Twenty-four-hour (h) urinary copper content is considered as the most suitable tool for the diagnosis of Wilson's disease (WD); however, it is less accurate, time-consuming, and non-economical. Consequently, in the present study, an alternative method through measuring the morning (first) urine copper (Cu) concentration is proposed for the diagnosis of WD, which is more accurate, precise, faster, and cheaper. For this purpose, a sensitive, accurate, and precise analytical method was developed and validated in regard to Commission Decision 657/2002/EC, Council Directive 333/2007/EC, ISO/IEC 17025:2005, and EURACHEM 1998 for the determination of Cu in urine using flame atomic absorption spectrometry (FAAS). The methods LoD and LoQ for urine Cu were estimated as 6.68 μg/L and 16.7 μg/L respectively. The accuracy of the method was found to be 93.70-101.88% calculated from the spike recovery experiment. The RSDs for the repeatability and reproducibility precision were measured as 0.67-3.16 and 0.26-1.95 respectively. The method validation performance criteria indicated that the method was suitable for the determination of Cu in urine. The validated method was then applied for the determination of Cu in both 24 h and first urine. From the analysis, it was found that the amount of Cu per liter in the first urine was almost equivalent to the amount of Cu per 24 h indicating that instead of considering the 24-h urine, morning (first) urine investigation might be an alternative approach for the diagnosis of WD.
Keywords: 24-h urinary copper; FAAS; Method validation; Morning copper concentration; Wilson’s disease diagnosis.