Study of matrix effects on the direct trace analysis of acidic pesticides in water using various liquid chromatographic modes coupled to tandem mass spectrometric detection

Development of a column switching for direct online enrichment and separation of polar and nonpolar analytes from aqueous matrices

Trace substances in surface waters may threaten health and pose a risk for the aquatic environment. Moreover, separation and detection by instrumental analysis is challenging due to the low concentration and the wide range of polarities. Separation of polar and nonpolar analytes can be achieved by using stationary phases with different selectivity. Lower limits of detection of trace substances can be obtained by offline enrichment on solid phase materials. However, these practices require substantial effort and are time consuming and costly. Therefore, in this study, a column switching was developed to enrich and separate both polar and nonpolar analytes by an on-column large volume injection of aqueous samples. The column switching can significantly reduce the effort and time for analyzing trace substances without compromising on separation and detection. A reversed phase (RP) column is used to trap the nonpolar analytes. The polar analytes are enriched on a porous graphitized carbon column (PGC) coupled serially behind the RP column. A novel valve switching system is implemented to enable elution of the nonpolar analytes from the RP column and, subsequently, elution of polar analytes from the PGC column and separation on a hydrophilic interaction liquid chromatography (HILIC) column. To enable separation of polar analytes dissolved in an aqueous matrix by HILIC, the water plug that is flushed from the PGC column is diluted by dosing organic solvent directly upstream of the HILIC column. The developed method was tested by applying target analysis and non-target screening, highlighting the advantage to effectively separate and detect both polar and nonpolar compounds in a single chromatographic run. In the target analysis, the analytes, with a logD at pH 3 ranging from -2.8 to + 4.5, could be enriched and separated. Besides the 965 features in the RP phase, 572 features from real wastewater were observed in the HILIC phase which would otherwise elute in the void time in conventional one-dimensional RP methods.

Matrix effects demystified: Strategies for resolving challenges in analytical separations of complex samples

Matrix effects can significantly impede the accuracy, sensitivity, and reliability of separation techniques presenting a formidable challenge to the analytical process. It is crucial to address matrix effects to achieve accurate and precise measurements in complex matrices. The multifaceted nature of matrix effects which can be influenced by factors such as target analyte, sample preparation protocol, composition, and choice of instrument necessitates a pragmatic approach when analyzing complex matrices. This review aims to highlight common challenges associated with matrix effects throughout the entire analytical process with emphasis on gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, and sample preparation techniques. These techniques are susceptible to matrix effects that could lead to ion suppression/enhancement or impact the analyte signal at various stages of the analytical workflow. The assessment, quantification, and mitigation of matrix effects are necessary in developing any analytical method. Strategies can be implemented to reduce or eliminate the matrix effect by changing the type of ionization, improving extraction and clean-up methods, optimization of chromatography conditions, and corrective calibration methods. While development of an effective strategy to completely mitigate matrix effects remains elusive, an integrated approach that combines sample preparation, analytical extraction, and effective instrumental analysis remains the most promising avenue for identifying and resolving matrix effects.

Matrix effects in the analysis of polar organic water contaminants with HILIC-ESI-MS

Matrix effects have been shown to be very pronounced and highly variable in the analysis of mobile chemicals, which may severely exacerbate accurate quantification. These matrix effects, however, are still scarcely studied in combination with hydrophilic interaction liquid chromatography (HILIC) and for very polar chemicals. In this study, the matrix effects of 26 polar model analytes were investigated in enriched drinking water, wastewater treatment plant effluent and solutions of inorganic salts, utilizing post-column infusion of the analytes into a HILIC-electrospray ionisation (ESI)-high-resolution mass spectrometry system. These experiments revealed the occurrence of structure-specific and unspecific matrix effects. The unspecific matrix effects were mainly observed in positive ESI polarity and predominantly coincided with a high ion count, resulting in ion suppression of all analytes. Thus, the excess charge is hypothesized to be the limiting factor in ion formation. Structure-specific matrix effects were more pronounced in negative ESI polarity and even structurally similar compounds were observed to react entirely differently: perfluoroalkyl carboxylic acids were suppressed, while perfluoroalkane sulfonic acids were simultaneously enhanced. These matrix effects were traced back to inorganic anions and cations, which eluted over a significant fraction of the chromatographic run time with this setup. Hence, it was concluded that inorganic ions are a main cause for matrix effects in the analysis of mobile chemicals utilizing HILIC. Graphical abstract.

