Selectivity enhancement using sequential mass isolation window acquisition with hybrid quadrupole time-of-flight mass spectrometry for pesticide residues

Influence of extraction windows for data-independent acquisition on feature annotation during suspect screening

Non-target analysis (NTA) using high-resolution mass spectrometry is becoming a useful approach to screen for suspect and unknown chemicals. For comprehensive analyses, data-independent acquisition (DIA), like Sequential Windowed Acquisition of all THeoretical Mass Spectra (SWATH-MS) on Sciex instruments, is necessary, usually followed by library matching for feature annotation. The choice of parameters, such as acquisition window number and size, may influence the comprehensiveness of the suspect features detected. The goal of this study was to assess how mass spectrometric DIA settings may influence the ability to obtain confident annotations and identifications of features in environmental (river water, passive sample extract (PSE)), wastewater (unpreserved and acidified) and biological (urine) sample matrices. Each matrix was analysed using 11 different MS methods, with 5-15 variable size acquisition windows. True positive (TP) annotation (i.e., matching experimental and library spectra) rates were constant for PSE (40%) and highest for urine (18%), wastewater (34% and 36%, unpreserved and acidified, respectively) and river water (8%) when using higher numbers of windows (15). The number of annotated features was highest for PSE (12%) and urine (8.5%) when using more acquisition windows (9 and 14, respectively). Less complex matrices (based on average total ion chromatogram intensities) like river water, unpreserved and acidified wastewater have higher annotation rates (7.5%, 8% and 13.2%, respectively) when using less acquisition windows (5-6), indicating matrix dependency of optimum settings. Library scores varied widely for correct (scores between 6 and 100) as well as incorrect annotations (scores between 2 and 100), making it hard to define specific ideal cut-off values. Results highlight the need for properly curated libraries and careful optimization of SWATH-MS and other DIA methods for each individual matrix, finding the best ratio of total annotations to true positive, (i.e., correct) annotations to achieve best NTA results.

Non-targeted screening of pyranosides in Rhodiola crenulata using an all ion fragmentation-exact neutral loss strategy combined with liquid chromatography-quadrupole time-of-flight mass spectrometry

INTRODUCTION

Pyranosides as one kind of natural glycosides contain a pyran ring linked to an aglycone in the structure. They occur widely in plants and possess diverse biological activities. The discovery of new pyranosides not only contributes to research on natural products but also may promote pharmaceutical development.

OBJECTIVES

A non-targeted liquid chromatography-quadrupole time-of-flight mass spectrometry method coupled with an all ion fragmentation-exact neutral loss (AIF-ENL) strategy was developed for the screening of pyranosides in plants.

METHODS

Pyranosides in various types were collected as a model. The AIF-ENL strategy comprised three steps: AIF spectrum acquisition and generation, ENL-based searching and identification, and confirmation of structural type using target second-stage mass spectrometry (MS/MS). The strategy was systematically evaluated based on the matrix effects, fragmentation stability, scan rate and screening efficiency and finally applied to Rhodiola crenulata (Hook. f. et Thoms) H. Ohba.

RESULTS

The method was proved to be an efficient tool for the screening of pyranosides. When it was applied to R. crenulata, a total of 24 pyranoside candidates were detected. Among them, six were tentatively identified on the basis of the agreement of their elemental composition with the reported. The other 18 were detected in R. crenulata for the first time.

CONCLUSION

The method offers a new platform for discovering pyranosides. In addition, the developed non-targeted strategy can also be used for other natural products, such as flavonoids and coumarins, as long as there is a common fragmentation behaviour in their MS/MS to generate characteristic neutral losses or fragments.

Comparison of analyte identification criteria and other aspects in triple quadrupole tandem mass spectrometry: Case study using UHPLC-MS/MS for regulatory analysis of veterinary drug residues in liquid and powdered eggs

Ultrahigh-performance liquid chromatography (UHPLC) coupled with triple quadrupole tandem mass spectrometry (MS/MS) is one of the most powerful tools for the multiclass, multiresidue analysis of veterinary drugs, pesticides, mycotoxins, and other chemical contaminants in foods and other sample types. Until approximately 2010, commercial MS/MS instruments using multiple reaction monitoring (MRM) were generally limited to minimum dwell (and inter-dwell) times of 10 ms per ion transition. To achieve the needed accuracy and detection limits for hundreds of targeted analytes, older UHPLC-MS/MS methods typically acquired only two ion transitions per analyte (yielding only one ion ratio for qualitative identification purposes), which is still the norm despite technological advancements. Newer instruments permit as little as 1 ms (inter-)dwell times to afford monitoring of more MRMs/analyte with minimal sacrifices in accuracy and sensitivity. In this study, quantification and identification were assessed in the validation of 169 veterinary drugs in liquid and powdered eggs. Quantitatively, an "extract-and-inject" sample preparation method yielded acceptable 70-120% recoveries and < 25% RSD for 139-141 (82-83%) of the 169 diverse drug analytes spiked into powdered and liquid eggs, respectively, at three levels of regulatory interest. Qualitatively, rates of false positives and negatives were compared when applying three different regulatory identification criteria in which two or three MRMs/drug were used in each case. Independent of the identification criteria, rates of false positives remained <10% for 95-99% of the drugs whether 2 or 3 ions were monitored, but the percent of drugs with >10% false negatives decreased from 25-45 to 10-12% when using 2 vs. 3 MRMs/analyte, respectively. Use of a concentration threshold at 10% of the regulatory level as an identification criterion was also very useful to reduce rates of false positives independent of ion ratios. Based on these results, monitoring >2 ion transitions per analyte is advised when using MS/MS for analysis, independent of SANTE/12682/2019, FDA/USDA, or 2002/657/EC identification criteria. (Quant)identification results using all three criteria were similar, but the SANTE criteria were advantageous in their greater simplicity and practical ease of use.