Semi‐quantitative non‐target analysis of water with LC/HRMS: how far are we?
Rapid Communications in Mass Spectrometry 2018, in press
Combining high‐resolution mass spectrometry (HRMS) with liquid chromatography (LC) has considerably increased the capability of analytical chemistry. Among others, it has stimulated the growth of the non‐target analysis, which aims at identifying compounds without their preceding selection. This approach is already widely applied in various fields, such as metabolomics, proteomics, etc. The applicability of LC/HRMS‐based non‐target analysis in environmental analyses, such as water studies, would be beneficial for understanding the environmental fate of polar pollutants and evaluating the health risks exposed by the new emerging contaminants. During the last five to seven years the use of LC/HRMS‐based non‐target analysis has grown rapidly. However, routine non‐target analysis is still uncommon for most environmental monitoring agencies and environmental scientists. The main reasons are the complicated data processing and the inability to provide quantitative information about identified compounds. The latter shortcoming follows from the lack of standard substances, considered so far as the soul of each quantitative analysis for the newly discovered pollutants. To overcome this, non‐target analyses could be combined with semi‐quantitation. This Perspective aims at describing the current methods for non‐target analysis, the possibilities and challenges of standard substance‐free semi‐quantitative analysis, and proposes tools to join these two fields together.
Ionisation efficiencies can be predicted in complicated biological matrices: A proof of concept
Piia Liigand, Jaanus Liigand, Filip Cuyckens, Rob J. Vreeken and Anneli Kruve
Analytica Chimica Acta 2018, in press
The importance of metabolites is assessed based on their abundance. Most of the metabolites are at present identified based on ESI/MS measurements and the relative abundance is assessed from the relative peak areas of these metabolites. Unfortunately, relative intensities can be highly misleading as different compounds ionise with vastly different efficiency in the ESI source and matrix components may cause severe ionisation suppression. In order to reduce this inaccuracy, we propose predicting the ionisation efficiencies of the analytes in seven biological matrices (neat solvent, blood, plasma, urine, cerebrospinal fluid, brain and liver tissue homogenates). We demonstrate, that this approach may lead to an order of magnitude increase in accuracy even in complicated matrices. For the analyses of 10 compounds, mostly drugs, in negative electrospray ionisation mode we reduce the predicted abundance mismatch compared to the actual abundance on average from 660 to 8 times. The ionisation efficiencies were predicted based on i) the charge delocalisation parameter WAPS and ii) the degree of ionisation α, and the prediction model was subsequently validated based on the cross-validation method ‘leave-one-out’.
Modifying the Acidity of Charged Droplets
Mari Ojakivi, Jaanus Liigand and Anneli Kruve
Chemistry Select 2018, 3, 335 – 338
The concept of acidity in confined spaces is up to date poorly understood; especially, in case of media violating electroneutrality. Here, we describe the acidity of charged droplets via their ability to protonate simple nitrogen bases and we propose ways to modify the protonation efficiency with the help of additives. We observed that the protonation of compounds in charged water droplets is independent of solution-phase acidity; instead, it can be adjusted with the help of additive type. On the other hand, the extent of protonation in charged methanol droplets can be adjusted with the
conventional approach of changing the pH.
Quantitative and sensitive mapping of imidacloprid on plants using Multiphoton Electron Extraction Spectroscopy
Anneli Kruve, Valery Bulatov and Israel Schechter
Chemical Physics, in press
Neonicotinoids, including imidacloprid, are extensively used for plant protection against insects. Unfortunately, these effective pesticides are one of the reasons for the decline of the bee population in recent decades. Ensuring application of minimal pesticide quantity and preventing excess requires a fast method for monitoring the coverage on plants. We present a new, method based on multiphoton electron extraction spectroscopy (MEES), for detecting, quantifying and mapping of imidacloprid coverage on plants. Imaging and quantitative analyses were demonstrated on several plant surfaces including olive and mint leaves and orange peel. Method provides both low detection limits (down to nanogram level) and good trueness. This method is fast and can be directly performed with no sample pre-treatment, thus, it is a good candidate for field analyses.