Occurrence of microcystin-LR in vegetated lagoons used for urban runoff management

Phytoremediation with aquatic macrophyte has been considered as an eco-friendly technique for controlling harmful cyanobacteria outbreak and proven to be effective. The conventional water quality parameters are frequently measured to evaluate the effectiveness of phytoremediation. However, the concentration of microcystin-leucine-arginine (MC-LR) in different vegetated water still remains uncertain. In this study, the contents of MC-LR in four macrophyte-vegetated lagoons were determined by solid phase extraction and ultra-high-performance liquid chromatography with tandem mass spectrometry technology. Results indicated that MC-LR was found in Nymphaea tetragona lagoon (lagoon-S), Vallisneria spiralis lagoon (lagoon-B) and another Vallisneria spiralis lagoon (lagoon-J). Only in lagoon dominated by Pistia stratiotes L. (lagoon-D), MC-LR concentration was undiscovered regardless of seasonal variation. The levels of MC-LR varied seasonally and were affected by the different vegetated aquatic macrophytes. The results suggest that in addition to conventional physicochemical parameters and indicators of water quality, MC-LR levels should be taken into consideration when the effectiveness of phytoremediation is assessed.

Effect of oxidation and catalytic reduction of trace organic contaminants on their activated carbon adsorption

The combination of ozonation and activated carbon (AC) adsorption is an established technology for removal of trace organic contaminants (TrOCs). In contrast to oxidation, reduction of TrOCs has recently gained attention as well, however less attention has gone to the combination of reduction with AC adsorption. In addition, no literature has compared the removal behavior of reduction vs. ozonation by-products by AC. In this study, the effect of pre-ozonation vs pre-catalytic reduction on the AC adsorption efficiency of five TrOCs and their by-products was compared. All compounds were susceptible to oxidation and reduction, however the catalytic reductive treatment proved to be a slower reaction than ozonation. New oxidation products were identified for dinoseb and new reduction products were identified for carbamazepine, bromoxynil and dinoseb. In terms of compatibility with AC adsorption, the influence of the oxidative and reductive pretreatments proved to be compound dependent. Oxidation products of bromoxynil and diatrizoic acid adsorbed better than their parent TrOCs, but oxidation products of atrazine, carbamazepine and dinoseb showed a decreased adsorption. The reductive pre-treatment showed an enhanced AC adsorption for dinoseb and a major enhancement for diatrizoic acid. For atrazine and bromoxynil, no clear influence on adsorption was noted, while for carbamazepine, the reductive pretreatment resulted in a decreased AC affinity. It may thus be concluded that when targeting mixtures of TrOCs, a trade-off will undoubtedly have to be made towards overall reactivity and removal of the different constituents, since no single treatment proves to be superior to the other.

Automated determination of phenolic compounds in wine, berry, and grape samples using 96-blade solid phase microextraction system coupled with liquid chromatography-tandem mass spectrometry

An automated 96-thin-film solid phase microextraction system was optimized for high throughput analysis of phenolic compounds in wine, berry, and grape samples. Liquid chromatography and tandem mass spectrometry methods were optimized and applied for separation and detection of compounds. Evaluation of five different stationary phases showed that polystyrene-divinylbenzene-polyacrylonitrile (PS-DVB-PAN) is the optimum extraction phase for the extraction of phenolic compounds under study. The thin-film PS-DVB-PAN SPME coating provided almost exhaustive extraction recovery for all phenolics compounds under study, except for naringenin with 80% recovery. Extraction efficiency, inter- and intra-day reproducibility, sensitivity, linearity, limit of detection and quantitation, and matrix effect were evaluated. Intra-day and inter-day reproducibility were in the respective range of 4-8 and 7-13% relative standard deviation (RSD) for all eight phenolic compounds. Limits of detection and quantitation of the proposed SPME-LC-MS/MS system for the analysis of analytes under study were found in the range of 0.2-3 and 0.5-10 ng/mL, respectively. Standard addition calibration was applied for the quantitative determination of unknown phenolic compounds from wine, berry, and grape samples. The assessment of matrix effect showed significant reduction of ion suppression/enhancement using SPME method in comparison with that of solvent extraction technique.

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.

Occurrence and mass balance of isoflavones on an experimental grassland field

Isoflavones and coumestrol (COU) are estrogenic compounds that are naturally produced by plants (e.g., red clover, soybeans). Although these compounds have been extensively studied in food and feed, only little is known about their environmental fate. Therefore, we investigated the occurrence of isoflavones (formononetin, daidzein, equol, biochanin A, and genistein) and COU over 3.5 years in red clover, manure, and soil of a grassland field with and without manure application, as well as their emission via drainage water. Isoflavones were regularly quantified in plant (≤ 15 × 10(6) ng/g(dry weight (dw))), manure (≤ 230 × 10(3) ng/g(dw)), soil (≤ 3.4 × 10(3) ng/g(dw)), and drainage water samples (≤ 3.6 × 10(3) ng/L). In contrast, COU was observed only in manure and soil. Cumulative isoflavone loads emitted via drainage water were around 0.2 × 10(-3) kg/ha/y, which is very little compared to the amounts present in red clover (105-220 kg/ha/y), manure (0.5-1.0 kg/ha/y), and soil (0.1-5.1 kg/ha/y). Under good agricultural practice, no additional emission of isoflavones into drainage water was observed after manure application. With calculated 17β-estradiol equivalents up to 0.46 ng/L in drainage water, isoflavones can constitute a dominant and ecotoxicological relevant portion of the total estrogenicity in small rural river catchments.

