Multivariate optimization of hydrodistillation-headspace solvent microextraction of thymol and carvacrol from Thymus transcaspicus

In this paper multivariate response surface methodology (RSM) has been used for the optimization of hydrodistillation-headspace solvent microextraction (HD-HSME) of thymol and carvacrol in Thymus transcaspicus. Quantitative determination of compounds of interest was performed simultaneously using gas chromatography coupled with flame ionization detector (GC-FID). Parameters affecting the extraction efficiency were assessed and the optimized values were 5 min, 2 μL and 3 min for the extraction time, micro-drop volume and cooling time after extraction, respectively. The amounts of analyte extracted increased with plant weight. The calibration curves were linear in the ranges of 6.25-81.25 and 1.25-87.50 mg L⁻¹ for thymol and carvacrol, respectively. Limit of detection (LOD) for thymol and carvacrol was 1.87 and 0.23 mg L⁻¹, respectively. Within-day and between-day precisions for both analytes were calculated in three different concentrations and recoveries obtained were in the range of 89-101% and 95-116% for thymol and carvacrol, respectively.     

A new polyethylene glycol fiber prepared by coating porous zinc electrodeposited onto silver for solid-phase microextraction of styrene

A new polyethylene glycol fiber was developed for solid-phase microextraction (SPME) of styrene by electrodepositing porous Zn film on Ag wire substrate followed by coating with polyethylene glycol sol-gel (Ag/Zn/PEG sol-gel fiber). The scanning electron micrographs of fibers surface revealed a highly porous structure. The extraction property of the developed fiber-to-styrene residue from polystyrene packaged food was investigated by headspace solid-phase microextraction (HS-SPME) and analyzed with a gas chromatograph coupled with flame ionization detection (GC-FID). The new Ag/Zn/PEG sol-gel fiber is simple to prepare, low cost, robust, has high thermal stability and long lifetime, up to 359 extractions. Repeatability of one fiber (n = 6) was in the range of 4.7-7.5% and fiber-to-fiber reproducibility (n = 4) for five concentration values were in the range 3.4-10%. This Ag/Zn/PEG sol-gel fiber was compared to two commercial SPME fibers, 75 μm carboxen/polydimethylsiloxane (CAR/PDMS) and 100 μm polydimethylsiloxane (PDMS). Under their optimum conditions, Ag/Zn/PEG sol-gel fiber showed the highest sensitivity and the lowest detection limit at 0.28 ± 0.01 ng mL⁻¹.     

Preparation and applications of polypyrrole films in solid-phase microextraction

Polypyrrole (PPY) and poly-N-phenylpyrrole (PPPY) films were prepared and applied for solid-phase microextraction (SPME). The extraction properties of the new films to volatile organic compounds were examined using an SPME device coupled with GC-flame ionization detection. A PPY-coated capillary was applied for in-tube SPME to evaluate its extraction efficiency towards less volatile compounds and ionic species. The porous surface structures of the films, revealed by scanning electron microscopy, provided high surface areas and allowed for high extraction efficiency. Compared with commercial SPME stationary phases, the new phases showed better selectivity and sensitivity toward polar, aromatic, basic and anionic compounds, due to their inherent multifunctional properties. In addition, PPY and PPPY films showed different selectivity to various groups of compounds studied, indicating that the selectivity of the films could be modified by introducing a new functional group (phenyl in PPPY) into the polymer. For in-tube SPME, the PPY-coated capillary showed superior extraction efficiency to commercial capillaries for a variety of compounds, demonstrating its potential applications for a wide range of analytes when coupled with HPLC. The sensitivity and selectivity of the films for SPME could be tuned by changing the film thickness. These results are in line with both the theoretical expectations and the results obtained by other methods, which indicate not only that PPY films can be used as new stationary phases for SPME. but also that SPME method may provide an alternative tool for studying materials like polypyrrole.     

Reliability of fibres in solid-phase microextraction for routine analysis of the headspace of aromatic and medicinal plants

