Colorimetric reporters

Molecular recognition has influenced sensor development, first with alkali ions and later with more complex host-guest interactions. New materials likely to have an important impact in the future are conducting polymers, semiconductor nanoparticles, and fluorescent and colorimetric reporter molecules. 

Anion receptors based on metal centres can be classified into three broad categories those in which the metal plays a structural role, those in which it is a key component of the anion-binding site and those in which it acts as part of a redox, fluorescent or colourimetric reporter group. The latter types of compound will be covered in the next section, although, of course, there are examples of compounds that fall into more than one group, such as 2.77 in which the ferrocene-derived unit acts as both a colorimetric reporter and a structural element. 

In the DPD colorimetric method for the free chlorine residual, which is reported as parts per million of CI2, the oxidizing power of free chlorine converts the colorless amine N,N-diethyl-p-phenylenediamine to a colored dye that absorbs strongly over the wavelength range of 440-580 nm. Analysis of a set of calibration standards gave the following results... 

In view of the chromophoric character of the elemental iodine itself, many colorimetric methods have been proposed for the deterrnination of inorganic iodine (88—92). These methods use the visible portion of the spectmm in reading iodine concentrations. In the visible range the extinction coefficient for iodine is not high enough to be used for minute quantities of iodine in water and other solvents (93). Higher sensitivities have been reported for elemental iodine in potassium iodide solutions in the ultraviolet (93,94). 

Micro amounts of sulfur in polymer are usually determined by oxygen flask combustion, sodium peroxide fusion in a metal bomb followed by titration [30], pyroluminescence [36] or ICP-AES. An oxygen flask combustion photometric titration procedure capable of determining total sulfur in polymers in amounts down to 50 ppm was reported. The repeatability of the sulfur determination in polyolefins in the oxygen flask is 40% at 50 ppm level, improving to 2% at the 1 % level [21]. Crompton [31] has also combined Schoniger flask combustion with a colorimetric procedure for the determination of phosphorous in polymers in various concentration ranges (0.01 to 2%, 2 to 13%). 

Cavrini et al. [32] reported the development of a colorimetric method for the determination of miconazole nitrate in pharmaceutical preparation. The method is based on the formation of a yellow complex between the drug and bromocresol green. The absorption peak of this complex, extracted by chloroform over the pH 2—4 range, was at 424 nm, and linear response was obtained from 3—13 pg/mL. The molar absorptivity of the complex in chloroform was 1.845 x 104. This procedure is suitable for the analysis of miconazole nitrate in commercial dosage forms. 

Baker et al. [52] reported the use of a colorimetric method for the determination of primaquine metabolites, in urine. 

Larsson and Degens [171] devised an automated system for determining carbohydrates in biological samples using partition chromatography for the separation and the orcinol colorimetric method for the final analysis. Later versions of this kind of autoanalyser, using tetrazolium blue or a Cu1 complex of bicinchoninate for the final measurement, have been reported [172]. 

Ruggieri (56) reported a colorimetric test using 2-naphthoquinonesulfonate sodium to form a rose-violet color. 

An automated colorimetric assay for the quantitation of the separate components of neomycin (B, C and neamine) has also been reported- - . The method utilizes a separation of the components on a column of carbon and Kieslguhr G (4 1). The column eluate is reacted with nin-hydrin to determine the amounts of neomycin B, C and neamine. 

Morken and co-worker (57) recently reported using a visual colorimetric assay to evaluate a variety of catalyst systems for allylic alkylation. This method uses the reaction of naphthol with Fast Red diazonium salt as a method for determination of catalyst activity. Reaction of the naphthyl allyl carbonate (222) with palladium gives the naphthoxide (223) after loss of C02. The naphthoxide then deprotonates... 

Cyanide in biological tissue and fluids can be measured spectrophotometrically after reaction with methemoglobin (Tomoda and Hashimoto 1991). The detection limit is 0.4 pg/mL. Other performance data were not reported (Tomoda and Hashimoto 1991). Cyanide in urine has been determined using microdiffusion separation and colorimetric determination (Brimer and Rosling 1991). Detection limits are in the ng/L range other performance data were not reported (Brimer and Rosling 1991). 

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