Solid-phase extraction of polar pesticides from environmental water samples on graphitized carbon and Empore-activated carbon disks and on-line coupling to octadecyl-bonded silica analytical columns

Determination of trace organic contaminants by a novel mixed-mode online solid-phase extraction coupled to liquid chromatography-tandem mass spectrometry

In this study, a novel mixed-mode online solid-phase extraction (SPE) method was developed to recover miscellaneous trace organic contaminants (TrOCs) from environmental water samples. Six kinds of sorbents, including C₁₈ substances, hypercross-linked polymers (2), cation-exchange resins, anion-exchange resins, and graphitized nonporous carbons, were packed into a single online SPE cartridge. Furthermore, a fully automated analytic method was established by coupling this mixed-mode online SPE with liquid chromatography tandem mass spectrometry (online SPE-LC-MS/MS). Sixty-nine TrOCs with diverse properties were selected to examine the performance of this mixed-mode SPE cartridge in comparison with solo-mode online SPE cartridges. The method quantification limit (MQL) and the relative recovery coefficient of TrOCs in diverse water matrices, including groundwater, surface water and sewage effluent were evaluated. The MQL of most TrOCs was lower than 10 ng L^-1. The relative recovery coefficients for most TrOCs in the groundwater (50/69) and surface water (38/69) matrix fit in the satisfactory range. Moreover, mixed-mode online SPE coupled with LC-high-resolution MS was applied for a suspect screening of TrOCs in sewage effluents. A series of highly polar TrOCs that had scarcely been reported by previous studies were identified by this practical and easily accessible method. Finally, this novel mixed-mode online SPE with LC-MS/MS method was applied to quantify the TrOCs in the environmental water samples.

Label-free ultra-sensitive detection of atrazine based on nanomechanics

The alarming increase in the amount of dangerous pesticides such as atrazine in agricultural fields and drinking water is driving the growth of new technologies to detect these toxins well below their threat level. The recent elucidation of microcantilever nanomechanical bending in response to chemical and biomolecular interactions has added another significant facet to biochemical engineering research and has fostered the development of a variety of signal detection paradigms, at both the microscale and the nanoscale. We report the label-free detection of highly specific atrazine antibody-antigen interactions at the nanometer scale on microcantilevers, with 1 ppt (past per trillion) sensitivity. The chemical interaction-induced deflection of the cantilever beam reflects the interplay between the strain energy increase of the cantilever and the free energy reduction of the reaction, providing a unique system for investigating the connection between the nanomechanics and the chemistry of antibody-antigen interaction at picomolar concentration with nanometer resolution. Cantilevers were functionalized with highly specific and site-directed anti-atrazine antibodies and exposed to target antigen over a wide range of concentration from 4.65 pM to 46.5 µM of varying sequence in static and flow conditions. Antibody-antigen interaction of atrazine with the specific antibody resulted in net negative deflection of the cantilever. The results show that high specificity and site-directed antibody immobilization lead to ultra-high sensitivity detection of atrazine. The measurements provide results within minutes at the picomolar level, and exhibit high target specificity. This qualifies the technology as a rapid method to validate organic toxins and its progression.

Immunochromatographic dipstick assay format using gold nanoparticles labeled protein-hapten conjugate for the detection of atrazine

The present study describes a lateral-flow-based dipstick immunoassay format using a novel hapten-protein-gold conjugate for the rapid screening of atrazine in water samples. The immunoassay is based on the competitive inhibition, in which a newly developed hapten-protein-gold conjugate competes with the free antigen present in the sample, for the limited antibody binding sites available at test zone on dipstick membrane, housed in a plastic cartridge. The tracer used as the detection reagent was prepared by first conjugating hapten (a derivative of atrazine) molecules to a carrier protein (bovine serum albumin) via its surface lysine residues and then linking colloidal gold nanoparticles to the hapten-protein conjugate via cysteine residues of the carrier protein. The developed conjugate showed a high level of stability as it did not show any significant loss of activity even after 8 weeks of storage at ambient conditions. The color developed due to conjugate, based on competitive inhibition approach, is correlated with the concentration of atrazine sample. The sensitivity of the developed dipstick was enhanced by gold nanoparticles, as an amplification tag, presenting detection limit of atrazine in standard water samples down to 1.0 ppb level. The kit could serve as a rapid screening methodology for visual screening of atrazine contamination of water samples within 5 min of analysis time, and, when coupled with a portable colorimeter, as an inexpensive semi-quantitative assay. The method reported can be useful for screening a large number of pesticides samples in a very short time in the field.

