Control bovine plasma was spiked with authentic EC standard to obtain a final EC concentration of 24 ng/mL (medium level) and 48 ng/mL (high level) in plasma. The plasma sample combined from test group was used with no addition of EC and served as the low concentration level. For intra-day repeatability, samples of each level were assayed with six replicates. For inter-day repeatability, samples of each level were assayed with three replicates per day over a three-day period. The repeatability of distillers grains coproducts was examined by repeatedly assaying a quality control (QC) sample that was generated by pooling a small portion of each experiment sample.