Determination of polar organophosphorus pesticides in aqueous samples by direct injection using liquid chromatography-tandem mass spectrometry

A MOF nanozyme-mediated acetylcholinesterase-free colorimetric strategy for direct detection of organophosphorus pesticides

Although some simple and rapid colorimetric methods have been developed to detect organophosphorus pesticides (OPs), the difficult extraction and easy denaturation of acetylcholinesterase (AChE) are still drawbacks needing to be overcome. Here, we propose a MOF nanozyme-mediated AChE-free colorimetric strategy for the direct detection of OPs. In the presence of OPs (pirimiphos-methyl as a model), the intense blue of oxidized 3,3',5,5'-tetramethylbenzidine (TMB) becomes light due to the quenching effect of OPs towards hydroxyl radicals (˙OH) that are generated by the decomposition of H2O2 catalyzed by the Cu4Co6 ZIF nanozyme with excellent peroxidase (POD)-like activity. The developed colorimetric sensor exhibits assay performance and offers a universal and promising analysis strategy for detecting OPs in practical samples.

Impact of seasonality, redox conditions, travel distances and initial concentrations on micropollutant removal during riverbank filtration at four sites

Riverbank filtration (RBF) is a reliable water purification technique that has proven to be suitable for the removal of organic micropollutants. Its removal efficiency and dependency on a variety of factors such as redox conditions, temperatures, geology, travel times, level of initial micropollutant concentrations and seasonality were investigated during three seasonal sampling campaigns. Two anoxic (silty sand, Ems river) and two oxic (gravel, Ruhr river) RBF sites in Germany with different travel distances (42-633 m) were studied. Micropollutant concentrations were examined using a large-volume direct injection liquid chromatography method coupled to high-resolution mass spectrometry. Seasonal differences in micropollutant concentrations in the rivers were observed for chlorotolurone, diclofenac, terbuthylazine, mecoprop-P, MCPA (2-methyl-4-chlorophenoxyacetic acid) and propyphenazone. Redox dependencies in RBF were only found for sulfamethoxazole, propyphenazone, terbuthylazine and carbamazepine. Data for oxazepam, tramadol, N-desmethyl-tramadol, tilidin-desmethyl, carbamazepine and carbendazim indicate a required minimum travel distance of e.g. 100-200 m for the complete removal. Notably, travel time did not seem to be a substantial factor for their removal. High conductivity aquifers are also well suited for micropollutant removal. Seasonal initial concentration level variations showed no impact on the resulting abstraction well concentrations. Although the calculated removal efficiencies varied, they proved to be improper for seasonal raw water quality comparison. Knowledge of micropollutant behavior in riverbank filtration was broadened and RBF proved to be well suited for effective micropollutant reduction throughout the year, yet for a complete removal long travel distances or further technical purification steps are required.

Residues of pesticides and some metabolites in dissolved and particulate phase in surface stream water of Cachapoal River basin, central Chile

In the last twenty years, pesticide use in Chile has increased more than 160%, generating a greater risk of water resources pollution. The objective of this study was to assess the presence of 22 pesticides and 12 degradation products in surface water samples from the Cachapoal River basin, Central Chile, an area characterized by intense agricultural activity. Pesticide concentrations in the dissolved phase (DP) and particulate phase (PP) in samples collected in the dry season and after precipitation events was assessed. The solid-phase extraction technique was used to preconcentrate the samples and GC/MS and LC/MS were used to detect pesticides. The results present spatio-temporal variations in the proportion and concentration of pesticides and their degradation products in both the DP and PP for each site and sampling period. The most ubiquitous compounds in the dissolved phase were atrazine, atrazine-2-hydroxy (HA), cyprodinil, pyrimethanil, and tebuconazole, while in the particulate phase HA, imidacloprid, diazinon and pyrimidinol were detected. The results presented in this study make up the first record of pesticides in the dissolved and particulate phases in surface water in Chile. They show that the problem of pesticide contamination undoubtedly affects the quality of bodies of water in agricultural areas in Chile and support the need for a proper assessment of the water quality of the Cachapoal River in the future.

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.

Magnetic silica aerogels with high efficiency for selective adsorption of pyrethroid insecticides in juices and tea beverages

A new magnetic adsorbent silica aerogel was synthesized for concentration of organic compounds and to determine trace insecticides.

