Other colorimetric reagents

The other method is less accurate but more rapid and involves direct Nessleri2ation of the sample for colorimetric deterrnination. Other colorimetric indicators with more sensitivity, such as indophenol, have been used in place of Nessler s reagent. Ion-selective electrodes have also found use in analysis for trace ammonia (93). 

We have shown a new concept for selective chemical sensing based on composite core/shell polymer/silica colloidal crystal films. The vapor response selectivity is provided via the multivariate spectral analysis of the fundamental diffraction peak from the colloidal crystal film. Of course, as with any other analytical device, care should be taken not to irreversibly poison this sensor. For example, a prolonged exposure to high concentrations of nonpolar vapors will likely to irreversibly destroy the composite colloidal crystal film. Nevertheless, sensor materials based on the colloidal crystal films promise to have an improved long-term stability over the sensor materials based on organic colorimetric reagents incorporated into polymer films due to the elimination of photobleaching effects. In the experiments... 

When a determination is critical, it is often necessary to do two or more different colorimetric tests in parallel. A substance present in the sample could interfere with one test while not affecting others. In most cases, interference can be controlled. Interference can be detected by adding a known amount of sugar to a sample solution to be measured. The amount of sugar will differ from what is expected if there is interference. In addition, a very colored sample can interfere with the results obtained. In the case of colored samples, subtract the absorbance of the samples dissolved in water or buffer alone from the value obtained after addition of the colorimetric reagents. 

Allied with the chromatography of imidazoles have been methods of estimation of the compounds, particularly those of biological importance, either on the chromatograms or after elution. Most workers have used diazotized aromatic amines as colorimetric reagents,53,277-285 particularly nonsulfonated diazotized aniline derivatives.281-285 Mosebach et aZ.286 initially hydrolyzed. -substituted imidazoles with 10 A hydrochloric acid before separating the compounds by ion-exchange and paper chromatographic techniques prior to estimation. A number of other methods exist for the colori-... 

The use of imprinted polymer ion separation and photometric detection has been demonstrated for Pb [19] and for U02 [35]. In the case of Pb ", the imprinted Pb " resin described above was packed into columns and used to remove Pb " from tap and seawater at a variety of pH values [8], The extraction efficiency of the imprinted resin was compared to the efficiency of an imidodiacetate resin (Chelex-100), a thiol-functionalised resin (Duolite G-73) and a high-capacity polyacrylic acid/polyvinyl alcohol resin (a proprietary NASA resin). The imprinted polymer s extraction efficiency was equal or better than the other resins and the effluents from the imprinted polymer resin were shown to be virtually free of contamination by other metal ions (Fig. 19.13). The purity of the effluent allowed the determination of Pb using a very non-specific colorimetric reagent, dithizone. The method is suitable for automation as an FIA technique. 

Some other colorimetric assays involving diazotization with p-nitroaniline and nitrous acid (34), use of folin and Cioalteu phenol reagent (35), complexation with cupric ion in nitrous acid (36-38) or estimation as the nitro derivative (39) have been reported in the literature. 

Early methods for the determination of total bile acids involved heating samples with concentrated sulfuric acid to form compounds which could be measured spectrophotometrically by their absorbance of ultraviolet light (S33). Other colorimetric reactions, which utilized strong acids and other reagents to produce blue or red colored products, were also used. These methods were lacking in specificity, but this problem was overcome in 1964 with the introduction of an enzymatic method for bile acid determination... 

COLOR PLATE 16 Colorimetric Reagent for Phosphate (Box 18-2) The reagent in Box 18-2 was designed to turn yellow when phosphate is added, but not to respond to other common anions. Vials contain 50 xm colorimetric... 

For many years the use of dithizone as a colorimetric reagent for lead was almost standard practice. Nowadays it is rather rarely used because of a range of disadvantages. These include the rather modest sensitivity and the possibility of interference from other metals [1]. In particular, the time-consuming nature of the method and the considerable experience necessary to achieve reliable results discourage many potential users. The method may still however be of use in laboratories lacking instrumentation for the other analytical methods. 

Colorimetric reagent for primary and secondary amines has other anal. uses. Bright-orange needles. 

It is certainly clear that a coulometric titration, like any other type of titration, needs an end-point detection system in principle any detection method that chemically fits in can be used, be it electrometric, colorimetric, photoabsorptionmetric, etc. for instance, in a few cases the colour change of the reagent generated (e.g., I2) may be observed visually, or after the addition of a redox, metal or pH indicator the titration end-point can be detected photoabsorptiometrically by means of a light source and photocell combination. Concerning the aforementioned coulometric titration of Fe(II), it is... 

More experimental work has been done with DDT than with all the other five chlorinated hydrocarbons combined, probably because DDT was the first of the group found to have insecticidal value. Carter (10) has summarized the several colorimetric methods for DDT. The one proposed by Stiff and Castillo (51), as modified by Claborn (14), and the one by Schechter and Haller (47) have probably been most widely used. In the Stiff and Castillo method, when the DDT is heated in pyridine solution containing xanthydrol and potassium hydroxide, a red color develops which is proportional to the quantity of DDT present. The reaction is sensitive to 10 micrograms. As TDE does not give a color with this reagent, Claborn (14) has proposed the reaction for the determination of DDT in the presence of TDE. He has also shown that for the development of the color the amount of water in the pyridine is critical. 

Figure 2.4. Flow diagram for the colorimetric determination of nitrite and nitrate. The internal diameter of the Tygon tubing was 0.64 mm for the 0.23 ml/min flow rates and 1.30 mm for the 1.00 ml/min flow rates all other tubing was 0.7 mm id. The reagents were (A) carrier stream, (B) sulfanilamide solution, and (C) N(1-naphthyl) ethylene diamine solution. S denotes the point of injection and W waste. From [168]...

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