PRESSURIZED HOT WATER EXTRACTION COUPLED WITH LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY FOR THE FULLY AUTOMATED DETERMINATION OF PHARMACEUTICALS IN SOIL SAMPLES

In this study, a fully automated method based on pressurized hot water extraction directly coupled with liquid chromatography-tandem mass spectrometry has been developed for the analysis of pharmaceutical compounds in soil samples. For this purpose, a new apparatus for the extraction of solid samples was built, using suitably modified standard chromatographic equipment. The extraction system allows the extractant (i.e., hot water) to be recirculated through a cell, thus allowing to perform an extraction in dynamic mode, for the desired number of cycles. The system allows for monitoring the temperature and pressure inside the extraction cell. During the tests, the solvent flow through the system was kept constant at 1 mL/min, while different values of temperature and pressure were tested, in order to evaluate the impact of these variables on the recovery percentage. Based on an univariate approach, the influence of the temperature, pressure, and number of extraction cycles (1, 6, and 12 cycles) on the recovery was evaluated, finding more or less significant effects, depending on the compound investigated. Starting from these results, a multivariate approach was developed, extending the group of target analytes and investigating the aforementioned in wide ranges of values. The main effect was due to the temperature, while pressure and number of extraction cycles exerted a less important influence. Furthermore, the use of aqueous solutions modified with volatile salts (e.g., ammonium acetate) allowed for improving the recovery of some analytes.