Penamaldate assay: improved methodology for the quantitation of penicilloic acids, penicilloyl amides and penicilloyl esters.

Conversion of penicilloic acids or their derivatives with modified alpha-carboxyl function to penamaldic acid derivatives involves formation of strong absorption bands in the UV. The penamaldate absorbances generated in the optical cell by HgCl2 addition can be used for quantitation and detailed accounts on the procedures are given. Methodological improvements allow determinations of penicilloyl derivatives within a range of 3% (+/- 1.5%). Free penicilloic acid determinations fall within a range of 8%. The penamaldate band at 282 nm from penicilloyl derivatives decreases to 95% within 10 min depending on conditions. The band from penicilloic acid at 275 nm decreases to 25%. The decay appears to be complex and measurements fall within a range of 15% even under carefully controlled conditions. The penamaldate stability can be used for characterization and for semiquantitative assessments of penicilloic acid/penicilloyl derivative mixtures.