Determination of nitrate esters in water samples Comparison of efficiency of solid-phase extraction and solid-phase microextraction

This paper deals with comparison of efficiency of extraction techniques (solid-phase extraction, SPE and solid-phase microextraction, SPME) used for extraction of nitrate esters (ethyleneglycoldinitrate, EGDN and nitroglycerin, NG), representing the first step of the method of quantitative determination of trace concentrations of nitrate esters in water samples. EGDN and NG are subsequently determined by means of high-performance liquid chromatography with ultraviolet detection (HPLC-UV). Optimization of SPE and SPME conditions was carried out using model water samples. Seven SPE cartridges were tested and the conditions were optimized (type of sorbent, type and volume of solvent to be used as eluent). For both nitrate esters the limit of detection (LOD) and the limit of quantification (LOQ) obtained using SPE/HPLC-UV were 0.23 microg mL(-1) and 0.70 microg mL(-1), respectively. Optimization of SPME conditions: type of SPME fibre (four fibres were tested), type and time of sorption/desorption, temperature of sorption. PDMS/DVB (polydimethylsiloxane/divinylbenzene) fibre coating proved to be suitable for extraction of EGDN and NG. For this fibre the LOD and the LOQ for both nitrate esters were 0.16 microg mL(-1) and 0.50 microg mL(-1), respectively. Optimized methods SPE/HPLC-UV and SPME/HPLC-UV were then used for quantitative determination of nitrate esters content in real water samples from the production of EGDN and NG.     

Determination of phthalate esters in water samples by solid-phase microextraction and gas chromatography with mass spectrometric detection

Solid-phase microextraction (SPME) with an 85 microm polyacrylate fiber, coupled to gas chromatography-mass spectrometry was used to determine six phthalate esters and bis(2-ethylhexyl) adipate in water samples. The variables affecting the SPME absorption process were optimized and the method developed was applied to analyze both tap and commercial mineral water samples as well as water from the Ebro river and fishing and industrial ports. For real samples, the linear range in full scan acquisition mode was between 0.02 and 10 microg l(-1) for most compounds, and the limits of detection of the method were between 0.006 and 0.17 microg l(-1). Commercial water samples contained in recipients which were made from different materials were analyzed, and the influence of the material of the recipients on the concentration of phthalates was evaluated.     

Multivariate optimization of a solid-phase microextraction method for the analysis of phthalate esters in environmental waters

A solid-phase microextraction method (SPME) coupled to gas chromatography-mass spectrometry (GC-MS) has been developed for the determination of the six phthalate esters included in the US Environmental Protection Agency (EPA) Priority Pollutants list in water samples. These compounds are dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), butylbenzyl phthalate (BBP), di-2-ethylhexyl phthalate (DEHP) and di-n-octyl phthalate (DOP). Detailed discussion of the different parameters, which could affect the extraction process, is presented. Main factors have been studied and optimized by means of a multifactor categorical design. Different commercial fibers, polydimethylsiloxane (PDMS), polydimethylsiloxane-divinylbenzene (PDMS-DVB), polyacrylate (PA), Carboxen-polydimethylsiloxane (CAR-PDMS) and Carbowax-divinylbenzene (CW-DVB), have been investigated, as well as the extraction mode, exposing the fiber directly into the sample (DSPME) or into the headspace over the sample (HS-SPME), and different extraction temperatures. The use of this experimental design allowed for the evaluation of interactions between factors. Extraction kinetics has also been studied. The optimized microextraction method showed linear response and good precision for all target analytes. Detection limits were estimated considering the contamination problems associated to phthalate analysis. They were in the low pg mL(-1), excluding DEHP (100 pg mL(-1)). The applicability of the developed SPME method was demonstrated for several real water samples including mineral, river, industrial port and sewage water samples. All the target analytes were found in real samples. Levels of DEP and DEHP were over 1 ng mL(-1) in some of the samples.     

