Colorimetric agents

Quinoxaline-2,3-dithione (2,3-dimercaptoquinoxaline) (90) forms chelates with several transition elements and is used as a colorimetric agent for the detection and quantitative estimation of nickeT and also for the quantitative estimation of palladium. " Nickel gives a pink coloration with (90) in ammoniacal solution, and palladium an orange-red color in AA-dimethylformamide solution containing a little hydrochloric acid. Spectrophotometric studies of the chelate compounds of (90) with Ni(II), Co(II), and Pd(II) in alkaline solu-... 

A more successful strategy for developing sensitive and facile assays to monitor PLCBc activity involves converting the phosphorylated headgroup into a colorimetric agent via a series of enzyme coupled reactions. For example, phosphatidylcholine hydrolysis can be easily monitored in a rapid and sensitive manner by enzymatically converting the phosphorylcholine product into a red dye through the sequential action of alkaline phosphatase, choline oxidase, and peroxidase [33]. This assay, in which 10 nmol of phosphorylcholine can be readily detected, may be executed in a 96-well format and has been utilized in deuterium isotope and solvent viscosity studies [34] and to evaluate inhibitors of PLCBc [33] and site-directed mutants of PLCBc [35,36]. 

Analysis. Atomic absorption, emission, and mass spectrographic separation are the most sensitive methods for the analysis of Si. Electrothermal atomization-atomic absorption spectroscopy ETAAS has a sensitivity of 10 ppb, ICPAES 1 ppb, and ICPMS 10 ppb. Colorimetric agents permit spectrometric analysis down to about 10 ppb. 

Analysis. The most sensitive techniques for the analysis of Ge include ICPAES (1 ppb) and IGPMS (0.1 ppb). Colorimetric agents (phenylfluo-ronone) and molecular absorption spectroscopy can detect 100 ppb. One of the better spot tests involves treatment of a slightly basic germanate solution with phenolphthalein to produce a red color, then the addition of mannitol which turns the solution colorless. Sensitivity is 100 ppm. A major interference is B. 

The reversible inhibition of an enzyme by an association-sensitive colorimetric agent is the novel aspect of this detection technique. In detail, the poiphyrin interacts with the enzyme in a manner that requires its dissociation to allow analyte binding. The porphyrin-enzyme complex absorbance spectrum is different from that of the porphyrin alone. Changes in the absorbance spectrum that occur upon dissociation of the porphyrin from the enzyme are used to indicate the presence of the analyte. In addition, the degree of change is analyte concentration dependent. 

Van Gennip in Sherma and Fried (8) also reviewed the use of colorimetric agents for the detection of nucleic acid and their derivatives. Common reagents include mercuric acetate (purine and... 

Colorimetric agents, 938-939 Color reactions (pesticide detection system), 804-806... 

The earliest methods for detection and assay of sialic acids were colorimetric procedures that capitalized on the more or less specific chromogens derived from these carbohydrates. Over the years a variety of colorimetric agents have been employed orcinol (Klenk and Langer-beins, 1941), diphenylamine (Ayala et aL, 1951), hydrochloric acid... 

Colorimetric. A sensitive method for the deterrnination of small concentrations of dissolved iron is the spectrophotometric deterrnination of the orange-red tris(1,10-phenanthroline)iron (IT) complex. Other substituted phenanthrolines can be even more sensitive. Only the inon(II) complexes of these Ligands are highly colored. The sample is first treated with an excess of reducing agent. The complexes are stable from pH 2 ndash 9 and analysis preferably is done at about pH 3.5. 

Phthaleins. Dyes of this class are usually considered to be triaryhnethane derivatives. Phenolphthalein [77-09-8] (23, R = CO) and phenol red [143-74-8] (23, R = SO2) are used extensively as indicators in colorimetric and titrimetric determinations (see Hydrogen-ION activity). These compounds are prepared by the condensation of phenol with phthaUc anhydride or i9-sulfoben2oic anhydride, respectively, in the presence of a dehydrating agent. 

Discussion. Small quantities of dissolved silicic acid react with a solution of a molybdate in an acid medium to give an intense yellow coloration, due probably to the complex molybdosilicic acid H4[SiMo12O40]. The latter may be employed as a basis for the colorimetric determination of silicate (absorbance measurements at 400 nm). It is usually better to reduce the complex acid to molybdenum blue (the composition is uncertain) a solution of a mixture of l-amino-2-naphthol-4-sulphonic acid and sodium hydrogensulphite solution is a satisfactory reducing agent. 