An overview of matrix effects in liquid chromatography-mass spectrometry

Matrix-dependent signal suppression or enhancement represents a major drawback in quantitative analysis with liquid chromatography coupled to atmospheric pressure ionization mass spectrometry (LC-API-MS). Because matrix effects (ME) might exert a detrimental impact on important method parameters (limit of detection, limit of quantification, linearity, accuracy, and precision), they have to be tested and evaluated during validation procedure. This review gives a detailed description on when these phenomena might be expected, and how they can be evaluated. The major sources of ME are discussed and illustrated with examples from bioanalytical, pharmaceutical, environmental, and food analysis. Because there is no universal solution for ME, the main strategies to overcome these phenomena are described in detail. Special emphasis is devoted to the sample-preparation procedures as well as to the recent improvements on chromatographic and mass spectrometric conditions. An overview of the main calibration techniques to compensate for ME is also presented. All these solutions can be used alone or in combination to retrieve the performance of the LC-MS for a particular matrix-analyte combination.

Comparison of APPI, APCI and ESI for the LC-MS/MS analysis of bezafibrate, cyclophosphamide, enalapril, methotrexate and orlistat in municipal wastewater

The applicability of three different ionization techniques: atmospheric pressure photoionization (APPI), atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) was tested for the liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of five target pharmaceuticals (cyclophosphamide, methotrexate, bezafibrate, enalapril and orlistat) in wastewater samples. Performance was compared both by flow injection analysis (FIA) and on-column analysis in deionized water and wastewater samples. A column switching technique for the on-line extraction and analysis of water samples was used. For both FIA and on-column analysis, signal intensity and signal-to-noise (S/N) ratio of the target analytes in the three sources were studied. Limits of detection and matrix effects during the analysis of wastewater samples were also investigated. ESI generated significantly larger peak areas and higher S/N ratios than APCI and APPI in FIA and in on-column analysis. ESI was proved to be the most suitable ionization method as it enabled the detection of the five target compounds, whereas APCI and APPI ionized only four compounds.

Multi-residue screening method to quantify mycotoxins in aqueous environmental samples

Mycotoxins are naturally occurring secondary metabolites of fungi colonizing agricultural products on the field or during storage. In earlier work, we have shown that two common mycotoxins, i.e., zearalenone and deoxynivalenol, can be present at significant levels in the aquatic environment. This raises the question about the relevance of a wider range of mycotoxins in natural waters. In this investigation, we present the first validated method for analysis of some additional 30 mycotoxins in drainage, river, and wastewater treatment plant effluent water. The method includes solid-phase extraction over Oasis HLB cartridges, followed by liquid chromatography with electrospray ionization triple quadrupole mass spectrometry. Absolute method recoveries for 13 of the 33 mycotoxins were higher than 70% in wastewater treatment plant effluent (at 25 ng/L), and 27 compounds had method detection limits (MDLs) below 10 ng/L. The applicability of this method is illustrated with selected data from our ongoing monitoring campaigns. Specifically and for the first time, beauvericin and nivalenol were quantified in drainage and river water samples with mean concentrations of 6.7 and 4.3 ng/L and 6.1 and 5.9 ng/L, respectively. These compounds thus add to the complex mixture of natural and anthropogenic micropollutants in natural waters, where their ecotoxicological risk remains to be evaluated.

Mass spectrometry of the photolysis of sulfonylurea herbicides in Prairie waters

This review of mass spectrometry of sulfonylurea herbicides includes a focus on studies relevant to Canadian Prairie waters. Emphasis is given to data gaps in the literature for the rates of photolysis of selected sulfonylurea herbicides in different water matrices. Specifically, results are evaluated for positive ion electrospray tandem mass spectrometry with liquid chromatography separation for the study of the photolysis of chlorsulfuron, tribenuron-methyl, thifensulfuron-methyl, metsulfuron-methyl, and ethametsulfuron-methyl. LC-MS/MS is shown to be the method of choice for the quantification of sulfonylurea herbicides with instrumental detection limits ranging from 1.3 to 7.2 pg (on-column). Tandem mass spectrometry coupled with the use of authentic standards likewise has proven to be well suited for the identification of transformation products. To date, however, the power of time-of-flight MS and ultrahigh resolution MS has not been exploited fully for the identification of unknown photolysis products. Dissipation of the herbicides under natural sunlight fit pseudo-first-order kinetics with half-life values ranging from 4.4 to 99 days. For simulated sunlight, radiation wavelengths shorter than 400 nm are required to induce significant photolytic reactions. The correlation between field dissipation studies and laboratory photolysis experiments suggests that photolysis is a major pathway for the dissipation of some sulfonylurea herbicides in natural Prairie waters.

