a gas chromatograph, to determine their isotopic compositions. 

The capability to obtain accurate isotope ratio results at very low concentrations as presented here is dependent on the system used. MS-ICP-MS is a more sensitive instrumentation than is a Q-ICP-MS.The use of a desol-vating introduction system permits greater sensitivity than does use of a standard double-pass, cyclonic, or conical spray chamber, even if Peltier cooled. The use of desolvation also permits lower polyatomic ion formation as demonstrated by very low uranium oxides during optimization. Thus, instrumental setups that differ from those utilized here will have to be evaluated for limitations of their capabilities. The results obtained using SPE, a desolvating introduction system with nitrogen addition, and an MS-ICP-MS instrument will differ dramatically from those obtained at the same concentration using dilution only with a Q-ICP-MS and a standard introduction system. One should not expect to use QC samples spiked with only 20 ng/L total uranium with the latter system. 

The tumaroimd time was 24-72 hours, depending on the substances targeted. Instruments used were GCMS and GC with a nitrogen-phosphorus detector (NPD). The mass spectrometers included quadrupole, time-of-flight, and isotope ratio systems. Isotope ratios of were used... 

An instrument that measures the isotopic mass ratio of a gas by bombarding the sample in an electron beam, such that the molecular ions generated can be deflected in their trajectories through a magnetic field in accordance to their charge/mass ratios. These devices are extremely accurate and reliable, and many stable isotope experiments can be analyzed by converting the isotopi-caUy substituted metabolite into carbon dioxide, water, or molecular nitrogen prior to I RMS measurements. 

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