Development and validation of an analytical method based on liquid chromatography-tandem mass spectrometry detection for the simultaneous determination of 13 relevant wastewater-derived contaminants in lettuce

We present an analytical method developed and validated to study the potential uptake of 13 selected drugs (ten pharmaceuticals, one illicit drug, and two transformation products) into lettuce plants from contaminated water and soil. Some of the selected drugs (i.e., cocaine, methadone, cis-diltiazem, valsartan, and valsartan acid), which are commonly present in treated wastewater, were investigated for the first time in plant tissues. The method is based on ultrasonic solvent extraction with acetonitrile-methanol (1:1, v/v) and subsequent automated extract cleanup and analysis by means of online solid-phase extraction-liquid chromatography-tandem mass spectrometry. Optimum extraction conditions were selected after evaluation of analyte recoveries with four different extraction techniques (ultrasonic solvent extraction, solid-liquid extraction, pressurized liquid extraction, and a "quick, easy, cheap, effective, rugged, and safe" based method) and six different solvent mixtures. Furthermore, two different solid-phase extraction cleanup sorbents were evaluated. The method developed has high sensitivity (with limits of detection between 0.1 and 12.6 ng per gram dry weight and limits of quantification between 0.5 and 42.0 ng per gram dry weight), satisfactory accuracy (with analyte relative recoveries above 80% for all analytes but acridone and oxcarbazepine), and good repeatability (with relative standard deviations below 9% for all analytes). As part of the validation procedure, the analytical method was applied to the analysis of lettuce plants irrigated with water fortified with the selected compounds for the entire growing period. The results obtained evidenced the transfer of all the investigated drugs into lettuce leaves.