Comparison of electrospray ionization and atmospheric pressure chemical ionization for multi-residue analysis of biocides, UV-filters and benzothiazoles in aqueous matrices and activated sludge by liquid chromatography-tandem mass spectrometry

This paper describes the development of a multi-residue method for the determination of 36 emerging organic pollutants (26 biocides, 5 UV-filters and 5 benzothiazoles) in raw and treated wastewater, activated sludge and surface water using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The target analytes were enriched from water samples adjusted to pH 6 by solid-phase extraction (SPE) on Oasis HLB 200mg cartridges and eluted with a mixture of methanol and acetone (60/40, v/v). Extraction of freeze-dried sludge samples was accomplished by pressurized liquid extraction (PLE) using a mixture of methanol and water (50/50, v/v) as extraction solvent followed by SPE. LC-tandem MS detection was compared using electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in positive and negative ionization mode. ESI exhibited strong ion suppression for most target analytes, while APCI was generally less susceptible to ion suppression but partially leading to ion enhancement of up to a factor of 10. In general, matrix effects could be compensated using stable isotope-labeled surrogate standards, indicated by relative recoveries ranging from 70% to 130%. In wastewater, activated sludge and surface water up to 33 analytes were detected. Maximum concentrations up to 5.1 and 3.9mugL(-1) were found in raw wastewater for the water-soluble UV-filters benzophenone-4 (BZP-4) and phenylbenz-imidazole sulfonic acid (PBSA), respectively. For the first time, the anti-dandruff climbazole was detected in raw wastewater and in activated sludge with concentrations as high as 1.4 microg L(-1) and 1.2 microg gTSS(-1), respectively. Activated sludge is obviously a sink for four benzothiazoles and two isothiazolones, as concentrations were detected in activated sludge between 120 ng gTSS(-1) (2-n-octyl-4-isothiazolin-3-one, OIT) to 330 ng gTSS(-1) (benzothiazole-2-sulfonic acid, BTSA).

Development of an immunochromatographic assay for the rapid detection of bromoxynil in water

A rapid immunochromatographic one-step strip test was developed to specifically determine bromoxynil in surface and drinking water by competitive inhibition with the nano colloidal gold-conjugated monoclonal antibody (mAb). Bromoxynil standard samples of 0.01-10 mg L(-1) in water were tested by this method and the visual limit was 0.06 mg L(-1). The assay only required 5 min and one-step by dispensing a drop of sample solution onto a strip. Parallel analysis of water samples with bromoxynil showed comparable results from one-step strip test and ELISA. Therefore, the one-step strip test is very useful as a screening method for qualitative detection of bromoxynil in water.

Quantification of zearalenone in various solid agroenvironmental samples using D6-zearalenone as the internal standard

Because of its pronounced estrogenicity, zearalenone may be of concern not only in the aqueous but also in the terrestrial environment. Therefore, we developed several analytical methods to quantify zearalenone in different solid matrices of agroenvironmental relevance (i.e., plant organs, soil, manure, and sewage sludge). The use of D(6)-zearalenone as the internal standard (IS) was essential to render the analytical method largely matrix-independent because it compensated for target analyte losses during extract treatment and ion suppression during ionization. Soil and sewage sludge samples were extracted with Soxhlet, whereas plant material and manure samples were extracted by liquid solvent extraction at room temperature. Absolute recoveries for zearalenone were 70-104% for plant materials, 105% for soil, 76% for manure, and 30% for sewage sludge. Relative recoveries ranged from 86 to 113% for all matrices, indicating that the IS was capable to largely compensate for losses during analysis. Ion suppression, between 8 and 74%, was in all cases compensated by the IS but influenced the method quantification levels. These were 3.2-26.2 ng/g(dryweightdw) for plant materials, 0.7 ng/g(dw) for soil, 12.3 ng/g(dw) for manure, and 6.8 ng/g(dw) for sewage sludge. Plant material concentrations varied from 86 ng/g(dw) to more than 16.7 microg/g(dw), depending on the organ and crop. Soil concentrations were between not detectable and 7.5 ng/g(dw), depending on the sampling depth. Zearalenone could be quantified in all manure samples in concentrations between 8 and 333 ng/g(dw). Except for two of the 85 investigated sewage sludge samples, zearalenone concentrations were below quantification limit.

