Home > Chemical Reaction Interface Mass Spectrometry: Roots, Research, and Implications
Chemical Reaction Interface Mass Spectrometry: Roots, Research, and Implications
Chemical Reaction Interface Mass Spectrometry (CRIMS) is a new and innovative analytical instrument for the selective detection of elements or isotopes. Initially developed by Dr. Fred Abramson at the George Washington University in conjunction with colleagues at the NIH in 1981, CRIMS opens up new possibilities in the field of Mass Spectrometry applications. CRIMS decomposes integral analytes down to elemental form with plasma gas. The resulting mixture is exposed to a reactant gas to form small compounds such as CO2 or NO2, and are then identified and quantified by conventional mass spectrometry. CRIMS hosts a wide range of cutting edge applications in a wide variety of research fields including the pharmaceutical, petrochemical, and biotechnology industries.
Chemical Reaction Interface Mass Spectrometry was originally developed by Fred Abramson while on sabbatical at the NIH from the George Washington University in 1981. Originally faced with a mass-spectrometry problem involving the characterization of methylated lipids, Abramson set out to find a method to detect 14C labeled compounds. With the help of colleagues a method developed in which a large compound containing 14C would be decomposed from its original form and react with oxygen to form 14CO2 (1). A gas chromatography machine was coupled with a Mass Spectrometer via a chemical reaction interface (see Figure 1). Helium carrier gas from a microwave induced plasma source was used to decompose the analyte and a reactant gas, oxygen, was added to the resulting solution of gasses. The polyatomic species were then carried to a mass spectrometer for analysis.
Early experiments and testing showed that analyte molecules decomposed thoroughly in the reaction chamber. Furthermore, an initial experiment using methylated-14C-palamitic acid revealed that 14CO2 was detected by MS at m/z 46 (1). NO2 was also detected at m/z 46, however, initially limiting CRIMS to non-nitrogen containing compounds.
A number of technical obstacles had to be initially overcome. Most importantly, CRIMS would have to be a perfectly sealed system, as atmospheric gasses from leaks would cause interference by integrating with the analyte products. Another analytical problem resulted from the inherent instability of CO2. CO2 readily converts to CO in a microwave plasma, causing interference peaks in the MS reading. Later tests found that using SO2 as a reactant gas generates more CO2 and is tolerated by the MS (1).
Figure
1: Schematic for CRIMS.
Figure 2: CRIMS Interface
Since 1981, CRIMS has been modified for various analytical roles.
Because the CRIMS instrumentation breaks down large molecules into smaller molecules, MS mass limits of detection are curtailed. By using a direct probe, Abramson and his team tested the upper size or molecular weight limit. A quartz probe with a magnetic hub was constructed to test this. Solutions of up to 65 KDa were placed on the probe tip and tested. A r = .8 relationship between the predicted sulfur/carbon ratio and that instrumentally observed was found (2). Not only did the direct probe method push the bounds of macromolecular analysis, unlike the GC method of introduction, it allowed the analysis of non-volatile material. The ability to analyze nonvolatile analytes has huge implications in biological work.
Perhaps the most promising innovation is use of HPLC instead of GC with CRIMS (see figure 4). Because of large amounts of analyte produced in HPLC, a direct line from HPLC to CRIMS would exceed the capacity of the interface. The first interface between HPLC and CRIMS used a moving belt to connect HPLC with the interface. Using a system of graduated vacuums and evaporation techniques, most of the solvent is removed. Using a 1/16” belt, 70% of the sample was conducted with a detection of 20ng (4). The system had its drawbacks, including a high breakdown rate and a tendency of contamination from atmospheric air.
In 1990, Abramson collaborated with Marvin Vestal to replace the moving belt method with a Vestec Universal Interface. The interface adds a “countercurrent membrane component to a particle beam” which removes the solvent vapors, leaving an analyte particle beam in a stream of helium (1). The HPLC/UI/CRIMS machine was field tested with 13 pmol of both
-globulin and polyguanilic acid. Both samples had large molecular weights (158 KDa and 150 KDa respectively). Both samples gave strong responses for12CO2 and 13CO2. Molecules with MW up to 850 KDa were tested with adequate success. The conjunction of HPLC and CRIMS seems to be a good universal analysis machine, able to handle mass analysis of large spectrum of molecules with disregard to size, shape, ionic state, and lipophilicity (1).
Possibly the most powerful application of CRIMS is the measurement of stable isotope ratios. The method shows special promise in the measurement of deuterium isotopic enrichment. Current Mass Spectrometric measurements of deuterium detection rely on heavy rates of labeling and become less effective when the labeling rate is not high. The process uses nitrogen as the reactant gas to react with hydrogen to ammonia, which decomposes in the CRIMS interface to H2 and N2.
