Validation of a flame photometric method for serum lithium estimation

Abstract

BackgroundLithium is a first line drug used to treat bipolar affective disorder requiring frequent monitoring due to its narrow therapeutic index. Flame photometry is a reliable quick and cost-effective method of serum lithium estimation. ObjectiveWe aimed to validate a flame photometry method for serum lithium estimation to compare the results with a different model flame photometer and an ionselective electrode. MethodSherwood 410 flame photometer was used for the analysis. Serum samples were diluted 1:2 using a lithium blank solution containing sodium and potassium. Aqueous lithium standards were prepared using the same blank. The method was validated for the concentration range 0.2-1.5mmol/l. Linearity, recovery, accuracy, precision and stability were determined by standard lithium serum samples representing the lower limit of quantification (LLOQ) 0.2mmol/l, median level of quantification (MLOQ) 0.8mmol/l and the upper limit of quantification (ULOQ) 1.5mmol/l. Five replicates of serum and aqueous lithium samples were used to determine linearity in the range between LLOQ and ULOQ using the coefficient of determination (R2). Five standard serum replicates were used for recovery, accuracy and precision studies. Precision was determined by the coefficient of variation (CV%) on three different days. Results of the flame photometric method were compared with those of a different flame photometric method and an ion-selective electrode method. Results:The R2 for the aqueous samples and the serum samples was >0.995 demonstrating linearity. The matrix effect ranged between 92.5% and 105% for the LLOQ, MLOQ and ULOQ. The accuracy and precision for LLOQ, MLOQ of and ULOQ were below 15%. Similar results were obtained for the QC samples with the different model flame photometer and ion-selective electrode method.

Modern instrumentation and practical application of flame atomic emission spectrometry

“…The FAES method has also shown its suitability for determining the concentration of Li administered for therapeutic purposes in biological fluids, for example, in bipolar disorders [40,41]; sodium concentration and osmolality in plasma and cerebrospinal fluid (the so-called water-salt homeostasis of the brain) [42]; concentrations of sodium and potassium ions to study the physiological state of the kidneys [43]; levels of Ca, K, and Na in oral fluid [44], potassium levels in the vitreous body of the eye [45]; metals in hair [46]; calcium in urine [47], sodium and potassium in blood serum and urine [48,49]; level of magnesium in blood plasma in patients with chronic alcoholism during withdrawal syndrome [50].…”