Spectrophotometric analysis with sodium salicylate

Nitrate ions and sodium salicylate together form yellow sodium nitrosalicy-late, which can be determined spectrophotometrically at 420 nm. 

Nitrate concentrations between 0.2 and 40 mg/1 may be determined. If concentrations are lower than 0.5 mg/1, however, the method is inaccurate. The water sample should be cooled to + 4 C and examined within 1 to 2 days at the latest. 

Dissolve 0.5 g of reagent purity sodium salicylate in distilled water to 100 ml. The solution must be freshly prepared daily. 

Dissolve 400 g of reagent purity sodium hydroxide and purity potassium sodium, tartrate in dist. water, cooling make up to 1 litre. Store the solution in a plastic flask. 

Dissolve 0.137 g sodium nitrate of reagent purity in distilled water, add 1 ml of chloroform, and make up to 1 litre, 1 ml of this solution contains 0.1 mg of NO3 , 

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The United States Pharmacopoeia 23 [11] and Indonesian Pharmacopoeia IV [9] describe the assay of benzoic acid and salicylic acid in ointments. Two chromatographic columns (20 x 2.5 cm) are used to effect the separation. One transfers a mixture of 1 g siliceous earth and 0.5 mL diluted phosphoric acid (3 in 10) to the first column (A), then packs above this a mixture of 4 g siliceous earth and ferric chloride-urea reagent. A mixture of 4 g siliceous earth and 2mL of sodium bicarbonate solution (1 in 12) is packed into the second column (B). For analysis, column A is mounted directly above column B. The sample solution is inserted onto column A, allowed to pass into the column, and then washed with 2-40 mL of chloroform. Benzoic acid can be eluted from column B by using a 3 in 100 solution of glacial acetic acid in chloroform. The benzoic acid content then can be determined by a spectrophotometric method such as that described earlier (section 4.5). 

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