Enzymatic substrate analysis is an attractive means of analysis in clinical chemistry because of its sensitivity and specificity. The GeMSAEC Fast Analyzer, in conjunction with a small computer, provides a means of performing routine enzymatic substrate analysis and offers the following advantages: (a) selectivity of approaches to enzymatic analysis, i.e., end-point or kinetic; (b) essentially parallel analyses of multiple samples, yielding a unique method for performing kinetic fixed-time analysis; (c) on-line data reduction, resulting in rapid calculation and output of results and the minimization of data handling errors; and (d) a small reagent volume per test (400 µl), which reduces the cost of analysis. The analysis of substrate with enzymatic end-point and kinetic procedures is examined by use of a computer-interfaced Fast Analyzer. Computer programs were written to facilitate this study. Glucose (hexokinase/GPD), urea (urease/GMD), and uric acid (uricase) have been used as examples in evaluating both end-point and kinetic analyses. The advantages and limitations of each type of analysis are presented, with the emphasis being placed on enzymatic substrate analysis and means by which the computer-interfaced Fast Analyzer can facilitate both end-point and kinetic analyses.
A modified version of a previously described miniature Fast Analyzer [Clin. Chem. 18, 753 (1972)] was used as the basis for developing a compact, potentially portable, analytical system. This system includes an automated and versatile sample-reagent loader, a miniature Fast Analyzer, several plastic rotors and their cleaning station, and a portable data system. The sample-reagent loader combines a unique turntable assembly and two "Micromedic" pipets to quickly (5 min per rotor), accurately, and precisely obtain, transfer, and dispense small volumes of sample (1 to 10 µl of sample, 50 µl of diluent) and reagent (20 µl of reagent, 50 µl of diluent) into their respective cavities in a 17-cuvet rotor. The loader uses separate sample and reagent carousels, which allows operation of the system in either the single-sample—multiple-chemistry, multiple-sample— single-chemistry, or multiple-sample—multiple-chemistry analytical modes. The miniature Fast Analyzer rotates a loaded 17-cuvet rotor through a stationary optical system at speeds up to 5000 rpm. The resulting centrifugal force is used to mix and to transfer the discrete aliquots of sample(s) and reagent(s) into their respective cuvets. The ensuing reactions are monitored photometrically, and the data are processed in real time by either a portable Data Processor [Clin Chem. 18, 762 (1972)] or an on-line computer. A major improvement to the analyzer has been the addition of a temperature-control system that allows the temperature of the spinning rotor to be monitored and controlled to within ±0.2°C. After completion of an analytical run, the rotor is automatically washed and dried in the rotor cleaning station. Many of the standard clinical analyses, including most of the NADH-linked enzymatic analyses, have been adapted for use with this system.
Cr20,2-+ 14H' MnOp + 4H' + EO = +1.52 volts (1) EO = +1.33 volts (2) Eo = +123 volts (3)Fe3+ + e e Fez+ Eo 5 +0.77 volts (5)Thus, there is no problem of any interference from Mn2+ or C r s which are in general present in rocks in small amounts (Mn from 0.05 to 0.2%, Cr from 1 to 4000 ppm). The presence of an appreciable amount of "acid decomposable sulfide" invalidates the ferrous iron determination. Pyrite is not appreciably attacked by mixture of HF and HC1 but other sulfides, such as pyrrhotite, are more extensively decomposed liberating hydrogen sulfide which will result in higher values of ferrous iron. Organic matter other than graphite will completely invalidate the meth-
od.The relative 70 deviation has been calculated on the amounts present.
CONCLUSIONSFerrous iron can be determined by the iodine monochloride method without any possible aerial oxidation and without any interference from manganese or chromium. Ferrous iron in carbonate and other acid decomposable rocks (which are attacked by HCl or HCl and HF) can also be determined. Acid decomposable sulfides and organic matter other than graphite invalidate the method.
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