Chromogenic reagent

Tabushi, I. Yamamura, K. Water Soluble Cyclophanes as Hosts and Catalysts, 113,145-182 (1983). Takagi, M., and Ueno, K. Crown Compounds as Alkali and Alkaline Earth Metal Ion Selective Chromogenic Reagents. 121, 39-65 (1984). 

Xylenol orange and methylthymol blue as chromogenic reagents. B. Budesinsky, Chelates Anal. Chem., 1967,1,15-47 (124). 

Crown compounds as alkali and alkaline earth metal ion selective chromogenic reagents. M. Takagi and K. Ueno, Top. Curr. Chem., 1984,121, 39-65 (37),... 

Afansev et al. [61] have described an extraction photometric method for the determination of arsenic at the xg/l range in seawater. This method uses diantipyrilmethane as the chromogene reagent. The coefficient of variation is... 

Various chromogenic reagents have been used for the spectrophotometric determination of boron in seawater. These include curcumin [108,109], nile blue [110], and more recently 3,5 di-tert butylcatechol and ethyl violet [111]. Uppstroem [108] added anhydrous acetic acid (1 ml) and propionic anhydride (3 ml) to the aqueous sample (0.5 ml) containing up to 5 mg of boron per litre as H3BO3 in a polyethylene beaker. After mixing and the dropwise addition of oxalyl chloride (0.25 ml) to catalyse the removal of water, the mixture is set aside for 15-30 minutes and cooled to room temperature. Subsequently, concentrated sulfuric-anhydrous acetic acid (1 1) (3 ml) and curcumin reagent (125 mg curcumin in 100 ml anhydrous acetic acid) (3 ml) are added, and the mixed solution is set aside for at least 30 minutes. Finally 20 ml standard buffer solution (90 ml of 96% ethanol, 180 g ammonium acetate - to destroy excess of protonated curcumin - and 135 ml anhydrous acetic acid diluted to 1 litre... 

Abraham et al. [286] determined total copper in seawater spectrophotometri-cally using quinaldehyde 2-quinolyl-hydrazone as chromogenic reagent. This method is capable of determining copper at the ppb level. 

Table 4.15(a) Chromogenic reagents for visualizing thin-layer chromatograms... 

Apply a freshly prepared chromogen reagent mixture to the slide and incubate them in a humidity chamber/box at room temperature. Observe the color development under the light microscope and terminate the reaction by soaking in rinse solution when it is appropriate (see Note 22). 

Hiermann, A. and Bucar, E., Diphenyltin chloride as a chromogenic reagent for the detection of flavonoids on thin-layer plates, J. Chromatogr., 675, 276, 1994. 

Molybdenum VI) has also been determined spectrophotometrically in soil extracts using toluene-3,4-dithiol chromogenic reagent. However, copper(II) interferes in this procedure. Milham et al. [169] discussed an isoamylacetate extraction procedure for overcoming such interference. 

Abbasi [234] has described a spectrophotometric method employing N-p-methoxyphenyl-2,-furohydroxic acid for the determination of titanium in soils. In this method, the soil sample was subjected to alkali fusion. The ash was treated with nitric acid to adjust it to pH 2.0 and filtered prior to adjustment to 10 pM with respect to hydrochloric acid. Stannous chloride (5M) was added to the filtrate, and the chromogenic reagent was dissolved in chloroform. The chloroform extract was evaluated spectrophotometrically at 385 nm against the reagent solution as blank. Approximately 61 ppm of titanium was found in a soil sample by this method. 

Waughman [26] has described a simple microdiffusion method for estimating nitrate (and ammonia) in soils. In this method, nitrate in the soil extract is reduced to ammonia by titanous sulfate and the ammonia is then released from the solution and diffused and absorbed onto a nylon square impregnated with dilute sulfuric acid. The nylon is then dipped into a solution of a chromogenic reagent for ammonia and the colour evaluated spectrophoto-metrically. 

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