Identification tree based on fragmentation rules for structure elucidation of organophosphorus esters by electrospray mass spectrometry

Organophosphorus compounds have played important roles as pesticides, chemical warfare agents and extractors of radioactive material. Structural elucidation of phosphonates poses a particular challenge because their initial forms can be hydrolyzed, thus, degradation products may predominate in samples acquired in the field. The analysis of non-volatile organophosphorus compounds and their degradation products is possible using electrospray tandem mass spectrometry ESI-MS/MS. Here, we present a generic strategy that allows the unambiguous identification of substituents for two families of organophosphorus compounds: the phosphonates and phosphates. General fragmentation rules were deduced based on the study of decomposition pathways of 55 organophosphorus esters, including examples found in the literature. Multistage MS (MS(n)) experiments at high resolution in a hybrid mass spectrometer provide accurate mass measurements, whereas collision-induced dissociation experiments in a triple quadrupole give access to small fragment ions. The creation of a specific nomenclature for each possible structure of organophosphorus compound, depending on the alkyl side chain linked to the oxygen, was achieved by applying these fragmentation rules. This led to the creation of an 'identification tree' based upon the unique consecutive decomposition pathways uncovered for each individual compound. Hence, seven structural motifs were created that orient an unequivocal identification using the 'identification tree'. Despite the similar structures of the ensemble of phosphate and phosphonate esters, distinct identifications based upon characteristic neutral losses and diagnostic fragment ions were possible in all cases.

Is SPE necessary for environmental analysis? A quantitative comparison of matrix effects from large-volume injection and solid-phase extraction based methods

Environmental analysis by large-volume injection (LVI) was compared to solid-phase extraction (SPE) based methods using matrix effects as a quantitative indicator of analytical signal quality. LVI was performed by the direct injection of 900 μL of wastewater onto a high-performance liquid chromatography (HPLC) column while SPE-based methods utilized octadecyl silane (C18) and hydrophobic-lypophilic balance (HLB) solid phases to preconcentrate wastewater prior to analysis. Model analytes from three classes of environmental contaminants were selected for study including four estrogens (estrone, estradiol, estriol, and ethinylestradiol), eight perfluoroalkyl carboxylates (C4-C11), and five perfluoroalkyl sulfonates (C4, C6-C8, and C10). The matrix effects on analytes were assessed by two approaches (quantitatively by calculating percent matrix effects and qualitatively with postcolumn infusions) and compared across LVI- and SPE-based methods at constant (high and low) analyte-to-matrix mass ratios. The results from this study demonstrated that the LVI-based method produced analytical signals of quality similar to the two SPE-based methods. Furthermore, LVI presented a clear advantage over SPE because it was performed at lower cost, required fewer materials, involved less labor and eliminated the analyte loss associated with SPE.

Analysis of androgenic steroids in environmental waters by large-volume injection liquid chromatography tandem mass spectrometry

A new method was developed for the analysis of natural and synthetic androgenic steroids and their selected metabolites in aquatic environmental matrixes using direct large-volume injection (LVI) high-performance liquid chromatography (HPLC) tandem mass spectrometry (MS/MS). Method accuracy ranged from 87.6 to 108% for analytes with well-matched internal standards. Precision, quantified by relative standard deviation (RSD), was less than 12%. Detection limits for the method ranged from 1.2 to 360 ng/L. The method was demonstrated on a series of 1 h composite wastewater influent samples collected over a day with the purpose of assessing temporal profiles of androgen loads in wastewater. Testosterone, androstenedione, boldenone, and nandrolone were detected in the sample series at concentrations up to 290 ng/L and loads up to 535 mg/h. Boldenone, a synthetic androgen, had a temporal profile that was strongly correlated to testosterone, a natural human androgen, suggesting its source may be endogenous. An analysis of the sample particulate fraction revealed detectable amounts of sorbed testosterone and androstenedione. Androstenedione sorbed to the particulate fraction accounted for an estimated 5 to 7% of the total androstenedione mass.

Advantages of the scheduled selected reaction monitoring algorithm in liquid chromatography/electrospray ionization tandem mass spectrometry multi-residue analysis of 242 pesticides: a comparative approach with classical selected reaction monitoring mode

This paper illustrates the advantages of using the scheduled selected reaction monitoring (sSRM) algorithm available in Analyst Software 1.5 to build SRM acquisition methods in the application field of pesticide multi-residue analysis. The principle is to monitor the SRM transitions only when necessary. Based on the analytes' retention times, the scheduled SRM algorithm decreases the number of concurrent SRM transitions monitored at any point in time, allowing both cycle time and dwell time to remain optimal at higher levels of SRM multiplexing. To compare the scheduled SRM and the classical SRM modes, a mixture containing 242 multi-class pesticides has been analyzed ten times by three acquisition methods, using liquid chromatography/tandem mass spectrometry (LC/MS/MS) with an API 4000 QTrap mass spectrometer. The scheduled SRM mode demonstrates better results in all fields: more data points per peak, better reproducibility (coefficients of variation (CVs) <5%) and higher signal-to-noise ratio (S/N), even when the number of SRM transitions is doubled. The use of scheduled SRM mode instead of the classical one gives an enhancement of the limits of quantification by a factor two or even higher (up to six), depending on the analyte transitions.

