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

Elemental quantitation of carbon via production of polyatomic anions in gas chromatography-plasma assisted reaction chemical ionization mass spectrometry

Elemental mass spectrometry offers quantitation and isotopic analysis without the need for compound-specific standards. We have recently introduced plasma assisted reaction chemical ionization (PARCI) as an efficient elemental ionization method for halogens. Here, we report a new ionization chemistry in PARCI for facile quantitation of elemental carbon in gas chromatography eluates. We demonstrate that in-plasma reactions of organic compounds followed by afterglow ionization lead to formation of polyatomic anions (CN^-, OCN^-, and CO₃^-), among which CN^- offers the best analytical sensitivity with a detection limit of ~25 pg (21 pg/s) carbon on column. Using a mixture of pesticides with wide variations in structures and heteroatom content, we demonstrate that CN^- ion response is quantitatively correlated with the carbon concentration over two orders of magnitude (r ² = 0.985). We show that the novel GC-PARCI-MS method provides recoveries within 80-120% using a single standard for all analytes, highlighting the strength of elemental quantitation. Further, the ability of GC-PARCI-MS to identify ¹³C-tagged molecules without a priori knowledge of chemical formulas of analytes is demonstrated. Graphical abstract ᅟ.

Chemical Reaction Interface Mass Spectrometry with High Efficiency Nebulization

A high efficiency nebulizer (HEN) coupled to a heated spray chamber and a membrane desolvator is used for liquid sample introduction in chemical reaction interface mass spectrometry (CRIMS). Compared to the conventional thermospray nebulizer operated at solvent flow rate of 1 mL/min, the HEN provides small droplets at lower flow rates (10-100 microL/min), improving the desolvation and analyte transport efficiency. As a result, the sensitivity for carbon detection by CRIMS is improved by a factor of 4. The new arrangement offers an easy-to-use and robust interface, facilitating the availability of a variety of liquid chromatographic techniques to the CRIMS. Separation and detection of labeled peptides in a mixture of unlabeled biopolymers is illustrated at a solvent flow rate of 45 microL/min as an example of new possibilities offered by the improved liquid introduction interface.

An innovative method for measuring hydrogen and deuterium: chemical reaction interface mass spectrometry with nitrogen reactant gas

A new method for measuring deuterium isotopic enrichment with CRIMS (chemical reaction interface mass spectrometry) is described. Using nitrogen as the reactant gas in a chemical reaction interface generates molecular hydrogen that provides the H2 and HD from which the deuterium content can be analyzed with a benchtop quadrupole mass spectrometer. Samples of deuterated leucine in unlabeled leucine were used as the primary test species. Detection of deuterium enrichment was accurate, precise, and linear. We used this scheme to evaluate the results of a process to acetylate lysine residues in a peptide-neurotensin. With separation on a C18 column, we found a 61% yield of the desired monoethylated product that had a D/H ratio very close to the theoretical one. Isotope ratio monitoring for deuterated species will be important in metabolism studies where CRIMS generates a comprehensive and quantitative view of products of deuterated precursors. Where concerns about metabolic isotope effects of deuterium are absent, the use of deuterium will enable these studies to be performed with simpler syntheses and at less cost than if using 13C or 15N.

Continuous-flow isotope ratio mass spectrometry using the chemical reaction interface with either gas or liquid chromatographic introduction

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%).

Element- and isotope-specific detection for high-performance liquid chromatography using chemical reaction interface mass spectrometry

We have developed a combination of high-performance liquid chromatography (HPLC) and the chemical reaction interface mass spectrometry (CRIMS) method by using a Vestec Universal Interface (UI). This interface provides the extremely high degree of solvent removal that the CRIMS process requires. In doing so, we have produced an HPLC detector with the ability to carry out the element- and isotope-selective analyses with detection that is inherently: linear, structure-independent, sensitive, selective, comprehensive and flexible. The characteristics of the instrumentation and its performance are described.

An inductively coupled plasma-time-of-flight mass spectrometer for elemental analysis. Part III: Analytical performance

A time-of-flight mass spectrometer (TOFMS) was evaluated as a mass analyzer for inductively coupled plasma mass spectrometry (ICP-MS). The long-term drift of signals was in the range of 7-8% relative standard deviation, whereas the short-term precision was between 5 and 20%, somewhat worse than is typically reported for commercial ICP-MS instruments (5%). However, precision can be improved considerably in the TOFMS by ratioing isotopic peaks or through internal standardization, a consequence of its ability to extract all measured ions simultaneously from the inductively coupled plasma. This feature was demonstrated by monitoring the (206)Pb/(208)Pb ratio with boxcar averagers. In this ratioing mode, precision was improved to approximately 0. 5%. Detection limits were measured with two alternative signal processing systems: (1) discriminator-gated integration and (2) integration of digitized spectra. Both methods improved the signal-to-noise ratio by a factor of from 10 to 100, although detection limits were still 1-2 orders of magnitude poorer for most elements than from the best commercial ICP-MS instruments. The dynamic range of the discriminator-gated integration system is over 4 orders of magnitude, but can be extended to 10(6) with planned increases in primary ion-beam current, which is currently 10-100 times lower than is found in other instruments. Virtually simultaneous multielement and multiisotope analysis is possible for masses from (7)Li to (209)Bi with minimal mass bias and detection limits on the 0. 4-2-ppb level.