Solid-phase microextraction—Gas chromatography to determine volatile organic sulfur compounds in the air at sewage treatment plants

Solid-phase microextraction (SPME) was applied to the determination of 7 volatile organic sulfur compounds (VOSCs), which were analysed by gas chromatography-mass spectrometry. The compounds studied were ethyl mercaptan (CH₃CH₂SH), dimethyl sulfide ((CH₃)₂S), carbon disulfide (CS₂), propyl mercaptan (C₃H₈S), butyl mercaptan (C₄H₁₀S), dimethyl disulfide ((CH₃)₂S₂) and 1-pentanethiol (C₅H₁₂S). Temperature and time conditions of SPME extraction were optimised and the method was validated, with good linearity in a calibration range between 0.1 and 1000 μg m⁻³. Method detection limits ranged between 0.01 and 0.08 μg m⁻³ and method quantification limits were between 0.10 and 0.25 μg m⁻³, allowing real samples taken from several different areas of a sewage treatment plant to be analysed. Repeatability of the method between samples went from 5.6% for pentanethiol up to 14.2% for carbon disulfide, and concentrations of total target compounds were found between 18 and 529 μg m⁻³, depending on the sampling site.     

Trace determination of sulfonamides residues in meat with a combination of solid-phase microextraction and liquid chromatography-mass spectrometry

An integrated method of combining solid-phase microextraction (SPME) with liquid chromatography-mass spectrometry (LC-MS) was evaluated for determination trace amount of sulfonamides in meat products. Eight commonly used sulfonamides, sulfadiazine (SDZ), sulfathiazole (STZ), sulfamerazine (SMR), sulfamethazine (SMT), sulfamonomethoxine (SMMX), sulfamethoxazole (SMXZ), sulfaquinoxaline (SQX) and sulfadimethoxine (SDMX), were investigated in this study. Chromatography was performed on a C₁₈ reversed-phase column using an isocratic acetonitrile in water as the mobile phase. Fiber coated with a 65 μm thickness of polydimethylsiloxane/divinylbenzene (PDMS/DVB) was used to extract sulfonamides at optimum conditions. Analytes were desorbed with static desorption in an SPME-HPLC desorbed chamber for 15 min and then determined by LC-MS. The detection limits of these sulfonamides in pork were from 16 μg kg⁻¹ (SMT) to 39 μg kg⁻¹ (SMMX). According to the analysis, the linear range was from 50 to 2000 μg kg⁻¹ with relative standard deviation (R.S.D.s) value below 15% (intra-day) and 19% (inter-day). The proposed method was tested by analyzing meats from a local market for sulfonamides residues. Some sulfonamides in our study were detected in the meat samples. The concentration of these residual sulfonamides ranged from 66 μg kg⁻¹ (SDZ) to 157 μg kg⁻¹ (SQX) in a chicken sample. The results demonstrate that the SPME-LC-MS system is highly effective in analyzing trace sulfonamides in meat products.     

纳米SiO2膜新型萃取头固相微萃取测定蔬菜中5种农药残留量的研究

建立了以纳米SiO2膜为萃取头涂层的固相微萃取(SPME)-气相色谱(GC)联用测定蔬菜中5种农药残留 (p,p′-DDD, p,p′-DDE, o,p′-DDT, p,p′-DDT, 联苯菊酯)的新方法. 探讨并优化了萃取时间、萃取温度和转子转速等参数.     

Photodegradation of the pharmaceuticals amoxicillin, bezafibrate and paracetamol by the photo-Fenton process—Application to sewage treatment plant effluent

Photodegradation of the pharmaceuticals amoxicillin (AMX), bezafibrate (BZF) and paracetamol (PCT) in aqueous solutions via the photo-Fenton process was investigated under black-light and solar irradiation. The influences of iron source, initial H₂O₂ concentration and matrix (distilled water and sewage treatment plant effluent) on degradation efficiency were discussed in detail. The results showed that (i) the degradation of the drugs was favored in the presence of potassium ferrioxalate (FeOx) in comparison to Fe(NO₃)₃; (ii) the increase of the H₂O₂ concentration improved the efficiency of AMX and BZF oxidation; however, the same was not observed for PCT; (iii) the influence of the matrix was observed for the degradation of BZF and PCT; (iv) under solar irradiation, the oxidation of the BZF and PCT is faster than under black-light irradiation. All these pharmaceuticals can be efficiently degraded employing the process evaluated.     

