Multiple headspace solid-phase microextraction of ethyl carbamate from different alcoholic beverages employing drying agent based matrix modification

Multiple headspace solid-phase microextraction (MHS-SPME) combined with gas chromatography-nitrogen phosphorus detector is proposed to determine the toxic contaminant ethyl carbamate (EC) in various alcoholic beverages after matrix modification. The remarkable feature of this method is that matrix effect, which commonly appears in SPME-based analysis, is avoided by determining the total amount of the analyte in the sample. To increase the sensitivity of the method, a novel polyethylene glycol/hydroxy-terminated silicone oil fiber was developed by sol-gel technique and applied for the analysis. Owing to the high polarity and hydrophilia of EC, an important problem still remains because the adsorption by sample matrix causes low transport of EC to the headspace and thus invalidates MHS-SPME for quantification. Mixing with anhydrous sodium sulphate, the sensitivity of the method can be improved. A Taguchi's L(16) (4(5)) orthogonal array design was employed to evaluate potentially significant factors and screen the optimum conditions for MHS-SPME of EC. Under the optimized conditions, limit of detection of 0.034 mg L(-1) was obtained. Relative standard deviation of replicate samples (n=6) was 2.19%. The proposed method was linear in the range of 0.04-100 mg L(-1), and the coefficient of determination was 0.9997. The method was used to determine EC in various alcoholic beverages. The concentrations obtained were compared with those obtained by standard addition method and no statistically significant differences were observed.     

基于基质修饰的多次顶空固相微萃取-气相色谱法检测酒精饮料中的氨基甲酸乙酯

氨基甲酸乙酯(EC)是发酵食品在发酵或贮存过程中产生的致癌副产物。建立了多次顶空固相微萃取-气相色谱法(MHS-SPME-GC)检测多种酒精饮料中EC的方法。采用自制的溶胶-凝胶聚乙二醇/羟基硅油复合SPME萃取头提高了方法的灵敏度,加入无水硫酸钠对基质进行修饰大大提高了EC的萃取效率。在优化条件下,方法的线性范围为0.04～100 mg/L,线性相关系数为0.9997,检出限为34 μg/L;方法重现性好,6次重复实验所得相对标准偏差为2.19%;准确度高,加标回收率在90.9%～103.6%之间。将建立的方法用于多种实际酒样中EC的检测,其结果与标准加入法得到的结果在统计学上无显著差异。本研究表明,MHS-SPME能够克服通常存在于SPME分析中的基质干扰效应,尤其适合于大量不同基质的样品分析。     

Multiple headspace solid-phase microextraction using a new fiber for avoiding matrix interferences in the quantitative determination of ethyl carbamate in pickles

Multiple headspace solid-phase microextraction (HS-SPME) using a novel fiber coated with anilino-methyl triethoxy silicane-methacrylic acid/terminated silicone oil has been introduced as a useful pretreatment technique coupled to gas chromatography-flame ionization detector for the detection of ethyl carbamate in pickles. Anilino-methyl triethoxy silicane and methacrylic acid are put into use simultaneously with the aim to increase the hydrogen interaction strength between ethyl carbamate and the coating. In addition, the new fiber exhibits high thermal stability, good reproducibility, and long lifetime. Extraction temperature, extraction time, amount of desiccant, and amount of sample were well optimized to guarantee the suitability of multiple HS-SPME. Significant matrix interference was observed among various types of pickles and the multiple HS-SPME procedure was proved to be effective in avoiding the matrix effect by a complete recovery of the analyte. The method showed satisfactory linearity (0.1-100 mg kg(-1)), precision (4.25%, n = 5), and detection limit (0.038 mg kg(-1)). The accuracy of the method was evaluated by comparison with standard addition method and the results were statistically equivalent. The study indicates that the multiple HS-SPME procedure is simple, convenient, accurate, and low-cost, and most of all, can be used for quantitative analysis in complex matrix without matrix effect.     

Optimization of headspace solid-phase microextraction for analysis of ethyl carbamate in alcoholic beverages using a face-centered cube central composite design

The headspace solid-phase microextraction (HS-SPME) of ethyl carbamate from alcoholic beverages was optimized for the first time using a face-centered cube central composite design (CCD). The factors expected to influence the extraction process are discussed. Firstly, some of factors are fixed based on the opinion of expert and previous experiments, which reduce the number of factors and then avoid very complex response models and large variability. Secondly, for three remaining inexplicit factors, sample temperature, pH and %NaCl, a face-centered cube central composite design was performed and a response surface equation was derived. The statistical parameters of the derived model were r = 0.974 and F = 20.183. The optimum conditions were obtained using a grid method. Next, the method was analytically evaluated using the optimum conditions. The detection limit, relative standard deviation, linear range and recovery were 3 μg L⁻¹, 4.3-8.6%, 10-160 μg L⁻¹, and 92.8-97.5%, respectively. Finally, the method was applied to a variety of alcoholic beverages.     

