Photometric methods

Aminothiazole present in urine or blood plasma forms a colored Schiff base when 5-nitrofurfural is added the colorimetric analysis of the Schiff base allows the quantitative determination of this thiazole (1571). The Schiff base may also be dosed by polarographic of spectro-photometric methods (1572). 

Referee Methods. The American Society for Testing Materials (ASTM) has collected a series of standard referee methods for the analysis of magnesium and its alloys (78). These methods are accurate over a larger range of concentration than the production methods, but are time consuming ia thek apphcation. The methods are based on potentiometric titration, photometric methods, or gravimetric methods. The photometric methods are most common and are relatively straightforward. 

Potassium is analyzed in chemicals that are used in the fertilizer industry and in finished fertilizers by flame photometric methods (44) or volumetric sodium tertraphenylboron methods (45) as approved by the AO AC. Gravimetric deterrnination of potassium as K2PtClg, known as the Lindo-Gladding method (46), and the wet-digestion deterrnination of potassium (47) have been declared surplus methods by the AO AC. Other methods used for control purposes and special analyses include atomic absorption spectrophotometry, inductively coupled plasma (icp) emission spectrophotometry, and a radiometric method based on measuring the radioactivity of the minute amount of the isotope present in all potassium compounds (48). 

Ana.lytica.1 Methods. Various analytical methods involve titration with oxidants, eg, hexacyanoferrate (ferricyanide), which oxidize dithionites to sulfite. lodimetric titration to sulfate in the presence of formaldehyde enables dithionite to be distinguished from sulfite because aldehyde adducts of sulfite are not oxidized by iodine. Reductive bleaching of dyes can be used to determine dithionite, the extent of reduction being deterrnined photometrically. Methods for determining mixtures of dithionite, sulfite, and thiosulfates have been reviewed (365). Analysis of dithionite particularly for thiosulfate, a frequent and undesirable impurity, can be done easily by Hquid chromatography (366). 

Because of the time and expense involved, biological assays are used primarily for research purposes. The first chemical method for assaying L-ascorbic acid was the titration with 2,6-dichlorophenolindophenol solution (76). This method is not appHcable in the presence of a variety of interfering substances, eg, reduced metal ions, sulfites, tannins, or colored dyes. This 2,6-dichlorophenolindophenol method and other chemical and physiochemical methods are based on the reducing character of L-ascorbic acid (77). Colorimetric reactions with metal ions as weU as other redox systems, eg, potassium hexacyanoferrate(III), methylene blue, chloramine, etc, have been used for the assay, but they are unspecific because of interferences from a large number of reducing substances contained in foods and natural products (78). These methods have been used extensively in fish research (79). A specific photometric method for the assay of vitamin C in biological samples is based on the oxidation of ascorbic acid to dehydroascorbic acid with 2,4-dinitrophenylhydrazine (80). In the microfluorometric method, ascorbic acid is oxidized to dehydroascorbic acid in the presence of charcoal. The oxidized form is reacted with o-phenylenediamine to produce a fluorescent compound that is detected with an excitation maximum of ca 350 nm and an emission maximum of ca 430 nm (81). 

When radiating and receiving surfaces are not in parallel, as in rotary-ldln devices, and the sohds burden bed may be only intermittently exposed and/or agitated, the calculation and procedures become veiy complex, with photometric methods of optics requiring consideration. The following equation for heat transfer, which allows for convective effects, is commonly used by designers of high-temperature furnaces ... 

The organic reagents are used extensively for determinations series of elements by different methods of analysis. We carry out the systematical investigation of organic derivatives of hydrazine as a reagent for determinations ion of metals by photometric and extractive-photometric methods or analysis, as well as methods of atomic absorption spectrometry. Series procedure determinations ion of metals in technical and environmental objects have been developed. 

The results obtained have allowed us to develop the analytical procedures for the preconcentration and determination of microquantities of the monatomic phenols, aromatic amines and total volatile primary amines by HPLC and photometric methods. 

The worked out soi ption-photometric method of NIS determination calls preliminary sorption concentration of NIS microamounts from aqueous solutions on silica L5/40. The concentrate obtained is put in a solution with precise concentration of bromthymol-blue (BTB) anionic dye and BaCl, excess. As a result the ionic associate 1 1 is formed and is kept comparatively strongly on a surface. The BTB excess remains in an aqueous phase and it is easy to determinate it photometrically. The linear dependence of optical density of BTB solutions after soi ption on NIS concentration in an interval ITO - 2,5T0 M is observed. The indirect way of the given method is caused by the fact the calibration plot does not come from a zero point of coordinates, and NIS zero concentration corresponds to initial BTB concentration in a solution. 

Interaction between osmium(IV) and osmium(VI) and derivatives of dimerkaptotiopiron (DT) has been studied by amperemetric, potentiometric and spectral photometric methods in different mediums. It has been found out that in reactions of methyldimerkaptotiopiron (R) with Os(IV) and Os(VI) complex formation prevails. It has a step-like nature, being revealed by such change of ratio of Os R in the course of titration as Os(VI) R - from 1 1 to 1 4 in acid medium and from 2 1 to 1 4 in weak alkaline medium Os(IV) R - from 1 1 to 1 5 in medium of H SO and from 1 1 to 1 6 - in HCl medium. 