Optimisation of the derivatisation reaction and subsequent headspace solid-phase microextraction method for the direct determination of chlorophenols in red wine

An acetylation reaction for the derivatisation of the three chlorophenols involved in cork taint was optimised using a Doehlert design for direct application in wine samples. In this first step, the optimum reaction pH, by adding different amounts of KHCO3, and the required quantity of derivatisation reagent were fixed. Then a series of parameters relevant for the headspace solid-phase microextraction process, such as desorption conditions, salt addition and agitation sample were evaluated. A simultaneous study of the type of fibre and extraction temperature was performed at five levels and based on the results obtained the rest of factors (sample volume and exposition time) that could potentially affect the extraction yields were optimised by a central composite design. According to the validation of the method, we propose here, to our knowledge, the first application of solid-phase microextraction for the direct analysis of chlorophenols in red wine samples.     

Pressurised hot water extraction followed by simultaneous derivatization and headspace solid-phase microextraction and gas chromatography-tandem mass spectrometry for the determination of aliphatic primary amines in sewage sludge

In this paper we describe an environmentally friendly and sensitive method for the determination of ten primary amines in sewage sludge. The method is based on pressurised hot water extraction (PHWE) followed by simultaneous derivatization with pentafluorobenzaldehyde (PFBAY) and headspace solid-phase microextraction (HS-SPME) and subsequent gas-chromatography ion-trap tandem mass spectrometry (GC-IT-MS-MS) analysis. The influence of the main factors on the PHWE of sludge was optimized by a central composite design. For all species the optimal conditions were water at pH 4 as the extracting solvent, an extraction temperature of 100 °C and an extraction time of 15 min. The separation and detection of the ten amines by GC-IT-MS-MS took just 10 min and the entire process took approximately 1 h. Repeatability and reproducibility between days, expressed as RSD (%) (n = 5), were less than 19 and 24%, respectively. The average limit of detection (LOD) was of 65 μg kg⁻¹ s (range found 9-135) and the average limit of quantification (LOQ) was of 230 μg kg⁻¹ (range found 50-450) of dry weight (d.w.). Under optimized conditions we used this method to determine the compounds in industrial and municipal sewage sludge samples and in sludge from a potable water treatment plant. Methylamine and isobutylamine showed the highest levels in one of the industrial sewage sludge samples (404 and 543 mg kg⁻¹ (d.w.), respectively). To our knowledge, this paper presents for the first time the determination of ten primary amines in sewage sludge samples using PHWE.     

Optimisation of a simple and reliable method based on headspace solid-phase microextraction for the determination of volatile phenols in beer

A simple, accurate and sensitive method based on headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography–tandem mass spectrometry (GC–MS/MS) was developed for the analysis of 4-ethylguaiacol, 4-ethylphenol, 4-vinylguaiacol and 4-vinylphenol in beer. The effect of the presence of CO₂ in the sample on the extraction of analytes was examined. The influence on extraction efficiency of different fibre coatings, of salt addition and stirring was also evaluated. Divinylbenzene/carboxen/polydimethylsiloxane was selected as extraction fibre and was used to evaluate the influence of exposure time, extraction temperature and sample volume/total volume ratio (V_s/V_t) by means of a central composite design (CCD). The optimal conditions identified were 80 °C for extraction temperature, 55 min for extraction time and 6 mL of beer (V_s/V_t 0.30). Under optimal conditions, the proposed method showed satisfactory linearity (correlation coefficients between 0.993 and 0.999), precision (between 6.3% and 9.7%) and detection limits (lower than those previously reported for volatile phenols in beers). The method was applied successfully to the analysis of beer samples. To our knowledge, this is the first time that a HS-SPME based method has been developed to determine simultaneously these four volatile phenols in beers.     

Optimization of a solid-phase microextraction procedure for the determination of herbicides by micellar electrokinetic chromatography

The use of a different optimization procedure that involves Experimental Design (ED) and Artificial Neural Networks (ANN) for the off-line coupling solid-phase microextraction-micellar electokinetic chomatography (SPME-MEKC) is presented. This combination of ED and ANN, mathematical tools not previously used in SPME-MEKC optimization, allowed us to obtain good extraction efficiencies in the SPME procedure for the determination of a group of eleven triazine herbicides in groundwater samples. Both extraction and desorption steps were carried out by solution stirring at 900 rpm. Optimal conditions for the off-line SPME procedure were: extraction with a poly(dimethylsiloxane)/divinylbenzene SPME fiber for 120 min, 10% (w/v) NaCl, desorption time 40 min, and 70% (v/v) of methanol/buffer as desorption mixture. Detection limits lay between 0.80 microg L(-1) and 4.89 microg L(-1). Finally, the optimized method was applied to the determination of these compounds in spiked and non-spiked groundwater samples using a previously optimized MEKC separation.     