This article evaluates the HS-SPME recovery repeatability, intermediate precision and their performance over time when applied to HS-SPME sampling for quality control of medicinal and aromatic plants. Experiments were carried out on two sets of fibres coated with two different coatings and belonging to different lots (i.e 100 microm polydimethylsyloxane (PDMS) and Carboxen/divinylbenzene/PDMS 50/30 microm, l: 1 cm (CAR/DVB/PDMS)) and on chamomile (Matricaria chamomilla L.), sage (Salvia lavandulifolia Vahl.) and a standard solution containing 3-hexanol, isoamyl acetate, 1,8-cineole and menthol in diisobutyl phthalate. The performance of each set of fibres was evaluated by determining a group of complementary statistical parameters including: (i) repeatability of the absolute areas of each marker from each matrix with each fibre; (ii) intra-fibre repeatability of the total absolute areas of the markers of each matrix obtained with each fibre of each set; (iii) inter-fibre intermediate precision of the total absolute areas of the markers of each matrix obtained with all fibres of each set; and (iv) analysis of variance by one-way ANOVA with Fisher and Tukey tests. The influence of the number of analyses on fibre effectiveness (fibre life-time) was studied by linear regression analysis (LRA). The results proved that HS-SPME can successfully be used for routine control analysis of aromatic ad medicinal plants since both types of fibres showed good repeatability and intermediate precision of analytes recovery and consistency over time. Unlike data previously reported by other authors, CAR/DVB/PDMS coated fibres gave better results than those coated with PDMS. The fibre-life seemed mainly to be influenced by the number and conditions of samplings and nature of the matrix investigated.     

Polypyrrole/hexagonally ordered silica nanocomposite as a novel fiber coating for solid-phase microextraction

A highly porous fiber coated polypyrrole/hexagonally ordered silica (PPy/SBA15) materials were prepared for solid-phase microextraction (SPME). The PPy/SBA15 nanocomposite was synthesized by an in situ polymerization technique. The resulting material was characterized by the scanning electron microscopy, thermogravimetric analysis and differential thermal analysis. The prepared nanomaterial was immobilized onto a stainless steel wire for fabrication of the SPME fiber. The fiber was evaluated for the extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample solutions in combination with gas chromatography-mass spectrometry (GC-MS). A one at-the-time optimization strategy was applied for optimizing the important extraction parameters such as extraction temperature, extraction time, ionic strength, stirring rate, desorption time and desorption temperature. In optimum conditions (extraction temperature 70°C, extraction time 20 min, ionic strength 20% (WV(-1)), stirring rate 500 rpm, desorption temperature 270°C, desorption time 5 min) the repeatability for one fiber (n=3), expressed as relative standard deviation (R.S.D. %), was between 5.0% and 9.3% for the tested compounds. The quantitation limit for the studied compounds were between 13.3 and 66.6 pg mL(-1). The life span and stability of the PPy/SBA15 fiber are good, and it can be used more than 50 times at 260°C without any significant change in sorption properties. The developed method offers the advantage of being simple to use, with shorter analysis times, lower cost of equipment, thermal stability of fiber and high relative recovery in comparison to conventional methods of analysis.     

Evaluation of carbon nanocones/disks as sorbent material for solid-phase extraction

The potential of carbon nanocones/disks as sorbent material in solid-phase extraction (SPE) procedures has been evaluated. For this aim, a model analytical problem, the determination of chlorophenols in water samples, was selected. An accurately weighed amount of 20 mg of purified carbon nanocones/disks was packed in 3 mL commercial SPE cartridges. Once conditioned, up to 8 mL of water samples can be preconcentrated without analyte losses. The chlorophenols were eluted by using 200 μL of hexane. Aliquots of 2 μL of the organic extract were injected in the gas chromatograph–mass spectrometer for separation and quantification. The purification of the commercial nanocones/disks to reduce the presence of amorphous carbon has been successfully achieved by heating the carbon nanocones/disks at 450 °C for 20 min. Detection limits of chlorophenols were in the range 0.3–8 ng mL⁻¹ by using 2 mL of sample. Moreover, excellent average recovery values (98.8–100.9%) have been obtained after the analysis of water samples from different nature. Finally, the performance of the carbon nanocones/disks as sorbent material has been compared with that of multiwalled carbon nanotubes, providing the former better results under the experimental conditions assayed.     

以铅笔芯为吸附基质的顶空-固相微萃取法测定酒中的甲醇

固相微萃取(SPME)是以固相萃取(SPE)为基础发展起来的新方法。在多次实验后发现,主要成分为碳的铅笔芯在经过一定的物理,化学处理后对被分析物能产生定量吸附,因此可用作SPME的萃取基质。对该吸附基质,选择了其萃取、解吸的最佳条件如:萃取时间,水浴温度,搅拌速度,解吸时间及温度等。在选定的最佳条件下,以铅笔芯作吸附基质对甲醇进行顶空 固相微萃取测定,其线性范围是5×10-6～2×10-7g/mL,线性相关系数r=0.9975。富集20min后,检出限为0.5×10-7g/mL。使用该法测定了5种酒中的甲醇含量,回收率在95%～110%之间。在对同一样品的3次平行测定中,其相对标准偏差在6%以下。     

