In biochemical research

For mixture.s the picture is different. Unless the mixture is to be examined by MS/MS methods, usually it will be necessary to separate it into its individual components. This separation is most often done by gas or liquid chromatography. In the latter, small quantities of emerging mixture components dissolved in elution solvent would be laborious to deal with if each component had to be first isolated by evaporation of solvent before its introduction into the mass spectrometer. In such circumstances, the direct introduction, removal of solvent, and ionization provided by electrospray is a boon and puts LC/MS on a level with GC/MS for mixture analysis. Further, GC is normally concerned with volatile, relatively low-molecular-weight compounds and is of little or no use for the many polar, water soluble, high-molecular-mass substances such as the peptides, proteins, carbohydrates, nucleotides, and similar substances found in biological systems. LC/MS with an electrospray interface is frequently used in biochemical research and medical analysis. 

Although the free amino acids are present only at very low concentrations in oceanic waters, their importance in most biological systems has led to an inordinate amount of effort toward their determination in seawater. A sensitive, simple, and easily automated method of analysis, the colorimetric nin-hydrin reaction, has been known in biochemical research for many years. In order for the method to be useful in seawater, the amino acids had to be concentrated. This concentration was usually achieved by some form of ion exchange [251]. An automated method not using a concentration step was developed by Coughenower and Curl [252]. While the method was used successfully in Lake Washington, its limit of detection (0.5 imol/l) is just too great for most oceanic samples. 

Used in biochemical research as an antagonist to serotonin. Also used as an illegal street drug. 

Used in industry as a chemical intermediate for dyestuffs, pharmaceuticals, rubber chemicals, flotation agents, insecticides, and plasticizers used as a water-soluble reducing agent and reagent in biochemical research. 

Our understanding of protein structure and function has been derived from the study of many individual proteins. To study a protein in detail, the researcher must be able to separate it from other proteins and must have the techniques to determine its properties. The necessary methods come from protein chemistry, a discipline as old as biochemistry itself and one that retains a central position in biochemical research. 

IR spectroscopy is useful in biochemical research and has aided in the structural determinations of amino acids, nucleic acids, and polypeptides the IR spectra of viruses and bacteria have been studied.9 The controversial cancer drug Krebiozen was identified by its IR spectrum as the amino acid derivative creatine, which is present in humans in large quantities.10... 

Gas chromatography will continue to be used in biochemical research however, its major disadvantage is that many biochemical samples either are not volatile or are thermally unstable. HPLC, which can be operated at ambient temperatures, does not have this limitation. 

The stability of a nucleus depends on the ratio of neutrons to protons. Some nuclei are unstable and undergo spontaneous nuclear disintegration accompanied by emission of particles. Unstable isotopes of this type are called radioisotopes. Three main types of radiation are emitted during nuclear decay a particles, j8 particles, and y rays. The a particle, a helium nucleus, is emitted only by elements of mass number greater than 140. These elements are seldom used in biochemical research. 

The properties of several radioisotopes that are important in biochemical research are listed in Table 6.1. Note that many of the isotopes are /3 emitters however, a few are y emitters. 

The half-life, defined in the previous section and listed for each isotope in Table 6.1, is an important property when designing experiments using radioisotopes. Using an isotope with a short half-life (for example, 24Na with ty2 = 15 hr) is difficult because the radioactivity lost during the course of the experiment is significant. Quantitative measurements made before and after the experiment must be corrected for this loss of activity. Radioactive phosphorus, 32P, an isotope of significant value in biochemical research, has a relatively short half-life (14 days), so if quantitative measurements are made they must be corrected as described in Equations 6.7 and 6.8. More information about the choice of a radioisotope in an experiment, the detec-... 

Since most of the radioisotopes used in biochemical research are j8 emitters, only methods that detect and measure /3 particles will be emphasized. Two counting techniques are in current use, scintillation counting and Geiger-Miiller counting. 

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