Microwave-assisted headspace solid-phase microextraction for the rapid determination of organophosphate esters in aqueous samples by gas chromatography-mass spectrometry

The rapid and solvent-free determination of organophosphate esters (OPEs) in aqueous samples via one-step microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS) analysis is described. Tri-n-butyl phosphate (TnBP) and tris-(2-ethylhexyl) phosphate (TEHP) were selected as model compounds for the method of development and validation. The effects of various extraction parameters for the quantitative extraction of these analytes by MA-HS-SPME were systematically investigated and optimized. The analytes, in a 20 mL water sample (in a 40 mL sample bottle containing 2 g of NaCl, pH 3.0), were efficiently extracted by a polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber placed in the headspace when the system was microwave irradiated at 140 W for 5 min. The limits of quantification (LOQs) for TnBP and TEHP were 0.5 and 4 ng/L, respectively. Using the standard addition method, MA-HS-SPME coupled with GC-MS was utilized to determine selected OPEs in surface water and wastewater treatment plants (WWTP) influent/effluent samples. Preliminary results show that TnBP was commonly detected OPEs in these aqueous samples, the correlation coefficients (r²) of the standard addition curves were greater than 0.9822, indicating that the developed method appears to be a good alternative technique for analyzing OPEs in aqueous samples.     

A critical review of vacuum-assisted headspace solid-phase microextraction for environmental analysis

Vacuum-assisted headspace solid-phase microextraction (Vac-HSSPME) is an emerging analytical technique, which further advances HSSPME by providing lower detection limits of analytes with poor volatility at shorter extraction times. This review discusses the theoretical aspects and possibilities of the Vac-HSSPME technique for analysis of environmental samples. Optimization of key parameters, currently available equipment and methods for quantification of organic pollutants in water and soil are considered. Key problems and limitations of the technique are discussed along with possible approaches for its future development. The technique has a well-developed theory, which could be used for modeling of the extraction process, faster method development, and optimization. Wider application of the technique is limited by the lack of automation, which, however, seems possible to develop and implement by manufacturers of commercial multi-purpose autosamplers for gas chromatography instruments. It has been shown that Vac-HSSPME allows decreasing cross-contamination of samples from the laboratory air, which is advantageous for identification and quantification of trace environmental pollutants. Simple equipment for the technique makes it possible to apply for on-site sample preparation and analysis of environmental samples.     

Determination of odour-causing volatile organic compounds in cork stoppers by multiple headspace solid-phase microextraction

Multiple headspace solid-phase microextraction (MHS-SPME) coupled with gas chromatography-mass spectrometry has been applied in order to determine 2,4,6-trichloroanisole (2,4,6-TCA), guaiacol, 1-octen-3-ol and 1-octen-3-one in three samples of cork stoppers. These compounds are responsible for cork taint in wine and can modify the organoleptic properties of bottled wine. Variables such as temperature, addition of water, extraction time, and amount of cork were studied. The extractions were performed with a 50/30 microm divinylbenzene-carboxen-polydimethylsiloxane (DVB-CAR-PDMS) fibre for 45 min at 100 degrees C using 20 mg of cork. For calibration, 50 microL of VOC aqueous solutions were used and the extraction were carried out for 45 min at 75 degrees C. The limits of detection of the method expressed as ng of VOC per g of cork were 0.3 for 2,4,6-TCA, 7.5 for guaiacol, 1.7 for 1-octen-3-one and 1.9 for 1-octen-3-ol. Relative standard deviation of replicate samples was less than 10%. Significant losses of analytes were observed when the samples were ground at room temperature. Finally, a recovery study was performed and the MHS-SPME results were validated using Soxhlet extraction results.     

