Apply Protein crash using ice-cold ACN, centrifuge, and filter supernatant. Evaporate and perform a solvent exchange or directly inject after proper dilution. If the purposed amounts are at trace levels and/or too much matrix effect is occurred at MS then apply SPE for additional clean-up step prior to analysis.
Use the C8 column for separation and analytical purity standard for external or matrix-matched calibration...Build an SRM acquisition using standard and collect data...