Analysis of pesticides in environmental water samples by solid-phase micro-extraction-high-performance liquid chromatography

Rapid Identification and Quantification of Adulteration in Methyl Eugenol using Raman Spectroscopy Coupled with Multivariate Data Analysis

Identification of adulterants in commercial samples of methyl eugenol is necessary because it is a botanical insecticide, a tephritid male attractant lure that is used to attract and kill invasive pests such as oriental fruit flies and melon flies on crops. In this study, Raman spectroscopy was used to qualitatively and quantitatively assess commercial methyl eugenol along with adulterants. For this purpose, commercial methyl eugenol was adulterated with different concentrations of xylene. The Raman spectral features of methyl eugenol and xylene in liquid formulations were examined, and Raman peaks were identified as associated with the methyl eugenol and adulterant. Principal component analysis (PCA) and partial least-squares regression analysis (PLSR) have been used to qualitatively and quantitatively analyze the Raman spectral features. PCA was applied to differentiate Raman spectral data for various concentrations of methyl eugenol and xylene. Additionally, PLSR has been used to develop a predictive model to observe a quantitative relationship between various concentrations of adulterated methyl eugenol and their Raman spectral data sets. The root-mean-square errors of calibration and prediction were calculated using this model, and the results were found to be 1.90 and 3.86, respectively. The goodness of fit of the PLSR model is found to be 0.99. The proposed approach showed excellent potential for the rapid, quantitative detection of adulterants in methyl eugenol, and it may be applied to the analysis of a range of pesticide products.

Monitoring and risk assessment of pesticide residues in selected herbal medicinal products in Ghana

The high patronage of herbal medicinal products in Ghana for the treatment of diverse disease conditions raises concerns about patient safety, given that much of the raw materials for production are obtained from the wild or farmlands potentially exposed to varied agrochemical residues. Therefore, the work sought to investigate the contamination of herbal medicinal products with pesticide residues and assess the potential risk posed to patients. As a result, validated gas chromatography with mass spectrometry as a detector was used to determine forty-two pesticides in thirty herbal medicinal products. The performance parameters of the method such as linearity, accuracy, and precision were found as acceptable. Pesticide residues such as chlorpyrifos and/or bifenthrin were found in 4/30 herbal medicinal products. Specifically, 3/30 herbal medicinal products contained only one pesticide, while 1/30 was contaminated with both pesticide residues. The levels of pesticide residue contamination ranged between 2.5 and 5.0 µg/kg. The acute hazard quotient and chronic hazard quotient for the two pesticide residues were evaluated and ranged between 0.21 and 0.92% and between 8.21 × 10^-4 and 5.88 × 10^-3%. The detected pesticide residue levels are below the maximum residue limit values, which may not cause acute and chronic health risks due to intake of the selected herbal medicinal product. Nevertheless, patient safety and potential public health risk can be reduced by regular monitoring, and regulation of pesticide residue levels in herbal medicinal products.

Tantala-based sol-gel coating for capillary microextraction on-line coupled to high-performance liquid chromatography

A sol-gel organic-inorganic hybrid sorbent, consisting of chemically integrated tantalum (V) ethoxide (TaEO) and polypropylene glycol methacrylate (PPGM), was developed for capillary microextraction (CME). The sol-gel sorbent was synthesized within a fused silica capillary through hydrolytic polycondensation of TaEO and chemical incorporation of PPGM into the evolving sol-gel tantala network. A part of the organic-inorganic hybrid sol-gel network evolving in the vicinity of the capillary walls had favorable conditions to get chemically bonded to the silanol groups on the capillary surface forming a surface-bonded coating. The newly developed sol-gel sorbent was employed to isolate and enrich a variety of analytes from aqueous samples for on-line analysis by high-performance liquid chromatography (HPLC) equipped with a UV detector. CME was performed on aqueous samples containing trace concentrations of analytes representing polycyclic aromatic hydrocarbons, ketones, alcohols, amines, nucleosides, and nucleotides. This sol-gel hybrid coating provided efficient extraction with CME-HPLC detection limits ranging from 4.41pM to 28.19 pM. Due to direct chemical bonding between the sol-gel sorbent coating and the fused silica capillary inner surface, this sol-gel sorbent exhibited enhanced solvent stability. The sol-gel tantala-based sorbent also exhibited excellent pH stability over a wide pH range (pH 0-pH 14). Furthermore, it displayed great performance reproducibility in CME-HPLC providing run-to-run HPLC peak area relative standard deviation (RSD) values between 0.23% and 3.83%. The capillary-to-capillary RSD (n=3), characterizing capillary preparation method reproducibility, ranged from 0.24% to 4.11%. The results show great performance consistency and application potential for the sol-gel tantala-PPGM sorbent in various fields including biomedical, pharmaceutical, and environmental areas.