Design and testing of a new sampler for simplified vacuum-assisted headspace solid-phase microextraction

The design and testing of a new and low-cost experimental setup used for vacuum-assisted headspace solid-phase microextraction (Vac-HSSPME) is reported here. The device consists of a specially designed O-ring seal screw cap offering gas-tight seal to commercially available headspace vials. The new polytetrafluoroethylene (PTFE) cap was molded by a local manufacturer and had a hole that could tightly accommodate a septum. All operations were performed through the septum: air evacuation of the sampler, sample introduction and HSSPME sampling. The analytical performance of the new sampler was evaluated using 22 mL headspace vials with 9 mL water samples spiked with polychlorinated biphenyls (PCBs). Several experimental parameters were controlled and the optimized conditions were: 1000 rpm agitation speed; 30 min extraction time; 40 °C sampling temperature; polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber. The lack of accurate Henry's law constant (K_H) values and information regarding how they change with temperature was a major limitation in predicting the phase location of evaporation resistance during Vac-HSSPME. Nevertheless, the combined effects of system conditions indicated the increasing importance of gas phase resistance with increasing degree of PCBs chlorination. Stirring enhancements were not recorded for the higher chlorinated PCBs suggesting that the hyperhydrophobic gas/water interface was the preferred location for these compounds. Analytically, the developed method was found to yield linear calibration curves with limits of detection in the sub ng L⁻¹ level and relative standard deviations ranging between 5.8 and 14%. To compensate for the low recoveries of the higher chlorinated PCB congeners in spiked river water the standard addition methodology was applied. Overall, the compact design of the new and reusable sample container allows efficient HSSPME sampling of organic analytes in water within short extraction times and at low sampling temperatures compared to other published HSSPME methods.     

Multiple headspace single-drop microextraction coupled with gas chromatography for direct determination of residual solvents in solid drug product

This paper proposed a multiple headspace single-drop microextraction (MHS-SDME) method coupled to gas chromatography with flame-ionization detection (GC-FID) for direct determination of residual solvents in solid drug product. The MHS-SDME technique is based on extrapolation to an exhaustive extraction of consecutive extractions from the same sample which eliminates the matrix effect on the quantitative analysis of solid samples. The total peak area of analyte is calculated with a beta constant which can be obtained from the slope of the linear regression that related to the peak area of each extraction and the number of extraction times. In this work, a model drug powder was chosen and the amounts of residues of two solvents, methanol and ethanol, were investigated. The factors influencing the extraction process including extraction solvent, microdrop volume, extraction time, sample amount, thermostatting temperature and incubation time were studied. 10 mg of drug powder was incubated for 3 h at 140 °C prior to the first extraction and thermostatted for 15 min at 140 °C between each extraction. Extraction was carried out with 2 μL of dimethyl sulfoxide (DMSO) as the microdrop for 5 min. The features of the method were established using standard solutions. Validation of the proposed method showed good agreement with the traditional dissolution method for analysis of residual solvents in drug product. The results indicated that MHS-SDME has a great potential for the quantitative determination of residual solvents directly from the solid drug products due to its low cost, ease of operation, sensitivity, reliability and environmental protection.     

Polymeric ionic liquid based fused silica fiber by chemical binding for headspace solid-phase microextraction of organophosphate esters in water samples

In this paper, a convenient method was developed for preparing polymeric ionic liquid based fiber coating onto a fused silica fiber by using covalent bonding for headspace solid-phase microextraction of five organophosphorus esters from real water samples. 1-vinyl-3-(3-triethoxysilylpropyl)-4,5-dihydroimidazolium chloride was anchored on the silica layer by covalent bonding and then the polymeric ionic liquid layer was formed via free radical copolymerization with vinyl-substituted imidazolium in the presence of azobisisobutyronitrile as initiator. The limits of detection ranged from 0.68 to 100 ng L^?1. The intra- and inter-day precisions, evaluated by relative standard deviation, were in the range of 4–8% and 1–10%, respectively. The recoveries of spiked real water samples were in the range of 73–110% and 77–118%, respectively, at two different concentration levels.     