Solid-phase microextraction of phthalate esters in water sample using different activated carbon-polymer monoliths as adsorbents

In this study, the application of different activated carbon-polymer (AC-polymer) monoliths as adsorbents for the solid-phase microextraction (SPME) of phthalate esters (PAEs) in water sample were investigated. The activated carbon (AC) was embedded in organic polymers, poly(butyl methacrylate-co-ethylene dimethacrylate) (poly(BMA-EDMA)) or poly(styrene-co-divinylbenzene) (poly(STY-DVB)), via a 5-min microwave-assisted or a 15-min water bath heating polymerization. Preliminary investigation on the performance of the native poly(BMA-EDMA) and poly(STY-DVB) demonstrated remarkable adsorption efficiencies for PAEs. However, due to the strong hydrophobic, π-π, and hydrogen bonding interactions between the analytes and polymers, low extraction recoveries were achieved. In contrast, the presence of AC in native polymers not only enhanced the adsorption efficiencies but also assisted the PAE desorption, especially for AC-poly(STY-DVB) with extraction recovery ranged of 76.2–99.3%. Under the optimized conditions, the extraction recoveries for intra-, inter-day and column-to-column were in the range of 76.5–100.8% (<3.7% RSDs), 77.2–97.6% (<5.6% RSDs) and 75.5–99.7% (<6.2% RSDs), respectively. The developed AC-poly(STY-DVB) monolithic column showed good mechanical stability, which can be reused for more than 30 extraction times without any significant loss in the extraction recoveries of PAEs. The AC-poly(STY-DVB) monolithic column was successfully applied in SPME of PAEs in water sample with extraction recovery ranged of 78.8%–104.6% (<5.5% RSDs).     

Bamboo charcoal as a novel solid-phase microextraction coating material for enrichment and determination of eleven phthalate esters in environmental water samples

This study demonstrates the potential of bamboo charcoal as a novel and inexpensive solid-phase microextraction (SPME) coating material for enrichment and determination of organic pollutants in water samples. Bamboo charcoal was prepared and used as a SPME coating material. Eleven phthalate esters (PAEs) were used as model analytes, and gas chromatography–mass spectrometry was used for separation and detection. Important extraction conditions (ionic strength, stirring rate, and extraction time) and desorption conditions (desorption temperature and time) were systematically investigated and optimized. Linearity of 0.1–100 μg?L^?1 and correlation coefficients of 0.9992–0.9998 were obtained under optimum conditions. Inter-day and intra-day repeatability were 2.15–9.93 % and 1.89–9.85 %, respectively, and fiber-to-fiber reproducibility was 5.42–9.66 %. On the basis of a chromatographic signal-to-baseline noise ratio of three, the limits of detection reached 0.004–0.023 μg?L^?1. Satisfactory results were achieved when the bamboo coating was used for determination of 11 PAEs in real water samples. The experimental results indicate that bamboo charcoal has significant potential as a SPME coating material for rapid enrichment and sensitive determination of organic pollutants in environmental samples.     

Comparison of different coatings in solid-phase microextraction for the determination of organochlorine pesticides in ground water

A solid-phase microextraction (SPME) procedure using three commercialised fibers (Carbowax-divinylbenzene, Carboxen-polydimethylsiloxane and divinylbenzene-Carboxen-polydimethylsiloxane) is presented for the determination of a selected group of organochlorine compounds in water samples. The extraction performances of these compounds were compared using fibers with two and three coatings. The optimal experimental procedures for the adsorption and desorption of pesticides were determined. The limits of detection with the divinylbenzene-Carboxen-polydimethylsiloxane fiber at levels below ng l(-1) were similar or lower than values presented in the literature for several of these compounds using polydimethylsiloxane fiber. The advantages of using this fiber, such as no salt addition, are discussed. Finally, the optimised procedures were applied successfully for the determination of these compounds in polluted ground water samples.     

Development of a solid-phase microextraction method for the determination of phthalic acid esters in water

Solid-phase microextraction method (SPME) coupled to GC/ECD has been developed and validated for the determination of phthalic acid esters (dimethyl-, diethyl-, di-n-butyl-, butylbenzyl-, di-2-ethylhexyl- and di-n-octyl phthalate) in water samples. Two types of coatings (PDMS, PA), altogether four different kinds of fibers have been investigated. Both parameters affecting the partition of analytes between a fiber coating and aqueous phase (i.e. extraction time, extraction temperature, agitation) and conditions of the thermal desorption in a GC injector were optimized. The final SPME method employing the polyacrylate fiber, extraction time 20 min, heating and stirring of the sample enabled the determination of all six phthalates in water samples. The method showed linear response over four orders of magnitude and the limits of quantification of the method ranged between 0.001 and 0.050 μg l⁻¹. The repeatability expressed as R.S.D. was in the range 4-10% for the spiking level 7 μg l⁻¹ of each analyte. The applicability of the developed SPME method was demonstrated for real water samples.     

