Determination of stable carbon isotopes of organic acids and carbonaceous aerosols in the atmosphere

A wet oxidation method for the compound-specific determination of stable carbon isotopes (delta(13)C) of organic acids in the gas and aerosol phase, as well as of water-soluble organic carbon (WSOC), is presented. Sampling of the organic acids was done using a wet effluent diffusion denuder/aerosol collector (WEDD/AC) coupled to an ion chromatography (IC) system. The method allows for compound-specific stable carbon isotope analysis by collecting different fractions of organic acids at the end of the IC system using a fraction collector. delta(13)C analyses of organic acids were conducted by oxidizing the organic acids with sodium persulfate at a temperature of 100 degrees C and determining the delta(13)C value of the resulting carbon dioxide (CO(2)) with an isotope ratio mass spectrometer. In addition, analysis of delta(13)C of the WSOC was performed for particulate carbon collected on aerosol filters. The WSOC was extracted from the filters using ultrapure water (MQ water), and the dissolved organic carbon was oxidized to CO(2) using the oxidation method. The wet oxidation method has an accuracy of 0.5 per thousand with a precision of +/-0.4 per thousand and provides a quantitative result for organic carbon with a detection limit of 150 ng of carbon.     

Fast miniaturised sample preparation for the screening and comprehensive two-dimensional gas chromatographic determination of polychlorinated biphenyls in sludge

Polychlorinated biphenyls (PCBs) in sludge are usually extracted by a technique such as Soxhlet with subsequent fractionation prior to long GC runs using GC-ECD or GC-HRMS. In this study, the extraction of selected chlorinated biphenyls (CBs) from a spiked sludge sample by three rapid techniques, i.e. ultrasonic (USE), pressurised-liquid (PLE), and microwave-assisted (MAE) extraction using a domestic microwave, was studied, with subsequent direct GC-ECD, GC-MS, or GC x GC-microECD analysis of the extracts. The main goal was to select an appropriate, and miniaturised, extraction method after only a brief optimisation and demonstrate the power of GC x GC analysis of dirty extracts. For PLE similar CB recoveries were found when extracting with either n-hexane or n-hexane/acetone (1/1). For USE and MAE, n-hexane/acetone (1/1) was the preferred extraction solvent. USE gave the best recoveries (80-95%; except 130% for CB 105). The only clean-up needed prior to GC-MS or GC x GC-gECD analysis was the removal of sulphur-containing compounds. GC-ECD was not suitable for these dirty extracts. The lowest LODs for the CBs (20 fg or 0.1 ng/g sludge) were found when combining USE and GC x GC-microECD, because of the powerful extraction, high separation power and excellent detectability provided by this technique.     

A Comparison of Three Methods of Extraction for the Determination of Polyphenols and Organic Acids in Tobacco by UPLC–MS–MS

Matrix solid phase dispersion (MSPD), ultrasonic extraction followed by a solid phase extraction (USE–SPE) and reflux extraction (REFLUX) were studied for the analysis of polyphenols and organic acids in tobacco. The analysis was by ultra-high performance liquid chromatography tandem mass spectrometry (UPLC–MS–MS). The multi-mode support sorbent Zirconia/AA12S50 in MSPD is more suitable for the extraction of tobacco polyphenols than conventional silica or C18 silica. Although the matrix effect of USE–SPE is slightly stronger than MSPD and REFLUX for most target compounds, it gave higher extraction capacity, recoveries and sensitivity.     