顶空固相微萃取-气相色谱-质谱联用测定香水中5种合成麝香

建立了香水中5种合成麝香的顶空固相微萃取-气相色谱-质谱联用分析方法。实验选用65 μm的聚二甲基硅氧烷-二乙烯基苯(PDMS-DVB)萃取纤维,在磁力搅拌600 r/min条件下,考察了萃取温度、平衡时间、萃取时间、解吸时间、进样口温度和盐效应6个方面对实验结果的影响。优化后的条件为: 10 mL顶空瓶中加入适量用水稀释过的样品,于60 ℃平衡3 min后,顶空萃取20 min,随即插入气相色谱进样口,于250 ℃解吸3 min进行定性、定量分析。5种合成麝香在0.05～1.00 μg/g范围内线性关系良好,检出限(LOD)为0.6～2.1 ng/g。空白样品在3个浓度加标水平下(0.05, 0.50, 1.00 μg/g)的回收率为82.0%～103.3%,相对标准偏差(RSD)为1.8%～9.4%。本方法简便、准确、快速、灵敏,适用于香水中合成麝香的分析检验工作。     

Determination of synthetic polycyclic musks in water by microwave-assisted headspace solid-phase microextraction and gas chromatography-mass spectrometry

This paper describes a rapid and solvent-free method, microwave-assisted headspace solid-phase microextraction (MA-HS-SPME), for the extraction of six commonly used synthetic polycyclic musks: galaxolide (HHCB), tonalide (AHTN), celestolide (ADBI), traseolide (ATII), cashmeran (DPMI) and phantolide (AHMI) from water samples prior to their determination using gas chromatography-mass spectrometry (GC-MS). The effects of various extraction parameters for the quantitative extraction of these analytes by MA-HS-SPME were systematically investigated and optimized. The analytes in a 20-mL water sample (in a 40-mL sample-vial containing 4 g of NaCl) were efficiently extracted by a polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber placed in the headspace when the system was microwave irradiated at 180 W for less than 4 min. The limits of detection (LODs) ranged from 0.05 to 0.1 ng/L, and the limits of quantification (LOQs) were less than 0.2 ng/L. A preliminary analysis of wastewater samples revealed that HHCB and AHTN were the two most commonly detected synthetic polycyclic musks; using a standard addition method, their concentration were determined to range from 1.2 to 37.3 ng/L with relative standard deviation (RSD) ranging from 2 to 6%. The results obtained using this approach are better than those from the conventional oil-bath HS-SPME.     

Molecularly imprinted matrix solid-phase dispersion combined with dispersive liquid-liquid microextraction for the determination of four Sudan dyes in egg yolk

A new kind of aniline-naphthol molecularly imprinted microsphere (MIM) synthesized by aqueous suspension polymerization was applied as a selective sorbent of miniaturized matrix solid-phase dispersion combining with dispersive liquid-liquid microextraction (MSPD-DLLME) for the simultaneous determination of four Sudans in egg yolk samples. The solid sample was directly blended with MIM in MSPD procedure and the eluent of MSPD was used as the dispersive solvent of the followed DLLME for further purification and enrichment of the analytes before HPLC analysis. Good linearity for all the Sudan dyes was ranged from 0.02 μg g(-1) to 2.0 μg g(-1) (r(2)≥0.9990) and their recoveries at three spiked levels were ranged from 87.2% to 103.5% with RSD less than 6.1% (n=3). The presented MIM-MSPD-DLLME method combined the advantages of MIM, MSPD and DLLME, and could be applied for the determination of Sudans in complicated food samples.     

Headspace solid-phase microextraction of phthalic acid esters from vegetable oil employing solvent based matrix modification

A new solvent-free analytical procedure based on headspace solid-phase microextraction (SPME) coupled to gas chromatography employing an electron capture detector (GC/ECD) or alternatively a mass spectrometric detector (GC/MSD) has been developed for the determination of phthalic acid esters (dimethyl-[DMP], diethyl-[DEP], di-n-butyl-[DnBP], butylbenzyl-[BBP], di-2-ethylhexyl-[DEHP] and di-n-octyl [DnOP] phthalate) in vegetable oils. Four different fiber coatings were evaluated, among them polydimethylsiloxane with a thickness of 100 μm appeared to be the best choice for allowing extraction of the whole group of analytes. Various solvents were tested as sample matrix modification agents with the aim to facilitate the transfer of esters with low vapour pressure (DEHP and DnOP) from oil matrix into the headspace. The addition of methanol resulted in optimal set-up applicable for all phthalate esters. Temperature control and the way of sample stirring were recognized as critical points of the whole procedure. Primarily, because shaking rather than stirring of the sample is carried out using a CombiPal multipurpose sampler, the automation of the SPME method employing this instrument was found to be not fully suitable for efficient stripping of phthalates from the oil matrix into the sample headspace. Nevertheless, the optimized manual SPME method, encompassing GC/ECD or GC/MSD for the separation and detection of target analytes, offers a unique solution and showed acceptable performance characteristics: linear response in the range of 0.5-2 mg kg⁻¹ and repeatability expressed as R.S.D. between 14 and 23% at the spiking level of 2 mg kg⁻¹.     

