The test reagent consisted of 0Æ4 g
1-naphthyl phosphate, disodium salt (Sigma, product
code N-7255) and 0Æ8 g Fast Blue B [o-dianisidine bis
(diazotized) zinc double salt] (Sigma, product code
D-9805) dissolved in 20-ml of acetate buffer (Riedelde-
Hae¨n, Gillingham, UK, product code 33581) at pH 4Æ6
and prepared according to Mead et al. (1981).