Reduced graphene-decorated covalent organic framework as a novel coating for solid-phase microextraction of phthalate esters coupled to gas chromatography-mass spectrometry

Two analytical methods were developed using electrochemical and spectrometric techniques for the simultaneous determination of endocrine disruptors triclosan and methylparaben in the monitoring of personal care products. For the electroanalytical analyses, a sensitive electrode based on graphene quantum dots supported in chitosan was employed. Under optimized conditions and a working potential of typically + 0.60 V for triclosan and + 0.81 V (vs. Ag/AgCl) for methylparaben, the calibration plots obtained by differential pulse voltammetry were linear in the range 0.10 to 10.0 μmol L−1. The detection limits were 0.03 and 0.04 μmol L−1 for triclosan and methylparaben, respectively. For the spectrometric method, UV/VIS spectrometry was used with a mathematical processing of non-linear deconvolution. This processing was used to solve the problem of overlapping absorption bands of triclosan (282 nm) and methylparaben (257 nm), which enabled simultaneous determination. The calibration plots by UV/VIS spectrometry were linear in the range 1.0 to 14.0 μmol L−1 with detection limits of 0.42 and 0.37 μmol L−1, respectively, for triclosan and methylparaben. Similar results obtained from the calibration plots of individual analytes suggest that the methods can be applied for individual or simultaneous determination of these species. Both methods were employed in the analysis of five samples of personal care products: toothpaste, antiseptic soap, antiseptic deodorant, shampoo, and a bath kit (soap and shampoo). The statistical tests indicated that there were no significant differences regarding the accuracy and precision of the data provided by the two methods described herein.     

Comparison of solid-phase extraction and solid-phase microextraction for carbofuran in water analyzed by high-performance liquid chromatography-photodiode-array detection

In this study a direct solid-phase microextraction (SPME) procedure has been developed for the determination of carbofuran in water. Experimental parameters such as selection of SPME coating, effect of temperature, effect of salt addition and solvent desorption were studied and optimized. Analytical parameters such as linearity, precision, detection and quantitation limits, and matrix effects for solid-phase extraction (SPE) and SPME methods were evaluated for comparison purposes with the aim of selecting the most appropriate depending on the detection capabilities required. SPE and SPME were followed by high-performance liquid chromatography with diode-array detection, using a 50 x 4.6 mm I.D. guard column and a 150 x 4.6 mm I.D. analytical column, both packed with C18 silica. Both methods can be applied to real samples and give the same results, but SPE allows the detection of lower carbofuran concentrations (0.06 microg/L) as compared to     

Development of a solid-phase microextraction method with micellar desorption for the determination of chlorophenols in water samples. Comparison with conventional solid-phase microextraction method

A novel analytical method is presented for the determination of chlorophenols in water. This method involves pre-concentration by solid-phase microextraction (SPME) and an external desorption using a micellar medium as desorbing agent. Final analysis of the selected chlorophenols compounds was carried out by high-performance liquid chromatography (HPLC) with diode array detection (DAD). Optimum conditions for desorption, using the non-ionic surfactant polyoxyethylene 10 lauryl ether (POLE), such as surfactant concentration and time were studied. A satisfactory reproducibility for the extraction of target compounds, between 6 and 15%, was obtained, and detection limits were in the range of 1.1-5.9ngmL(-1). The developed method is evaluated and compared with the conventional one using organic solvent as a desorbing agent. The method was successfully applied to the determination of chlorophenols in water samples from different origin. This study has demonstrated that solid-phase microextraction with micellar desorption (SPME-MD) can be used as an alternative to conventional SPME method for the extraction of chlorophenols in water samples.     