The use of peroxyacids, including PMSA, makes it possible to improve photometric method of nickel determination - to increase selectivity, accuracy and reproducibility of measurements. Peroxyacids as oxidants ai e used for nickel determination in aluminium and copper alloys, natural waters, stomatological products. 

The concentration of acid impurities is an important indication of the quality of petroleum products and the purity of organic solvents, plasticizers, mineral oils, food fats, and polymers. Methods are used to detect organic acids in such compounds have many disadvantages the alkalimetry - low sensitivity, especially in the determination of weak acids, the extraction-photometric method is laborious, instmmental methods are expensive. In addition, most of methods are commonly unsuitable for direct analysis. 

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... 

D in working liquids is worked out on the basis of extractive and photometric method. 

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

The purpose of the nebuliser-burner system is to convert the test solution to gaseous atoms as indicated in Fig. 21.2, and the success of flame photometric methods is dependent upon the correct functioning of the nebuliser-burner system. It should, however, be noted that some flame photometers have a very simple burner system (see Section 21.13). 

Methods are described for determining the extent to which original natural color is preserved in processing and subsequent storage of foods. Color differences may be evaluated indirectly in terms of some physical characteristic of the sample or extracted fraction thereof that is largely responsible for the color characteristics. For evaluation more directly in terms of what the observer actually sees, color differences are measured by reflectance spectrophotometry and photoelectric colorimetry and expressed as differences in psychophysical indexes such as luminous reflectance and chromaticity. The reflectance spectro-photometric method provides time-constant records in research investigation on foods, while photoelectric colorimeters and reflectometers may prove useful in industrial color applications. Psychophysical notation may be converted by standard methods to the colorimetrically more descriptive terms of Munsell hue, value, and chroma. Here color charts are useful for a direct evaluation of results. 

Table IV. Photometric Methods First Used to Determine Amino Acids...

K. Mehlhose, Explosivstoffe 20 (3-4), 37-70 (1972) CA 78, 113513 (1973) Methods developed for detn of H20 in gun and rocket propints are column distn with n-PrOH and gas-chromatographic analysis of the distillate, corrected for continuous formation of water in decompn reactions and photometric methods, both based on the reaction of CoCl2 with water. Choice of the methods is based on a critical review (117 refs) of the usual methods of water detn by chemical and physical methods. A theoretical and exptl analysis of the new methods was made and their results compared with those of older methods. Application to mono-, di-, and tribasic and to double-base NC and poly (vinyl nitrate) propints is discussed... 

The addition of sodium dodecyl sulfate improves the conventional spectro-photometric method for the determination of fluoride/lanthanum/alizarine flour-ine blue tertiary complex [172]. 

Besides the photometric method, a HPLC method could also be used. (Cf. the first constraint under the earlier head PROBLEM. The HPLC has a higher relative standard deviation for two reasons The transient nature of the signal results in a short integration time, and the short pathlength makes... 

Experimental A photometric method was found in the literature which seemed to suit the particular circumstances. Two cyanide stock solutions were prepared, and an electromechanical dispenser was used to precisely prepare solutions of 20, 40,. .., 240 respectively 10, 30, 50,. .., 250 fig CN /100 ml. 10 ml of each calibration solution were added to 90 ml of the color-forming reagent solution and the absorbance was measured using 1-cm cuvettes. (See Table 4.17 (left and middle panels) and data file CYANIDE.dat.)... 

ALL METHODS FOR PRESENTING DATA FROM THE MEASUREMENT OF PARTICLE SIZE DISTRIBUTIONS, WHETHER INSTRUMENTAL, SEIVING, SEDIMENTATION, OR PHOTOMETRIC METHODS, MEASURE FRACTIONS OF THE TOTAL PARTICLE DISTRIBUTION. IF THE METHOD IS SENSITIVE, THE FRACTION-SEGMENTS CAN BE SMALL, AND THE MEASURED PARTICLE DISTRIBUTION WILL BE CLOSE TO THE ACTUAL ONE. IF THE MEASUREMENT IS LESS SENSITIVE, THERE MAY BE SIGNIFICANT DEVIATIONS FROM THE CORRECT PSD. 

Analytical Visible and Ultra-violet Spectrometry Photometric Methods in Inorganic Trace Analysis New Developments in Conductometric and Osdllometric Analysis Titrimetric Analysis in Organic Solvents... 

Photometric methods are widely used to determine overall metallicity, and measure the blanketing in either broad or narrow bands due primarily to Fe and Fe-peak blends, or common molecular features, such as CN. These measures can be calibrated to a true [Fe/H] or can be interpreted through analysis of color-magnitude diagrams with the help of theoretical isochrones through their... 

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