Determination of chloroquine and its metabolites in urine: a field method based on ion-pair extraction

A new straightforward photometric method for the assay of the antimalarial drug chloroquine and its metabolites in urine is described. The method involves an ion-pair extraction procedure with dichloromethane using the acid-base indicator bromthymol blue as counter-ion. The ion pair formed with chloroquine in the organic phase is yellow, and absorbance is measured at lambda = 410 nm using a filter photometer. The absorbance is a linear function of concentration up to 400 mumol/l (120 mg/l) chloroquine. The method is suitable for the determination of chloroquine and its metabolites in urine down to a limiting concentration of about 10 mumol/l (3 mg/l). Additionally, the method is suitable for semiquantitative visual estimation of the concentration of chloroquine in urine. A single dose of 5 mg/kg chloroquine base could be determined in urine from two volunteers for at least 8 days after administration of the drug. The results obtained for the analysis of chloroquine and its metabolites with the colorimetric method described here correlate well with those obtained using high performance liquid chromatography.