Procedural Challenges in Soil Sample Preparation for Pharmaceuticals Analysis

The determination of trace levels of pharmaceuticals in complex environmental samples requires an appropriate sample preparation stage prior to final determination. Currently, special attention should be paid to pharmaceuticals extensively used on industrial farms due to their possible emission into the soil environment, which has become a public health concern. The greatest challenge in such sample analyses lies in selecting the appropriate analyte extraction procedure. To address these challenges, five sample preparation procedures were evaluated for the determination of 24 pharmaceuticals, aiming to compare analyte recovery. We focused on commonly used stages of the procedure, such as ultrasonication and filtration, to minimize potential analyte loss. Our results indicate that some compounds can be eliminated even up to 100% (including amoxicillin, ampicillin, and lincomycin) during ultrasonication and/or filtration. The selected procedure allowed for the improvement of the recovery value in the case of 15 pharmaceuticals in comparison with the primary method. Consequently, the proposed procedure was applied to analyze environmental soil samples from the area surrounding a poultry farm. This study demonstrates that even problematic compounds, despite their low recovery, can be analyzed by the addition of isotopically labelled internal standards with acceptable accuracy. This finding is particularly important for environmental monitoring, where trace-level detection of pharmaceutical residues is often challenged by matrix complexity and analyte instability.