Detection colorimetry

Greater range of detection systems to which the desorbed gas can be subjected (e.g. chromatography, infra-red and ultraviolet spectroscopy, colorimetry) Limitations Certain resins undergo degradation even below 250°C Test sample may be thermally unstable Not all compounds readily desorb ... 

Colorimetry. Laboratory data on the persistence of biocides formulated in glutaraldehyde and acrolein are available [1260]. A colorimetric general aldehyde detection method based on m-phenylenediamine was used. Such studies follow the demand for better understanding of ecologic systems in the aspect of environmental protection. 

Simultaneous determination of both cations and anions in acid rain has been achieved using a portable conductimetric ion-exclusion cation-exchange chromatographic analyzer.14 This system utilized the poly(meth-ylmethacrylate)-based weak acid cation exchange resin TSK-Gel OA-PAK-A, (Tosoh , Tokyo, Japan) with an eluent of tartaric acid-methanol-water. All of the desired species, 3 anions and 5 cations, were separated in less than 30 minutes detection limits were on the order of 10 ppb. Simultaneous determination of nitrate, phosphate, and ammonium ions in wastewater has been reported utilizing isocratic IEC followed by sequential flow injection analysis.9 The ammonium cations were detected by colorimetry, while the anions were measured by conductivity. These determinations could be done with a single injection and the run time was under 9 minutes. 

Nonspectroscopic detection schemes are generally based on ionisation (e.g. FID, PID, ECD, MS) or thermal, chemical and (electro)chemical effects (e.g. CL, FPD, ECD, coulometry, colorimetry). Thermal detectors generally exhibit a poor selectivity. Electrochemical detectors are based on the principles of capacitance (dielectric constant detector), resistance (conductivity detector), voltage (potentiometric detector) and current (coulometric, polarographic and amperometric detectors) [35]. 

Although UV/VIS diffuse reflectance spectroscopy has not been used extensively in the study of pharmaceutical solids, its applications have been sufficiently numerous that the power of the technique is evident. The full reflectance spectra, or the derived colorimetry parameters, can be very useful in the study of solids that are characterized by color detectable by the human eye. It is evident that questions pertaining to the colorants used for identification purposes in tablet formulations can be fully answered through the use of appropriately designed diffuse reflectance spectral experiments. With the advent of newer, computer-controlled instrumentation, the utility of UV/VIS diffuse reflectance as a characterization tool for solids of pharmaceutical interest should continue to be amply demonstrated. 

Aliphatic amines have been determined by a number of methods. Batley et al. [290] extracted the amines into chloroform as ion-association complexes with chromate, then determined the chromium in the complex colorimetri-cally with diphenylcarbazide. The chromium might also be determined, with fewer steps, by atomic absorption. With the colorimetric method, the limit of detection of a commercial tertiary amine mixture was 15ppb. The sensitivity was extended to 0.2 ppb by extracting into organic solvent the complex formed by the amine and Eosin Yellow. The concentration of the complex was measured fluorometrically. Gas chromatography, with the separations taking place on a modified carbon black column, was used by Di Corcia and Samperi [291] to measure aliphatic amines. 

An improved HPLC-photohydrolysis-colorimetry method was validated for twenty-eight reference nitrosamines. These were separated by HPLC and photolytically cleaved by UV radiation. The resulting nitric oxide was oxidized and hydrolyzed to nitrite ions, which were derivatized into an azo dye with Griess reagent and measured spectrophoto-metrically. The method was applied to separate and detect hitherto unknown nonvolatile nitrosamines in biological fluids and food extracts591. 

The analytic principles that have been applied to accumulate air quality data are colorimetry, amperometry, chemiluminescence, and ultraviolet absorption. Calorimetric and amperometric continuous analyzers that use wet chemical techniques (reagent solutions) have been in use as ambient-air monitors for many years. Chemiluminescent analyzers, which measure the amount of chemiluminescence produced when ozone reacts with a gas or solid, were developed to provide a specific and sensitive analysis for ozone and have also been field-tested. Ultraviolet-absorption analyzers are based on a physical detection principle, the absorption of ultraviolet radiation by a substance. They do not use chemical reagents, gases, or solids in their operation and have only recently been field-tested. Ultraviolet-absorption analyzers are ideal as transfer standards, but, as discussed earlier, they have limitations as air monitors, because aerosols, mercury vapor, and some hydrocarbons could, interfere with the accuracy of ozone measurements made in polluted air. 

