SPECTROPHOTOMETRIC DETERMINATION OF LITHIUM WITH QUINIZARIN IN DRUGS AND SERUM

A very sensitive analytical method is proposed for the determination o f lithium based on the reaction of Li+ ion wiht 1,4-dihydroxyanthraqui none (Quinizarin). In dimethylsulfoxide medium (90%) and in the presen ce of sodium hydroxide and sodium carbonate, a bluish-violet color (la mbda(max) = 601 nm) develops and is stable over a period of 30 min to 2.5 h. The NaOH and Quinizarin concentrations were optimized simultane ously using the response surface methodology from sequential experimen tal Doehlert designs. Beer's law is obeyed in the concentration range 14-250 ppb Li+ in aqueous and serum matrices, and the errors (RSD) in the determination of 100 ppb Li+ are 4.0% and 3.9% respectively. The p roposed procedure was satisfactorily applied to the determination of l ithium in drugs and human serum (no deproteinization is required).