In patients on EDTA therapy, calcium cannot be determined by the Indirect colorimetric or fluorometrlc methods based on the chelation of a calcium - EDTA complex. However, In calcium determinations by atomic-absorption spectroscopy, the complexlng agent Is destroyed In the flame and the direct concentration of calcium can be determined. 

The concentration of an oxidative gel breaker can be measured by colorimetric methods, by periodically or continuously sampling the gel [341]. The colorimetric reagent is sensitive to oxidizing agents. It contains iron ions and thiocyanate. Thus the quantity of breaker added to the fracturing fluid can be controlled. 

LDPE or HDPE extracts has been determined colorimet-rically at 430 nm by oxidation with H202 in the presence of H2S04 [66]. p-Phenylenediamine derivatives such as Flexzone 3C, used as antiozonants in rubber products, have been determined colorimetrically after oxidation to the corresponding Wurster salts [67]. A wide range of amine AOs in polyolefins has been determined by the p-nitroaniline spectrophotometric procedure [68]. Monoethanolamine (MEA) in a slip agent in PE film has been determined as a salicylaldehyde derivative by spectrophotometric quantification at 385 nm [69]. Table 5.6 contains additional examples of the use of 1JV/VIS spectrophotometry for the determination of additives in polymers. 

Phenolic antioxidants in rubber extracts were determined indirectly photometrically after reaction with Fe(III) salts which form a red Fe(II)-dipyridyl compound. The method was applicable to Vulkanox BKF and Vulkanox KB [52]. Similarly, aromatic amines (Vulkanox PBN, 4020, DDA, 4010 NA) were determined photometrically after coupling with Echtrotsalz GG (4-nitrobenzdiazonium fluoroborate). For qualitative analysis of vulcanisation accelerators in extracts of rubbers and elastomers colour reactions with dithio-carbamates (for Vulkacit P, ZP, L, LDA, LDB, WL), thiuram derivatives (for Vulkacit I), zinc 2-mercaptobenzthiazol (for Vulkacit ZM, DM, F, AZ, CZ, MOZ, DZ) and hexamethylene tetramine (for Vulkacit H30), were mentioned as well as PC and TLC analyses (according to DIN 53622) followed by IR identification [52]. 8-Hydroquinoline extraction of interference ions and alizarin-La3+ complexation were utilised for the spectrophotometric determination of fluorine in silica used as an antistatic agent in PE [74], Also Polygard (trisnonylphenylphosphite) in styrene-butadienes has been determined by colorimetric methods [75,76], Most procedures are fairly dated for more detailed descriptions see references [25,42,44],... 

Brinkley et al. demonstrated89 a simple to use, easy to interpret, low cost, and environmentally friendly colorimetric detector of the chemical warfare agent - mustard gas (HD, l,l-thiobis(2-chloroethane)). An optically transparent xerogel encapsulating Cu(II) acetate was fabricated to detect HD analogues and can serve as the optical sensor based on metal-ligand charge-transfer mechanism. 

Acoustic wave sensors are also used to detect nerve and blister agents. The surface acoustic wave chemical agent detector (SAW Mini-CAD) is a commercially available, pocket-sized instrument that can monitor for trace levels of toxic vapors of sulfur-based mustard agents (e.g., distilled mustard) and G nerve agents (e.g., tabun, sarin, soman) with a high degree of specificity. Colorimetric tubes are the... 

A colorimetric version of the method uses a tetrazolium salt. The oxidation of the NADH is coupled to the reduction of 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide by a diaphorase (EC 1.6.4.3) and a deep blue formazan develops. The absorbance is read at a wavelength between 540 and 600 nm. This is more sensitive than the ultraviolet method but is more prone to interference, especially from any reducing agents present in the sample, which will result in a positive error. 

Baleux B. Colorimetric determination of nonionic, poly(oxyethylene) surface-active agents using an iodine-iodide solution. CR Acad Sci Sci Chim 1972 274 1617. 

Before 1970, most of the data for nitrogen oxides were obtained by continuous measurements with a colorimetric analyzer that was similar in principle to the colorimetric oxidant analyzer shown in Figure 6-8. The scrubbing agent is a mixture of -(l-naphthyl)ethylenediamine, sulfanilic acid, and acetic acid in aqueous solution. The color is produced when both nitrogen dioxide and nitrites react with this reagent to form an azo dye. The color is not affected by nitric oxide in the air sample. 

---