Nanostructured polypyrrole for automated and electrochemically controlled in-tube solid-phase microextraction of cationic nitrogen compounds

The authors describe an efficient method for microextraction and preconcentration of trace quantities of cationic nitrogen compounds, specifically of anilines. It relies on a combination of electrochemically controlled solid-phase microextraction and on-line in-tube solid-phase microextraction (SPME) using polypyrrole-coated capillaries. Nanostructured polypyrrole was electrically deposited on the inner surface of a stainless steel tube and used as the extraction phase. It also acts as a polypyrrole electrode that was used as a cation exchanger, and a platinum electrode that was used as the anode. The solution to be extracted is passed over the inner surface of the polypyrrole electrode, upon which cations are extracted by applying a negative potential under flow conditions. This method represents an ideal technique for SPME of protonated anilines because it is fast, easily automated, solvent-free, and inexpensive. Under optimal conditions, the limits of detection are in the 0.10–0.30 μg L‾¹ range. The method works in the 0.10 to 300 μg L‾¹ concentration range. The inter- and intra-assay precisions (RSD%; for n = 3) range from 5.1 to 7.5 % and from 4.7 to 6.0 % at the concentration levels of 2, 10 and 20 μg L‾¹, respectively. The EC-in-tube SPME method was successfully applied to the analysis of methyl-, 4-chloro-, 3-chloro and 3,4-dichloroanilines in (spiked) water samples.

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Electropolymerized multiwalled carbon nanotubes/polypyrrole fiber for solid-phase microextraction and its applications in the determination of pyrethroids

A novel solid-phase microextraction (SPME) fiber coated with multiwalled carbon nanotubes/polypyrrole (MWCNTs/Ppy) was prepared with an electrochemical method and used for the extraction of pyrethroids in natural water samples. The results showed that the MWCNTs/Ppy coated fiber had high organic stability, and remarkable acid and alkali resistance. In addition, the MWCNTs/Ppy coated fiber was more effective and superior to commercial PDMS and PDMS/DVD fibers in extracting pyrethroids in natural water samples. Under optimized conditions, the calibration curves were found to be linear from 0.001 to 10 μg mL⁻¹ for five of the six pyrethroids studied, the exception being fenvalerate (which was from 0.005 to 10 μg mL⁻¹), and detection limits were within the range 0.12-0.43 ng mL⁻¹. The recoveries of the pyrethroids spiked in water samples at 10 ng mL⁻¹ ranged from 83 to 112%.     

Study of polyethylene glycol as a green solvent in the microwave-assisted extraction of flavone and coumarin compounds from medicinal plants

In this paper, the application of polyethylene glycol (PEG) aqueous solution as a green solvent in microwave-assisted extraction (MAE) was firstly developed for the extraction of flavone and coumarin compounds from medicinal plants. The PEG solutions were optimized by a mono-factor test, and the other conditions of MAE including the size of sample, liquid/solid ratio, extraction temperature and extraction time were optimized by means of an orthogonal design L(9) (3(4)). Subsequently, PEG-MAE, organic solvent-MAE, and conventional heating reflux extraction (HRE) were evaluated with nevadensin extraction from Lysionotus pauciflorus, aesculin and aesculetin extraction from Cortex fraxini. Furthermore, the mechanism of PEG-MAE was investigated, including microwave-absorptive property and viscosity of PEG solutions, the kinetic mechanism of PEG-MAE and different microstructures of those samples before and after extraction. Under optimized conditions, the extraction yields of nevadensin from L. pauciflorus, aesculin and aesculetin from C. fraxini were 98.7%, 97.7% and 95.9% in a one-step extraction, respectively. The recoveries of nevadensin, aesculin and aesculetin were in the range of 92.0-103% with relative standard derivation lower than 3.6% by the proposed procedure. Compared with organic solvent-MAE and conventional extraction procedures, the proposed methods were effective and alternative for the extraction of flavone and coumarin compounds from medicinal plants. On the basis of the results, PEG solution as a green solvent in the MAE of active compounds from medicinal plants showed a great promising prospect.     

