Determination of chloroquine in dried blood spots on filter paper: importance of sample handling.

During determination of chloroquine (CQ) and its main metabolite desethylchloroquine (CQM) in blood samples applied to filter paper, we observed contamination of the paper by CQ. CQ and CQM in the dried spots were analyzed with two different high performance liquid chromatographic methods. The identity of the contamination was confirmed as CQ with mass spectrometry.