Microporous silica with nanolayer structure coated with renewable organic solvent film as a novel extracting phase: A combination of solid- and liquid-phase microextraction

A new method based on combination of solid- and liquid-phase microextraction was developed. For the first time, porous flower-like silica microstructures with nanometric layers were created on the surface of the stainless steel wire by a new facile hydrothermal process. The fiber, coated with a suitable organic solvent, was applied for microextraction of some organophosphorus pesticides from aqueous samples followed by gas chromatography-nitrogen phosphorous detection. Method detection limits were between 0.6 and 3 ng L⁻¹. Relative standard deviations for intra- and inter-day precision were 4.4–7.3% and 5.1–7.8%, respectively. Fiber-to-fiber reproducibility for five prepared fibers was 6.3–8.4%. Tap, river and waste water samples were analyzed for evaluation of the method in real sample analysis. Relative recoveries for spiked tap, river and waste water samples were in the range of 94–101%, 89–97% and 82–103%, respectively. In addition, the method was compared with two commercial solid-phase microextraction (SPME) fibers, single drop microextraction (SDME) and liquid-phase microextraction (LPME). The present method showed higher extraction efficiency as compared with SDME, LPME and commercial SPME fibers.     

Application of NiTi alloy coated with ZrO2 as a new fiber for solid-phase microextraction for determination of halophenols in water samples

A new fiber for solid-phase microextraction (SPME) employing a metallic support coated with an inorganic material is proposed. A nitinol alloy (NiTi) was used as the support material due to its super elasticity and shape memory properties. Zirconium oxide (ZrO₂) was electrodeposited onto NiTi using chronoamperometry. The surface characteristics and morphology of the coated and uncoated support were evaluated through scanning electronic microscopy and dispersive energy microanalysis. This assembly was applied in the extraction of three halophenols from aqueous samples. A multivariate approach was used for optimization of the variables involved in the system. The Doehlert matrix was used for evaluation of the best derivatization conditions and a Box-Behnken design to obtain the best extraction conditions. In order to investigate the repeatability, one fiber was used for six extraction tests under similar conditions and the relative standard deviations (R.S.D.) were lower than 12.5%. Detection limits were lower than 0.30 ng mL⁻¹. Correlation coefficients were higher than 0.997. Extraction efficiency of the NiTi-ZrO₂ fiber was similar to a PDMS 7 μm commercial fiber, even though it had a lower coating thickness of 1.35 μm. Considering the amount extracted per unit volume, the NiTi-ZrO₂ fiber had a better extraction profile when compared to commercial fibers. The new SPME fiber has a lifetime of over 500 extractions. Thus, it is a promising alternative for low-cost analysis, as the proposed fiber is robust, and easily and inexpensively prepared.     

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.     

A combination of Tedlar bag sampling and solid-phase microextraction for the analysis of trimethylamine in air: Relationship between concentration level and sample size

To extend the experimental applicability of the solid-phase microextraction (SPME) method to the analysis of trimethylamine (TMA) by the grab sampling method (i.e., Tedlar bag sampler), we investigated how experimental results are affected by the interaction between the concentration level of TMA standard and the volume size of its sample that is exposed to SPME fiber. To obtain comparative data sets for TMA analysis, all standards were analyzed as triplicate at five different concentrations (10, 20, 50, 100, and 200 ppb) each of which was prepared in four different bag sizes (1, 3, 5, and 10 L capacity). The sorptive characteristics of TMA were then evaluated in terms of recovery rate (RR) values derived by relationship between added and found quantities of TMA standard. The results of randomized block design showed that the determination of TMA is affected by the two major variables (i.e., TMA concentration level and sample size) at 95% confidence interval.     