Zinc oxide/polypyrrole nanocomposite as a novel solid phase microextraction coating for extraction of aliphatic hydrocarbons from water and soil samples

In this work, ZnO/PPy nanocomposite coating was fabricated on stainless steel and evaluated as a novel headspace solid phase microextraction (HS-SPME) fiber coating for extraction of ultra-trace amounts of environmental pollutants; namely, aliphatic hydrocarbons in water and soil samples. The ZnO/PPy nanocomposite were prepared by a two-step process including the electrochemical deposition of PPy on the surface of stainless steel in the first step, and the synthesis of ZnO nanorods by hydrothermal process in the pores of PPy matrix in the second step. Porous structure together with ZnO nanorods with the average diameter of 70 nm were observed on the surface by using scanning electron microscopy (SEM). The effective parameters on HS-SPME of hydrocarbons (i.e., extraction temperature, extraction time, desorption temperature, desorption time, salt concentration, and stirring rate) were investigated and optimized by one-variable-at-a-time method. Under optimized conditions (extraction temperature, 65 ± 1 °C; extraction time, 15 min; desorption temperature, 250 °C; desorption time, 3 min; salt concentration, 10% w/v; and stirring rate, 1200 rpm), the limits of detection (LODs) were found in the range of 0.08–0.5 μg L⁻¹, whereas the repeatability and fiber-to-fiber reproducibility were in the range 5.4–7.6% and 8.6–10.4%, respectively. Also, the accuracies obtained for the spiked n-alkanes were in the range of 85–108%; indicating the absence of matrix effects in the proposed HS-SPME method. The results obtained in this work suggest that ZnO/PPy can be promising coating materials for future applications of SPME and related sample preparation techniques.     

Plunger-in-needle solid-phase microextraction with graphene-based sol-gel coating as sorbent for determination of polybrominated diphenyl ethers

A solid-phase microextraction (SPME) device, assembled with a commercially available plunger-in-needle microsyringe, with the plunger coated with graphene via a sol-gel approach, was developed for the gas chromatographic-mass spectrometric determination of polybrominated diphenyl ethers (PBDEs) in environmental samples. This is the first application of graphene-based sol-gel coating as SPME sorbent. Parameters affecting the extraction efficiency were investigated in detail. The new coating exhibited enrichment factors for PBDEs between 1378 and 2859. The unique planar structure of graphene enhanced the π-π interaction with the aromatic PBDEs; additionally, the sol-gel coating technique created a porous three-dimensional network structure which offered larger surface area for extraction. The stainless steel plunger provided firm support for the coating and enhanced the durability of the assembly. The plunger-in-needle microsyringe represents a ready-made tool for SPME implementation. Under the optimized conditions, the method detection limits for five PBDEs were in the range of 0.2 and 5.3 ng/L (at a signal/noise ratio of 3) and the precision (% relative standard deviation, n=5) was 3.2-5.0% at a concentration level of 100 ng/L. The linearities were 5-1000 or 10-1000 ng/L for different PBDEs. Finally, the proposed method was successfully applied to the extraction and determination by gas chromatography-mass spectrometry of PBDEs in canal water samples.     

Fibers coated with a graphene-polyaniline nanocomposite for the headspace solid-phase microextraction of organochlorine pesticides from seawater samples

We have prepared a fiber for solid-phase microextraction of organochlorine pesticides. A graphene-polyaniline composite was electrochemically deposited on a platinum fiber by exploiting the unique properties of polyaniline and graphene. The modified fiber displays thermal stability up to 320 °C and can be used more than 70 times. It possesses high extraction efficiency due to the high specific surface of graphene. The Pt fiber was used for the extraction and subsequent GC determination of the pesticides heptachlor, aldrin, endrin and p,p’-DDT in aqueous samples. The effects of extraction time, extraction temperature, stirring rate, salinity and headspace volume were optimized. Calibration plots are linear (with an R² of 0.990) in the 0.2 to 250 μg L^–1 concentration range, and the limits of detection are below 11 ng L^–1 (at an S/N of 3). The relative standard deviations for three replicate measurements with a single fiber were <11.0 %. The recovery of the pesticides from spiked seawater samples ranged from 81 % to 112 %.

A platinized stainless steel fiber with in‐situ coated polyaniline/polypyrrole/graphene oxide nanocomposite sorbent for headspace solid‐phase microextraction of aliphatic aldehydes in rice samples

The surface of a stainless steel fiber was made larger, porous and cohesive by platinizing for tight attachment of its coating. Then it was coated by a polyaniline/polypyrrole/graphene oxide (PANI/PP/GO) nanocomposite film using electrochemical polymerization. The prepared PANI/PP/GO fiber was used for headspace solid‐phase microextraction (HS‐SPME) of linear aliphatic aldehydes in rice samples followed by GC‐FID determination. To achieve the highest extraction efficiency, various experimental parameters including extraction time and temperature, matrix modifier and desorption condition were studied. The linear calibration curves were obtained over the range of 0.05–20 μg g⁻¹ (R ² > 0.99) for C₄–C₁₁ aldehydes. The limits of detection were found to be in the range of 0.01–0.04 μg g⁻¹. RSD values were calculated to be <7.4 and 10.7% for intra‐ and inter‐day, respectively. The superiority of the prepared nanocomposite SPME fiber was established by comparison of its results with those obtained by polydimethylsiloxane, carbowax–divinylbenzene, divinylbenzene–carboxen–polydimethylsiloxane and polyacrylate commercial ones. Finally, the nanocomposite fiber was used to extract and determine linear aliphatic aldehydes in 18 rice samples.     

