Determination of polar organophosphorus pesticides in water samples by hydrophilic interaction liquid chromatography with tandem mass spectrometry

Trends in sample preparation and separation methods for the analysis of very polar and ionic compounds in environmental water and biota samples

Recent years showed a boost in knowledge about the presence and fate of micropollutants in the environment. Instrumental and methodological developments mainly in liquid chromatography coupled to mass spectrometry hold a large share in this success story. These techniques soon complemented gas chromatography and enabled the analysis of more polar compounds including pesticides but also household chemicals, food additives, and pharmaceuticals often present as traces in surface waters. In parallel, sample preparation techniques evolved to extract and enrich these compounds from biota and water samples. This review article looks at very polar and ionic compounds using the criterion log P ≤ 1. Considering about 240 compounds, we show that (simulated) log D values are often even lower than the corresponding log P values due to ionization of the compounds at our reference pH of 7.4. High polarity and charge are still challenging characteristics in the analysis of micropollutants and these compounds are hardly covered in current monitoring strategies of water samples. The situation is even more challenging in biota analysis given the large number of matrix constituents with similar properties. Currently, a large number of sample preparation and separation approaches are developed to meet the challenges of the analysis of very polar and ionic compounds. In addition to reviewing them, we discuss some trends: for sample preparation, preconcentration and purification efforts by SPE will continue, possibly using upcoming mixed-mode stationary phases and mixed beds in order to increase comprehensiveness in monitoring applications. For biota analysis, miniaturization and parallelization are aspects of future research. For ionic or ionizable compounds, we see electromembrane extraction as a method of choice with a high potential to increase throughput by automation. For separation, predominantly coupled to mass spectrometry, hydrophilic interaction liquid chromatography applications will increase as the polarity range ideally complements reversed phase liquid chromatography, and instrumentation and expertise are available in most laboratories. Two-dimensional applications have not yet reached maturity in liquid-phase separations to be applied in higher throughput. Possibly, the development and commercial availability of mixed-mode stationary phases make 2D applications obsolete in semi-targeted applications. An interesting alternative will enter routine analysis soon: supercritical fluid chromatography demonstrated an impressive analyte coverage but also the possibility to tailor selectivity for targeted approaches. For ionic and ionizable micropollutants, ion chromatography and capillary electrophoresis are amenable but may be used only for specialized applications such as the analysis of halogenated acids when aspects like desalting and preconcentration are solved and the key advantages are fully elaborated by further research. Graphical abstract.

Rapid identification of organophosphorus pesticides on contaminated skin and confirmation of adequate decontamination by ambient mass spectrometry in emergency settings

RATIONALE

Dermal exposure to pesticides may cause severe intoxication and even result in a fatal outcome. To expedite rescue in the emergency department, it is mandatory to develop a point-of-care analytical method for immediate identification of pesticides on the skin of exposed personnel, and to perform immediate dermal decontamination to prevent further harm and optimize the chance for full clinical recovery.

METHODS

Four of the most commonly used highly toxic pesticides that contaminate the skin were rapidly characterized by thermal desorption electrospray ionization mass spectrometry. The technique was also applied to confirm the completeness of pesticide decontamination from the skin. Pesticide sampling, desorption, ionization, and detection altogether took less than 30 s. In addition, different fabrics of protective garments worn by farmers were assessed with this efficient ambient mass spectrometric technique for their protective capabilities against dermal exposure to pesticides, and scanning electron microscopy was used to observe their different microstructures. The decontaminating efficacies of different cleansing agents for these skin contaminants were also evaluated by this technical platform.

RESULTS

The repeatability of this method had a low relative standard deviation (<22%) for the detection of pesticides on the surface of swine skin. The detection limits of the pesticides in solution were found to be in the range of 3-20 ng/mL. Linearity was observed between the signal intensities and the concentrations of the four pesticides in solution within the range of 50 ng/mL to 50 μg/mL (R² between 0.9921 and 0.9966). In addition, it was found that PVC fabric is optimal in preventing skin contamination by fenthion and detergent had the best efficiency for fenthion decontamination.

CONCLUSIONS

Since the whole analytical process is extremely fast, this technique allows early point-of-care identification of contaminating pesticides on the skin of exposed patients in the emergency room, as well as rapid assessment of the adequacy of decontamination.

Analysis of mobile chemicals in the aquatic environment-current capabilities, limitations and future perspectives

Persistent and mobile water contaminants are rapidly developing into a focal point of environmental chemistry and chemical regulation. Their defining parameter that sets them apart from the majority of regularly monitored and regulated contaminants is their mobility in the aquatic environment, which is intrinsically tied to a high polarity. This high polarity, however, may have severe implications in the analytical process and thus the most polar of these mobile contaminants may not be covered by widely utilized trace-analytical methods, and thus, alternatives are required. In this review, we infer the physical and chemical properties of mobile water contaminants from a set of almost 1800 prioritized REACH chemicals and discuss the implications these substance properties may have on four integral steps of the analytical process: sampling and sample storage, sample pre-treatment, separation and detection. We discuss alternatives to widely utilized trace-analytical methods, examine their application range and limitations, highlight potential analytical techniques on the horizon and emphasize research areas we believe still offer the most room for further improvement. While we have a comprehensive set of analytical methods to cover a large portion of the known mobile chemicals, these methods are still only infrequently utilized. Graphical abstract.