烟草中有机氯类农药多残留分析前处理方法对比研究

以烟草中有机氯类农药为研究对象,从检出限、回收率、重复性和色谱图4个方面系统比较了机械振荡萃取法、超声波溶剂萃取法、微波辅助萃取法和加速溶剂萃取法4种常用前处理方法。由于加速溶剂萃取法是在高温高压下进行萃取,在提取出残留农药的同时,也提取出更多的干扰物。机械振荡法、超声波溶剂萃取法和微波辅助萃取法各项结果差别较小,其中机械振荡萃取法回收率和重复性最好,但提取时间较长。考虑溶剂消耗和提取时间等方面的因素,微波辅助萃取是较理想的样品前处理方法。     

Microwave-assisted steam distillation for the determination of organochlorine pesticides and pyrethroids in Chinese teas

In this work, microwave-assisted steam distillation (MASD) extraction method followed by gas chromatography/electron capture detection (GC/ECD) was developed for the determination of organochlorine pesticides (OCPs) and pyrethroids in the Chinese teas. MASD is a combination of microwave-assisted extraction (MAE) and steam distillation techniques. Water vapor generated by microwave irradiation is used to accelerate desorption of the analytes from the sample, and the nonpolar organic solvent used for trapping the analytes is kept from direct contact with the sample by the water. Therefore, relatively clean extracts were obtained compared to the method directly using organic solvent as extraction solvent, such as ultrasonic extraction (USE). Microwave power of 200 W and irradiation time of 2 min was found to be the optimum conditions for the MASD process, and n-heptane was chosen as the analyte-trapping solvent in the study. Five OCPs (α-HCH, γ-HCH, dicofol, p,p′-DDE, p,p′-DDT) and two pyrethroids (bifenthrin, fenvalate) were determined using this extraction method in the tea samples. The relative standard deviation (R.S.D.) of the analytes varied from 2.2 to 8.4%, and the method detection limits (MDLs) found were lower than 0.23 μg/kg. The recoveries of the seven compounds in the Jasmine tea sample were between 84.04 and 110.1%. Comparative results obtained by MASD and USE were also discussed in the study.     

Application of water as a solvent in microwave-assisted extraction for analysis of PCBs and CBzs in fly ash

Polychlorinated biphenyls (PCBs) and chlorobenzenes (CBzs) are two classes of dioxin precursors formed in municipal solid waste incinerators (MSWIs); they produce negative health effects similar to those of dioxins. Reducing the analytical time required for determining the concentrations of these compounds in MSWIs is important for quickly evaluating their importance and assessing associated health risks. In the present study, water is used as a safe and environmentally friendly solvent in microwave-assisted extraction (MAE) for PCB and CBz analyses. MAE is compared with traditional Soxhlet extraction (SE) to determine the extraction efficiencies. The evaluation of extraction efficiencies shows that MAE has a high extraction efficiency compared with that of SE when water content is lower than 60%. Furthermore, the extraction time and organic solvent consumption are reduced with MAE compared with SE.     

An anion-exchange high-performance liquid chromatography method coupled to total organic carbon determination for the analysis of water-soluble organic aerosols

The chemical composition of water-soluble organic carbon (WSOC) in atmospheric aerosol particles is largely unexplored, due to the myriad of individual compounds, which has hampered attempts to attain a full characterization at the molecular level. An alternative approach, focusing on the analysis of a few main chemical classes, allowed the quantitative fractionation of WSOC into neutral compounds (NC), mono- and di-acids (MDA) and polyacids (PA) through an anion-exchange liquid chromatographic method. Previous attempts to quantify NC, MDA and PA relied on a low-pressure chromatographic technique using a volatile buffer, followed by total organic carbon (TOC) analysis of the fractions, or alternatively on a faster HPLC-UV method which provided a quantification of the fractions based on empirical relationships between UV signal and TOC concentration. Here, we report an upgraded anion-exchange HPLC technique, allowing direct TOC analysis of the eluted fractions, without any pre-treatment, thus permitting a great simplification of quantitative analysis and preventing sample losses. The new HPLC-TOC methodology, employing completely inorganic eluents shows the same efficiency of the former HPLC-UV method employing organic additives, with the exception of phenolic compounds, which are retained on the column by secondary interactions, and low-molecular weight tricarboxylic acids, which are recovered among MDA. The new anion-exchange liquid chromatographic method can recover a substantial amount (86-100%) of water-soluble organic carbon from atmospheric aerosol extracts, thus allowing a higher retention and fractionation capacity with respect to alternative techniques, like solid phase extraction.     