Synthesis and characterization of a nano‐hydroxyapatite/chitosan/polyethylene glycol nanocomposite for bone tissue engineering

A novel nanocomposite involving nano‐hydroxyapatite/chitosan/polyethylene glycol (n‐HAP/CS/PEG) has been successfully synthesized via co‐precipitation approach at room temperature. The purpose to synthesize such nanocomposite is to search for an ideal analogue which may mimick the composition of natural bone for bone tissue engineering with respect to suitable biocompatibility, cytotoxicity and mechanical properties. The FTIR spectra of n‐HAP/CS and n‐HAP/CS/PEG scaffolds indicated significant intermolecular interaction between the various components of both the nanocomposites. The results of XRD, TEM and TGA/DTA suggested that the crystallinity and thermal stability of the n‐HAP/CS/PEG scaffold have decreased and increased respectively, relative to n‐HAP/CS scaffold. The comparison of SEM images of both the scaffolds indicated that the incorporation of PEG influenced the surface morphology while a better in‐vitro bioactivity has been observed in n‐HAP/CS/PEG than in n‐HAP/CS based on SBF study, referring a greater possibility for making direct bond to living bone if implanted. Furthermore, MTT assay revealed superior non‐toxic nature of n‐HAP/CS/PEG to murine fibroblast L929 cells as compared to n‐HAP/CS. The comparative swelling studies of n‐HAP/CS/PEG and n‐HAP/CS scaffolds revealed a better swelling rate for n‐HAP/CS/PEG. Also n‐HAP/CS/PEG showed higher mechanical strength relative to n‐HAP/CS supportive of bone tissue ingrowths. Copyright © 2014 John Wiley & Sons, Ltd.     

Fe3O4/polyethylene glycol nanocomposite as a solid‐phase microextraction fiber coating for the determination of some volatile organic compounds in water

A high‐performance metal oxide polymer magnetite/polyethylene glycol nanocomposite was prepared and coated in situ on the surface of the optical fiber by sol–gel technology. The magnetite nanoparticles as nanofillers were synthesized by a coprecipitation method and bonded with polyethylene glycol as a polymer. The chemically bonded coating was evaluated for the headspace solid–phase microextraction of some environmentally important volatile organic compounds from aqueous samples in combination with gas chromatography and mass spectrometry. The prepared fiber was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The mass ratio of nanofiller and polymer on the coating extraction efficiency, morphology, and stability were investigated. The parameters affecting the extraction efficiency, including the extraction time and temperature, the ionic strength, desorption temperature, and time were optimized. The sol–gelized fiber showed excellent chemical stability and longer lifespan. It also exhibited high extraction efficiency compared to the two types of commercial fibers. For volatile organic compounds analysis, the new fiber showed low detection limits (0.008–0.063 ng/L) and wide linearity (0.001–450 × 10⁴ ng/L) under the optimized conditions. The repeatability (interday and intraday) and reproducibility were 4.13–10.08 and 5.98–11.61%, and 7.35–14.79%, respectively (n = 5). For real sample analysis, three types of water samples (ground, surface, and tap water) were studied.     

Optimization of the headspace solid-phase microextraction for determination of glycol ethers by orthogonal array designs

A headspace solid-phase microextraction (HS-SPME), in conjunction with gas chromatography-flame ionization detection for use in the determination of six frequently used glycol ethers at the microg/l level is described. A 75 microm Carboxenpolydimethylsiloxane fiber was used to extract the analytes from an aqueous solution. Experimental HS-SPME parameters such as extraction temperature, extraction time, salt concentration and sample volume, were investigated and optimized by orthogonal array experimental designs. The relative standard deviations for the reproducibility of the optimized HS-SPME method varied from 1.48 to 7.59%. The correlation coefficients of the calibration curves exceeded 0.998 in the microg/l range of concentration with at least two orders of magnitude. The method detection limits for glycol ethers in deionized water were in the range of 0.26 to 3.42 microg/l. The optimized method was also applied to the analysis of glycol ethers in urine and blood samples with the method detection limits ranged from 1.74 to 23.2 microg/l.