Quantitative performance of liquid chromatography coupled to Q-Exactive high resolution mass spectrometry (HRMS) for the analysis of tetracyclines in a complex matrix

The presence of antibiotics in the environment is of increased interest and, as modern mass spectrometers become more efficient, we are increasingly aware of traces of pharmaceuticals appearing in a wide range of environmental and biological matrices. The Q-Exactive mass spectrometer is part of these innovative hybrid high-resolution mass spectrometers (HRMS) which is often associated with peptide sequencing or metabolomics but with a limited number of studies focusing on its application to the quantification of small molecules in environmental and biological matrices. It combines the high resolving power (RP) performance of the Orbitrap with the high performance selectivity of the quadrupole. Tetracyclines (TCs) are a family comprising some of the most widely used antibiotics in veterinary medicine. This study presents the quantitative performances of the Q-Exactive by illustrating a new approach to quantify TCs using liquid chromatography coupled to a HRMS in a complex matrix, i.e., swine manure. The Q-Exactive was used at high-resolution in both full scan (FS) and targeted ion fragmentation (tMS(2)) modes. These two modes were optimized and compared to determine the most reliable and efficient approach to quantify TCs with good accuracy. The proposed method was optimized to obtain the best selectivity and sensitivity, thus eliminating false positive and allowing the detection of trace levels of analyte. The TCs were extracted from the matrix by sonication using McIlvaine buffer followed by an off-line solid phase extraction method to concentrate and clean the extracts. Both FS and tMS(2) modes presented good linearity (R-2 > 0.991) and repeatability (RSD < 15%). Mass accuracy was acceptable with values below 2 ppm. The method detection limits (MLD) calculated from the calibration curves ranged from 2.0 to 12 ng g(-1) for FS mode and from 1.5 to 3.6 ng g(-1) for tMS(2) mode. Accuracy and interday/intraday relative standard deviations were below 21% for both modes studied. TCs were quantified in real samples of swine manure with concentrations ranging from 29 to 75 ng g(-1). This study showed the possibility of using hybrid HRMS for trace detection and quantification of TCs in a complex matrix, thus avoiding false positive while achieving good selectivity and sensitivity. (C) 2014 Elsevier B.V. All rights reserved.