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REPORT FOR ANALYTICAL CHEMISTS
analysis {41) and determination of barbiturates {48). Lipide frac tionation, including cholesterol esti mation {25, 35), is also practical be cause these materials occur in rela tively large amounts in serum. Titrimetric methods, in the ultramicro range, are used widely in the clinical laboratory for chloride esti mation {52), acid and base deter mination, and calcium and magne sium estimation by complexometric titration {4, 78) • Several practical and rather inexpensive ultramicroburets are available which will de liver 0.1 ml. of solution with an ac curacy to better than ± 2 % . Of interest are instruments spe cially designed for the clinical labo ratory for microestimation of chlo ride by a coulometric method {22). Here the time required for the com plete precipitation of the chloride as silver chloride is measured by in struments with automatic stop end points. From 10 to 100 μ\. of serum are used in these instruments. Al though this same determination •TRADEMARK may be performed by some by potentiometric titration with the silver chloride electrode {38), the coulo metric method seems more practical because of the problems involved in maintaining efficient silver chloride electrodes used in the potentiometric method. A potentiometric conirollifiq method, using the glass electrode, finds important application in pH measurement {62): Microelectrodes for pH measurement on biological fluids work with samples ranging from 10 to 100 μ\. This determina tion is becoming increasingly im portant in management of fluid therapy. For quantities of the order of tenths or hundredths of a micro gram, fluorometric methods find Write for Illustrated wide application. Porphyrins {73), irochure -various applications epinephrine {18), vitamins {14, %6, 27), and steroid hormones {46) are INSTRUMENTS for RESEARCH so assayed. Of particular interest are instruments which permit spec tral analysis of the emitted radia tion after irradiation with a selected and INDUSTRY monochromatic light. which are catalyzed by CHELTENHAM, PENNAtheReactions unknown factor sought, such as the effect of iodine on the ceric-arDesigners and Manufacturers senite system, are widely used in the of Instruments for clinical laboratory. Here amounts Automation of Tedious and of the order of 0.02 γ of iodine are Repetitive Laboratory Tasks being routinely determined {78).
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ANALYTICAL CHEMISTRY
Related to this class are a host of enzymatic assays. In these cases, amylase {81), trypsin {S3), lipase {13), phosphatases {11), transami nases {69), lactic dehydrogenase {86), and aldolase {45), for exam ple, it is the catalyst concentration that is sought. Both qualitative and quantitative estimates of glu cose are made utilizing a system in which glucose oxidase catalyzes air oxidation of glucose, generating peroxide. The peroxide in turn oxi dizes an organic compound such as anisidine to produce a color, under the influence of the enzyme peroxi dase (7, 71). Thus, complicated enzyme systems have moved from the research laboratory into the routine laboratory. The emission spectrograph has found application in the clinical laboratory for analysis of heavy elements {6, 15). The multiplicity of lines obtained and the cumber some nature of the techniques used with the more modestly priced in struments has limited its usefulness. Of most practical use, in emission spectroscopy, is the flame photom eter {51, 82). Sodium and potas sium determinations, and in some cases calcium, are performed rou tinely with this instrument. Multi channel instruments have also been developed for rapid, simultaneous analysis of more than one element. With the ordinary flame photom eter, sodium and potassium estima tions are done routinely using as lit tle as 0.025 ml. of serum for both determinations. Radioactive elements are used routinely for such analytical pro cedures as estimation of the clear ance rate of iron with iron-59 {37), blood volume with chromium-51 ( i ) , measurement of extracellular space with sodium-24 {24), meas urement of protein-bound iodine produced after administration of iodine-131 {28, 43), and excretion of vitamin Bi 2 after oral administra tion of the cobalt-69—labeled com pound {72). In most institutions these determinations are now being performed by a separate laboratory set up for that purpose. During the development of com pounds of biochemical importance, bioassay determinations are made. This was true of many of the vita mins and hormones. Various ani-
