Non-target analysis (NTA) using high resolution mass spectrometry (HRMS) is a comprehensive approach to characterise untargeted, suspect and unknown chemicals including chemicals of emerging concern and has recently seen a steady increase. NTA typically acquires a full mass scan of each sample analysed and can be applied to investigate new samples or to perform retrospective analysis on previously analysed samples. Numerous studies presented in the literature discuss the development of new workflows and approaches using HRMS to characterise chemicals that are present in a given sample.
Given the relative novelty of this type of analysis, robust quality assurance and quality control (QA/QC) measures are imperative to ensure quality and consistency of results obtained using these different workflows. Due to fundamental differences to established targeted workflows, one goal of QA/QC must be to understand which information regarding the analysed chemical space (i.e. the totality of all chemicals in a specific environment/sample) is lost. Therefore, it is important to know how parameters and settings influence the acquired data; with the goal of minimizing the risk of losing potential substances of interest (i.e. false negatives) or introducing contamination (i.e. false positives), which can happen during each step of an analytical workflow.
Here we present how different mass spectrometric settings influence the ability to obtain confident identifications of as many components in river water as possible. For this, we first investigated the ideal number of SWATH windows (a way of data independent acquisition), before assessing several other parameters that were considered essential for successful identifications (including declustering potential and collision energy), using a central composite design (CCD) approach. This was done for each SWATH window (and therefore m/z range) individually.