CONVENTIONAL AND THERMAL LENS SPECTROPHOTOMETRIC DETERMINATION OF P-AMINOBENZOIC ACID AND ARYLAMINE DIURETICS PREVIOUS AZODYE FORMATION IN A MICELLAR MEDIUM

The determination of the diuretics hydrochlorothiazide, bendroflumethiazide and furosemide by both conventional and thermal lens spectrophotometry (TLS, 100 mW of pump power at 514.5 nm) following previous hydrolysis, diazotization and coupling with N-(naphthyl)ethylenediamine (NED) in a sodium dodecyl sulphate (SDS) micellar medium of pH almost-equal-to 1 was studied. p-Aminobenzoic acid (PABA) was used as a model compound to optimize the derivatization procedures. 3-Substituted indoles, such as 5-hydroxyindole-3-acetic acid and tryptophan, gave N-nitroso derivatives which interfered with the determination of the diuretics in urine. The derivatized diuretics in urine were separated using HPLC with a Spherisorb ODS-2 C18 column, and a 0.1M SDS mobile phase containing 5% n-propanol and 0.01M sodium dihydrogen phosphate (pH 3). The diuretics gave limits of detection (LODs) of ca. 5 x 10(-9)M for the TLS procedure. The LODs were 20-50-fold higher for the corresponding spectrophotometric procedure.