What are common sample preparation approaches before chromatographic analysis for trace-level analysis?

What are common sample preparation approaches before chromatographic analysis for trace-level analysis?

• A. Liquid-liquid extraction (LLE), solid-phase extraction (SPE), protein precipitation, solid-phase microextraction (SPME), derivatization, filtration, dilution, and matrix cleanup.
• B. Only dilution.
• C. Only filtration.
• D. No preparation is needed.

Answer: (A)