A Simple and Quick Method for the Determination of Pesticides in Environmental Water by HF-LPME-GC/MS

This paper describes a simple and quick method for sampling and also for carrying out the preconcentration of pesticides in environmental water matrices using two-phased hollow fiber liquid phase microextraction (HF-LPME). Factors such as extraction mode, time, solvents, agitation, and salt addition were investigated in order to validate the LPME method. The following conditions were selected: 6 cm of polypropylene hollow fiber, ethyl octanoate as an acceptor phase, and extraction during 30 min under stirring at 200 rpm. The optimized method showed good linearity in the range of 0.14 to 200.00 μg L^-1; the determination coefficient (R²) was in the range of 0.9807-0.9990. The LOD ranged from 0.04 μg L^-1 to 0.44 μg L^-1, and LOQ ranged from 0.14 μg L^-1 to 1.69 μg L^-1. The recovery ranged from 85.17% to 114.73%. The method was applied to the analyses of pesticides in three environmental water samples (a spring and few streams) collected in a rural area from the state of Minas Gerais, Brazil.

Microextraction techniques used in the procedures for determining organomercury and organotin compounds in environmental samples

Due to human activities, the concentrations of organometallic compounds in all parts of the environment have increased in recent decades. The toxicity and some biochemical properties of mercury and tin present in the environment depend on the concentration and chemical form of these two elements. The ever-increasing demand for determining compounds at very low concentration levels in samples with complex matrices requires the elimination of interfering substances, the reduction of the final extract volume, and analyte enrichment in order to employ a detection technique, which is characterised by high sensitivity at low limits of quantification. On the other hand, in accordance with current trends, the analytical procedures should aim at the miniaturisation and simplification of the sample preparation step. In the near future, more importance will be given to the fulfilment of the requirements of Green Chemistry and Green Analytical Chemistry in order to reduce the intensity of anthropogenic activities related to analytical laboratories. In this case, one can consider the use of solvent-free/solvent-less techniques for sample preparation and microextraction techniques, because the use of the latter leads to lowering the quantity of reagents used (including solvents) due to the reduction of the scale of analysis. This paper presents an overview of microextraction techniques (SPME and LPME) used in the procedures for determining different chemical forms of mercury and tin.

Improvement of solid phase microextraction fiber assembly and interface for liquid chromatography

Modifications were made on commercial SPME fiber assembly and SPME-LC interface to improve the applicability of SPME for LC. Polyacrylonitrile (PAN)/C18 bonded fuse silica was used as the fiber coating for LC applications because the fiber coating was not swollen in common LC solvents at room temperature. The inner tubing of SPME fiber assembly was replaced with a 457 μm outside diameter (o.d.) solid nitinol rod. And the coated fiber (o.d. 290 μm) was installed onto the nitinol rod. The inner diameter (i.d.) of the through hole of the ferrule in the SPME-LC interface was enlarged to 508 μm to accommodate the nitinol rod. The much larger inner rod protected the fiber coating from being stripped when the fiber was withdrawn from the SPME-LC interface. The system was evaluated in term of pressure test, desorption optimization, peak shape, carryovers, linear range, precision, and limit of detection (LOD) with polycyclic aromatic hydrocarbons (PAHs) as the test analytes. The results demonstrated that the improved system was robust and reliable. It overcame the drawbacks, such as leak of solvents and damage of fiber coatings, associated with current SPME fibers and SPME-LC interface. Another sealing mechanism was proposed by sealing the nitinol rod with a specially designed poly(ether ether ketone) (PEEK) fitting. The device was fabricated and tested for manual use.

