Rapid photometric methods

RAPID PHOTOMETRIC METHODS FOR WATER ANALYSIS IN FIELD. EXTRACTION-FREE RAPID PROCEDURES FOR THE DETERMINATION OF TRACES OF REGULATED METALS WITH l-(2-PYRIDYLAZO)-NAPHTOL-2... 

Rapid equilibrium assumption 467 Rapid photometric methods 468 Ras 577-579... 

Photometric methods are simple and rapid for the determination of components of active chlorine. But photometric reagents not always are enough sensitive and reliable. 

At present few hospital laboratories use gas chromatographic methods because colorimetric, fluorometric, and other spectro-photometric methods can give data more rapidly, are less expensive, and are often of sufficient accuracy and precision for clinical evaluation of the patient. Radioimmunoassay procedures are available, but these are limited because of availability of the necessary antibodies and a sufficient demand to justify the expense of setting up the laboratory. For versatility and adaptability, many different analyses can be done on a single gas chromatograph. The only requirement is the proper column and choice of operating conditions. Furthermore, the techniques, in many cases, are now automated. The utility of GC coupled with... 

Gross, K.C. 1982. A rapid and sensitive spectro-photometric method for assaying polygalacturonase using 2-cyanoacetamide. Hort. Sci. 17 9.33-934. 

KdisR. Ac+ are the dissociation constants of the ion pairs Rf Ac+ and R Ac+. Under suitable conditions, the equilibria (29)—(31) can be followed by spectro-photometric methods [167c, 169], There exist some very important specific reactions of the type shown in eqns. (29) and (30) which are poorly characterized. This concerns, for example, the electron transfer from naphthalene- metal+ (Szwarc initiator) to styrene or other monomers [see Chap. 3, eqn. (46)]. The rapid consecutive reactions of the styrene radical ion make a direct measurement of the equilibrium impossible. Indirect data are not reliable. 

ALA can be measured directly but is converted more usually into an Ehrlich s-reacting pyrrole by condensation with a reagent such as acetylacetone after separation from PBG by two-stage anion exchange chromatography. A method for the measurement of PBG and ALA, based on that of MauzeraU and Granick, is available commercially (Bio-Rad Laboratories, Hercules, Calif.). An alternative photometric method has been proposed for more rapid testing. 

It is perhaps surprising that no p f measurements in water for even the most prototypical of all Fischer carbene complexes such as 68 had been reported before 1989/ 9 The most likely explanation for this state of affairs is that in aqueous solution the conjugate anions of carbene complexes hydrolyze rapidly which precludes equilibrium determinations by classical photometric methods. In fact, most p f values of Fischer complexes in aqueous solution were obtained by kinetic rather than equilibrium methods. For 68 the p f was determined in KOH solution by applying the relationship where is the rate... 

Inasmuch as cytochrome c is a relatively small protein easily extractable and easily recognized by spectro-photometric methods, it is quite natural that its biosynthesis was investigated in vivo in a variety of tissues. Much of the in vivo work comes from Drabkin s laboratory [116]. These workers used labeled glycine as a precursor and followed its incorporation in both the heme and the protein moiety of cytochrome c. The following is a summary of their findings (1) the isotope is incorporated in both the porphyrin and the protein portion of the molecule (2) the incorporation is more rapid in the heme than in the protein fraction (3) practically all tissues are capable of independent cytochrome c synthesis (4) studies in regenerating liver also demonstrate that the rate of cytochrome c synthesis outweighs the active increase in the cellular population and (5) new cytochrome c is made in the endoplasmic reticulum and transferred by an unknown mechanism to mitochondria. 

Recently, Green and his co-workers have described a new assay for CoA which is based on a different principle from the previous assays. It has been reported that CoA is required for the oxidation of a-ketoglu-tarate. Since this reaction also requires the presence of DPN, a spectro-photometric method in which the reactants are so adjusted that the reduction of DPN is dependent upon CoA concentration is possible. This method is rapid and very sensitive. 

Although recent developments, especially in the areas of atomic absorption and emission spectroscopy, make these methods superior for the determination of trace amounts of individual rare earths, chemical methods, especially for elements such as Ce continue to be of interest. New more sensitive and selective reagents have been synthesized and techniques such as extraction-photometric methods and the use of competing ligands to improve the selectivity of chemical methods have made spectrophotometric methods more attractive in view of the rapidly rising cost of the sophisticated instruments necessary to determine the rare earths. 

In order to use the stopped-flow technique, the reaction under study must have a convenient absorbance or fluorescence that can be measured spectro-photometrically. Another method, called rapid quench or quench-flow, operates for enzymatic systems having no component (reactant or product) that can be spectrally monitored in real time. The quench-flow is a very finely tuned, computer-controlled machine that is designed to mix enzyme and reactants very rapidly to start the enzymatic reaction, and then quench it after a defined time. The time course of the reaction can then be analyzed by electrophoretic methods. The reaction time currently ranges from about Sms to several seconds. 

Direct nonchromatographic methods target screening of either ampicillin residues in milk extracts by fluorometric detection (126) or -lactam residues in kidney extracts by photometric detection (120). These methods are rapid but cannot differentiate among particular -lactams and are less sensitive than other screening tests usually employed for regulatory purposes. 

Castro et al. [64] reported a comparison between derivative spectro-photometric and liquid chromatographic methods for the determination of omeprazole in aqueous solutions during stability studies. The first derivative procedure was based on the linear relationship between the omeprazole concentration and the first derivative amplitude at 313 nm. The first derivative spectra were developed between 200 and 400 nm (A/ = 8). This method was validated and compared with the official HPLC method of the USP. It showed good linearity in the range of concentration studied (10—30 /ig/ ml), precision (repeatability and interday reproducibility), recovery, and specificity in stability studies. It also seemed to be 2.59 times more sensitive than the HPLC method. These results allowed to consider this procedure as useful for rapid analysis of omeprazole in stability studies since there was no interference with its decomposition products. 

Berijani, S., Y. Assadi, M. Anbia, M.-R. Milani Hosseini, and E. Aghaee. 2006. Dispersive liquid-liquid microextraction combined with gas chromatography-flame photometric detection Very simple, rapid and sensitive method for the determination of organophosphorus pesticides in water. J. Chromatogr. A 1123 1-9. 

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