Determination of kinetic and equilibrium regimes in the operation of polar organic chemical integrative samplers

This work set out the laboratory calibration of the passive samplers such as polar organic chemical integrative samplers (POCISs) which preconcentrate hydrophilic organic contaminants in aqueous medium. We compared the two different configurations available (i.e. pesticide and pharmaceutical POCISs) for sampling different classes of herbicides representative of a wide range of polarity (5.34>of=log Kow>or=-1.70). The results showed that pharmaceutical configuration was probably more convenient for sampling basic, neutral or acidic herbicides. Afterward, we performed a kinetic study with the pharmaceutical POCIS only. This calibration revealed linear and integrative uptakes of several herbicides for 21 days. For some compounds like sulcotrione, mesotrione, deisopropylatrazine (DIA) and deethylatrazine (DEA), the linear uptake model was only valid for 10 days. Lastly, we observed an increase of the sampling rates with the hydrophobicity of the herbicides.

Environmental analysis of fluorinated alkyl substances by liquid chromatography–(tandem) mass spectrometry: a review

Fluorinated alkyl substances (FASs) are widely distributed contaminants that have been found in many environmental, human and biological samples throughout the world. Perfluorochemicals are used in many industry and consumer products, such as polymers and surfactants, because they have unique and useful properties (they are stable, chemically inert and generally unreactive). However, these compounds have also been found to be toxic, persistent and bioaccumulative. In recent years various analytical methods have been developed for the analysis of FASs in environmental samples. Most of these methods are based on liquid chromatography coupled to mass spectrometry (LC-MS) or tandem mass spectrometry (LC-MS/MS), since this is considered to be the technique of choice. This article reviews the various LC-(tandem)MS methods described so far for the analysis of FASs in water, sediment, sludge and biota samples. It discusses the main experimental conditions used for sample pretreatment and for analysis as well as the most relevant problems encountered and the limits of detection achieved.

Isolation of poly(propylene glycol)s from water for quantitative analysis by reversed-phase liquid chromatography

Procedures for the isolation of poly(propylene glycol)s (PPGs) from a water matrix have been developed. Solid-phase extraction with an octadecylsilica cartridge and elution with methanol or with a graphitised carbon black cartridge and elution with a mixture of dichloromethane-methanol (4:1) or liquid-liquid extraction with chloroform were all suitable for model samples. However, only liquid-liquid extraction was suitable both for model and real environmental samples. Methods for reversed-phase liquid chromatographic determination of PPGs based on derivatisation and ultraviolet or fluorescence detection have been developed. Four derivatisation agents [3,5-dinitrobenzoyl chloride, phenyl isocyanate, 1-naphthoyl chloride and 1-naphthyl isocyanate (NIC)] were tested. Only NIC was found to give good reproducibility as well as a satisfactory detection limit. Finally, a method with liquid-liquid extraction with chloroform, derivatisation with NIC and liquid chromatographic separation with fluorescence detection was established. The developed method shows a highly correlated linearity of the analytical signals of particular homologues within a wide concentration range (approximately from 0.01 to 10 mg l(-1)). The precision of measurements is satisfactory for homologues having 5-9 oxypropylene subunits and becomes worse with an increase in the number of oxypropylene subunits. The limit of detection is 2 microg l(-1) for the majority of homologues. The method is suitable for the isolation and quantitative determination of PPGs in river water samples and as a tool for biodegradation testing.

Determination of perfluorooctane sulfonate in river water by liquid chromatography/atmospheric pressure photoionization mass spectrometry by automated on-line extraction using turbulent flow chromatography

A simple, fast and sensitive liquid chromatography/atmospheric pressure photoionization mass spectrometry (LC/APPI-MS) method, with automated on-line extraction using turbulent flow chromatography (TFC), was developed for the determination of perfluorooctane sulfonate (PFOS) in river water. In this method, following an on-line extraction by injection onto a column under TFC conditions, PFOS is back-flushed onto a reversed-phase column via on-line column switching, and resolved chromatographically at a laminar flow rate of 1 mL min(-1). Using this tandem LC-LC/APPI-MS system the extraction, separation and selective detection of PFOS in river water could be achieved with satisfactory selectivity and sensitivity. The limit of detection (LOD) (S/N = 3) and the limit of quantitation (LOQ) (S/N = 10)were 5.35 and 17.86 pg mL(-1). The described procedure was very simple since no off-line sample preparation was required, total analysis time being 18.75 min.