Matrix effect in liquid chromatography–electrospray ionization mass spectrometry analysis of benzoxazinoid derivatives in plant material

Despite the increasing success of liquid chromatography (LC) coupled to mass spectrometry (MS), matrix effects have limited the ESI applications. Matrix effects result from co-eluting residual matrix components affecting the ionization efficiency of target analytes and can lead to erroneous results. The present work evaluates the LC-electrospray ionization (ESI)-MS behaviour of benzoxazinoid derivatives in wheat plant material as a case where endogenous matrix components were found to interfere with the ionization of target analytes. When LC-MS was applied to the analysis of foliage and root extracts, significant signal suppressions were observed. To compensate for this matrix signal suppression, different methods were applied: the use of internal standards, the application of standard dilution method and the dilution of the extracts before instrumental determination. The results obtained indicated that evaluation of matrix effects should become an integrated part of quantitative LC-ESI-MS method development and validation.

Quantification of estrogenic mycotoxins at the ng/L level in aqueous environmental samples using deuterated internal standards

Because of their pronounced estrogenicity, resorcyclic acid lactones (RALs) are of concern in aqueous environments even at the low ng/L level. Therefore, we developed an accurate, precise and sensitive HPLC-MS/MS method to detect these mycotoxins in different aqueous environmental samples. The compounds investigated included zearalenone (ZON), alpha- and beta-zearalenol, zearalanone as well as alpha- and beta-zearalanol. The use of isotope labelled internal standards (in this case deuterated RAL-analogues) ensured an accurate quantification of the target analytes, independent of matrix compounds interfering with the analytes during ionisation and analyte losses occurring during sample preparation. Sample enrichment was carried out by solid-phase extraction (SPE) using Supelclean Envi-18 cartridges. Absolute method recoveries for all analytes ranged from 95 to 108%, 70 to 102%, and 76 to 109%, method detection limits from 0.5 to 2.1 ng/L, 0.4 to 1.1 ng/L, and 0.8 to 12.4 ng/L and precision from 3 to 14%, 2 to 13% and 4 to 16% in drainage water, river water and wastewater treatment plant (WWTP) effluent, respectively. The method was applied to verify the emission of RALs from a Fusarium graminearum infested crop field into the drainage system. Zearalenone was present in drainage water in concentrations up to 30 ng/L. So far, none of the other five investigated compounds have been detected.

Matrix effects in quantitative pesticide analysis using liquid chromatography-mass spectrometry

Combined liquid chromatography-mass spectrometry using electrospray or atmospheric-pressure chemical ionization has become an important tool in the quantitative analysis of pesticide residues in various matrices in relation to environmental analysis, food safety, and biological exposure monitoring. One of the major problems in the quantitative analysis using LC-MS is that compound and matrix-dependent response suppression or enhancement may occur, the so-called matrix effect. This article reviews issues related to matrix effects, focusing on quantitative pesticide analysis, but also paying attention to expertise with respect to matrix effects acquired in other application areas of LC-MS, especially quantitative bioanalysis in the course of drug development.

Analysis of pesticides in water by liquid chromatography-tandem mass spectrometric techniques

Pesticide residues continue to be the focus of many environmental studies, and the number of articles describing the development of more advanced, multiresidue analytical methodologies does not decline. The use of liquid chromatography-mass spectrometry based on single quadrupole or ion trap analyzers is consolidated for this purpose. The implementation, in the near future, of more sophisticated mass analyzers, such as triple quadrupole and hybrid quadrupole-time-of-flight is anticipated for routine analysis. This article reviews the various works published so far in the literature for the determination of pesticides and transformation products (TPs) in water by means of liquid chromatography (LC) coupled to tandem mass spectrometry. It discusses the various ionization sources and analyzers used for this purpose, as well as the extraction procedures employed for previous sample preconcentration. Because of the widespread use of triple quadrupole analyzers for the generation of pesticides levels in water using tandem mass spectrometry, a table compiling the transitions monitored for ca. 70 compounds is also included.

Quantification and confirmation of anionic, cationic and neutral pesticides and transformation products in water by on-line solid phase extraction-liquid chromatography-tandem mass spectrometry

Two on-line SPE-LC-ESI-MS/MS methods have been developed for the rapid determination and confirmation of 18 polar pesticides and nine transformation products (TPs) in water samples. Given the very different physico-chemical characteristics of the analytes, it was not feasible the simultaneous determination of all selected compounds in only one method. Thus, it was necessary to use heptafluorobutyric acid and formic acid in order to obtain good retention in the SPE cartridge for basic and acidic analytes, respectively. The developed analytical methodology based on the direct injection of 2 mL of water sample in the system allowed the quantification of all analytes at the 25 ng/L level (LOQ) with limits of detection normally lower than 5 ng/L. Satisfactory recoveries (70-110%) were obtained for most compounds in ground and surface water samples. Some exceptions were found mainly in surface water, due to the ion suppression produced by the higher amount of matrix interferents in these samples. The acquisition of two MS/MS transitions for each compound allowed the reliable confirmation of positive findings even at the LOQ level. The developed methodology was applied to real ground and surface water samples showing the interest of including TPs in monitoring methods, as several of them were found at concentrations higher than that of parent compounds.