Negative-pressure cavitation extraction for the determination of flavonoids in pigeon pea leaves by liquid chromatography-tandem mass spectrometry

A new method, namely negative-pressure cavitation extraction (NPCE), followed by liquid chromatography–tandem mass spectrometry (LC–MS/MS) is presented for the extraction and quantification of flavonoids in pigeon pea leaves. This method combines the high efficiency of NPCE and the sensitivity and accuracy of MS/MS. The influential parameters of the NPCE procedure including liquid/solid ratio, extraction time, nitrogen flow and number of extraction cycles were optimized. Under optimized conditions, the efficiency of NPCE for extracting five flavonoids was compared to microwave-assisted extraction (MAE), ultrasonic extraction (USE) and heating reflux extraction (HRE). Additionally, structural disruption to pigeon pea leaves samples with different extraction methods was investigated by scanning electron microscopy. The relative recovery with NPCE was equivalent to or higher than that with USE and obviously higher than those with MAE and HRE which are usually conducted in higher temperatures. Furthermore, because NPCE was performed with nitrogen at room temperature, the degradation and oxidation of analytes were avoided. In addition, the NPCE method was validated in terms of repeatability and reproducibility, relative standard deviation for relative recovery was lower than 5.84 and 8.83%, respectively. The method was also successfully applied for the quantification of five flavonoids in pigeon pea leaves. All these results suggest that the developed NPCE-LC–MS/MS method represents an excellent alternative for the extraction and quantification of flavonoids in other plant materials.     

Fast determination of chlorogenic acid in tobacco residues using microwave-assisted extraction and capillary zone electrophoresis technique

In this work, for the first time, capillary zone electrophoresis (CZE) technique combined with microwave-assisted extraction (MAE) was developed for the fast quantification of chlorogenic acid (CA) in tobacco residues. CA in tobacco residue samples were extracted by MAE technique, and then analyzed by CZE. As a new sample preparation method for tobacco residues, the MAE procedure is optimized, validated and compared with conventional methods including ultrasonic extraction (USE) and reflux extraction (RE). It is found that MAE gives the best result due to the highest extraction efficiency within shortest extraction time (only 4.0 min). Here, CA is determined by CZE based on the calibration curve of its authentic standard. The method linearity, detection limit, precision and recovery are studied. The results show that the combined MAE and CZE method has a linearity (R² 0.991, 0.003-0.5 mg ml⁻¹), a limit of detection (0.003 mg ml⁻¹), a limit of quantification (0.01 mg ml⁻¹), good precision (R.S.D. = 4.28%) and a finer recovery (89.0%). The proposed method was successfully applied to the analysis of CA in tobacco residue samples. The experiment results have demonstrated that the CZE combined with MAE is a convenient, fast, economical and reliable method for the determination of CA in tobacco residues.     

Application of polyphenylmethylsiloxane coated fiber for solid-phase microextraction combined with microwave-assisted extraction for the determination of organochlorine pesticides in Chinese teas

Polyphenylmethylsiloxane (PPMS) as a novel coating for solid-phase microextraction (SPME) combined with microwave-assisted extraction (MAE) has been applied to determine the concentrations of organochlorine pesticides (OCPs) in Chinese teas. The characteristics of PPMS fiber, the extraction modes of SPME, the extraction time, temperature, and salt effects were investigated. Microwave irradiation time and power were also studied. Compared with commercial polydimethylsiloxane (PDMS) fiber and homemade sol-gel polymethylsiloxane (PMS) fiber, the novel porous sol-gel PPMS fiber exhibited high sensitivity and selectivity for OCPs compounds, higher thermal stability (to 350 degrees C) and long service life (more than 150 times). The recoveries of MAE is compared with that of ultrasonic extraction (USE), MAE-SPME-gas chromatography (GC)/electron-capture detection (ECD) methods showed better results for Chinese teas. Linear ranges of OCPs in the blank green tea was 0.1-10(3) ng/l. Detection limits of this method are below 0.081 ng/l. Recoveries of this method are between 39.05 and 94.35%. The repeatability of the technique was less than 16% relative standard deviation (R.S.D.). The tested pesticides in three Chinese teas were at the ng/g level.     

