The document presents a methodology for simultaneous multi-element determination of copper (Cu), manganese (Mn), and selenium (Se) using electrothermal atomic absorption spectrometry with the SIMAA 6000 instrument. Optimal conditions for single and multi-element analyses were established, and detection limits were evaluated using certified biological reference materials, confirming method accuracy. This technique demonstrates rapid, cost-effective, and sensitive analysis capabilities for trace elements in various biological samples.