Quinine directly determined in serum or urine by separation fluoroimmunoassay

We developed and validated a magnetizable solid-phase fluoroimmunoassay for directly determining quinine in serum or urine. We prepared the immunogen by coupling quinine hemisuccinate to keyhole-limpet hemocyanine, using this to immunize three sheep, and coupling the antisera to magnetizable solid-phase particles to facilitate separation of bound antigen from interfering components of serum or urine. We tested the stability of two fluorescein-labeled derivatives of quinine--one prepared by direct conjugation of quinine to dichlorotriazenyl aminofluorescein, the other by conjugating quinine hemisuccinate to fluorescein thiocarbamyl ethylenediamine. The latter was unstable. Using the former label and an 30-min incubation, we saw no interference by quinidine (an enantiomer of quinine) or other antimalarial drugs at their therapeutic concentrations.