广州大气细粒子中有机碳、元素碳和水溶性有机碳的分布特征

在广州市中山大学采样点进行了为期1年的大气细粒子(PM2.5)采样,监测分析得到PM2.5及有机碳(OC)、元素碳(EC)和水溶性有机碳(WSOC)等组分的质量浓度,并进行了比较和评价分析。结果表明广州市细粒子碳污染较严重。对OC、EC和WSOC质量浓度的月变化和季节变化特征进行了讨论,并分析了原因。OC、EC浓度相关性好,表明OC、EC来源大部分相同。根据OC/EC比值,估算二次有机碳(SOC)量,结果是SOC占OC的1/3。讨论了SOC和SOC/OC比值的季节分布,结果证明SOC夏季生成比冬季多。     

Quantitative determination of chlorogenic acid in Honeysuckle using microwave-assisted extraction followed by nano-LC-ESI mass spectrometry

The chlorogenic acid (CA) in Honeysuckle is determined and identified by nano-liquid chromatography-electrospray ionization mass spectrometry (nano-LC-ESI/MS) after extraction with microwave-assisted extraction (MAE). As a new sample preparation method for Honeysuckle, the MAE procedure is optimized, validated and compared with conventional methods including reflux extraction (RE) and ultrasonic extraction (USE). It is found that MAE gives the best result due to the highest extraction efficiency within shortest extraction time (only 4 min). Here, CA is determined by nano-LC-ESI/MS based on the calibration curve of its authentic standard. The method linearity, detection limit, precision and recovery are studied. The results show that the combined MAE and nano-LC-ESI/MS method has a linearity (R² 0.991, 0.8-20 ng mL⁻¹), a low limit of detection (0.5 ng mL⁻¹), good precision (R.S.D. = 2.54%) and a recovery (84.8%). The experiment has demonstrated that the nano-LC-ESI/MS following MAE is a fast and reliable method for quantitative analysis of CA in Honeysuckle.     

Microwave-assisted extraction of coumarin and related compounds from Melilotus officinalis (L.) Pallas as an alternative to Soxhlet and ultrasound-assisted extraction

Soxhlet extraction, ultrasound-assisted extraction (USAE) and microwaves-assisted extraction (MAE) in closed system have been investigated to determine the content of coumarin, o-coumaric and melilotic acids in flowering tops of Melilotus officinalis. The extracts were analyzed with an appropriate HPLC procedure. The reproducibility of extraction and of chromatographic analysis was proved. Taking into account the extraction yield, the cost and the time, we studied the effects of extraction variables on the yield of the above-mentioned compounds. Better results were obtained with MAE (50% v/v aqueous ethanol, two heating cycles of 5 min, 50 degrees C). On the basis of the ratio extraction yield/extraction time, we therefore propose MAE as the most efficient method.     

LC–UV determination of atrazine and its principal conversion products in soil after combined microwave-assisted and solid-phase extraction

A multiresidue method developed for the analysis of atrazine and its principal conversion products, deisopropylatrazine (DIA), deethylatrazine (DEA) and hydroxyatrazine (HA), in soil is presented. The method is based on the microwave-assisted extraction (MAE) of soil with aqueous methanol followed by solid-phase extraction (SPE) of the extracts and subsequent analysis by LC–UV with a diode array detector. MAE operational parameters (extraction solvent, extractant volume) were optimized with respect to extraction efficiency of the target compounds from soils with 2.5% organic matter (OM) content. Recoveries above 80% were obtained for all solutes. Soil OM content did not affect analyte recoveries. Recoveries from fresh and aged residues, the latter weathered under cold storage conditions, were not statistically different. Finally, MAE was found to be superior in terms of extraction efficiency, sample throughput, and solvent consumption to conventional flask-shaking extraction.     