A novel chemiluminescence assay of organophosphorous pesticide quinalphos residue in vegetable with luminol detection

BACKGROUND

Organophosphorous pesticides are the most popular pesticides used in agriculture. As acetylcholinesterase inhibitors, organophosphorous pesticides are toxic organic chemicals. The control and detection of organophosphorous pesticide residue in food, water, and environment therefore plays a very important role in maintaining physical health. A sensitive, rapid, simple chemiluminescence(CL) method has been developed for the determination of quinalphos based on the reaction of quinalphos with luminol-H2O2 in an alkaline medium. The method has been applied to detection of quinalphos in vegetable samples with satisfactory results.

RESULTS

The CL method for the determination of organophosphorous pesticide quinalphos is based on the phenomenon that quinalphos can apparently enhance the CL intensity of the luminol-H2O2 system. The optimal conditions were: luminol concentration 5.0 x 10-4 mol/L, H2O2 concentration 0.05 mol/L.pH value 13. In order to restrain the interference from metal ions, 1.0 x 10-3 mol/L of EDTA was added to the luminol solution. The possible mechanism was proposed.

CONCLUSION

Under the optimum reaction conditions, CL was linear with the concentration of quinalphos in the range of 0.02 mug/mL -1.0 mug/mL and the detection limit was 0.0055 mug/mL (3sigma). This method has been successfully applied to the detection of quinalphos in vegetable samples. According to the experimental data, the average recoveries for quinalphos in cherry tomato and green pepper 97.20% and 90.13%. Meanwhile, the possible mechanism was proposed.

Molecularly imprinted polymer for analysis of trace atrazine herbicide in water

A molecularly imprinted polymer (MIP) for atrazine was synthesized by non-covalent method. The binding capacity of MIP was 1.00 mg g(-1) polymer. The selectivity and recovery were investigated with various pesticides which are mostly, found in the environment, for both similar and different chemical structure of atrazine. The competitive recognition between atrazine and structurally similar compounds was evaluated and it was found that the system provided highest recovery and selectivity for atrazine while low recovery and selectivity were obtained for the other compounds. The highest recovery was obtained from MIP compared with non-imprinted polymer (NIP), a commercial C(18) and a granular activated carbon (GAC) sorbent. The method provided high recoveries ranged from 94 to 99% at two spiked levels with relative standard deviations less than 2%. The lower detection limit of the method was 80 ng L(-1). This method was successfully applied for analysis of environmental water samples.

Eliminating solid phase extraction with large-volume injection LC/MS/MS: analysis of illicit and legal drugs and human urine indicators in U.S. wastewaters

Large-volume (1800 microL) injection (LVI) followed by liquid chromatography/tandem mass spectrometry was developed and optimized to eliminate the need for off- and on-line solid phase extraction as a sample preparation step. Centrifugation of raw municipal influent followed by LVI was optimized for the routine determination of illicit drugs and related substances in municipal wastewaters. The accuracy of the method is demonstrated by standard addition for analytes with concentrations ranging from 4 to 3,500,000 ng/L. Precision, as indicated by relative standard deviation is <12% within a day and < or =20% for between-days for analytes with corresponding stable-isotope-labeled internal standards. Instrumental detection limits range from 0.5 to 4 ng/L while lower limits of quantification range from 2.5 to 10 ng/L The method is demonstrated on wastewater treatment plant influents (24 h, flow-normalized) collected from seven municipalities located in the US. Methamphetamine concentrations and loads are the greatest yet reported while cocaine concentrations and index loads are similar to European locations. Creatinine is introduced as human urine indicatorthat can be potentially used as an alternative to population estimates for indexing illicit drug loads for different municipalities.