Injection Port Derivatization Following Ion-Pair Hollow Fiber-Protected Liquid-Phase Microextraction for Determining Acidic Herbicides by Gas Chromatography/Mass Spectrometry

Injection port derivatization following ion-pair hollow fiber-protected liquid-phase microextraction (LPME) for the trace determination of acidic herbicides (2,4-dichlorobenzoic acid, 2,4-dichlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy)propionic acid, 3,5-dichlorobenzoic acid, 2-(2,4,5-trichlorophenoxy)propionic acid) in aqueous samples by gas chromatography/mass spectrometry (GC/MS) was developed. Prior to GC injection port derivatization, acidic herbicides were converted into their ion-pair complexes with tetrabutylammonium chloride in aqueous samples and then extracted by 1-octanol impregnated in the hollow fiber. Upon injection, ion pairs of acidic herbicides were quantitatively derivatized to their butyl esters in the GC injection port. Thus, several parameters related to the derivatization process (i.e., injection temperature, purge-off time) were evaluated, and main parameters affecting the hollow fiber-protected LPME procedure such as extraction organic solvent, ion-pair reagent type, pH of aqueous medium, concentration of ion-pair reagent, sodium chloride concentration added to the aqueous medium, stirring speed, and extraction time profile, optimized. At the selected extraction and derivatization conditions, no matrix effects were observed. This method proved good repeatability (RSDs <12.3%, n = 6) and good linearity (r2 > or = 0.9939) for spiked deionized water samples for five analytes. The limits of detection were in the range of 0.51-13.7 ng x L(-1) (S/N =3) under GC/MS selected ion monitoring mode. The results demonstrated that injection port derivatization following ion-pair hollow fiber-protected LPME was a simple, rapid, and accurate method for the determination of trace acidic herbicides from aqueous samples. In addition, this method proved to be environmentally friendly since it completely avoided open derivatization with potentially hazardous reagents.

A New On-line Sample Preparation System for the Liquid Chromatography/Time-of-Flight Mass Spectrometry Simultaneous Analysis of Pesticides in River Water

Current on-line solid-phase extraction methods combined with HPLC for shortening the clean-up operation are not suitable for simultaneously detecting compounds that have a wide variety of hydrophobicities. To solve these problems, we designed a new on-line sample preparation system. The system consists of an eluting pump, a mixing TEE connector, a 10-port 2-position valve and a solid-phase extraction precolumn. The eluate from the precolumn is diluted with a weak solvent from the HPLC at the TEE connection to load low hydrophobic compounds onto the analytical column. The proposed on-line sample preparation system was successfully applied to the simultaneous analysis of 21 pesticides in river water using LC/TOF-MS. In this method, the recoveries from river water samples were 67 to 126% (mean 83%), the reproducibility (CV%) was in the range from 1.1 to 11% (mean 5.6%), the calibration curve was linear in the range from 1 ppb to 500 ppb (r > 0.999) and the detection limits (S/N = 3) were in the range from 0.0034 ppb (daimuron) to 3.3 ppb (oxine-copper).

Chemiluminescent Determination of the Pesticide Bromoxynil by On-line Photodegradation in a Flow-Injection System

A new, robust and simple method is proposed for the chemiluminescent determination of the pesticide Bromoxynil. The empirical procedure is performed with the aid of a flow-injection manifold provided with an on-line photo-reactor to obtain chemiluminescent photofragments. After a period of 12 s of irradiation with an 8 W low-pressure mercury lamp, a chemiluminescent oxidation was performed with the system potassium permanganate in a polyphosphoric acid medium. The photolysis required a basic medium (KOH 0.014 mol l(-1)) with ethanol (1%) as a sensitizer. The method allowed the determination of 134 samples (h-1) of Bromoxynil in a wide interval of concentrations, over the range 5 x 10(-3) - 1 mg l(-1); the detection limit was 5 x 10(-3) mg l(-1). The RSD (n=24) at 0.25 mg l(-1) of the pesticide level was 2.3%. The method was applied to a water sample and to a formulation.

