Use of a three-factor interpretive optimisation strategy in the development of an isocratic chromatographic procedure for the screening of diuretics in urine samples using micellar mobile phases

Screening of diuretics in urine is feasible through direct injection of the samples into the chromatographic system and isocratic reversed-phase liqui d chromatography (RPLC) with micellar-organic mobile phases of sodium dodec yl sulfate (SDS) and I-propanol. The surfactant coverage of the chromatogra phic column makes the addition of organic competing amines less necessary t han in conventional aqueous-organic RPLC to achieve well-shaped peaks. Also , the range of elution strengths of micellar mobile phases required to elut e mixtures of hydrophobic and hydrophilic diuretics is smaller. This allows the isocratic separation of the diuretics within adequate analysis times. An interpretive methodology is applied to optimise the resolution of a mixt ure of 15 diuretics of diverse polarity and acid-base behaviour (althiazide , amiloride, bendroflumethiazide, benzthiazide, bumetanide, canrenoic acid, chlorthalidone, ethacrynic acid, furosemide, piretanide, probenecid, toras emide, triamterene, trichloromethiazide and xipamide), using pH and concent rations of surfactant and organic modifier in the mobile phase as separatio n factors. Twelve diuretics were resolved in 25 min using 0.055 M SDS-6.0% I-propanol at pH 3.0. The mixture of 15 diuretics was also resolved with tw o mobile phases showing complementary behaviour: 0.05 M SDS-5.6% l-propanol at pH 5.4 and 0.11 M SDS-5.4% l-propanol at pH 4.2, The results were appli ed to the analysis of urine samples with limits of detection similar to tho se usually reported for aqueous-organic RPLC, taking into account that the samples were injected without any previous treatment to separate or preconc entrate the analytes. (C) 2000 Elsevier Science B.V. All rights reserved.