The difficulty in quantifying compounds in LC/ESI/HRMS arises from vastly different responsiveness of the compounds. At the same concentration, two compounds may yield very different signals due to the differences in the ionization efficiency of the compounds. The different responsiveness has made semi-quantitative non-targeted screening challenging. Still, research has been increasingly focussing on enabling the semi-quantification of the compounds detected from non-targeted screening even if analytical standards have are not available. During the upcoming interlaboratory comparison by NORMAN network we will compare 5 different approaches.
Currently, accessible semi-quantification approaches focus on (1) applying structurally similar compounds for the quantification and (2) predicting the response of the compounds in LC/HRMS. The similarity approached relay on the similarity of the internal standard and analyte based on chromatographic retention times and structure. The predicted response approach is based on the understanding of how the structure of the compound as well as the eluent and instrumental conditions are affecting the response in LC/ESI/HRMS. Based on this we have developed a quantitative prediction model to predict the response of different compounds in LC/ESI/HRMS and applied this for the semi-quantification of suspects. See my talk at the Annual ASMS conference this year for an example of applying semi-quantification to water screening.
The registration is due on 30th of October, 2020. Please register here: https://forms.gle/r4SfYRj9v5oYBWbcA