*4.8. Matrix Effects Study*

The matrix effects of the method were evaluated within two types of feed matrices: swine and dairy feed. Matrix-matched calibration curves were prepared at seven levels in the range 0.5–100.0 ng/g (*n* = 3 per each concentration). The matrix effects expressing the matrix-induced SSE% were defined as percentage ratios of the matrix-matched calibration slope to the solvent calibration slope. Therefore, the matrix-matched calibration curves were used for quantitative analysis.

**Author Contributions:** Conceptualization, A.P.; investigation, S.P., N.K. and A.P.; methodology, A.P., Z.Z. and M.G.; Resources, M.G., Z.Z. and A.F.L.; Validation, writing-original draft preparation, S.P. and A.P.; Supervision, review and editing, A.P., Z.Z., M.G. and A.F.L.; Project administration and funding acquisition, A.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research is supported by the Center of Excellence on Agricultural Biotechnology, Office of the Permanent Secretary, Ministry of Higher Education, Science, Research and Innovation. (AG-BIO/MHESI).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare that there is no conflict of interest.