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

A method combining hydrophilic interaction liquid chromatography (HILIC) with tandem mass spectrometry (MS/MS) was developed for the determination of polar organophosphorus pesticides (OPPs; acephate, methamidophos, monocrotophos, omethoate, oxydemeton-methyl, and vamidothion) in water samples. To extract the polar OPPs and minimize matrix effects from the water sample, an activated carbon cartridge was used for pretreatment. After pretreatment of the water sample, the eluate from the activated carbon cartridge was directly injected into the HILIC/MS/MS system. The OPPs were separated on an Atlantis HILIC silica column by isocratic elution with a mixture of acetonitrile, isopropanol, and ammonium formate buffer as a mobile phase, and they were detected by positive electrospray ionization MS/MS in the selected reaction monitoring mode. The method was validated at 0.05, 0.5, and 5 microg/L levels in water samples, and the recoveries of polar OPPs were between 76.4 and 98.6%. The limits of detection were between 0.13 and 1.0 pg on-column, and the limits of quantification were between 0.43 and 3.4 pg on-column. The method can be applied to the determination of trace amounts of OPPs in environmental water samples.

Direct aqueous injection LC-ESI/MS/MS analysis of water for 11 chloro- and thiomethyltriazines and metolachlor and its ethanesulfonic and oxanilic acid degradates

A multianalyte method is reported for the determination of atrazine, simazine, propazine, and their respective dealkylated chlorotriazine metabolites; ametryn and prometryn and their respective dealkylated thiomethyltriazine metabolites; and S-metolachlor and its ethanesulfonic and oxanilic acid degradates in deionized, ground, surface, and finished drinking water. Water samples are analyzed using direct aqueous injection (DAI) liquid chromatography-electrospray ionization/mass spectrometry/mass spectrometry (LC-ESI/MS/MS). No preanalysis sample manipulation is required other than transfer of a small portion of sample to an injection vial. The lower limit of the method validation is 0.050 microg/L (ppb) for all analytes except 2,4-diamino-6-chloro- s-triazine (didealkylatrazine, DDA, or G-28273). For this compound the LLMV is 0.50 microg/L (ppb). The overall mean procedural recoveries (and percent relative standard deviations) for all water types for all analytes ranged from 95 to 101% (4.5-11%). The method validation was conducted under U.S. EPA FIFRA Good Laboratory Practice Guidelines 40 CFR 160.

Fast multiresidue screening of 300 pesticides in water for human consumption by LC-MS/MS

The study tested the determination of 300 pesticides in mineral water at levels of 0.1 and 1.0 microg/L. Measurements were conducted by direct sample injection into a liquid chromatograph coupled to a tandem mass spectrometer without any sample enrichment and/or cleanup. Two separate injections enabled the recording of two transitions per analyte (600 selected reaction monitoring transitions in total). For 285 analytes the sensitivity of direct sample injection (100 microL) was sufficient to quantify residues at 0.1 microg/L. All remaining pesticides were detected at 1.0 microg/L. Calibration functions were linear for more than 80% of analytes. Signal suppression or enhancement compared with signals in high-performance liquid chromatography water was equal to or smaller than 20% for 240 analytes. Even the largest matrix-induced suppression did not result in the disappearance of peaks. Combining the results of seven mineral waters, the relative standard deviation of "recovery" was 20% or less for 87% of the substances. A second transition for confirmatory purposes was often available. Consequently, the proposed direct injection of samples without any sample enrichment and/or cleanup is suitable for screening of many pesticides in mineral and drinking water.

Method for determination of acephate, methamidophos, omethoate, dimethoate, ethylenethiourea and propylenethiourea in human urine using high-performance liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry

Because of increasing concern about widespread use of insecticides and fungicides, we have developed a highly sensitive analytical method to quantify urine-specific urinary biomarkers of the organophosphorus pesticides acephate, methamidophos, omethoate, dimethoate, and two metabolites from the fungicides alkylenebis-(dithiocarbamate) family: ethylenethiourea and propylenethiourea. The general sample preparation included lyophilization of the urine samples followed by extraction with dichloromethane. The analytical separation was performed by high-performance liquid chromatography (HPLC), and detection by a triple quadrupole mass spectrometer with and atmospheric pressure chemical ionization source in positive ion mode using multiple reaction monitoring and tandem mass spectrometry (MS/MS) analysis. Two different Thermo-Finnigan (San Jose, CA, USA) triple quadrupole mass spectrometers, a TSQ 7,000 and a TSQ Quantum Ultra, were used in these analyses; results are presented comparing the method specifications of these two instruments. Isotopically labeled internal standards were used for three of the analytes. The use of labeled internal standards in combination with HPLC-MS/MS provided a high degree of selectivity and precision. Repeated analysis of urine samples spiked with high, medium and low concentration of the analytes gave relative standard deviations of less than 18%. For all compounds the extraction efficiency ranged between 52% and 63%, relative recoveries were about 100%, and the limits of detection were in the range of 0.001-0.282 ng/ml.