Trace-level determination of pesticides in water by means of liquid and gas chromatography

The trace-level determination of pesticides and their transformation products (TPs) in water by means of liquid and gas chromatography (LC and GC) is reviewed. Special attention is given to the use of (tandem) mass spectrometry for identification and confirmation purposes. The complementarity of LC- and GC-based techniques and the potential of comprehensive GCXGC are discussed, and also the impressive performance of time-of-flight mass spectrometry. It is also indicated that, in the near future, the TPs rather than the parent compounds should receive most attention--with a better understanding of matrix effects and eluent composition on the ionization efficiency of analytes being urgently required. Finally, the merits of using much shorter LC columns, or even no column at all (flow-injection analysis) in target analysis are shown, and a more cost-efficient and sophisticated strategy for monitoring programmes is briefly introduced.

Determination of herbicides and metabolites by solid-phase extraction and liquid chromatography evaluation of pollution due to herbicides in surface and groundwaters

A procedure based on solid-phase extraction (SPE) has been developed for the simultaneous preconcentration of three widely used herbicides and seven of their most common degradation products. The compounds studied were atrazine and its metabolites, desethylatrazine, desethyldesisopropylatrazine (DEDIA), 2-hydroxyatrazine, desethyl-2-hydroxyatrazine and desisopropyl-2-hydroxyatrazine (DIHA), terbutryne and its metabolite 2-hydroxyterbutylazine, and chlorotoluron and its metabolite 3-chloro-4-methylphenylurea. A HPLC system with diode array detection was used for the separation, identification and quantification of all these analytes. In the SPE preconcentration step, different types of sorbent were studied: C18 on silica and polymeric sorbents (Oasis and LiChrolut EN), the best results being obtained with the styrene-divinylbenzene cartridge and when the elution was performed with methanol and ethyl acetate. The detection limits obtained were between 0.1 microg l(-1) for DIHA and DEDIA and 0.02 microg l(-1) for the other analytes. The method used permitted the determination of these herbicides in drinking water at the concentration levels demanded by current legislation. The proposed method was used to evaluate the presence and evolution with time of these herbicides and their degradation products in samples of surface and ground waters from agricultural zones of the provinces of Salamanca and Zamora (basins of the Rivers Guarefia and Almar), Spain.

Identification and quantification of 77 pesticides in groundwater using solid phase coupled to liquid-liquid microextraction and reversed-phase liquid chromatography

This paper describes a method for the extraction, separation, identification, and quantification of 77 pesticides (neutral, acidic, and basic) including some s-triazine metabolites. The method is appropriate for organically (e.g. with humic acids) highly loaded groundwater samples. A comparative study of a pH-controlled mixed solid phase (LiChroprep RP18/LiChrolut EN) extraction with different desorption solvents (acetonitrile or acetonitrile and dichloromethane/methanol) is elaborated. A subsequent liquid-liquid microextraction reduces matrix effects. The pesticides in the sample are separated using RP-HPLC, detected, and identified by diode array. The efficiency is illustrated on a natural groundwater sample from a phreatic aquifer.

Multiresidue methods using solid-phase extraction techniques for monitoring priority pesticides, including triazines and degradation products, in ground and surface waters

The review describes the use of solid-phase extraction (SPE) techniques for monitoring priority pesticides in ground and surface waters. The focus is on triazine herbicides and their degradation products. Data concerning the fate, occurrence, properties and extraction of triazines and their degradation products using different SPE techniques are tabulated and discussed.

On-line dual-precolumn-based trace enrichment for the determination of polar and acidic microcontaminants in river water by liquid chromatography with diode-array UV and tandem mass spectrometric detection

Dual-pre-column-based trace enrichment combined on-line with liquid chromatography-diode-array UV and tandem mass spectrometric detection was used to determine a wide polarity range of organic microcontaminants in river water. Various sorbents were studied for their extraction efficiency of (highly) polar and acidic compounds and their ability to selectively remove humic substances, which are normally co-extracted and interfere in the UV detection of polar microcontaminants. An optimised on-line dual-pre-column set-up with PLRP-S in the first pre-column and Hysphere-1 in the second pre-column was used to study the analytical performance of the procedure. Tandem MS was used for confirmation purposes and to quantify the organic microcontaminants in river water at the low-ng/l level. In addition, the influence of the type of sample (drinking and river water) on suppression of analyte responses in electrospray ionization MS was studied.

