Phenolphthalein colorimetric method

The principle is that the absorbency of phenolphthalein can be reduced after phenolphthalein is embedded by CD and absorbency reduction has linear relation with CD content in certain concentration range. Apparent CD can be calculated through the content of phenolphthalein which is embedded by CD. 

A series of CD standard solutions (concentration range from 0 to 30 /ug/mL) are prepared and added to phenolphthalein standard solution (pH = 10.8), and oscillated for 30 min. Absorbency value is determined at 552 nm and then the working curve is drawn. An accurate amount of CDP sample is taken, added to the above standard solution and oscillated for 30 min. It is filtered to remove insoluble polymer. The absorbency value is determined at 552 nm. The CD content is calculated on the basis of the working curve. 

The determination result is on the high side because the CDP net structure does not powers adsorption ability. For some polymer, the immobilized CD can be taken off through alkali elution, and then colorimetric assay. 

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CGTase activity was measured at the following temperatures (40, 50, 70, 80, and 90 °C) and pH 6.0 (pH of maximum catalytic activity), keeping fixed the biocatalyst mass (307.5 mg). Samples of the reaction medium were taken in duplicates at the times of 0 and 25 min and added to a test tube containing 20 pL of 5 M HCl. These tubes were immersed in boiling water for 5 min to inactivate the enzyme. After cooling, a sample was taken to determine P-CD concentration using the phenolphthalein colorimetric method. The same assay was conducted from pH 4.0 to 10.0 and 60 °C, the temperature for maximum enzyme activity. 

By mixing suitable indicators together changes in colour may be obtained over a considerable portion of the pH range. Such mixtures are usually called universal indicators . They are not suitable for quantitative titrations, but may be employed for the determination of the approximate pH of a solution by the colorimetric method. One such universal indicator is prepared by dissolving 0.1 g of phenolphthalein, 0.2 g of methyl red, 0.3 g of methyl yellow, 0.4 g of... 

The concentration of 3-CD was measured by the dye-extinction colorimetric method using phenolphthalein, as described by Tardioli et al. [9],... 

Ammonium chloride is analyzed by treatment with formaldehyde (neutralized with NaOH) and the product HCl formed is analyzed by titration using an acid-base color indicator such as phenolphthalein. Alternatively, it may be mixed with caustic soda solution and distdled. The distillate may be analyzed for NH3 by titration with H2SO4 or by colorimetric Nesslerization or with an ammonia-selective electrode (APHA, AWWA, WEF. 1995. Standard Methods for the Examination of Water and Wastewater. 19th ed. Washington, DC, American Pubhc Health Association). The presence of ammonia or any other ammonium compound would interfere in the test. The moisture content in NH4CI may be determined by Karl—Fischer method. 

The reactions of alcohols related to phenolphthalein and fluorescein with Ag1 ions have been investigated for their application as colorimetric reagents in determining trace amounts of silver. A simple, rapid and sensitive method was found which used 2,4,5,7-tetra-bromofluorescein and 1,10-phenanthroline. A ternary complex was formed with a deep pink colour (Ama 550 nm) in the presence of silver(I) ions and the two reagents. No significant colour change was observed in the absence of the diimine.227... 

The choice of titration protocol to determine the TA of a sample is dependent primarily on the color of the sample. The colorimetric titration uses phenolphthalein indicator solution to determine the endpoint of the titration. Phenolphthalein indicator solution turns from colorless to pink upon reaching the endpoint therefore, if the color of the sample interferes with this color change, the potentiometric titration is the best method. However, when using colorimetric titration, it is also common to titrate to an endpoint of pH 8.2, the endpoint of the phenolphthalein solution. 

With the conductivity cell as described by Ehrhardt (1976), the change in conductivity of a stream of dilute sodium hydroxide solution is related to the mass of carbon dioxide absorbed. Disadvantages to this method include the temperature dependence of electrical conductivity and the potential for interference from compounds other than carbon dioxide, which must be removed from the gas stream. Flame ionisation detector (FID) systems measure methane, which results from the reduction of the carbon dioxide in the gas stream from the DOC analyser by an in-line reductor. Whilst FID systems have a wide dynamic range, and good sensitivity, additional gases are required in the analysis, and the hydrogen used for the flame is explosive. A colorimetric technique described by Schreurs (1978) relies on the partial neutralisation of an acid solution by the carbon dioxide. The neutralization is followed by the change in absorbance of a coloured phenolphthalein solution. The technique is compatible with autoanalyser systems it is not as sensitive as the other techniques mentioned here. 

Most published methods for the colorimetric determination of phenolphthalein depend upon formation of the red colour in alkaline solution. Earlier procedures, such as that of Frederick and Koff, made use of a... 

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