Novel polymer monolith microextraction using a poly-(methyl methacrylate-co-ethylene dimethacrylate) monolith and its application to the determination of polychlorinated biphenyls in water samples

A novel and simple method based on polymer monolith microextraction (PMME) coupled to gas chromatography with electron-capture detection (GC-ECD) was developed for the determination of six polychlorinated biphenyls (PCBs) residues in water samples. The proposed method used poly-(methyl methacrylate-co-ethylene dimethacrylate) (MMA-co-EDMA) monolith as extraction media. Several factors affecting experiments such as sample flow rate, sample volume, the type of eluent, eluent volume, eluent flow rate, effect of salt addition and carry over effect were investigated and optimized systematically. The limits of detection (LODs) for six PCBs were 0.028-0.043 ng mL(-1) in water samples. The intra-day and inter-day precisions (R.S.D.) were less than 9.2% and 9.6%, respectively. The proposed method was successfully applied to the determination of six PCBs in tap water, lake water and industrial waste water and the trueness has been evaluated by recovery experiments. The obtained relative recoveries were in the range of 63.3-105.6%.

Enantioselective analysis of mirtazapine, demethylmirtazapine and 8-hydroxy mirtazapine in human urine after solid-phase microextraction

A selective and reproducible off-line solid-phase microextraction procedure was developed for the simultaneous enantioselective determination of mirtazapine (MRT), demethylmirtazapine and 8-hydroxymirtazapine in human urine. CE was used for optimization of the extraction procedure whereas LC-MS was used for method validation and application. The influence of important factors in the solid-phase microextraction efficiency is discussed, such as the fiber coatings, extraction time, pH, ionic strength, temperature and desorption time. Before extraction, human urine samples were submitted to enzymatic hydrolysis at 37 degrees C for 16 h. Then, the enzyme was precipitated with trichloroacetic acid and the pH was adjusted to 8 with 1 mol/L pH 11 phosphate buffer solution. In the extraction, the analytes were transferred from the aqueous solution to the polydimethylsiloxane-divinylbenzene fiber coating and then desorbed in methanol. The mean recoveries were 5.4, 1.7 and 1.0% for MRT, demethylmirtazapine and 8-hydroxymirtazapine enantiomers, respectively. The method was linear over the concentration range of 62-1250 ng/mL. The within-day and between-day assay precision and accuracy were lower than 15%. The method was successfully employed in a preliminary cumulative urinary excretion study after administration of racemic MRT to a healthy volunteer.

Sample preparation

A panorama of sample preparation methods has been composed from 481 references, with a highlight of some promising methods fast developed during recent years and a somewhat brief introduction on most of the well-developed methods. All the samples were commonly referred to molecular composition, being extendable to particles including cells but not to organs, tissues and larger bodies. Some criteria to evaluate or validate a sample preparation method were proposed for reference. Strategy for integration of several methods to prepare complicated protein samples for proteomic studies was illustrated and discussed.

Strategies for interfacing solid-phase microextraction with liquid chromatography

Solid-phase microextraction (SPME) techniques are equally applicable to both volatile and non-volatile analytes, but the progress in applications to gas-phase separations has outpaced that of liquid-phase separations. The interfacing of SPME to gas chromatographic equipment has been straight-forward, requiring little modification of existing equipment. The requirement of solvent desorption for non-volatile or thermally labile analytes has, however, proven challenging for interfacing SPME with liquid-phase separations. Numerous options to achieve this have been described in the literature over the past decade, with applications in several different areas of analysis. To date, no single strategy or interface device design has proven optimal. During method development analysts must select the most appropriate interfacing technique among the options available. Out of these options three general strategies have emerged: (1) use of a manual injection interface tee; (2) in-tube SPME; and (3) off-line desorption followed by conventional liquid injection. In addition, there has been interest in coupling SPME directly to electrospray ionisation and matrix-assisted laser desorption ionisation (MALDI) for mass spectrometry. Several examples of each of these strategies are reviewed here, and an overview of their use and application is presented.

Automation of solid-phase microextraction on a 96-well plate format

Studies have been performed assessing the feasibility and characterizing the automation of solid-phase microextraction (SPME) on a multi-well plate format. Four polycyclic aromatic hydrocarbons (PAHs), naphthalene, fluorene, anthracene and fluoranthene, were chosen as test analytes to demonstrate the technique due to their favorable partition coefficients, K(fw), between polydimethylsiloxane (PDMS) extraction phases and water. Four different PDMS configurations were investigated regarding their suitability. These included (i) a PDMS membrane; (ii) a multi-fiber device containing lengths of PDMS-coated flexible wire; (iii) a stainless steel pin covered with silicone hollow fiber membrane and (iv) commercial PDMS-coated flexible metal fiber assemblies. Of these configurations, the stainless steel pin covered with silicone tubing was chosen as a robust alternative. An array of 96 SPME devices that can be placed simultaneously into a 96-well plate was constructed to demonstrate the high-throughput potential when performing multiple microextractions in parallel. Different agitation methods were assessed including magnetic stirring, sonication, and orbital shaking at different speeds. Orbital shaking whilst holding the SPME device in a stationary position provided the optimum agitation conditions for liquid SPME. Once the analytes had been extracted, desorption of the analytes into an appropriate solvent was investigated. Liquid-phase SPME and solvent desorption on the multi-well plate format is shown to be a viable alternative for automated high-throughput SPME analysis compatible with both gas- and liquid-chromatography platforms.

