Bromocresol purple reagent

In Inorganic Chemistry, typical spray reagents for cations include potassium iodine (0.2%, aqueous), hydrogen sulphide (saturated aqueous solution), ammonium sulphide (0.2 N, aqueous), quercetin (0.1%, alcoholic), l-(2-pyridylazo)-2-naphthol (PAN) (0.2%, methanolic), oxine (8-hydroxyquinoline) (1% methanolic, view under visible and UV light), and sodium rhodizonate (0.5%, aqueous). Reaction with dithizone to produce coloured dithizonate chelates of many metals is particularly suitable if quantitative spectrometric analysis (in situ or after elution) is to be carried out. Anions are detected with bromocresol purple (0.1%, alcoholic), 1% ammoniacal silver nitrate + 0.1% alcoholic fluorescein/UV light, zirconium alizarin lake (0.1% in HC1 solution), and ammonium molybdate (1%, aqueous) followed by SnCl2 (1%) and HC1 (10%). Typical detection limits range from 10 ng (10 9g) to several pg (10 6g). 

The reagent is prepared by the addition of a weakly buffered solution of urea (pH 4.8) in the presence of bromocresol purple. The urea is hydrolyzed to liberate ammonia in the presence of urease, which raises the pH of the solution, resulting in a color change from yellow to purple. The reaction can be stopped by the addition of 10 pL of a 1% solution of merthiolate (thimerosal) to each well. Tables 4 and 5 smnmarize the properties of various enzyme systems. 

Maphenide responds to the Ehrlich reagent only in amounts exceeding 25 [xg, after longer heating at 90° C. It is better detected by spraying with 0.3% ninhydrin solution in butanol and then heating 30 min at 90° C [102, 134]. N4-succinic and phthalic acid derivatives of sulphonamides have been detected through their ability to quench the fluorescence of suitable layers and also with a 0.05% ethanolic solution of bromocresol purple [84]. 

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