Standard Reference Materials: A Reference Method for the Determination of Lithium in Serum

摘要

A reference method was established for the determination of serum lithium based on flame atomic absorption spectroscopy (FAAS). Its accuracy was evaluated by comparing the values obtained by use of the method in 14 laboratories against the results obtained by a definitive analytical method based on isotope dilution-mass spectrometry (IDMS). Ten serum pools with lithium concentrations in the range 0.534 to 2.9554 mmol/L were analyzed. Manual and semiautomated pipetting alternatives were tested using sample sizes of 4.00 and 2.00 mL, respectively. The laboratories used several different FAAS instruments. The results showed that the standard error for a single laboratory's bias of about 2.0 percent over the range of serum lithium concentrations studied. These values are within the accuracy and precision goals that had been set. The calibration curve data showed excellent linearity over the total concentration range, with 24 of 25 curves having standard deviations of fit of 0.025 mmol/L or less. With appropriate experimental design, the reference method may be used to establish the accuracy of field methods as well as to determine reference lithium values for pooled sera.