New cloud vapor zone (CVZ) coupled headspace solid-phase microextraction technique

A new cloud vapor zone (CVZ)-based headspace solid-phase microextraction (HS-SPME) technique has been demonstrated with the capability of heating the sample matrix and simultaneously cooling the sampling zone. A bi-temperature-controlled (BTC) system, allowing 10 mL of test sample heating and headspace external-cooling, was employed for the CVZ formation around the SPME-fiber sampling area. In the CVZ procedure, the heated headspace vapor undergoes a sudden cooling near the SPME to form a dense cloud of analyte-water vapor, which is helpful for adsorption or absorption of the analyte. The device was evaluated for the quantitative analysis of aqueous chlorothalonil. Parameters influencing sampling efficiency, e.g., SPME fiber coating, SPME sampling temperature and time, solution modifier, addition of salt, sample pH, and temperature, were investigated and optimized thoroughly. The proposed BTC-HS-SPME method afforded a best extraction efficiency of above 94% accuracy (less than 4.1% RSD, n=7) by using the PDMS fiber to collect chlorothalonil in the headspace at 5 degrees C under the optimized condition, i.e., heating sample solution (added as 10% ethylene glycol and 30% NaCl, at pH 7.0) at 130 degrees C for 15 min. The detection was linear from 0.01 to 80 microg L-1 with a regression coefficient of 0.9998 and had a detection limit of 3.0 ng L-1 based on S/N=3. Practical application was demonstrated by analyzing chlorothalonil in farm water samples with promising results and recoveries. The approach provided a very simple, fast, sensitive, and solvent-free procedure to collect analytes from aqueous solution. The approach can provide a new platform for other sensitive HS-SPME assays.

Application of a polysiloxane-based extraction method combined with large volume injection-gas chromatography-mass spectrometry of organic compounds in water samples

This work describes a novel, simple, and inexpensive approach for an absorptive extraction of organic contaminants from aqueous samples applying polysiloxane tubes. After the extraction, the tubes were desorbed with 200 microL of an organic solvent and 50 microL of the extract were transferred via large volume injection (LVI) into a gas chromatography-mass spectrometry system (GC-MS). Fourteen organic compounds covering a broad range in polarity with log K(o/w)-values between 2.6 (atrazine) and 7 (polychlorinated biphenyl 138, PCB 138) were chosen as model compounds. The experimental parameters affecting the efficiency of the process such as desorption solvents, the addition of salt and pH-change, the extraction and desorption time were carefully optimised. The recoveries were compared with theoretical values. The limits of detection (LODs) were in the range of 0.5-5 ng/L and the precision was 7-15%. The method was successfully applied to the analysis of a contaminated river water sample.

Determination of sulfonamide antibiotics in wastewater: A comparison of solid phase microextraction and solid phase extraction methods

In recent years, pharmaceutical and personal care products (PPCPs) have been detected in diverse environments (including groundwater, river water, and municipal wastewater). In order to evaluate their environmental impact, PPCPs must first be accurately determined. In this study, we focused on developing methods to accurately determine 10 sulfonamide antibiotics: sulfaguanidine, sulfacetamide, sulfadiazine, sulfathiazine, sulfapyridine, sulfamerazine, sulfamethazine, sulfamethoxazole, sulfadimethoxine, and sulfasalazine. While sulfonamides can easily be determined in pure water, wastewater influent and effluent collected from sewage treatment plants in Burlington and Toronto (Ontario) were found to generate confounding matrix effects. In an effort to overcome these matrix effects, we developed a solid phase microextraction (SPME) method to determine sulfonamides. Of the five different fiber assemblies investigated, the carbowax/divinylbenzene (CW/DVB) fiber produced the optimal response to sulfonamides. The SPME method was further optimized for sorption time (20min), solution salinity (10%, w/v, KCl), pH (4.5), and static desorption time (30min). When compared to solid phase extraction (SPE) using MCX cartridges, we observed that despite having higher MDLs and poorer sensitivity, SPME possessed the advantage of speed and reduced solvent usage. Most importantly, in contrast to SPE, when we applied the SPME method to fortified wastewater samples, we were generally able to accurately determine (i.e., recover) those sulfonamides that were present. Therefore, we conclude that SPME is a viable method for overcoming matrix effects in environmental samples.

