Ion chromatography‐based determination of lithium in human urine for monitoring medication compliance

Continuous Li monitoring is vital in ensuring the safety and treatment efficacy of probationers with psychotic disorders, such as bipolar disorder, depression, and mania. This study introduced a validated quantitative analysis method using ion chromatography (IC) to monitor Li+ concentration in urine. The methodology involved centrifuging the urine sample, diluting the supernatant with deionized water, and subsequent IC analysis using guard and analytical columns for precise Li+ concentration measurement. The method quantified Li+ within the range of 2–400 ng/mL, demonstrating its excellent linearity (r2 = 0.9983) with a weighting factor of 1/x. Precision levels below 12.8% were observed for both intraday and interday measurements with an accuracy of −5.9% to 15.2%. The detection limit was identified as 0.12 ng/mL. The method conformed to analytical standards in terms of selectivity, matrix effect, process efficiency, dilution integrity, and stability. Moreover, the method distinctly quantified Li+ while effectively eliminating interference from Na+, which had a similar retention time as Li+ with higher concentrations. Further, the developed method was successfully applied to analyze forensic urine samples of Li users, demonstrating its applicability for medication compliance monitoring using urine samples of mentally disordered probationers.