Multiple headspace solid-phase microextraction for eliminating matrix effect in the simultaneous determination of haloanisoles and volatile phenols in wines

This paper proposes a multiple headspace solid-phase microextraction (MHS-SPME) method coupled to gas chromatography-tandem mass spectrometry detection (GC/MS/MS) for the simultaneous determination of 2,4,6-trichloroanisole, 2,3,4,6-tetrachloroanisole, pentachloroanisole, 2,4,6-tribromoanisole, 4-ethylphenol, 4-ethylguaiacol, 4-vinylphenol and 4-vinylguaiacol in wines. These compounds are involved in the presence of "cork taint" and Brett character in wines. The MHS-SPME method is a modification of SPME developed for quantitative analysis that avoids possible matrix effects based on an exhaustive analyte extraction from the sample. After demonstrating the existence of matrix effect in the analysis of the target compounds by HS-SPME with a divinylbenzene/Carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fibre, the MHS-SPME method was developed and validated. The proposed method showed satisfactory linearity, precision and detection limits, all below the odour detection thresholds of the compounds in wine matrices. Good recoveries were observed for all compounds, always above 90%, and the repeatability obtained was considered acceptable, ranging between 2 and 11%. After checking the applicability of the method by comparing the results recorded with those obtained with the standard addition method, the method was applied successfully to the analysis of wine samples. To our knowledge, this is the first time that MHS-SPME combined with GC/MS/MS has been applied to simultaneously determine haloanisoles and volatile phenols in wine.     

Applicability of headspace solid-phase microextraction to the determination of multi-class pesticides in waters

The applicability of headspace solid-phase microextraction (HS-SPME) to pesticide determination in water samples was demonstrated by evaluating the effects of temperature on the extraction of the pesticides. The evaluations were performed using an automated system with a heating module. The 174 pesticides that are detectable with gas chromatograph were selected objectively and impartially based on their physical properties: vapor pressure and partition coefficient between octanol and water. Of the 174 pesticides, 158 (90% of tested) were extracted with a polyacrylate-coated fiber between 30 and 100 degrees C and were determined with gas chromatograph-mass spectrometry. The extraction-temperature profiles of the 158 extracted pesticides were obtained to evaluate the effects of temperature on the extraction of pesticides. The pesticides were classified into four groups according to the shape of their extraction-temperature profiles. The line of demarcation between extractable pesticides and non-extractable pesticides could be drawn in the physical property diagram (a double logarithmic plot of their vapor pressure and partition coefficient between octanol and water). The plot also revealed relationships between classified extraction features and their physical properties. The new method for multi residue screening in which the analytes were categorized into sub-groups based on extraction temperature was developed. In order to evaluate the quantitivity of the developed method, the 45 pesticides were chosen among the pesticides that are typically monitored in waters. Linear response data for 40 of the 45 was obtained in the concentration range below 5 microg/l with correlation coefficients ranging between 0.979 and 0.999. The other five pesticides had poor responses. Relative standard deviations at the concentration of the lowest standard solution for each calibration curve of the pesticides ranged from 3.6 to 18%. The value of 0.01 microg/l in the limits of detection for 17 pesticides was achieved only under the approximate conditions for screening, not under the individually optimized conditions for each pesticide. Recoveries of tested pesticides in actual matrices were essentially in agreement with those obtained by solid-phase extraction.     

Elimination of matrix effects for headspace solid-phase microextraction of important volatile compounds in red wine using a novel coating

In this paper, hydroxy-terminated silicone oil-butyl methacrylate-divinylbenzene (OH-TSO-BMA-DVB) copolymer was first synthesized and used as stationary phase with the aid of γ-methacryloxypropyltrimethoxylsilane (KH-570) as bridge in solid-phase microextraction (SPME) using sol–gel method and cross-linking technique. It has high extraction efficiency for both polar alcohols and fatty acids and nonpolar esters in comparison with commercial PDMS, PDMS-DVB and PA fibers. A simple and sensitive headspace SPME-gas chromatography (HS-SPME-GC) method using the novel fiber was presented for the simultaneous analysis of both polar alcohols and fatty acids and nonpolar esters in wine. To check the matrix effects, various model wine matrices, including distilled water; 11.5% ethanol/water (v/v) solution; a concentrated synthetic wine; a ‘volatile-free’ wine and a real wine were investigated in detail. Matrix effects were compensated for by using internal standard method and selecting the ‘volatile-free’ wine as working standard. The method presented in this study showed satisfactory linearity, precision, detection limits and accuracy. The recoveries obtained ranged from 85.87 to 104.2%, and the relative standard deviation values were below 9%. The results obtained indicated that the present method is a validated and accurate procedure for the simultaneous determination of both polar and nonpolar aroma compounds in wine.     