Determination of organophosphorus pesticides using membrane-assisted solvent extraction combined with large volume injection-gas chromatography-mass spectrometric detection

Eight organophosphorus pesticides (parathion-methyl, fenitrothion, malathion, fenthion, bromophos, bromophos-ethyl, fenamiphos and ethion) in aqueous samples were analysed by means of membrane-assisted solvent extraction. First a 20 ml extraction vial was filled with 15 ml of aqueous sample. Then the membrane bag consisting of nonporous polypropylene was put into the vial and filled with 800 microl of organic solvent. The analytes were separated from the aqueous layer by transporting them through the membrane material into the small amount of solvent. The technique was fully automated and successfully combinable with large volume extraction and GC-MS. To achieve an optimum performance several extraction conditions were investigated. Cyclohexane was chosen as acceptor phase. Then the impact of salt, methanol, pH value, as well as working parameters like stirring rate of the agitator and extraction time, were studied. Moreover, the influence of matrix effects was examined by adding different concentrations of humic acid sodium salt. Detection limits in the ng/l level were achieved using large volume injection with the injecting volume of 100 microl. The recovery values ranged from 47 to 100% and the relative standard deviation for three standard measurements was between 4 and 12% (except for bromophos-ethyl: 22%). The linear dynamic range was between 0.001 and 70 microg/l. The applicability of the method to real samples was tested by spiking the eight organophosphorus pesticides to red wine, white wine and apple juice samples.

Guidelines for capillary extraction–capillary gas chromatography: preparation of extractors and analysis of aromatic compounds in water

The benzene, toluene, ethylbenzene and xylenes system (BTEX) in clean water is studied to verify the performance of capillary extraction as an extraction-preconcentration technique well hyphenated with GC. The approach uses pieces of coated capillaries usually 5-30 cm long, trimmed from customary high-resolution GC columns but carrying glass press-fits at their ends. The preparation of these 'capillary extractors' is explained, and their performance is discussed providing guidelines for use. Injection by capillary extraction is such that (i) band broadening in time is null, and (ii) band broadening in space cannot be higher than the extractor length. Speed, cleanliness and operative simplicity of the capillary extraction approach are remarkable, pros and cons are complementary to those of solid phase microextraction (SPME) or stir bar sorptive extraction (SBSE). Capillary extraction-capillary GC analysis of aqueous BTEX samples, in a clean water matrix, allows low part-per-billion detection limits, and does not require heated injectors or cryofocusing devices.

Miniaturized sample preparation combined with liquid phase separations

Miniaturized sample preparation methods designed as the sample pretreatment for liquid phase separations, such as liquid chromatography, capillary electrophoresis and capillary electrochromatography, have been reviewed especially for the on-line coupling of the sample preparation process and the separation process. The development of the desorption interfaces for the effective combining of the sample preparation and subsequent liquid phase separations is briefly described along with the applications of the combined analytical systems to the analysis of complex sample mixtures such as biological and environmental matrices. Novel use of fine polymeric filaments as the extraction medium for microscale liquid phase separation methods are investigated and a comparison is made with other sample preparation techniques. Polymer coating onto the fibrous material is also introduced to further develop microscale sample preparation methods with improved extraction performance. Several other microscale sample preparation methods having a potential compatibility to the liquid phase separations are also described for future applications of these techniques.

Solid-phase microextraction for herbicide determination in environmental samples

Liquid-liquid extraction or solid-phase extraction followed by gas chromatography (GC) or high-performance liquid chromatography are traditional herbicide residue determination methods for environmental samples. Solid-phase microextraction (SPME) is a solventless, fast, and sensitive alternative herbicide residue extraction method that can be applied to numerous environmental matrices. The objective of this paper was to review SPME literature regarding extraction theory, extraction modes, fiber types, and method optimization in conjunction with present and future SPME applications for herbicide determination in environmental samples.