Fully automated multianalyte determination of different classes of pesticides, at picogram per litre levels in water, by on-line solid-phase extraction–liquid chromatography–electrospray–tandem mass spectrometry

This paper reports the development of a fully automated method for the multianalyte determination of twenty pesticides belonging to different classes (triazines, phenylureas, organophosphates, anilines, acidic, propanil, and molinate) in natural and treated waters. The method, based on on-line solid-phase extraction-liquid chromatography-electrospray-tandem mass spectrometry, is highly sensitive (limits of detection between 0.004 and 2.8 ng L(-1)), precise (relative standard deviations between 2.0 and 12.1%), reliable (two selected reaction-monitoring transitions are monitored per compound), rapid (45 min per sample), and simple. The application of this method to the monitoring of the target compounds in a waterworks revealed the presence of the pesticides investigated at concentrations up to 516 and 82 ng L(-1) (total pesticide concentration) in river water and ground water, respectively, used as sources, and their gradual removal through the purification process.

A liquid chromatography--tandem mass spectrometry multiresidue method for quantification of specific metabolites of organophosphorus pesticides, synthetic pyrethroids, selected herbicides, and deet in human urine

The ability to estimate low-dose human exposure to commonly used pesticides often is requested in epidemiologic studies. Therefore, fast and robust methods are necessary that can measure many analytes in the same sample. We have developed a method for high-throughput analysis of 19 markers of commonly used pesticides in human urine. The analytes were seven specific metabolites of organophosphorus pesticides, five metabolites of synthetic pyrethroids, six herbicides or their metabolites, and one insect repellant. Human urine (2 mL) was spiked with stable isotopically labeled analogues of the analytes, enzymatically hydrolyzed, extracted using solid-phase extraction, concentrated, and analyzed using high-performance liquid chromatography-tandem mass spectrometry. The sample was divided into two portions and analyzed on two different mass spectrometers, one using atmospheric pressure chemical ionization (APCI) and the other using turbo ion spray atmospheric pressure ionization (TIS). All analytes except the pyrethroid metabolites were analyzed using APCI. The detection limits for all analytes ranged from 0.1 to 1.5 ng/mL of urine, with the majority (17) below 0.5 ng/mL. The analytical precision for the different analytes, estimated as both the within-day and between-day variation, was 3-14 and 4-19%, respectively. The extraction recoveries of the analytes ranged from 68 to 114%. The throughput, including calibration standards and quality control samples, is approximately 50 samples a day. However, the analysis time with the TIS application is much shorter, and if only pyrethroid metabolite data are of interest, the throughput can be increased to 100-150 samples/day.

Development of an ELISA for the detection of bromoxynil in water

For development of an indirect competitive enzyme-linked immunosorbent assay (ELISA) for the nitrile herbicide bromoxynil, the polyclonal antibodies raised against 2,6-dibromo-4-cyano-phenoxyacetic acid (hapten) conjugated to bovine serum albumin (BSA) by the N-hydroxysuccinimide-activated ester method. Antiserum with a sufficiently high titer to provide the determinations of targeted compounds was obtained only 77 days after the primary immunization. Antiserum A2 was applied to the residual analysis of some water samples, under optimized ELISA condition, the quantitative working range was from 10 to 500 ppb with a limit of detection of 5 ppb. Cross-reactivity to structurally similar agrochemicals and related chemicals was determined. The antiserum showed little cross-reactivity with 2,6-dibromophenol and bromoxynil octanoate ester which have a dibromophenol group as common structure, but showed no cross-reactivity with other herbicides. Each water sample (river water, tap water, purified water, and bottled water) had a matrix effect and was investigated by adding Tween20 in the assay buffer. These four kinds of water samples were fortified with bromoxynil at several concentration levels and were directly analyzed with only dilution with an equal volume of antiserum solution, the mean recovery was 102.3%, and the mean coefficient of variation was 5.96%. The proposed ELISA turned out to be a powerful tool for monitoring of residual bromoxynil in water samples at trace level.

Coupled-column liquid chromatography method with photochemically induced derivatization for the direct determination of benzoylureas in vegetables

The coupled-column (LC-LC) system, consisting of a first column packed with internal surface reversed phase (ISRP) (50 x 4.6mm ID) and a Chrompack C18 (100 x 4.6 mm ID) as second column, allowed the simultaneous determination of five benzoylurea insecticides in dichloromethane (CH2Cl2) extracts of vegetable samples without any clean-up step. This system was combined with a photochemically induced fluorescence (PIF) post-column derivatization in order to provide strongly fluorescent photoproducts from the non-fluorescent benzoylureas. Limits of detection ranged from 0.21 to 0.98 microg L(-1) of pesticide (equivalent to 0.14-0.65 microg kg(-1) in vegetable samples) and limits of determination ranged from 4.0 to 10.0 microg L(-1) (equivalent to 2.7-6.7 microg kg(-1)). Linearity of the method was established between 2 and 1800 microg L(-1), depending upon the compound. Validation of the total method was performed by randomly analyzing recoveries of four vegetable samples (aubergine, cucumber, green bean, and tomato) spiked at two levels of concentration (10.0 and 33.3 microg kg(-1)). The combination of the LC-LC system with PIF detection provides a sensitive, selective, and rapid method for the determination of pesticides in vegetable samples at levels lower than the maximum residue levels (MRLs) established for these compounds by Spanish legislation.

