Treatments of plasma protein precipitation and the addition of NaCl were compared with a direct extraction from plasma without protein precipitation or salt addition. Bovine plasma from control groups where EC was not detected using the current method was spiked with authentic EC standard to obtain a final EC concentration of 1 µg/mL in plasma. The first treatment with protein removal and salt addition, referred to as [deprotein+salt], was carried out as described above. The second treatment with protein removal only, referred to as [deprotein], skipped the addition of NaCl. The third treatment, referred to as [control], applied MTBE extraction directly to the plasma as is. All the extractions started with 400 µL of spiked plasma and then used MTBE with a solvent-tosample ratio of 4:1. Recovered MTBE extracts (1 mL) were spiked with 20 µL of 10 µg/mL of EC-d5 (dissolved in MTBE) before being dried down to ~100 µL.