Analysis of sesquiterpene emissions by plants using solid phase microextraction

Solid phase microextraction (SPME) was characterized for the sampling and analysis of sesquiterpenes (SQTs) emitted by plants. Constant mixing ratio SQT standards were produced using a capillary diffusion system. Polydimethylsiloxane SPME fibers were characterized with respect to relative absorption of SQTs, and the effects of sample linear velocity and sample relative humidity on SQT absorption. SPME was then utilized to measure SQT emissions from gray pine (Pinus sabiniana) and ponderosa pine (Pinus ponderosa). Total SQT emission rates at a photosynthetic photon flux density of 1200 μmol m⁻² s⁻¹ and 28 °C ranged 0.025–0.050 μgC m⁻² h⁻¹ (α-farnesene) and 0.450–3.325 μgC m⁻² h⁻¹ (α-farnesene, β-farnesene, and α-bergamotene) for gray pine and ponderosa pine, respectively.     

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.     

Preparation and investigation of polymethylphenylvinylsiloxane-coated solid-phase microextraction fibers using sol-gel technology

Summary Poly(methylphenylvinylsiloxane) (PMPVS) coating was first prepared using sol-gel technology and applied for solid-phase microextraction (SPME). The extraction properties of the novel coating for volatile and semi-volatile organic compounds were investigated using a homemade SPME device coupled with GC-FID. The porous surface structure of the coating provided high surface area and allowed for high extraction efficiency. Compared with commercial SPME stationary phase, the new phase showed better selectivity and sensitivity toward the various analytes, due to their inherent multifunctional properties and the features of sol-gel chemistry. Furthermore, PMPVS coating showed good thermal stability and long lifetime.     

Solventless determination of caffeine in beverages using solid-phase microextraction with fused-silica fibers.

Caffeine concentrations in beverages were determined using a simple and rapid method based on microextraction of caffeine onto the surface of a fused-silica fiber. The uncoated fiber was dipped into the beverage sample for 5 min after the addition of isotopically labeled (trimethyl 13C)caffeine. The adsorbed caffeine was then thermally desorbed in a conventional split/splitless injection port, and the concentration of caffeine was determined using gas chromatography with mass spectrometric detection. Quantitative reproducibilities were ca. 5% (relative standard deviation) and the entire scheme including sample preparation and gas chromatographic analysis was completed in ca. 15 min per sample. The potential of the microextraction technique for the analysis of flavor and fragrance compounds in non-caffeinated beverages is also demonstrated. Since no solvents or class-fractionation steps are required, the method has good potential for automation.     

介孔涂层固相微萃取-高效液相色谱法测定水样中邻苯二羧酸酯化合物

以苯基官能化MCM-41介孔复合体作为固相微萃取(SPME)的吸附涂层, 与高效液相色谱(HPLC)联用测定了不同水样中邻苯二甲酸二甲酯(DMP)、邻苯二甲酸二乙酯(DEP)、邻苯二甲酸二丁酯(DBP)和邻苯二甲酸二辛酯(DOP)的含量, 对SPME的吸附和解吸时间、温度、搅拌速度进行了优化, 线性范围分别为1.19×10-4～119 μg/L、 1.12×10-4～112 μg/L、 1.05×10-4～105 μg/L和9.80×10-5～98 μg/L, 检出限依次为0.030、 0.027、 0.029和0.022 ng/L. 使用该方法测定了多种水样中邻苯二羧酸酯类化合物.     

Comparison of different fibers for the solid-phase microextraction of phthalate esters from water

Solid-phase microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS) has been applied to determine six phthalate esters and one adipate ester in water. The SPME parameters were optimized for several commercially available fibers. A 65-microm polydimethylsiloxane-divinylbenzene (PDMS-DVB) was the fiber selected and was applied to analysis of water from the Ebro river and the industrial port of Tarragona. The studied compounds were found at concentrations ranging from 0.4 microg l(-1) for di-n-butyl phthalate ester (DnBP) to 3.2 microg l(-1) for bis(2-ethylhexyl) phthalate ester (DEHP). The linear range for real samples was from 0.1 to 10 microg l(-1) for most phthalates, and the limits of detection of the method were between 3 and 30 ng l(-1). Repeatability and reproducibility between days (n = 5) for 1 microg l(-1) samples were below 13 and 18%, respectively.     

