Sulphonamides assays

Non-aqueous titration of acidic groups is carried out in pharmacopoeial assays of barbiturates, uracils and sulphonamides. 

The HPLC-receptorgram assay combined the advantages of HPLC separation with the multiresidue detection of the Charm II tests. The procedure was tested for identification and quantitation of the most common veterinary drugs at regulatory levels or lower. It was validated for 40 individual drugs from seven antibiotic families 10 /3-lactams, 13 sulphonamides, 8 tetracyclines, 4 macrolides, 3 amphenicols, and other miscellaneous antimicrobials. This procedure combined a simple aqueous extraction and SPE with HPLC fractionation of individual drugs. Final identification and quantitation was achieved with the Charm II test. A drug contaminant could be identified in less then 3 hours (50). 

Spinks, C.A., G.M. Wyatt, S. Everest, et al. 2002. Atypical antibody specificity Advancing the development of a generic assay for sulphonamides using heterologous ELISA. J. Sci. Food Agric. 82 428-434. 

For colorimetric assay, although the diazo compound can be coupled with A -(l-naphthyl)ethylenediamine (see Sulphonamides, p. 609) Dewing and Foster found that for routine assay a more satisfactory determination could be carried out if the acid hydrolysate were treated with sodium nitrite and coupled with dimethyl-a-naphthylamine. 

The official sulphonamides are all derivatives of sulphanilamide and the assay for all members of the group by diazotisation follows that of the parent substance either directly or after preliminary hydrolysis or reduction (para-nitrosulphathiazole) except for sulphafurazole and sulphafurazole diethanolamine. Sulphafurazole cannot be diazotised quantitatively since the product consumes more than one equivalent of nitrous acid. Non-aqueous titration can also be applied. 

Table 35 on page 610 summarises the official sulphonamides, the factor for O IM sodium nitrite assay in all cases is 1 X 10 of the molecular weight. 

The most convenient standards to prepare are 1 0, 0 3 and 0 1 mg of the corresponding sulphonamide per 100 ml. The A -(l-naphthyl)-ethylenediamine dihydrochloride solution should be kept in a dark-coloured bottle and stored in a refrigerator when the solution becomes at all yellow it should be discarded. Aminosalicylic acid will interfere with this colorimetric assay. 

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