Rationale

Femtoamp and picoamp electrospray ionization (ESI) characteristics of a nonpolar solvent were explored. The direct ESI mass spectrometry analysis of chloroform extract solution enabled rapid analysis of perfluorinated sulfonic acid analytes in drinking water.

Methods

Neat chloroform solvent and extracts were directly used in a typical wire-in ESI setup using micrometer emitter tips. Ionization currents were measured with femtoamp sensitivity while ramping the spray voltage from 0 to −5000 V. Methanol was used as a comparison to illustrate the characteristics of electrospraying chloroform. The effects of spray voltage and inlet temperature were studied. A liquid–liquid extraction workflow was developed to analyze perfluorooctanoate sulfonate (PFOS) in drinking water using an ion-trap mass spectrometer.

Results

The ionization onset of chloroform solution was 41 ± 17 fA at 300 V. The ionization current gradually increased with voltage while remaining below 100 pA when using voltages up to −5000 V. The ion signal of PFOS was significantly enhanced to improve the limit of detection (LoD) to 25 ppt in chloroform. Coupled with a liquid–liquid extraction workflow, LoD of 0.38–5.1 ppt and a quantitation range of 5–400 ppt were achieved for perfluorinated sulfonic compounds in 1-ml water samples.

Conclusions

Femtoamp and picoamp modes expand the solvent compatibility range of ESI and can enable quantitative analysis in parts per trillion (ppt) concentrations.

Rationale

Steam equilibration overcomes the problem of the traditional measurements of H isotope compositions, which leave an arbitrary amount of adsorbed water in the sample, by controlling for the entire exchangeable H pool, including adsorbed water and hydroxyl-H. However, the use of steam equilibration to determine nonexchangeable stable H isotope compositions in environmental media (expressed as δ
²H_n values) by mathematically eliminating the influence of exchangeable H after sample equilibration with waters of known H-isotopic composition requires the knowledge of the equilibrium isotope fractionation factor between steam-H and exchangeable H of the sample (α_ex-w), which is frequently unknown.

Methods

We developed a new method to determine the α_ex-w values for clay minerals, topsoil clay fractions, and mica by manipulating the contributions of exchangeable H to the total H pool via different degrees of post-equilibration sample drying. We measured the δ
²H values of steam-equilibrated mineral and soil samples using elemental analyzer-pyrolysis-isotope ratio mass spectrometry.

Results

The α_ex-w values of seven clay minerals ranged from 1.071 to 1.140, and those of 19 topsoil clay fractions ranged from 0.885 to 1.216. The α_ex-w value of USGS57 biotite, USGS58 muscovite, and of cellulose was 0.965, 0.871, and 1.175, respectively. The method did not work for kaolinite, because its small exchangeable H pool did not respond to the selected drying conditions. Structurally different mineral groups such as two- and three-layer clay minerals or mica showed systematically different α_ex-w values. The α_ex-w value of the topsoil clay fractions correlated with the soil clay content (r = 0.63, P = 0.004), the local mean annual temperature (r = 0.68, P = 0.001), and the δ
²H values of local precipitation (r = 0.72, P < 0.001), likely to reflect the different clay mineralogy under different weathering regimes.

Conclusions

Our new α_ex-w determination method yielded realistic results in line with the few previously published values for cellulose. The determined α_ex-w values were similar to the widely assumed values of 1.00–1.08 in the literature, suggesting that the adoption of one of these values in steam equilibration approaches is appropriate.

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.