Preparation and characterization of porous carbon material-coated solid-phase microextraction metal fibers

Two kinds of porous carbon materials, including carbon aerogels (CAs), wormhole-like mesoporous carbons (WMCs), were synthesized and used as the coatings of solid-phase microextraction (SPME) fibers. By using stainless steel wire as the supporting core, six types of fibers were prepared with sol-gel method, direct coating method and direct coating plus sol-gel method. Headspace SPME experiments indicated that the extraction efficiencies of the CA fibers are better than those of the WMC fibers, although the surface area of WMCs is much higher than that of CAs. The sol-gel-CA fiber (CA-A) exhibited excellent extraction properties for non-polar compounds (BTEX, benzene, toluene, ethylbenzene, o-xylene), while direct-coated CA fiber (CA-B) presented the best performance in extracting polar compounds (phenols). The two CA fibers showed wide linear ranges, low detection limits (0.008-0.047μgL(-1) for BTEX, 0.15-5.7μgL(-1) for phenols) and good repeatabilities (RSDs less than 4.6% for BTEX, and less than 9.5% for phenols) and satisfying reproducibilities between fibers (RSDs less than 5.2% for BTEX, and less than 9.9% for phenols). These fibers were successfully used for the analysis of water samples from the Pearl River, which demonstrated the applicability of the home-made CA fibers.     

Applications of solid-phase microextraction to chemical analysis of live biological samples

This work reviews some recent applications of solid-phase microextraction (SPME) for the chemical analysis of live biological samples. Application of SPME to microbiological analysis, organic volatile compounds emitted by vegetables and insect semiochemicals will be discussed. A short discussion on the principles and the basic parameters of SPME is also included.     

Headspace solid-phase microextraction of sulphides and disulphides using Carboxen-polydimethylsiloxane fibers in the analysis of wine aroma

Headspace solid-phase microextraction was applied to gas chromatography coupled to flame photometric detection to develop a method for analysing volatile sulphides and disulphides in wine. The Carboxen-polydimethylsiloxane-coated silica fiber was tested and different parameters such as presampling time, ionic strength, stirring, headspace volume, ethanol concentration, time and temperature of extraction were optimized to make extraction as efficient as possible. The optimized conditions enabled limits of detection to be obtained at the ng/l levels. The fiber tested has a strong affinity for the sulphur compounds studied and enables these analytes to be quantitatively determined in wines. The Carboxen-polydimethylsiloxane-coated fiber is more efficient at extracting than fibers such as those which are polydimethylsiloxane-coated and polyacrylate-coated, but its repeatability is worse. The overall process was successfully applied to identify and quantify sulphur compounds in white, red, rose and vintage wines.     

Electrochemical synthesis and characterization of solid-phase microextraction fibers using conductive polymers: application in extraction of benzaldehyde from aqueous solution

In this work, polyaniline, polypyrrole, and polyaniline/polypyrrole composite fibers were synthesized in the absence and presence of oxidized multiwalled carbon nanotubes using electrochemical cyclic voltammetry with CF₃COOH as dopant. Thermal stability of these fibers was studied by differential scanning calorimetry. Then, headspace solid-phase microextraction process coupled with gas chromatography and flame ionization detector was used for comparing extraction capability of benzaldehyde from aqueous solution. Since polyaniline fiber showed better extraction efficiency than the other fibers, its preparation conditions including acid concentration, aniline concentration, scan rate, and amount of multiwalled carbon nanotubes were studied by means of the “one-factor-at-a-time method”. The analytical performance of polyaniline fibers were investigated to determine benzaldehyde from the aqueous solution. The morphology and texture of polyaniline fibers were examined by field emission scanning electron microscopy and Fourier transform infrared spectroscopy analyses. The attained results revealed that the perfect conditions for acid concentration, aniline concentration, scan rate, and multiwalled carbon nanotubes content were 0.5 M, 0.2 M, 25 mV s^?1, and 0.02 wt%, respectively. The limit of detection for the proposed polyaniline fiber was 15 ng ml^?1.     

Preparation and application of poly(dimethylsiloxane)/beta-cyclodextrin solid-phase microextraction fibers

A novel poly(dimethylsiloxane)/beta-cyclodextrin (PDMS/beta-CD) coating was prepared for solid-phase microextraction (SPME). The PDMS/beta-CD coating proved to have a porous structure, providing high surface areas and allowing for high extraction efficiency. The coating had a high thermal stability (340 degrees C) and a long lifetime due to its chemical binding to the fiber surface. Polar phenols and amines were used to evaluate the character of the coating fiber by headspace (HS) extraction and thermal desorption, followed by GC-FID analysis. Parameters that affected the extraction process were investigated; these include extraction time and temperature, desorption time, pH, and ionic strength of the solution. For phenols, the range of linearity of the method was 4-500 microg/L and the LOD was 1.3-2.1 microg/L. For amines, the range of linearity was 1-1000 microg/L and the LOD was 1.2-2.8 microg/L. The presence of beta-CD not only increases the thermal stability of the fiber coating, but also enhances its selectivity. Compared with commercially available SPME fibers, the new phases show better selectivity and sensitivity towards polar compounds.     

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.     

Low temperature liquid chromatographic separation of oxygenated terpenes from terpene hydrocarbons

Summary The separation of β-pinene and menthone by HPLC on a silica gel column can be significantly improved with decreasing the column temperature. On a perparative scale complete separation of oxygenated terpenes from terpene hydrocarbons could be carried out under such conditions.     