Multi-residue analysis of N-methylcarbamate pesticides and their hydrolytic metabolites in environmental waters by use of solid-phase extraction and micellar electrokinetic chromatography

A method for the simultaneous separation and determination of N-methylcarbamate pesticides and their hydrolytic metabolites by micellar electrokinetic chromatography (MEKC) was developed. A mixture of five pesticides (carbaryl, propuxur, carbofuran, aminocarb, and methiocarb) and their corresponding phenols was studied to optimize the separation of its components in terms of various electrophoretic parameters such as buffer type, pH and concentration, sodium dodecyl sulfate concentration, injection conditions, and applied voltage. Excellent separation of all ten analytes was achieved within about 20 min. The optimized method was used for determinations in environmental water samples. Sample volumes of 250 mL were first preconcentrated in the pesticides and metabolites by passage through a LiChrolut EN sorbent column and then further enriched by on-column stacking. Dynamic ranges of 40 ng/L - 6 microg/L, limits of detection at the nanogram-per-liter level, and relative standard deviations from 2.6 to 7.4% were obtained. The proposed method surpasses high-performance liquid chromatography (HPLC) in separation efficiency. In fact, it provides more expeditious separations and allows more flexible adjustment of the selectivity. Also, it enables the quantification for the analytes studied in this work with decreased limits of detection.

Ultra-trace-level determination of polar pesticides and their transformation products in surface and estuarine water samples using column liquid chromatography-electrospray tandem mass spectrometry

A method is developed for the determination of polar pesticides and their transformation products [atrazine, deethylatrazine, deisopropylatrazine, hydroxyatrazine, diuron, 3,4-dichlorophenylmethylurea, 3,4-dichlorophenylurea (DPU), monuron, bentazone, anthranil-isopropylamide, chloridazon, metolachlor] in surface, estuarine and sea water samples at the low ng/l level. Solid-phase extraction is combined off-line with column liquid chromatography-electrospray ionization tandem mass spectrometric detection (LC-ESI-MS-MS). The applicability of two solid-phase materials, i.e., LiChrolut EN cartridges and graphitized carbon black extraction disks, is evaluated. The influence of the organic solvent used in gradient LC, as well as the amount of co-extracted humic material on the ESI process is studied. The eluotropic strength of the organic solvent was found to have a distinct effect on the sensitivity of ESI-MS if coupled with LC gradient separations. Methanol gave much better results than acetonitrile and phenylurea compounds are more susceptible to solvent changes than triazines. Co-extracted humic material causes signal suppression in ESI-MS-MS detection. The degree of suppression depends upon the sample pH and the nature of the samples, i.e., surface or estuarine water. Detection limits in LC-ESI-MS-MS ranged from 0.2 to 2 ng/l, with the exception of DPU (8 ng/l). The applicability of the procedure was demonstrated by analyzing surface and estuarine water.

Particle-loaded membranes for sample concentration and/or clean-up in bioanalysis

Solid-phase extraction nowadays is a major sample preparation tool. The latest development in this area is the introduction of particle-loaded membranes (membrane-extraction disks). The potential of these extraction membranes in bioanalysis is discussed with respect to recoveries, reproducibility, sensitivity and speed. A comparison is made between liquid-liquid extraction and solid-phase extraction using traditional sorbents and extraction disks, and off-line and on-line techniques. Particle-loaded membranes are available in disks with diameters of 4-90 mm. The 25-90 mm disks are mainly used for off-line extractions of mainly environmental samples, while the 4 mm disks are available in the so-called drug tubes that can be used in the same way as conventional extraction cartridges for the extraction of drugs from biological fluids. The main advantage of using drug tubes is the smaller desorption volume and, therefore, the increased sensitivity. Cutting smaller disks, from the commercially available disks, allows the use of on-line extractions in column-switching systems. The main conclusion is that in many cases particle-loaded membranes are more efficient than packed solid-phase extraction cartridges.