Increasing the accuracy and the reproducibility of the processing method for polar organic chemical integrative samplers

Passive samplers are devices able to merge the sampling and the purification steps, directly in-situ. Among these, Polar Organic Chemical Integrative Samplers (POCIS) are widely diffused for water matrices1 . They consist of a sorbent placed between two protective membranes held together by stainless-steel rings. Despite their advantages, POCIS are rarely used as a tool for regulated environmental studies2 , also due to the lack of a standardized processing method. While in a previous work of ours the elution step was studied in detail (to maximize analysis accuracy)3 , the sorbent transfer from the POCIS to a glass cartridge was not optimized. Variable amounts of ultra-pure water2,3 or methanol1 are generally employed to transfer the sorbent in a damp way, even though some of the more polar compounds are washed away3 . A dry-transfer was previously proposed4 , but this could lead to stronger matrix effects. Thus, this work studied six POCIS deployed together in the Ligurian sea, evaluating the recoveries and matrix effects of 38 target analytes (logDpH=7 -3.8 ÷ 6.8). Two of these POCIS were processed as usually3 , while the remaining four were dried overnight and then transferred into a glass cartridge using only a stainless-steel spatula. The sorbent of two of the four dry-transferred POCIS was spiked with a known amount of the analytes. Then, prior to the elution3 , 5 mL of water were used to wash the sorbent. This water was recovered and processed through a Salt-Assisted Liquid-Liquid Extraction (SALLE) and analysed along with the sorbent eluates by LC-MS/MS. Each extract was divided in aliquots, properly diluted with or without spike, allowing to assess analytes’ recovery and matrix effect. Through SALLE, almost all the analytes were recovered from the water. Yet only acesulfame and chlormequat were significantly washed from the spiked sorbent, thus SALLE resulted useful only for these two analytes. The new dry-transfer procedure allowed better recoveries of several polar analytes (e.g. salbutamol recovery improved from 20%3 to ≃60%), while matrix effects were not substantially different from the usual method, resulting negligible (80-120%) for 30 out of the 38 target analytes. The proposed procedure is desirable to improve compounds detectability and method reproducibility.