|Screening of environmental passive sampling extracts using LC Q-TOF-MS in data-independent acquisition mode
|Screening Enviroment Pollutants, what can the data tell us?
|Dr Anthony Gravell
|Prof Graham Mills
|Natural Resources Wales
Abstract Information :
Two different approaches are currently used for compound identification in environmental screening analysis in combination with LC-MS. These are targeted MS/MS and data-dependent MS/MS. These two approaches have significant disadvantages, namely: targeted MS/MS operation performs MS/MS only on what is included in the target list and never on unknown or unexpected targets and with data-dependent MS/MS desired precursors can be missed where multiple adducts are formed in highly complex sample extracts.
We have employed an alternative methodology based on data-independent MS/MS which overcomes the disadvantages of the other two approaches. With the data-independent MS/MS technique, high resolution accurate mass data is acquired using different collision energies, formed of a low value and one or more higher energy values. Target and non-targeted compounds are fragmented without precursor selection in very fast sequential steps and accurate mass precursor and fragment data are recorded for all collision energies. The result of alternating the collision energy is a data file with a low energy channel that contains predominantly precursor ions and one or several high-energy channels that contain precursor and fragment ions. Pharmaceuticals are ubiquitous in surface waters because of continuous discharges from municipal wastewater treatment plants and we still do not know which pharmaceuticals (including those not currently monitored) are reaching the environment, the size of the problem for exposed fauna, nor what the effects, if any, of that exposure may be. A searchable accurate mass compound database containing all relevant ion species, and specific qualifier ions, for over 250 of the most commonly prescribed pharmaceuticals in Wales was developed for the screening of pharmaceuticals in extracts of polar passive samplers using an LC Q-TOF-MS system operating in data-independent mode. Chemcatcher® polar passive samplers were deployed for a period of almost four weeks at three sewage treatment works in west Wales.
Following retrieval and subsequent processing of the passive samplers the extracts obtained were screened using the newly developed data-independent MS/MS technique and a total of 79 pharmaceuticals were identified with high confidence using the compound's protonated or sodiated molecular ion. Fifty of the 79 pharmaceuticals were unequivocally confirmed by evaluating five of the most specific compound fragment ions from the MS/MS spectral library.
Excellent mass accuracy was obtained from the analysis with 75% and 85% of compounds identified with errors of less than 3 and 5 ppm respectively. Applying data-independent MS/MS methods resulted in a highly efficient workflow for the analysis of the passive sampling extracts. The data- independent MS/MS acquisition method is fast and the acquired data was later successfully interrogated for pharmaceutical metabolites that were outside the initial scope of analysis. The results obtained established the value of the approach developed and should prove invaluable for investigative monitoring purposes under the remit of the EU Water Framework Directive.