固相微萃取气相色谱法(SPME-GC)测定水体中邻苯二甲酸酯

选用85μm PA纤维,考证了萃取温度、萃取时间、搅拌、离子强度及解析时间等影响因素,最后确立了65℃萃取温度、60min萃取时间、稳定的磁力搅拌、5min解析时间、用带电子捕获检测器的毛细管气相色谱（CGC—ECD）分离测定、外标标准曲线法定量分析水体中邻苯二甲酸酯（PAEs）的方法。该方法具有较好的精密度（RSD≤16％）和较低的检出限（DLDBP=0．003μg/L,DLDEDEHP=0．05μg/L）,水样加标回收率在70％～130％之间。用该法测定了长江水样、太湖水样、自来水及蒸馏水的PAEs含量,DBP在0．1～0．4μg/L,DEHP在0．2～1．2μg/L,DMP、DEP、DOP均未检测到。     

Application of dispersive liquid-liquid microextraction and high-performance liquid chromatography for the determination of three phthalate esters in water samples

A novel method, dispersive liquid-liquid microextraction (DLLME) coupled with high-performance liquid chromatography-variable wavelength detector (HPLC-VWD), has been developed for the determination of three phthalate esters (dimethyl phthalate (DMP), diethyl phthalate (DEP), and di-n-butyl phthalate (DnBP)) in water samples. A mixture of extraction solvent (41 μL carbon tetrachloride) and dispersive solvent (0.75 mL acetonitrile) were rapidly injected into 5.0 mL aqueous sample for the formation of cloudy solution, the analytes in the sample were extracted into the fine droplets of CCl₄. After extraction, phase separation was performed by centrifugation and the enriched analytes in the sedimented phase were determined by HPLC-VWD. Some important parameters, such as the kind and volume of extraction solvent and dispersive solvent, extraction time and salt effect were investigated and optimized. Under the optimum extraction condition, the method yields a linear calibration curve in the concentration range from 5 to 5000 ng mL⁻¹ for target analytes. The enrichment factors for DMP, DEP and DnBP were 45, 92 and 196, respectively, and the limits of detection were 1.8, 0.88 and 0.64 ng mL⁻¹, respectively. The relative standard deviations (R.S.D.) for the extraction of 10 ng mL⁻¹ of phthalate esters were in the range of 4.3-5.9% (n = 7). Lake water, tap water and bottled mineral water samples were successfully analyzed using the proposed method.     

Enrichment of nitrophenols from water by means of solid-phase microextraction

The fundamental suitability of solid-phase microextraction (SPME) has been investigated for the enrichment of partially well water-soluble and differently substituted polar nitrophenols. Two commercially available fibers coated with 100 m polydimethylsiloxane or 85 m polyacrylate, respectively, were compared with regard to the efficiency of the enrichment of these compounds. For all the compounds investigated, polyacrylate fiber showed a better affinity when the exposure time was longer in comparison with polydimethylsiloxane fiber. The salting-out and the enrichment at low pH-values increased the sensitivity of the process significantly.Dedicated to Professor Dr. H. Kriegsmann on the occasion of his 70th birthday     

微萃取瓶富集-液相色谱法测定水中痕量邻苯二甲酸酯

邻苯二甲酸酯(PAEs)常用作增塑剂,在塑料、家具、汽车、服装等行业广泛应用.PAEs有雌激素活性,属内分泌干扰物,含PAEs工业废水的排放可污染水环境,从而引起人体内分泌失调,甚至可能阻害生殖机能或引发恶性肿瘤等影响生态和健康的问题.     

Headspace solid-phase microextraction of oil matrices heated at high temperature and phthalate esters determination by gas chromatography multistage mass spectrometry

A solvent-free analytical approach based on headspace solid-phase microextraction (SPME) of oil matrices heated at high temperatures coupled to gas chromatography with mass spectrometry detector (GC-ion trap) has been developed for the determination of phthalic acid esters (PAEs) in oil matrices without sample manipulation. For this study, three fibers, i.e., 85 μm-polyacrylate (PA), 50/30 μm-divinylbenzene-carboxen-polydimethylsiloxane (DVB/CAR/PDMS) and 100 μm-polydimethylsiloxane (PDMS) were tested. Variables affecting the SPME headspace composition such as incubation sample temperature, sample incubation time and fiber exposition time were optimized. The optimal values found were 250 °C for sample incubation temperature and 30 min for incubation and extraction time. PA fiber was not suitable for the lightest polar phthalates which showed poor extraction and repeatability values. PDMS fiber had very poor response for some of the heavier and non-polar phthalates, whereas DVB/CAR/PDMS fiber showed the best response and repeatability values for the majority of the phthalates studied. The main benefit of the analytical method proposed is the absence of sample manipulation and hence avoidance of possible contamination coming from glassware, environment, solvents and samples.     