Method development for simultaneous determination of polar and nonpolar pesticides in surface water by low-temperature partitioning extraction (LTPE) followed by HPLC-ESI-MS/MS

During this research, chemometric approaches were applied for optimization of the low-temperature partitioning extraction (LTPE) for the simultaneous analysis of the pesticides: acephate, difenoconazole, fenamidone, fluazifop, fluazinam, methamidophos, and thiamethoxam from surface water samples and determination by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry. It was used the 2³ full factorial and the Doehlert experimental designs. The extraction technique was optimized by evaluating the effects of the three variables: sample pH, ionic strength (addition of Na₂HPO₄), and organic solvent volume. Considering the interest to find an optimal condition for all analytes simultaneously, the best extraction parameters found were as follows: pH = 5.33, concentration of Na₂HPO₄ = 0.0088 mol L^-1 and organic phase volume = 4.5 mL. The optimized methodology showed LOD and LOQ levels from 0.33 to 8.13 ng L^-1 and from 1.09 to 26.84 ng L^-1, respectively. The recovery values ranged from 38.37 and 99.83% and the RSD values varied from 2.33 to 18.92%. The method was applied to surface water analysis sampled in areas with intensive agricultural practices in Ouro Branco City, Minas Gerais, Brazil. The difenoconazole was detected in concentrations between 12.53 and 94.76 ng L^-1.

Collision-induced mass spectrometric fragmentation of protonated dimethoate and omethoate generated by electrospray ionization

RATIONALE

Dimethoate (DIM, S=P(OMe)₂ -S-CH₂ -C(O)-NH-CH₃ ) is a dimethyl phosphorodithioate pesticide widely used in agri- and horticulture that undergoes biotransformation in vivo by desulfuration into its more toxic oxono-derivative omethoate (OM, O=P(OMe)₂ -S-CH₂ -C(O)-NH-CH₃ ). OM inhibits acetylcholinesterase thus provoking cholinergic crisis in vivo, ultimately leading to death. Quantitative approaches for the determination of DIM and OM in environmental and toxicological samples make use of tandem mass spectrometry (MS² ). Nevertheless, so far interpretation of resulting product ions is incomplete and sometimes contradictory.

METHODS

DIM and OM as well as their deuterated analogues (fully deuterated at both methoxy groups bound to the phosphorus atom) were analyzed by MS² and MS³ after positive electrospray ionization and collision-induced dissociation (CID) in a linear ion trap to characterize fragmentations. The accurate masses of product ions were determined in a time-of-flight mass analyzer. Hydrogen/deuterium (H/D)-exchange experiments were carried out for further support of product ion identification. In addition, density functional theory (DFT) computations were used to calculate both the most stable protonation sites of DIM and OM and the changes in the diverse bond lengths after protonation.

RESULTS

Some identical and some related product ions of DIM and OM were found but also striking individual differences. Fragmentation pathways were proposed and product ions identified. Most fragmentations followed the common rules of charge migration fragmentation. DFT calculations supported experimental findings.

CONCLUSIONS

Discrepancies present in the literature so far are clarified and a deeper insight is provided into the fragmentation processes of organophosphorus pesticides. The combination of diverse experimental and theoretical approaches yielded consistent results, thus demonstrating continuous progress in understanding gas-phase reactions in MS experiments.

Fluorescence Determination of Omethoate Based on a Dual Strategy for Improving Sensitivity

Omethoate is a frequently used organophosphorus pesticide, and the establishment of a sensitive, selective, and simple method to determine omethoate is very important for food safety. In this paper, a dual strategy was applied to improve the detection sensitivity of omethoate. In the first strategy, graphene quantum dots (GQDs) were doped with nitrogen to increase the fluorescence quantum yield to 30%. By coupling N-GQDs with omethoate aptamer, an N-GQDs-aptamer probe was synthesized. The fluorescence of the N-GQDs-aptamer probe was turned off by graphene oxide (GO), but recovered by omethoate. Based on this principle, the fluorescence method for detecting omethoate was established with a detection limit of 0.041 nM. To further improve the detection sensitivity, the fluorescence polarization analysis method was applied as another strategy based on the polarization signal of GQDs. The detection limit was decreased to 0.029 pM by using the fluorescence polarization method. The detection limits in this paper were lower than those in other reports. The imaging of omethoate on plant leaves showed that the probe could be used for visual semiquantitative determination of omethoate.

