Assessment and validation of the p-QuEChERS sample preparation methodology for the analysis of >200 veterinary drugs in various animal-based food matrices

QuEChERS as alternative extraction procedure in doping analyses

QuEChERS is a dispersive solid phase extraction commonly applied in food analysis for residues, such as pesticides or mycotoxins for more than 20 years. Due to the quick and easy sample preparation procedure, a QuEChERS method based on ammonium acetate combined with formic acid in acetonitrile was tested for the preparation of urine samples for doping control purposes. Testing urine samples with different pH and specific gravity, using the combination of 10 M ammonium acetate with 3% formic acid in acetonitrile, 312 out of 342 tested compounds could be extracted at their respective minimum required performance levels according to the World Anti-Doping Agency (WADA) technical documents. For nine selected analytes representing six categories of WADA's Prohibited List, we validated the QuEChERS extraction method fulfilling WADA's requirements for a confirmation procedure of the nonthreshold substances investigated. Especially for the intact stanozolol-glucuronides analyzed by high-resolution mass spectrometry, the described extraction method might be an alternative for confirmation procedures as it is time- and cost-saving compared with the commonly applied solid phase extraction.

Improved method robustness and ruggedness in liquid chromatography-mass spectrometry by increasing the acid content of the mobile phase

A routine multiresidue method developed for the detection and quantification of veterinary drug residues in animal-based food was used to analyze sheep (ovine) liver. Unlike when working with previously validated matrices (e.g., bovine liver), some of the analytes of interest chromatographed in the form of split- or even fully baseline separated peaks. In other cases a significantly longer retention times (tR) was observed. A detailed investigation led to the elucidation of taurocholic acid as the causative agent. This compound is present in sheep liver at significantly higher concentrations than in most other animal tissues. Taurocholic acid is a zwitterionic compound and likely acts as an ion pairing agent, which modifies the selectivity of the stationary phase in a highly spatial and dynamic way. Injecting smaller volumes of matrix extract or the use of a significantly higher formic acid concentration in the mobile phase reduced or even completely eliminated the peak splitting. A more detailed examination led to the observation that the problem is not restricted to this particular matrix and extraction procedure or the used stationary phase. In fact, a higher formic acid concentration (e.g., 1.0 % versus 0.1 %) significantly improves the peak shape of many analytes present in fortified matrix samples as well as in pure standard solutions. In addition, analytical column aging was observed as being slower with a higher formic acid concentration. Finally the peak shape of analytes interacting with the metallic parts along the flow path of the liquid chromatograph was also significantly improved. Use of 0.1 % acid in mobile phases is often taken for granted in LC-MS. Regardless of the stationary phase, a higher ionic strength better stabilizes the pH and reduces unwanted interactions, which ultimately improves the method robustness. Flow injection experiments often show that 0.1 % acid concentrations produce the highest analyte signals. Yet, the use of 1 % acid in the mobile phase often leads to narrower and therefore taller chromatographic peaks, which may lead to lower detection limits for many analytes and to an improved separation efficiency.