Paolo Lecchi and Fred Abramson published data on an anlaysis of unlabeled leucine and [d10]-leucine in The Journal of American Society of Mass Specctrometry (5). Research was done on a Hewlett-Packard 5971 MSD, modified for GC/CRIMS. An amino-bonded polymeric HPLC column was used to retain the leucine and avoid contamination. Using different concentrations of deuterated sample, the ability of CRIMS to detect deuterium isotopes was tested. Samples of 20
g with 10% deuterated leucine were injected, resulting in MS spectrums with both good linearity (r = 0.999) and accuracy (slope = 1.019). The method was able to make quantitative analysis on enrichments below 0.1% (5). Further experiments with other bio-molecules show that CRIMS in combination with a nitrogen reaction gas is accurate, linear, and reproducible.
While CRIMS can be used for
the detection of virtually any element with a stable isotope, it is
most commonly used with isotopes of hydrogen, carbon, nitrogen, oxygen,
phosphorous, sulfur, chlorine, selenium, and bromine (6).
CRIMS offers a plethora of
analytical applications in both research and medical applications.
CRIMS has extensive potential in wide range of industries, including
pharmacology, geology, manufacturing, petrochemical exploration, environmental
studies, and biotechnology.
Because of it’s precision in stable isotope analysis and applications to large biomolecules, CRIMS has a host of unique applications in drug metabolism studies. Analysis with CRIMS in tandem with stable isotopes is especially well suited for pharmaceutical research involving those most sensitive to radiation, including pregnant women and children.
It is well established through a number of studies on humans and animals that stable isotopes rarely generate toxicity in the patient. Common stable isotopes for drug metabolism studies include 2H, 13C, 15N, and 18O (7). Such isotopes when substituted into biomolecules are useful in studying reaction intermediates, pathways, gene expression, and metabolism rates.
Studies conducted by Abramson were compared the use of radioisotopes analyzed with an in-line radioactivity monitor (RAM) to stable isotopes analyzed with CRIMS. Doses of unlabeled neurosteroid tirilazad and that substituted with 13C, 15N, and 14C were administered to monkeys. The bile was collected and analyzed with both HPLC-CRIMS and HPLC-RAM. In terms of signal/noise, sensitivity, and chromatographic resolution, CRIMS proved superior.
Furthermore, the possibility of replacing radioisotopes in routine medical procedures lowers the personal risk of those exposed and the environmental risk of manufacture, transport, and disposal of radioisotopes.
With the dawn of nanotechnology, and the possibility of micro-machines that perform routine maintenance on cells and organs looms. CRIMS coupled with stable isotopic labeling poses an effective solution to the complicated problem of tracking these small machines during both research and routine medical procedures.
The chemical manufacturing industry is multibillion dollar industry dependent upon quality control. The quality and effectiveness of chemicals such as explosives and organic materials can be heavily influenced by a compounds breakdown. Isotopic labeling poses a possible solution to monitoring the quality of stored military ordinance, fertilizer, and lubricants.
The petrochemical industry is another possible source of applications. CRIMS could be used in petrochemical exploration, quality control, and chemical research. The oil industry has invested hundreds of millions of dollars into research to further understand the location, extent, and movement of subterranean oil reserves. They currently use radioactive tracers to monitor the size and flow of underground oil reserves. Furthermore, detection of leaks in refineries and our understanding of the physics of refining could be further understood by use of CRIMS and isotopic labeling.
Environmentalists find a host of applications to use CRIMS on. In sensitive environmental studies, including the monitoring of pollution, chemical leakage, underground water movement and atmospheric studies in pollution, CRIMS poses an optimal solution with high sensitivity and low environmental impact. The degradation and decomposition of chemicals such as DDT or plastics could be better studied.
Finally, one of the most lucrative
research areas today is biotechnology. Biotechnology studies the
largest and most sensitive molecules in the body including proteins,
enzymes, DNA, and RNA. CRIMS is especially well suited for the
study of all of these molecules. The ability to analyze non-volatile
analytes is essential. Also, being able to handle molecules with
molecular weights above the 100KDa level in a non-toxic manner is essential
to the industry.
Figure 3:
CRIMS Interface with attachment for MS.
Figure 4:
HPLC modified for interface with CRIMS
Figure 5:
Mass Spectrometry Unit with intake from CRIMS
1. Abramson, F. P.
Mass Spectrometry Reviews. 1994, 341-356.
2. Abramson, F. P. Markey,
S. P. Biomed. Environ. Mass Spectrom. 1986, 411-415.
3. Lecchi, P. Abramson,
F. P. Anal. Chem.
1999, 71, 2951-2955.
4. Moini, M. A.;
Abramson, F.P.; Vestal, M. A. Proc. ASMA Conf.
1992, 40, 1440-1441.
5. Lecchi, P.; Abramson,
F. P.; J Am. Soc. Mass Spectrom.2000, 11, 400-406.
6. Scientific Instruments,
Incorporated. CRIMS Applications. http://www.sisweb.com/ms/sis/crimsapp.htm
7. Abramson, F. P.
Seminars in Perinatology.
2001, 25, 133-138.
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