Comparison of gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry with electron ionization for determination of N-nitrosamines in environmental water

N-nitrosamines are trace organic contaminants of environmental concern when present in groundwater and river water due to their potent carcinogenicity. Therefore, N-nitrosamine analysis is increasingly in demand. Gas chromatography-mass spectrometry (GC-MS) and GC-tandem mass spectrometry (GC-MS/MS), both with electron ionization (EI), were compared for analysis of nine N-nitrosamines extracted from environmental water matrices. A total of 20 fishpond water, river water, and groundwater samples from Sihui and Shunde, China were collected for a survey of N-nitrosamine concentrations in real water samples. Various solid-phase extraction (SPE) conditions and GC conditions were first examined for the pre-concentration and separation steps. The analysis of N-nitrosamines in environmental waters demonstrated that their quantification with GC-MS poses a challenge due to the occurrence of co-eluting interferences. Conversely, the use of GC-MS/MS increased selectivity because of the fragmentation generated from precursor ions in the 'multiple reaction monitoring' (MRM) mode, which is expected to extract target analytes from the environmental water matrix. Thus, the high performance of GC-MS/MS with EI was used to quantify nine N-nitrosamines in environmental waters with detection limits of 1.1-3.1 ng L^-1. N-nitrosodimethylamine (NDMA) concentrations were in the range of N.D. to 258 ng L^-1. Furthermore, other N-nitrosamines, except N-nitrosomethylethylamine (NMEA), N-nitroso-di-n-propylamine (NDPA) and N-nitrosopiperidine (NPIP), were also detected. Our findings suggest that GC-MS/MS with EI would be widely applicable in identifying N-nitrosamines in environmental waters and can be used for routine monitoring of these chemicals.

Comprehensive two-dimensional liquid chromatography coupled to high resolution time of flight mass spectrometry for chemical characterization of sewage treatment plant effluents

For the first time a comprehensive two-dimensional liquid chromatography (LC×LC) system coupled with a high resolution time-of-flight mass spectrometer (HR-ToF MS) was developed and applied for analysis of emerging toxicants in wastewater effluent. The system was optimized and validated using environmental standard compound mixtures of e.g. carbamate pesticides and polycyclic aromatic hydrocarbons (PAHs), to characterize the chromatographic system, to test the stability of the retention times and orthogonality. Various stationary phases in the second dimension were compared for the LC×LC analysis of silicon rubber passive sampler extracts of a wastewater effluent. A combination of C18 and Pentafluorophenyl (PFP) was found to be most effective. Finally, the hyphenation of LC×LC with HR-ToF MS was optimized, including splitter settings, transfer of data files between the different software packages and background subtraction using instrument software tools, after which tentative identification of 20 environmental contaminants was achieved, including pesticides, pharmaceuticals and food additives. As examples, three pesticides (isoproturon, terbutryn and diazinon) were confirmed by two-dimensional retention alignment.

Current mass spectrometry strategies for the analysis of pesticides and their metabolites in food and water matrices

Analysis of pesticides and their metabolites in food and water matrices continues to be an active research area closely related to food safety and environmental issues. This review discusses the most widely applied mass spectrometric (MS) approaches to pesticide residues analysis over the last few years. The main techniques for sample preparation remain solvent extraction and solid-phase extraction. The QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) approach is being increasingly used for the development of multi-class pesticide residues methods in various sample matrices. MS detectors-triple quadrupole (QqQ), ion-trap (IT), quadrupole linear ion trap (QqLIT), time-of-flight (TOF), and quadrupole time-of-flight (QqTOF)-have been established as powerful analytical tools sharing a primary role in the detection/quantification and/or identification/confirmation of pesticides and their metabolites. Recent developments in analytical instrumentation have enabled coupling of ultra-performance liquid chromatography (UPLC) and fast gas chromatography (GC) with MS detectors, and faster analysis for a greater number of pesticides. The newly developed "ambient-ionization" MS techniques (e.g., desorption electrospray ionization, DESI, and direct analysis in real time, DART) hyphenated with high-resolution MS platforms without liquid chromatography separation, and sometimes with minimum pre-treatment, have shown potential for pesticide residue screening. The recently introduced Orbitrap mass spectrometers can provide high resolving power and mass accuracy, to tackle complex analytical problems involved in pesticide residue analysis.

[Development of a novel multi-functional adsorbent bearing with long-chain hydrophobic and anion exchange groups for the simple and rapid determination of residual acephate in vegetables]

A novel multi-functional adsorbent (RP-SAX adsorbent) bearing hydrophobic and anion exchange groups was synthesized for the simple and rapid determination of residual acephate (AP) in vegetables. Macroporous base resin was obtained by suspension copolymerization with glycidyl methacrylate, stearyl methacrylate and glycerin dimethacrylate, and then ethyldimethylamine was introduced at glycidyl groups on the base resin. The adsorbent was packed into a syringe-type tube and used for extraction of AP. AP in the vegetable extract was quantitatively entrapped on the adsorbent and was completely eluted with 3 mL of 30 mmol/L trisodium phosphate in 50% (v/v) methanol solution. The eluate was directly injected into an HPLC-UV detection system with a reverse-phased column. The recoveries of 5 mg/L AP spiked in vegetable extraction samples ranged from 77% to 100%.