Color colorimetric reagent

The total free chlorine in wastewaters as measured by colorimetric techniques constitutes both the dissolved molecular chlorine, hypochlorite ion, OCl, and hypochlorous acid. An equilibrium exists between these species, the concentrations of which depend on the temperature and pH of the waste-water. Concentration of the hypochlorous acid may be estimated from the K value or from the ratio (33% of the measured concentration of free chlorine). The free chlorine may be measured by amperometric titration after the addition of a phosphate buffer solution to produce a pH between 6.5 and 7.5. The sample is titrated against a standard solution of phenylarsine oxide. Alternatively, the syringaldazine (3,5-dimethoxy-4-hydroxybenzaldazine) colorimetric test may be performed. This color-forming reagent in 2-propanol yields a colored product with free chlorine, the absorbance of which may be... 

V. Treatment with Diphenylamine Reagent. See item E under colorimetric reagents and Charts A Si B. A yel color indicates the presence of one of the expls TNT, TNAns, HNDPhA, PA, AmmPic or DNPh viol, blue or black color indicates DNT, DNB, DINA, Tetryl, PETN, RDX, EDNA, EDD or AN red color indicates o-MNN... 

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. 

In colorimetric analysis, a reagent is selected that would form a colored complex or derivative with the analyte. Often, the analyte is extracted from the aqueous sample into an organic solvent before adding color-forming reagent. Such extractions become necessary, especially for organic analytes such as phenols, lignin, and tannin. 

The first step in any colorimetric analysis is to prepare a standard calibration curve (i.e., a series of standard solutions of the analyte is made at a specific concentration range), which are then treated with the color-forming reagent, the absorbance or transmittance of which is then measured. The lowest calibration... 

Reddy et al. described two spectrophotometric methods for nimodipine in its dosage forms [2]. The first method involves the use of para dimethylaminocinnamaldehyde as a colorimetric reagent, and the measurement of the generated color at 510 nm. The second method is... 

The title, "The Determination of Phosphorus, for example, would interest the present author, but at once questions arise. In what kind of material is the phosphorus determined Is a separation of the element necessary If so, what kind of method is applicable Is a colorimetric method of measurement used If so, what is the color-forming reagent If it is ammonium molybdate, is the system measured molybdophosphoric acid, molybdovanadophosphoric acid, or a heteropoly blue If the latter, what are the reductant and the conditions of reduction To the extent that the title does not answer these and other similar questions, the summary should. 

If a title is self-explanatory and adequate for indexing purposes, there is no abstract or annotation in Chemical Abstracts. Such cases are rare for analytical methods. In general one wants to know what was done, how, and the results obtainable for given substances or conditions. The information desired may be much the same as that suggested for a satisfactory summary. For example, the method may be for small amounts of silica. The reader wants to know if the procedure is colorimetric. If so, was the colored species developed a heteropoly acid If so, what was the color-forming reagent Too often these and similar questions are not answered. 

The method of standard additions was used to determine nitrite in a soil sample. An aliquot of 1.00 mL of the sample was mixed with 24.00 mL of a colorimetric reagent, and the nitrite was converted to a colored product with a blank-corrected absorbance of 0.300. To 50.00 mL of the original sample, 1.00 mL of a standard solution of 1.00 X W M nitrite was added. The same color-forming procedure was followed, and the new absorbance was 0.530. What was the concentration of nitrite in the original undiluted sample ... 

One gas analysis technique using sealed adsorbent tubes borrows from the colorimetry methods of manual procedures. Draeger and now also the Gastec and the Matheson-Kitagawa systems all use glass tubes packed with a solid support which is coated with an appropriate colorimetric reagent for the gas of interest. Company literature assesses the coefficient of variation for the tubes with most readily discernable color changes as 10%, and for the less efficient tubes as 20-30% [26] (Eqs. 2.15-2.17). 

The main sp>ectrophotometric techniques used in sugar determination are based on reactions of these carbohydrates with colorimetric reagents, forming a colored complex that can be detected and quantified in a sp>ectrophotometer. 

Colorimetric reagents generate a color change upon reaction with the reporter enzyme. Color changes are advantageous for rapid tests because they can be detected visually. Precise quantitation or assay automation requires absorbance (optical density, OD) measurement, and a wide variety of spectrophoto-metric and filter colorimeters are commercially... 

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... 

The most widely appHed colorimetric assay for amino acids rehes upon ninhydrin-mediated color formation (129). Fluorescamine [38183-12-9] and (9-phthalaldehyde [643-79-8] are popular as fluorescence reagents. The latter reagent, ia conjunction with 2-mercaptoethanol, is most often used ia post-column detection of amino acids separated by conventional automated amino acid analysis. More recently, determiaation by capillary 2one electrophoresis has been developed and it is possible to determine attomole quantities of amino acids (130). 

The most common colorimetric technique involves a reaction between ammonia and a reagent containing mercuric iodide in potassium iodide (Messier reagent) to form a reddish-brown complex. Turbidity, color, and hardness are possible interferences that can be removed by preliminary distiHation at pH 9.5. 

Colorimetric methods have been successfully used for determining trace amounts of ethanol. Ammonium hexanitratocerate(IV) has been used as a reagent (262) and for continuous automatic analysis. Alcohols form colored complexes with 8-hydroxyquinoline and vanadic compounds. The absorbance of these complexes, measured at 390 p.m has been used to provide an analytical procedure (263). 

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. 

---