In rapid screening methods for trace elements, the sample used is urine.

• A. Urine
• B. Blood
• C. Hair
• D. Sweat

Answer: (A)

For rapid screening of trace elements, the chosen sample should be easy to obtain in large numbers, quick to process, and provide information about recent exposure. Urine fits perfectly because it is non-invasive to collect, allows high-throughput sampling, and many trace elements are excreted in measurable amounts, reflecting recent intake or exposure. The matrix generally has fewer proteins and potential interferences than blood, which simplifies preparation and reduces analytical complications, making fast screening feasible with techniques like ICP-MS or atomic absorption. Hair would indicate longer-term history rather than current exposure, and sweat has highly variable results and contamination risks, making it unreliable for rapid screening.