High-performance polyethylene glycol-coated solid-phase microextraction fibers using sol-gel technology

The sol-gel method is applied for the preparation of solid-phase microextraction (SPME) fibers. An electron microscopy experiment suggested a porous structure for Superox-4 (polyethylene glycol, PEG) coating. SPME-GC analyses provided evidence that the sol-gel fibers have some advantages, such as high velocities of mass transfer, efficient extraction rates. high thermal stability, long life span, and spacious range of application for both polar and non-polar analytes. Efficient SPME-GC analyses of benzene-toluene-ethylbenzene-xylenes, phenols, phthalic diesters, naphthalene congeners and pesticides were achieved using sol-gel-coated PEG fibers.     

Indirect analysis of urea herbicides from environmental water using solid-phase microextraction

We described here a solid-phase microextraction procedure used to extract six urea pesticides — chlorsulfuron, fluometuron, isoproturon, linuron, metobromuron and monuron — from environmental samples. Two polydimethylsiloxanes and a polyacrylate fiber (PA) are compared. The extraction time, pH control, addition of NaCl to the water and the influence of organic matter such as humic acid on extraction efficiency were examined to achieve a sensitive method. Determination was carried out by gas chromatography with nitrogen–phosphorus detection. The proposed method requires the extraction of 2 ml of sample (pH 4, 14.3%, w/v, NaCl) for 60 min with the PA fiber. The limits of detection range from 0.04 for linuron to 0.1 μg/l for fluometuron and monuron and the relative standard deviations at the 1 μg/l level are between 15% and 9%. The apparent fiber–water distribution constants (K_fw) calculated in the proposed conditions were in the order of 10³. Phenylurea herbicides were indirectly determined in the form of their derived anilines and chlorsulfuron in the form of an aminotriazine as confirmed by gas chromatography–mass spectrometry. Natural waters were utilized to validate the final procedure. However, a unequivocal identification in unknown environmental samples should be done by LC–MS. The presence of dissolved organic matter such as humic acid produces losses during the extraction step. Adding sodium chloride to the sample compensates for this effect.     

Optimisation of alachlor solid-phase microextraction from water samples using experimental design

We have tested screening and response surface experimental designs to optimise the solid-phase microextraction (SPME) of the widely used herbicide alachlor. Extraction time and sample volume were the only statistically significant factors from those studied. In the final optimised conditions the procedure was applied to the SPME-HPLC analysis of alachlor in spiked water samples with excellent figures of merit.     

Quantifying sesquiterpene and oxygenated terpene emissions from live vegetation using solid-phase microextraction fibers

Biogenic terpenes play important roles in ecosystem functioning and atmospheric chemistry. Some of these compounds are semi-volatile and highly reactive, such as sesquiterpenes and oxygenated terpenes, and are thus difficult to quantify using traditional air sampling and analysis methods. We developed an alternative approach to quantify emissions from live branches using a flow through enclosure and sample collection on solid-phase microextraction (SPME) fibers. This method allows for collection and analysis of analytes with minimal sample transfer through tubing to reduce the potential for losses. We characterized performance characteristics for 65 microm polydimethylsiloxane-divinylbenzene (PDMS/DVB) fibers using gas chromatography followed by mass spectrometry and optimized experimental conditions and procedures for field collections followed by laboratory analysis. Using 10-45 min sampling times and linear calibration curves created from mixtures of terpenes, emissions of methyl chavicol, an oxygenated terpene, and an array of sesquiterpenes were quantified from a Ponderosa pine branch. The detection limit was 4.36 pmol/mol (ppt) for methyl chavicol and 16.6 ppt for beta-caryophyllene. Concentrations determined with SPME fibers agreed with measurements made using proton transfer reaction mass spectrometry (PTR-MS) within the estimated error of the method for well calibrated compounds. This technique can be applied for quantification of biogenic oxygenated terpene and sesquiterpene emissions from live branches in the field.