Determination of trimethoprim in milk, water and plasma using protein precipitation combined with liquid phase microextraction method

Abstract

A simple and effective microextraction method based on protein precipitation and continuous sample drop flow microextraction (CSDF-ME) for the extraction of trimethoprim from milk, water and plasma is reported. The precipitation with zinc acetate was used to appreciably separate trimethoprim (TMP) from the complex matrix of milk samples. After protein precipitation, TMP which was present in the upper phase was extracted and pre-concentrated using CSDF-ME. To this end, the pH of the upper phase was adjusted to 10.0 and filtered. Afterwards, the extracted TMPs were concentrated by pumping the aqueous solution into a conical vial containing 35.0 μL of chloroform and 7.5 μL of DMSO (as co-solvent) at a flow rate of 0.45 mL min-1. Finally, the concentrated TMPs were determined by HPLC-UV. This is the first report on the extraction and quantification of TMP from milk samples using protein precipitation coupled with CSDF-ME-HPLC-UV. Having optimized the experimental conditions, the proposed method was thoroughly validated for milk. plasma and water. The results showed that the method was linear between 10.0 and 1200.0 µg L-1. The LOD and LOQ for TMP in different matrices were 3.0–8.0 and 10.0–25.0 µg L− 1, respectively. The relative recovery and the enrichment factor were 81.6–101.3% and 19.0–40.0, respectively. The relative standard deviations for intraday precision and between-day precision at a concentration level of 200.0 μg L-1 were 3.3–6.0 and 2.6–8.3, respectively. The resulting LOQ with trueness over 81.6%, indicates the method's applicability for TMP analysis in complicated matrices such as milk with a considerable reduction in chemicals and reagents required for the determination.