Sulfanilic Acid, Diazotised

Gianguzza and Orecchio [147] have carried out comparative trials of various methods for estimating nitrites in seawaters. These workers compared a method using sulfanilic acid/a-naphthylamine complexes with a method using sulfanilamide/N( 1-naphthyl) ethylenediamine complexes for the determination of nitrites in saline waters. The second method has the greater sensitivity and lower detection limits. The former method is subject to interference from chlorides, and this interference can be completely eliminated by the coupling diazotisation procedure of the latter method. 

A method [17] has been described for the determination of nitrate and nitrite nitrogen and ammonium ions in the 2 M potassium chloride extracts of moist soils. Firstly, an aliquot of the extract is made alkaline and the released ammonia determined via an ammonia-selective probe or titrimetrically. The nitrate in the ammonia-free extract is then reduced to ammonia with Devarda s alloy and the ammonia removed by distillation and determined titrimetrically. The concentration of nitrite in the extract is then determined spectrophoto-metrically as the red dye formed by coupling diazotised sulfanilic acid with N naphthylethylenediamine hydro chloride. 

Many dyes used in the clothing industry contain sulfonic acid groups which impart water solubility and help to make the dye become fast to the fabric. The dye becomes fast by attaching itself to polar sites in the fibres of, for instance, cotton, wool or silk. Many azo dyes, like Congo Red (see Introduction, p. 5), contain one or more sulfonic acid groups. Another example is Orange II (7), synthesised by coupling p-naphthol (8) with diazotised sulfanilic acid (9) (Scheme 2). 

Phenolic antioxidants Polyamide powder Methanol - water (3 2) or methanol - carbon tetrachloride (1 9) Diazotised sulfanilic acid [13]... 

N=N— 1 azobenzene, methyl orange, benzocinnoline, formazane —N N j benzenediazonium chloride, diazotised sulfanilic acid... 

Alternatively, an aliquot of the original concentrated acetonitrile extract was treated with ethanol and diazotised sulfanilic acid, and the extinction of the resulting dye, measured at 480 nm. This was compared with that for a solution containing 10 pg of antioxidant in acetonitrile, treated similarly. 

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