Quantification of the new triketone herbicides, sulcotrione and mesotrione, and other important herbicides and metabolites, at the ng/l level in surface waters using liquid chromatography-tandem mass spectrometry

The LC/ESI/MSMS method allows the trace quantification (ng/l) of the new triketone herbicides, i.e. sulcotrione and mesotrione, and important herbicides and metabolites, in natural waters. Solid phase extraction (SPE) for sample enrichment is performed with OASIS (recoveries 94-112% for parent herbicides). Neutral and acidic compounds were analyzed separately with ESI in positive and negative mode, respectively. Quantification limits varied between 0.5 and 10 ng/l. The acidic herbicides detection was improved by a neutralizing post-column addition solution. The influence of ion suppression on quantification is discussed in detail. It is shown that we could overcome this problem and achieve reliable quantification using isotope labeled internal standards (ILIS) for every single analyte. The methods performance is illustrated with samples from a lake depth profile.

Countering matrix effects in environmental liquid chromatography–electrospray ionization tandem mass spectrometry water analysis for endocrine disrupting chemicals

In recent years, despite the increasing success of liquid chromatography (LC) coupled to tandem mass spectrometry (MS), reports on matrix susceptibility have shown the limitations of the this powerful analytical technique. Matrix effects (MEs) result from co-eluting residual matrix components affecting the ionization efficiency of target analytes and can lead to erroneous results. The present work evaluates the matrix effect of environmental water samples on 35 endocrine disrupting chemicals (EDCs) in negative and positive LC-ESI-MS/MS. It was shown that mobile-phase additives could significantly influence matrix effects. Addition of acids resulted in a severe signal suppression (average ME%: <65%), and 1 mM ammonium formate increased the average ME% to 84%. The importance of an efficient sample clean-up and internal standardization also was demonstrated. Cleaner extracts resulted in reduced matrix effects (average ME%: 89%) and labeled internal standards proved to have a beneficial effect especially on signal reproducibility (average CV% 4.2% versus 2.6%). The results from the present work indicate that evaluation of matrix effects should become an integrated part of quantitative LC-ESI-MS/MS method development and validation.

Liquid chromatography and tandem mass spectrometry: a powerful approach for the sensitive and rapid multiclass determination of pesticides and transformation products in water

In this paper we will show the results of our research on the direct simultaneous determination of multi-class pesticides and transformation products with different polarities and acid-base properties by applying an on-line trace enrichment coupled to the chromatographic system supplied with electrospray interface (SPE-LC-MS/MS method). The specific chromatographic separation allows the correct determination of almost fifty compounds (37 pesticides and 10 transformation products) using very low sample volume and very little sample handling. Recoveries between 70-120% were obtained for all compounds in drinking and groundwater, meanwhile in surface water 44 compounds were correctly quantified. Relative standard deviations lower than 15% were obtained for all compounds. Even at the lowest concentration level tested (25 ng L(-1)) 40 compounds presented satisfactory recoveries and repeatability. The use of methanol as organic modifier and the increase of injection volume are also studied. The applicability of the developed method to a monitoring programme is demonstrated by applying it to the analysis of hundreds of samples.

Environmental and food applications of LC-tandem mass spectrometry in pesticide-residue analysis: an overview

An overview is given on pesticide-residue determination in environmental and food samples by liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS). Pesticides comprise a large number of substances that belong to many completely different chemical groups, the only common characteristic is that they are effective against pests. They still constitute a challenge in MS because there is no collective pathway for fragmentation. A brief introduction to the theory of tandem MS permits a discussion of which parameters influence the ionization efficiency when the ions are subjected to different actions. Emphasis is placed on the different tandem MS instruments: triple and ion-trap quadrupoles, and hybrid quadrupole time-of-flight (Q-TOF), including advantages and drawbacks, typical detection limits, and ion signals at low concentrations. The instrumental setup, as well as LC and mass spectrometric experimental conditions, must be carefully selected to increase the performance of the analytical system. The capacity of each instrument to provide useful data for the identification of pesticides, and the possibility to obtain structural information for the identification of target and non-target compounds, are discussed. Finally, sample preparation techniques and examples of applications are debated to reveal the potential of the current state-of-the-art technology, and to further promote the usefulness of tandem MS.