A multiresidue analytical method using solid-phase extraction and high-pressure liquid chromatography tandem mass spectrometry to measure pharmaceuticals of different therapeutic classes in urban wastewaters

An analytical method with two extraction steps has been developed and validated for the simultaneous determination of 30 pharmaceuticals belonging to various therapeutic categories in urban wastewater. The aim was to boost the little available information on drugs' fates in sewage treatment plants (STPs) and in the receiving surface water. Aqueous samples were divided into two aliquots, each extracted by a different solid-phase extraction (SPE) method and analysed by reversed-phase liquid chromatography tandem mass spectrometry (HPLC-MS-MS). Recoveries of the pharmaceuticals were mostly greater than 70% and the overall variability of the method was below 8%. The instrumental quantification limit (IQL) varied between 30 and 400 pg injected, and the limits of quantification (LOQ) were in the low ng/L range. Nineteen pharmaceuticals were detected in concentrations between 0.5 and 2000 ng/L in effluents collected from several STPs in Italy. Atenolol, ciprofloxacin, furosemide, hydrochlorothiazide, ofloxacin, ranitidine and sulphamethoxazole were the most abundant compounds. The present analytical method was useful to check for pharmaceuticals in various Italian STPs and to identify the most abundant compounds.     

Chemometric study and optimization of extraction parameters in single-drop microextraction for the determination of multiclass pesticide residues in grapes and apples by gas chromatography mass spectrometry

A simple and rapid single-drop microextraction method coupled with gas chromatography and mass spectrometry (SDME–GC/MS) for the determination of 20 pesticides with different physicochemical properties in grapes and apples was optimized by the use of a multivariate strategy. Emphasis on the optimization study was given to the role of ionic strength, sugar concentration and pH of the donor sample solution prepared from the fruit samples. Since all three variables were found to affect negatively SDME (a lower extraction efficiency was observed as the values of variables were increased for most of the pesticides studied), donor sample solution was optimized using a central composite design to evaluate the optimum pH value and the optimum dilution of the sample extract. With some exceptions (chlorpyrifos ethyl, α-endosulfan, β-endosulfan, pyriproxyfen, λ-cyhalothrin and bifenthrin), the optimum method included the dilution of the analytical sample by 12.5-fold with a buffered acetone/water solution at pH = 4 and exhibited good analytical characteristics for the majority of target analytes (pyrimethanil, pirimicarb, metribuzin, vinclozolin, fosthiazate, procymidone, fludioxonil, kresoxim methyl, endosulfan sulfate, fenhexamid, iprodione, phosalone, indoxacarb and azoxystrobin) by providing high enrichment factors (14–328), low limits of detection (0.0003–0.007 μg/g), and good precision (relative standard deviations below 15%).     

SPME and SPE comparative study for coupling with microwave-assisted micellar extraction in the analysis of organochlorine pesticides residues in seaweed samples

Solid-phase microextraction (SPME) and solid-phase extraction (SPE) procedures were coupling with microwave-assisted micellar extraction for organochlorine pesticides residues determination in seaweed samples. They were optimized, compared and discussed.Preliminary experiments were performed in order to study experimental conditions for the extraction of pesticides from spiked seaweed samples with microwave-assisted micellar extraction (MAME) using a non-ionic surfactant (Polyoxyethylene 10 Lauryl Ether). After that, SPME and SPE were used to clean-up and preconcentrate MAME extract prior the analysis by liquid chromatography with photodiode array (PDA) detection.Excellent results were obtained for both procedures. Average pesticide recoveries between 80.5 and 104.3% for MAME-SPME and between 73.9 and 111.5% for MAME-SPE were obtained. Relative standard deviations (RSDs) were lower than 10.3% and 5.3% respectively for all recoveries tested, and LOD between 138–348 ng g^− 1 for MAME-SPME and 2–38 ng g^− 1 for MAME-SPE were obtained. The method was validated using Soxhlet extraction procedure.Both methods were applied to analyse target organochlorine pesticides in several seaweed samples and results were compared. These results show the great possibilities of combining MAME-SPE-HPLC-UV for the analysis of seaweed samples, improving the selectivity and sensitivity in the determination of organochlorine pesticides analysis for this kind of samples.     

Development and optimisation of a single extraction procedure for the LC/MS/MS analysis of two pharmaceutical classes residues in sewage treatment plant

A unique extraction procedure leading to the separation of 2 different pharmaceutical classes molecules has been developed and optimised by chemometric tools. From only one sampling, this analytical method allows the determination of 21 pharmaceuticals from corticosteroids and β-blockers classes. Performing the SPE on Oasis MCX (mixed-mode cation exchange), the sequential elution of each pharmaceutical class is achievable, allowing a high purity level of extracts as well as high recovery rates. Performing a unique sample preparation results in an important save of time. The extracts were then analysed by LC/MS/MS, using a Hibar Purospher Star column for β-blockers and an X-Bridge column for corticosteroids with formate buffer (pH 3.8)/AcN and water/AcN mobile phases, respectively. This work also includes a study of the chromatographic and mass spectrometric parameters in order to increase the analyte signal. The optimised SPE-LC/MS/MS method was then applied to environmental samples from sewage treatment plant (STP). β-Blockers and corticosteroids were detected, respectively, in concentrations up to 318 ng L⁻¹ (sotalol) and 174 ng L⁻¹ (cortisone), in STP influents. Moreover, both pharmaceutical classes have also been detected in STP effluents. As far as we know, this is the first paper reporting the detection of corticosteroids in environmental waters. The developed analytical method can be used in further studies to investigate the environmental contamination by these drugs.     