Solid-phase extraction versus matrix solid-phase dispersion: Application to white grapes

The use of matrix solid-phase dispersion (MSPD) was tested to, separately, extract phenolic compounds and organic acids from white grapes. This method was compared with a more conventional analytical method previously developed that combines solid liquid extraction (SL) to simultaneously extract phenolic compounds and organic acids followed by a solid-phase extraction (SPE) to separate the two types of compounds. Although the results were qualitatively similar for both techniques, the levels of extracted compounds were in general quite lower on using MSPD, especially for organic acids. Therefore, SL-SPE method was preferred to analyse white “Vinho Verde” grapes. Twenty samples of 10 different varieties (Alvarinho, Avesso, Asal-Branco, Batoca, Douradinha, Esganoso de Castelo Paiva, Loureiro, Pedernã, Rabigato and Trajadura) from four different locations in Minho (Portugal) were analysed in order to study the effects of variety and origin on the profile of the above mentioned compounds. Principal component analysis (PCA) was applied separately to establish the main sources of variability present in the data sets for phenolic compounds, organic acids and for the global data. PCA of phenolic compounds accounted for the highest variability (77.9%) with two PCs, enabling characterization of the varieties of samples according to their higher content in flavonol derivatives or epicatechin. Additionally, a strong effect of sample origin was observed. Stepwise linear discriminant analysis (SLDA) was used for differentiation of grapes according to the origin and variety, resulting in a correct classification of 100 and 70%, respectively.     

Multiple response optimisation based on desirability functions of a microwave-assisted extraction method for the simultaneous determination of chloroanisoles and chlorophenols in oak barrel sawdust

A microwave-assisted extraction (MAE) method was optimised for extracting 2,4,6-trichloroanisole (TCA), 2,3,4,6-tetrachloroanisole (TeCA), pentachloroanisole (PCA), 2,4,6-trichlorophenol (TCP), 2,3,4,6-tetrachlorophenol (TeCP) and pentachlorophenol (PCP) from oak barrels. The method was optimised by using a central composite experimental design with extraction time, temperature and solvent volume as influential parameters. A desirability function was then employed in addition to the simultaneous optimisation of the compounds. The optimal conditions identified were temperature 130 degrees C, solvent volume 35 mL and extraction time 50 min. The compounds were determined by gas chromatography with electron-capture detection. MAE was compared with conventional Soxhlet extraction; the results obtained with MAE were in good agreement with those obtained by Soxhlet extraction.     

Harmful azo colorants in leather. Determination based on their cleavage and extraction of corresponding carcinogenic aromatic amines using modern extraction techniques

This study concerns the possibilities of using microwave-assisted extraction (MAE) or supercritical fluid extraction (SFE) for detection of harmful azo colorants in leather. After degreasing of the leather sample with SFE there follows a reductive cleavage of the azo colorants to their corresponding aromatic amines in the MAE or SFE equipment. The aromatic amines are subsequently extracted using either MAE or SFE and then finally determined by liquid chromatography with diode-array detection. The results have been compared with recoveries obtained using the German DIN method 53316. This standard method, based on conventional solvent extraction, is used in several European countries. Overall much better recoveries were obtained using MAE or SFE. With both MAE and SFE the amine recoveries of spiked leather samples were generally above 50%. The average recoveries were 62% for MAE and 60% for SFE (solvent collection) compared to 24% with the DIN method. For genuine leather samples the recoveries decreased, especially for benzidine. In this case the average values for MAE, SFE and DIN were 54, 38 and 19%, respectively. The quantification limits in leather samples using MAE or SFE were below 1 mg/kg for all amines investigated. The within-laboratory precision was generally better than 10%, varying somewhat with the analyte considered. With the proposed methodology, the amount of hazardous organic solvents used could be decreased and the sample throughput increased with at least a factor of two with less manual handling compared to the DIN method.     

