Mass spec method used as biomedical tool - C&EN Global Enterprise

Oct 10, 1977 - Chemical ion mass spectrometry is an analytical technique that's barely more than a decade old. Yet, its comparatively gentle action on...
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hydrolyzable. Hence, deep well and ocean disposal have been advocated. Present knowledge of the peculiar metabolic ability of cephalopods and the fact that these organisms are numerous and widespread in the oceans add weight to this position. However, the effects of nerve gases on other classes of animals are not as well known, Hoskin points out, and ocean dumping of nerve gas may prove to be undesirable. Even so, the metabolic ability of the cephalopods cannot be readily discounted. At the least, it is another remarkable example of the ability of the hydrosphere to cleanse itself. Of obvious practical interest is the possibility that a nerve gas antidote eventually may be developed based on an enzymic hydrolysis reaction like the squid's. If the possibility does exist, the search for an enzymic antidote will be long and probably arduous. It is not known, for example, if humans can retain an effective hydrolytic enzyme, or even tolerate it, in the form managed by the squid or other cephalopods. But the hope persists, and the squid probably will be subjected to even closer scrutiny in the future. D

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Mass spec method used as biomedical tool Chemical ion mass spectrometry is an analytical technique that's barely more than a decade old. Yet, its comparatively gentle action on molecules coupled with high sensitivity is making it attractive, particularly for work on biomedical problems. Dr. Ajay K. Bose and his colleagues, Dr. Hideji Fujiwara and Dr. Birendra Pramanik, at Stevens Institute of Technology, Hoboken, N.J., are applying CIMS to several classes of molecules from many biological sources. "CIMS allows us to see comparatively minor changes that occur in biological fluids and tissues," Bose says. "Once we learn what to look for, these slight changes could be used, for example, to diagnose disease. The body is 'willing* to yield more biochemical information—if we just know how to look at it." The Bose group, as well as several others, is looking at highly diverse molecules, including steroids, bile acids, prostaglandins, triglycerides, sugars, peptides, and pesticides. That list is not limiting, Bose says. Probably the most important limitation to CIMS so far is that 1000 is about the highest molecular weight that can be detected directly. Of course, like electron ionization mass spectrometry (EIMS), CIMS looks at ions that are generated from molecules by bombardment with an electron beam. But unlike EIMS, the newer technique does not use the electron beam directly to fragment the sample substance. Instead, another substance serves as the primary target of electrons. In breaking down, this substance ionizes the sample material, which can then be captured in the instrument's detector.

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Various gases usually serve as the re­ agent, or primary target, Bose explains. For example, excess methane may be mixed with some steroid to be analyzed. Because methane is plentiful, the beam of electrons is more likely to collide with and ionize methane than the steroid. But the many methane ions so generated are un­ stable. Thus, they are likely to break down and donate charges to steroid molecules when the two species collide. This process is gentle, Bose says, and hence very little fragmentation of the steroid occurs. Because of that, much stronger peaks are seen than with con­ ventional MS, and with far less materi­ al. "In this same [CIMS] process," he adds, "one can produce low-energy electrons that tend to strip protons off of steroids.,, This forms negative ions. With a nega­ tive-ion detector in the instrument, the range and sensitivity can be extended because "this process is even milder than the one that produces positive ions." One disadvantage, however, is that negative ion detectors still "must be built to order." Another way of generating negative ions is to evolve chloride ions. They tend to be stripped off of organic chlorides readily, Bose says, and thus provide a way of putting a good-sized ion tag on sample molecules. Dr. Ralph C. Dougherty at the University of West Florida has used methylene chloride as a chloride source, and Bose recently has found that chlorofluorocarbons also serve this purpose. Chloride generated from chlorofluorocarbons enabled Bose's group to detect a tetrasaccharide fragment from a pentasaccharide-bearing antibiotic. "Enough chloride is floating around to give us such good sensitivity," he notes. The sensitivity of CIMS comes out in other ways. For example, a drop of deproteinated blood is sufficient to give a triglyceride profile. Blood triglycerides separate (when coupled to a gas chroma­ tography system) by virtue of their fatty acid content. Thus, the technique can detect the effects of drugs that reduce saturated fatty acids in blood triglycer­ ides. "With very little manual effort, we get detailed clinical chemistry data in very short times," Bose says. Another application in an early stage involves cholesterol analysis. "We've been looking at placque material [taken from blood vessels] and at gallstones," Bose says. In such samples, "homologs of cho­ lesterol with and without double bonds are found. This could lead to diagnostic methods," he notes. But CIMS also is valuable for moni­ toring chemicals in the environment. For instance, many halogenated compounds, such as polychlor- and polybrominated bfphenyls and pentachlorophenol (PCP), are detected readily in trace amounts by CIMS. PCP is rapidly metabolized by crabs, Bose says, and CIMS offers a way of following what happens to the pesti­ cide. Its presence alters lipids in crab tissues, attesting to its potency and po­ tential for harm, Bose asserts. D

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