A simple method for the purification of 5-aminosalicylic acid. Application of the product as substrate in enzyme-linked immunosorbent assay (ELISA).

Commercially available 5-aminosalicylic acid (5-AS) was recrystallised in the presence of Na2S2O5. A completely colourless solution was obtained when the purified product was dissolved at a concentration of 1 mg/ml in a phosphate buffer containing EDTA and H2O2. No significant increase in absorption was found upon storage for 18 h at 4 degrees C. A 8-fold increase in sensitivity of an enzyme-linked immunosorbent assay for the detection of rotavirus antigens was demonstrated by using the modified substrate solution instead of the conventional substrate solution of crude 5-AS. In addition, P/N values did not significantly change between 2 and 18 h after addition of the substrate, thus rendering the time of reading less critical. No difference in sensitivity of the assay was found between modified 5-AS solution and ortho-phenylenediamine (OPD). However, since OPD requires special care in handling the modified 5-AS solution is preferred for use in routine ELISAs.