Liquid chromatography tandem mass spectrometry (LC-MS/MS) is a widespread technology used for the quantitative determination of per- and polyfluoroalkyl substances (PFAS) in foodstuffs. Specifically, LC-MS/MS offers attractive performance combining the sensitivity and selectivity required by the European Union for testing perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA) and perfluorohexane sulfonic acid (PFHxS) with maximum limits of quantification (LOQs) in the sub part-per-billion (μg/kg) or the part-per-trillion (ng/kg) domains. In this article we highlight the important diversity in LOQ definitions applied in LC-MS/MS methods described in the literature that raise concerns about the capability of some of those to generate reliable data requested by the European regulation. Here, we point the risk of false response or misquantification if criteria for assessing LOQ suffer from a lack of rigor. We emphasize the need to use PFAS-free samples spiked with the analyte(s) of interest and the application of identification criteria according to official documents for a sound measurement of the LOQ.

RATIONALE

Rapid on-site detection of persistent organic pollutants (POPs) is highly desirable for environmental protection.

METHODS

Herein, a rapid on-site analytical workflow was developed for the investigation of polycyclic aromatic hydrocarbons (PAHs) and perfluorinated compounds (PFCs) using multi-walled carbon nanotube (MWCNT)-modified paper spray ionization (PSI) coupled with a miniature ion trap mass spectrometer. Critical parameters regarding PSI and miniature mass spectrometry analysis were optimized.

RESULTS

The analytical performance of the developed method was evaluated under optimized conditions, obtaining a short analysis duration of less than 1 min, sufficient linearity with correlation coefficients greater than 0.99, acceptable recovery rates of 93.1–105.8% with relative standard deviations of between 3.5–10.3%, and reasonable sensitivity with limits of detection and quantitation of 2–200 μg/L and 5–500 μg/L, respectively.

CONCLUSIONS

Considering these aspects, the present approach demonstrated a promising solution for rapid on-site detection of emerging POPs.

RATIONALE

For unambiguous identification of Chemical Weapons Convention-related chemicals in environmental and biological samples, access to mass spectra and expertise in spectral interpretation is required. As of today, there is no mass spectrum available for dialkyl alkylarsonodithioites in the literature. Therefore, it is essential to obtain spectral information about these compounds.

METHODS

The CWC-related organoarsenic compounds were synthesized and analyzed by GC-MS, and their retention index (RI) was calculated by Van Den Dool’s method. The relationship between RI and DFT-calculated polarizability (⍺) and molecular weight was also studied. Electron ionization (EI) mode was used to investigate the general fragmentation patterns of the synthesized compounds. A DFT analysis of some major fragment ions was performed in order to confirm the fragmentation pathways.

RESULTS

A linear relationship between RI and ⍺ is observed. The mass spectra of compounds 5-7 are affected by alkyl groups on sulfur and arsenic atom. The molecular ion of compounds 5-7 can be observed in their EI-MS with relatively good abundance. EI-MS studies revealed some interesting fragmentation pathways, such as the formation of arsenic analogue of benzilic and tropylium in EI-MS of chemicals 6.

CONCLUSIONS

By analyzing the mass spectra and RI values, it is possible to detect CWC-related chemicals in aqueous, blood, and urine samples during an on-site or off-site inspection.

Rationale

Electronically mismatched Diels–Alder reactions have gained much interests as an alternative pathway for C-C bond formation. To faciliate the development of facile organic transformations, mechanistic investigations are required. Spectroscopic methods (NMR, EPR and UV-Vis) are normally adopted for mechainism examinations, but further improvements on direct obtaining of structural information of short-lived intermediates are encouraged. Herein, an electronically mismatched Diels–Alder reaction between indole and 1,3-cyclohexadiene (1,3-CHD) was studied by an in situ electrospray ionization mass spectrometry (in-situ MS). Based on the direct sampling and detection of the in-situ MS without sample pre-treatment, the structures and dynamics of important intermediates were on-line examined.

Methods

A syringe-based photocatalytic reactor and in-situ AMS evaluation system was constructed for mechanism studies. The role of oxygen was confirmed via control reaction employed in the N₂-bubbled system. The stepwise cation radical-based pathway and the [2+2] cycloaddition process were determined through a series of experiments, including solvent evaluation, MS/MS experiments and dynamic monitoring.

Results

The dependence of the reaction on solvent polarity demonstrated that the reaction occurs via the formation of cation radicals, which were captured, identified and dynamically monitored via in situ ESI MS. Without pre-separation, the intermediate of [2+2] cycloaddition was identifiedand the cycloaddition process is thereby determined to be the combination of [4+2] cycloaddition and [2+2] cycloaddition. In addition, oxygen was proved to act as an electron mediator for both catalyst Ru (bpz)₃(PF₆)₂ and radical cations.

Conclusions

The mechanism of electronically mismatched Diels–Alder reaction was successfully deduced by in-situ MS associated with a syringe-based photocatalytic reactor. The structures and dynamics of cation radicals, the effect of O₂ for the reaction and the detailed process of [2+2] cycloaddition have been well demonstrated. This work could not only promote the understanding and development of facile photocatalytic transformations, but also enlarge the application of AMS in on-line monitoring.

Rationale

Gas chromatography-mass spectrometry (GC-MS) is the most frequently applied technique for analysis of Amaryllidaceae alkaloids in plant extracts. These compounds, known for their potent bioactivities, are a distinctive chemotaxonomic feature of the Amaryllidoideae subfamily (Amaryllidaceae). The Amaryllidaceae alkaloids of homolycorine type with a C3-C4 double bond generally show molecular and diagnostic ions at the high mass region with low intensity in EIMS mode leading to problematic identification in complex plant extracts.

Methods

Eleven standard homolycorine-type alkaloids (isolated and identified by 1D and 2D nuclear magnetic resonance) were subjected to separation with gas chromatography and studied with electron impact mass spectrometry including single quadropole (GC-EIMS), tandem (GC-EIMS/MS), and high resolution (GC-HR-EIMS) detectors, as well as with chemical ionisation mass spectrometry (GC-CIMS). Alkaloid fractions from two Hippeastrum species and Clivia miniata were subjected to GC-EIMS and GC-CIMS for alkaloid identification.

Results

GC-EIMS in combination with GC-CIMS provided significant structural information for homolycorine-type alkaloids with C3-C4 double bond facilitating their unambiguous identification. Based on the obtained typical fragmentation, other eleven homolycorine-type compounds were identified in extracts from two Hippeastrum species by parallel GC-EIMS, GC-CIMS and LC-ESI/ToF/MS and in extracts from Clivia miniata by GC-EIMS.

Conclusion

GC-MS can be successfully applied for identification of new and known homolycorine-type alkaloids, as well as for chemotaxonomical and chemoecological studies, among others within the Amaryllidoideae subfamily.