The extraction performance of methacrylic acid-trimethylolpropanetrimethacrylate solid-phase microextraction fibers in aqueous solutions

The extraction performance of solid-phase microextraction fibers, based on methacrylic acid-trimethylolpropanetrimethacrylate (MAA/TRIM) copolymers, was investigated in aqueous solutions using triazines as target analytes and 2-bromobiphenyl as a reference compound. The results revealed that the combination of electrostatic forces and hydrophobicity was the primary interaction between the MAA/TRIM coating and the triazines. To improve the selectivity of the MAA/TRIM-coated fiber for the triazines, several experimental parameters including pH of the sample solution, washing step, organic modifier, and salt concentration were optimized so as to amplify electrostatic interaction and suppress the hydrophobic effect. To evaluate the practicability of the proposed method, samples with complex matrixes, including corn extract and sewage sludge, were extracted with a MAA/TRIM-coated fiber under the optimized conditions chosen. The results showed that the extraction efficiency for target analytes was not enhanced, but the matrix effect of the interfering compounds in the samples was effectively restrained and thus the selectivity was obviously improved.     

Enantiomeric monoterpene emissions from natural and damaged Scots pine in a boreal coniferous forest measured using solid-phase microextraction and gas chromatography/mass spectrometry

In order to develop a valuable method for accurate screening of biogenic emissions from undisturbed living plants or for plant-insect interactions, solid-phase microextraction (SPME) has been combined with dynamic branch enclosure cuvettes and enantioselective GC/MS. The study was conducted at Hyyti?l? forest station, Finland within a boreal coniferous forest dominated by Scots pine (Pinus sylvestris). The SPME method was optimized for monoterpenes by testing three fibre coatings: polydimethylsiloxane (PDMS), polydimethylsiloxane/divinylbenzene (PDMS/DVB) and carbowax/divinylbenzene (CW/DVB) and determining the optimum exposure time. The PDMS/DVB fibre was found to be most suitable and was used to characterize emissions of P. sylvestris enclosed in dynamic branch enclosure cuvettes by exposure for 1 min followed by desorption and separation on a beta-cyclodextrin column installed in the GC/MS oven. Dynamic cuvette measurements have been compared to static headspace SPME samples of the emission of detached needles from the same tree species and a portable dynamic air sampler (PDAS)-SPME for sampling the ambient air around the same trees. The method developed has allowed an accurate characterization of the gaseous emission of P. sylvestris and the identification of 17 isoprenoids comprising chiral and achiral monoterpenes. Two chemotypes of Scots pine can be differentiated through their emission of (+)-delta-3-carene. While SPME-dynamic cuvette, portable dynamic sampler and absorbent results agreed well, significant differences in enantiomeric ratios were observed in natural emissions and those of damaged leaves. Therefore, in enantioselective studies of plant-insect and/or plant-plant interactions, the two enantiomers of a given monoterpene should be treated as two separate substances.     

Determination of acetone in seawater using derivatization solid-phase microextraction

Acetone plays an important role in the chemistry of both the atmosphere and the ocean, due to its potential effect on the tropospheric HO_x (= HO + HO₂) budget, as well as its environmental and health effects. We discuss the development of a mobile, sensitive, selective, economical and facile method for the determination of acetone in seawater. The method consists of derivatizing acetone to its pentafluorobenzyl oxime using 1,2,3,4,5-pentafluorobenzylhydroxylamine (PFBHA), followed by solid-phase microextraction (SPME) and analysis by gas chromatography/mass spectrometry (GC/MS). A detection limit of 3.0 nM was achieved. The buffering capacity of seawater imposes challenges in using the method’s optimum pH (3.7) on seawater samples, requiring calibration standards to be made in buffered salt water and the acidification of seawater samples and standards prior to extraction. We employed the technique for analysis of selected surface seawater samples taken on the Nordic seas during the ARK-XX/1 cruise (R.V. Polarstern). An upper limit of 5.5–9.6 nM was observed for acetone in these waters, the first acetone measurements reported for far North Atlantic and Arctic waters. Simplified schematic of transformations of organic compounds at the atmosphere–ocean interface     

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.     

Surface characterization of commercial fibers for solid-phase microextraction and related problems in their application

The surfaces of commercially available polydimethylsiloxane (PDMS) and Carboxen-PDMS fibers for solid-phase microextraction (SPME) were investigated by optical and electron microscopy. Damage to the coating as well as contamination of new fibers and a highly variable number of pores in Carboxen-PDMS coatings were observed. Together with the contamination of the fibers during their use with metallic particles originating from the SPME fiber holder they are possible explanations for the problems encountered in the analysis of organolead, organotin and organosulfur compounds, such as artifact formation and low repeatability.