Simultaneous multiresponse optimization of an HPLC method to separate seven cephalosporins in plasma and amniotic fluid: Application to validation and quantification of cefepime, cefixime and cefoperazone

An HPLC method for the separation of seven cephalosporins [Cefepime (CEP), ceftazidime (CTA), ceftizaxime (CTI), ceftriaxone (CTR), cefotaxime (COT), cefixime (CIX) and cefoperazone (COP)] in human plasma and amniotic fluid has been developed. Optimization of the chromatographic method was performed in three steps: a series of initial experiments followed by two sets of experiments based on different experimental designs. The initial experiments were performed to decide the basic analytical requirements of the method. Then screening experiment fractional factorial design was used in order to decrease the number of parameters by eliminating parameters which having insignificant effect on responses. The parameters having significant effect were further optimized through a full factorial design. Having studied two responses (retention times and resolutions), a desirability function that assess the responses together, was used to find experimental conditions where the system generated desirable results. The desirable results were obtained with XTerra C18 (250 mm × 4.6 mm, 5 μm i.d.) column, 40 mM phosphate buffer, pH 3.2, 18% MeOH, 0.85 mL min⁻¹ flow rate and 32 °C column temperature. Gradient elution with MeOH was applied. A simple and efficient solid-phase extraction was applied for the preparation of plasma and amniotic fluid samples. The validation parameters of the method were evaluated in accordance with ICH guideline. The method validated was applied to the analysis of CEP and COP in maternal venous, fetal venous and fetal arterial plasma, and to the analysis of CIX in maternal venous plasma and amniotic fluid.     

Robust and non-parametric statistics in the evaluation of figures of merit of analytical methods. Practices for students

A set of laboratory practices is proposed in which evaluation of the quality of the analytical measurements is incorporated explicitly by applying systematically suitable methodology for extracting the useful information contained in chemical data. Non-parametric and robust techniques useful for detecting outliers have been used to evaluate different figures of merit in the validation and optimization of analytical methods. In particular, they are used for determination of the capability of detection according to ISO 11843 and IUPAC and for determination of linear range, for assessment of the response surface fitted using an experimental design to optimize an instrumental technique, and for analysis of a proficiency test carried out by different groups of students. The tools used are robust regression, least median of squares (LMS) regression, and some robust estimators as median absolute deviation (m.a.d.) or Huber estimator, which are very useful as an alternatives to the usual centralization and dispersion estimators.     

A high-throughput approach for the determination of pesticide residues in cucumber samples using solid-phase microextraction on 96-well plate

A high-throughput solid-phase microextraction (SPME) on 96-well plate together with gas chromatography–mass spectrometry (GC–MS) was developed for the determination of some selected pesticides in cucumber samples. Pieces with the length of 1.0 cm of silicon tubing were precisely prepared and then coated on the end part of stainless steel wires. The prepared fibers were positioned in a home-made polytetrafluoroethylene (PTFE)-based constructed ninety-six holes block to have the possibility of simultaneous immersion of the SPME fibers into the center of individual wells. Pesticides such as diazinon, penconazol, tebuconazol, bitertanol, malathion, phosalone and chlorpyrifos-methyl were selected for their highly application in cucumber field. The performances of the SPME fibers, such as intra and inter-fibers reproducibility, were evaluated and the results showed a good similarity in extraction yields. A volume of 1 mL of the aquatic supernatant of the cucumber samples was transferred into the 96-well plate and the array of SPME fibers was applied for the extraction of the selected pesticides. The important parameters influencing the whole extraction process including, organic solvent percent, salt addition, dilution factor, stirring rate and extraction time were optimized. The inter- and intra-day RSD% were found to be less than 15.4%. Limits of detection (LOD) and limits of quantification (LOQ) were below 60 and 180 μg kg⁻¹, respectively. The coefficient of determination was satisfactory (r² > 0.99) for all the studied analytes. The developed method was successfully applied to the monitoring of several samples gathered from local markets.