Microwave‐assisted extraction followed by CE for determination of catechin and epicatechin in green tea

In this work, for the first time, microwave‐assisted extraction (MAE) followed by CE was developed for the fast analysis of catechin and epicatechin in green tea. In the proposed method, catechin and epicatechin in green tea samples were rapidly extracted by MAE technique, and then analyzed by CE. The MAE conditions and the method's validation were studied. It is found that the extraction time of 1 min with 400 W microwave irradiation is enough to completely extract catechin and epicatechin in green tea sample, whereas the conventional ultrasonic extraction (USE) technique needs long extraction time of 60 min. The method validations were also studied in this work. The calibration curve shows good linearity in 0.01–3 mg/mL for catechin (R²=0.993), and 0.005–3 mg/mL for epicatechin (R²=0.996), respectively. The RSD values for catechin and epicatechin are 0.65 and 2.58%, respectively. This shows that the proposed method has good reproducibility. The proposed method has good recoveries, which are 118% for catechin and 120% for epicatechin. The proposed method was successfully applied to determination of the catechin and epicatechin in different green tea samples. The experiment results have demonstrated that the MAE following CE is a simple, fast and reliable method for the determination of catechin and epicatechin in green tea.     

RP-HPTLC densitometric determination and validation of vanillin and related phenolic compounds in accelerated solvent extract of Vanilla planifolia*

A simple, fast and sensitive RP-HPTLC method is developed for simultaneous quantitative determination of vanillin and related phenolic compounds in ethanolic extracts of Vanilla planifolia pods. In addition to this, the applicability of accelerated solvent extraction (ASE) as an alternative to microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE) and Soxhlet extraction was also explored for the rapid extraction of phenolic compounds in vanilla pods. Good separation was achieved on aluminium plates precoated with silica gel RP-18 F(254S) in the mobile phase of methanol/water/isopropanol/acetic acid (30:65:2:3, by volume). The method showed good linearity, high precision and good recovery of compounds of interest. ASE showed good extraction efficiency in less time as compared to other techniques for all the phenolic compounds. The present method would be useful for analytical research and for routine analysis of vanilla extracts for their quality control.     

Validation of green‐solvent extraction combined with chromatographic chemical fingerprint to evaluate quality of Stevia rebaudiana Bertoni

An approach that combined green‐solvent methods of extraction with chromatographic chemical fingerprint and pattern recognition tools such as principal component analysis (PCA) was used to evaluate the quality of medicinal plants. Pressurized hot water extraction (PHWE) and microwave‐assisted extraction (MAE) were used and their extraction efficiencies to extract two bioactive compounds, namely stevioside (SV) and rebaudioside A (RA), from Stevia rebaudiana Bertoni (SB) under different cultivation conditions were compared. The proposed methods showed that SV and RA could be extracted from SB using pure water under optimized conditions. The extraction efficiency of the methods was observed to be higher or comparable to heating under reflux with water. The method precision (RSD, n = 6) was found to vary from 1.91 to 2.86% for the two different methods on different days. Compared to PHWE, MAE has higher extraction efficiency with shorter extraction time. MAE was also found to extract more chemical constituents and provide distinctive chemical fingerprints for quality control purposes. Thus, a combination of MAE with chromatographic chemical fingerprints and PCA provided a simple and rapid approach for the comparison and classification of medicinal plants from different growth conditions. Hence, the current work highlighted the importance of extraction method in chemical fingerprinting for the classification of medicinal plants from different cultivation conditions with the aid of pattern recognition tools used.