Measurement of serum lithium by atomic absorption spectroscopy.

Lithium concentrations in the serum of patients undergoing therapy with lithium salts were measured by atomic absorption spectroscopy. Serum was diluted 10-fold with water. Physiological amounts of sodium and potassium were included in the blank and standard solutions because these cations enhance the lithium signal by 2%. Calcium, magnesium, bicarbonate, sulfate, and phosphate at the concentrations found in serum were without effect. Protein clogging of the triple-slot Boling burner was not observed. The relative standard deviation of within-run variability was 0.6% (n = 20 and = 0.88 mEq/liter), and of daily precision, tested over a month, it was 2.5% (n = 30, = 0.91 mEq/Iiter). Recovery of 1.00 mEq of lithium added per liter of serum ranged from 97 to 103%, averaging 99.8%.