Salicylic acid, limit tests

Another limitation to the studies in Table 1 is the small number of plant species tested. Primarily monocotyledonous plants have been studied, although McClure et al. (26) found ferulic acid inhibitory in soybean. The restriction of studies to monocots is probably because the mechanism of mineral absorption has been more fully elucidated with monocots. Harper and Balke (32) reported some minor differences in the inhibition of K+ absorption by salicylic acid among oats (Avena sativa L.), wheat (Triticum aestlvum L.), barley, and maize roots. 

Arsenic Determine as directed under Arsenic Limit Test, Appendix IIIB, using 10 mL of the Sample Solution (above). Carbonate Mix 1 g of sample with 10 mL of water, cool, and keep the mixture cool while adding 5 mL of sulfuric acid. No effervescence occurs during the addition of the acid. Iron Mix 2 g of sample with 10 mL of water in a mortar, and add 500 mg of sodium salicylate. No more than a light red tint appears. 

A typical example of a limit test is the test for salicylic acid in a sample of Aspirin BP. Salicylic acid is formed by hydrolysis of aspirin (or may be an impurity from the synthesis). The test involves comparing the violet colour produced when the sample is reacted with ferric chloride with that obtained from a standard salicylic acid solution. 

Disodium-l,2-dihydroxybenzene-3,5-disulfonate (tiron) yields a strong yellow color when reacted with titanium salts in the pH range of 4.3-9.6 [15]. Titanium salts also react with 5- ilf< alicylic acid at pH 3-5 to yield yellow solutions [16]. Other reagents which have found limited use in identification testing are thymol [17], gallic acid [18], and salicylic acid [19]. 

The B,F, test for free salicylic acid is a modification of the method of Jones, and the limit of impurity allowed is equivalent to 0-05 per cent of salicylic acid in the aspirin. 

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