Colorimetry can be used to determine the concentration of coloured substances in solution. A colorimeter essentially consists of a light source, a coloured filter, a light detector and a recorder. The filter chosen is the complementary colour to the solution as this will result in the maximum absorbance. The light passes through the filter and then through the coloured solution. The difference in absorbance between the coloured solution and water is detected and noted as an absorbance value. Colorimetry uses the relationship between the intensity of the colour of the solution and the concentration. 

Spectrophotometry (or colorimetry) has been used to measure chlorine dioxide in water using indicators that change colors when oxidized by chlorine dioxide. Spectrophotometric analyzers determine the concentration of chlorine dioxide by measuring the optical absorbance of the indicator in the sample solution. The absorbance is proportional to the concentration of the chlorine dioxide in water. Indicators used for this technique include jV,jV-diethyl-p-phenylenediamine, chlorophenol red, and methylene blue (APHA 1998 Fletcher and Hemming 1985 Quentel et al. 1994 Sweetin et al. 1996). For example, chlorophenol red selectively reacts with chlorine dioxide at pH 7 with a detection limit of 0.12 mg/L. The interferences from chlorine may be reduced by the addition of oxalic acid, sodium cyclamate, or thioacetamide (Sweetin et al. 1996). 

Cadmium in acidified aqueous solution may be analyzed at trace levels by various instrumental techniques such as flame and furnace atomic absorption, and ICP emission spectrophotometry. Cadmium in solid matrices is extracted into aqueous phase by digestion with nitric acid prior to analysis. A much lower detection level may be obtained by ICP-mass spectrometry. Other instrumental techniques to analyze this metal include neutron activation analysis and anodic stripping voltammetry. Cadmium also may be measured in aqueous matrices by colorimetry. Cadmium ions react with dithizone to form a pink-red color that can be extracted with chloroform. The absorbance of the solution is measured by a spectrophotometer and the concentration is determined from a standard calibration curve (APHA, AWWA and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington, DC American Public Health Association). The metal in the solid phase may be determined nondestructively by x-ray fluorescence or diffraction techniques. 

Elemental composition Na 15.34%, I 84.66%. Aqueous solution is analyzed for sodium by AA or ICP and for iodide ion by ion chromatography or leuko-crystal violent colorimetry (See Iodine). Alternatively, in an acidified solution of sodium hypochlorite, a measured amount of sodium iodide is titrated against a standard solution of sodium thiosulfate or phenyl arsine oxide using starch indicator to detect the end point. 

Dialkyl peroxides (continued) colorimetry, 707-8 flame ionization detection, 708 NMR spectroscopy, 708 titration methods, 707 UV-visible spectrophotometry, 707-8 enthalpies of reactions, 153-4 graft polymerization initiation, 706 hydroperoxide determination, 685 peroxide transfer synthesis, 824-5 stmctural characterization, 708-16 electrochemical analysis, 715-16 electron diffraction, 713 mass spectrometry, 714 NMR spectroscopy, 709-11 thermal analysis, 714-15 vibrational spectra, 713-14 X-ray crystallography, 711-13 synthesis... 

Comparative values for several physicochemical analytical methods for establishing stability of the drug solutions and detecting impurities (including colorimetry) was reported [45]. 

Analysis. Be can be quantitatively determined by colorimetry down to 40 ppb using eriochrome cyanine R or acetylacetone. The sensitivity may be improved by electrothermal absorption spectroscopy (ETAS) to 1 ppb and to 0.1 ppb by inductively-coupled plasma emission spectroscopy (ICPES) or inductively-coupled plasma mass spectroscopy (ICPMS). A simple spot test for qualitative detection of Be is one with quinalizarin in alcoholic NaOH which can detect 3 ppm. The color is produced by both Be and Mg. If the color persists after the addition of Br2 water. Be is present. If the color is bleached. Mg is indicated. 

Analysis. Colorimetry with proper reagents (such as nitrophenylfluo-ronone) permits analysis down to about 100 ppb. ETAAS detects Sn down to 1 ppb, and ICPMS is effective down to 0.1 ppb, as is anodic stripping voltammetry. Spot testing involves the use of cacotheline or diazine green (a dye made by reacting diazotized safranine with dimethylaniline). Sensitivity of these is about 50 ppm. 

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