Electrically assisted solid-phase microextraction combined with liquid chromatography-mass spectrometry for determination of parathion in water

A novel method for electrically assisted microextraction coupled to liquid chromatography-mass spectrometry was evaluated for determination of trace levels of parathion in water. A pencil lead electrode was used in a di-electrode system to extract parathion onto the electrode surface with a reductive potential applied. The optimum extraction conditions were found to be a potential of −600 mV for 60 s in pH 2 phosphate buffer solution. The parathion was desorbed statically for 1 min and dynamically for 3 min in the commercial SPME-HPLC desorption chamber, then analyzed with LC-APCI-MS/MS. The detection limit (LOD) for parathion in water was found to be 0.3 ng/mL. The proposed technique was demonstrated to be fast, sensitive and not require a solvent sample pretreatment.     

Potentialities of two solventless extraction approaches—Stir bar sorptive extraction and headspace solid-phase microextraction for determination of higher alcohol acetates, isoamyl esters and ethyl esters in wines

A stir bar sorptive extraction with liquid desorption followed by large volume injection coupled to gas chromatography-quadrupole mass spectrometry (SBSE-LD/LVI-GC-qMS) was evaluated for the simultaneous determination of higher alcohol acetates (HAA), isoamyl esters (IsoE) and ethyl esters (EE) of fatty acids. The method performance was assessed and compared with other solventless technique, the solid-phase microextraction (SPME) in headspace mode (HS). For both techniques, influential experimental parameters were optimised to provide sensitive and robust methods. The SBSE-LD/LVI methodology was previously optimised in terms of extraction time, influence of ethanol in the matrix, liquid desorption (LD) conditions and instrumental settings. Higher extraction efficiency was obtained using 60 min of extraction time, 10% ethanol content, n-pentane as desorption solvent, 15 min for the back-extraction period, 10 mL min⁻¹ for the solvent vent flow rate and 10 °C for the inlet temperature. For HS-SPME, the fibre coated with 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) afforded highest extraction efficiency, providing the best sensitivity for the target volatiles, particularly when the samples were extracted at 25 °C for 60 min under continuous stirring in the presence of sodium chloride (10% (w/v)). Both methodologies showed good linearity over the concentration range tested, with correlation coefficients higher than 0.984 for HS-SPME and 0.982 for SBES-LD approach, for all analytes. A good reproducibility was attained and low detection limits were achieved using both SBSE-LD (0.03-28.96 μg L⁻¹) and HS-SPME (0.02-20.29 μg L⁻¹) methodologies. The quantification limits for SBSE-LD approach ranging from 0.11 to 96.56 μg L⁻and from 0.06 to 67.63 μg L⁻¹ for HS-SPME. Using the HS-SPME approach an average recovery of about 70% was obtained whilst by using SBSE-LD obtained average recovery were close to 80%. The analytical and procedural advantages and disadvantages of these two methods have been compared.Both analytical methods were used to determine the HAA, IsoE and EE fatty acids content in “Terras Madeirenses” table wines. A total of 16 esters were identified and quantified from the wine extracts by HS-SPME whereas by SBSE-LD technique were found 25 esters which include 2 higher alcohol acetates, 4 isoamyl esters and 19 ethyl esters of fatty acids. Generally SBSE-LD provided higher sensitivity with decreased analysis time.     

Multiple headspace single-drop micro-extraction for quantitative determination of lactide in thermally-oxidized polylactide

Single-drop micro-extraction (SDME), an emerging micro-extraction technique, was combined with multiple headspace (MHS) extraction to allow quantitative determination of lactide in thermally-oxidized polylactide. Different solvents, drop sizes and extraction times were tested to obtain best extraction efficiency and the method was further developed to obtain a linear regression plot for the multiple extractions. The combination of SDME and MHS extraction offered several advantages over traditional liquid-solid and headspace extraction techniques. No concentration step was needed and loss of volatiles was prevented as the ageing and extraction were performed in a closed system. Matrix effects, that disturb the quantitation of analytes in solid samples, were removed by the multiple headspace extraction.