Critical evaluation of methodology commonly used in sample collection, storage and preparation for the analysis of pharmaceuticals and illicit drugs in surface water and wastewater by solid phase extraction and liquid chromatography–mass spectrometry

The main aim of this manuscript is to provide a comprehensive and critical verification of methodology commonly used for sample collection, storage and preparation in studies concerning the analysis of pharmaceuticals and illicit drugs in aqueous environmental samples with the usage of SPE-LC/MS techniques. This manuscript reports the results of investigations into several sample preparation parameters that to the authors’ knowledge have not been reported or have received very little attention. This includes: (i) effect of evaporation temperature and (ii) solvent with regards to solid phase extraction (SPE) extracts; (iii) effect of silanising glassware; (iv) recovery of analytes during vacuum filtration through glass fibre filters and (v) pre LC–MS filter membranes. All of these parameters are vital to develop efficient and reliable extraction techniques; an essential factor given that target drug residues are often present in the aqueous environment at ng L−1 levels. Presented is also the first comprehensive review of the stability of illicit drugs and pharmaceuticals in wastewater. Among the parameters studied are: time of storage, temperature and pH. Over 60 analytes were targeted including stimulants, opioid and morphine derivatives, benzodiazepines, antidepressants, dissociative anaesthetics, drug precursors, human urine indicators and their metabolites. The lack of stability of analytes in raw wastewater was found to be significant for many compounds. For instance, 34% of compounds studied reported a stability change >15% after only 12 h in raw wastewater stored at 2 °C; a very important finding given that wastewater is typically collected with the use of 24 h composite samplers. The stability of these compounds is also critical given the recent development of so-called ‘sewage forensics’ or ‘sewage epidemiology’ in which concentrations of target drug residues in wastewater are used to back-calculate drug consumption. Without an understanding of stability, under (or over) reporting of consumption estimations may take place.

► Critical assessment of sample collection, storage and preparation for >60 drugs of abuse.
► First comprehensive stability study of drugs of abuse in wastewater.
► 24 h composite samplers are unsuitable with regards to some compounds due to poor stability.
► Silanisation of vials during the evaporation of SPE extracts is critical in achieving high SPE recoveries.
► There is a need for more rigorous reporting of method validation data.