Membrane-assisted solvent extraction of triazines, organochlorine, and organophosphorus compounds in complex samples combined with large-volume injection-gas chromatography/mass spectrometric detection

The performance of the fully automated membrane-assisted solvent extraction was investigated for 47 environmental contaminants (among them 30 organochlorine compounds, 9 organophosphorus compounds, and 7 triazines). The extraction took place in a 20-mL headspace vial filled with the aqueous sample and containing a polypropylene membrane bag with 1 mL of cyclohexane as extractant. This device was handled by a multipurpose sampler, which enabled the sample to be mixed at a defined temperature with subsequent large-volume injection of the organic extract taken out of the membrane bag. After optimization of extraction parameters, the method was validated for the three compound classes, triazines and organochlorine and organophosphorus compounds, using spiked distilled water. Then, the extraction yield of these analytes from several complex samples such as a natural and a synthetic wastewater, a bacterial culture, and orange juice was determined and compared to a conventional liquid-liquid extraction. Furthermore, the possibility of reducing matrix interference by adding salt, methanol, or detergent during membrane-assisted solvent extraction was investigated.     

Focused microwave-assisted soxhlet: an advantageous tool for sample extraction

A new type of microwave-assisted Soxhlet is here reported. The device uses conventional Soxhlet glassware for solid sample extraction and a focused-microwave digester for irradiation of the sample cartridge at the required intervals while the fresh solvent (condensed vapors from the distillation flask) drips on and passes through the solid sample. In this way breaking of the analyte-matrix bonds is facilitated by application of the appropriate energy. The new approach has been checked in a comparative study by its application to the extraction of analyte families of different polarity (namely, alkanes, polyaromatic hydrocarbons, and herbicides) from the same soil matrix using dichloromethane as extractant. The reduction of the extraction times (from 8 h to 50-60 min, depending on the polarity of the analytes) with efficiency similar to or even higher than that afforded by the conventional Soxhlet technique supports the suitability of the new approach. In addition, recycling of the solvent during extract preconcentration enables minimal environmental contamination to be achieved.     

Liquid membrane operations in a microfluidic device for selective separation of metal ions

A three-phase flow, water/n-heptane/water, was constructed in a microchannel (100-microm width, 25-microm depth) on a glass microchip (3 cm x 7 cm) and was used as a liquid membrane for separation of metal ions. Surface modification of the microchannel by octadecylsilane groups induced spontaneous phase separation of the three-phase flow in the microfluidic device, which allows control of interfacial contact time and off-chip analysis using conventional analytical apparatus. Prior to the selective transport of a metal ion through the liquid membrane in the microchannel, the forward and backward extraction of yttrium and zinc ions was investigated in a two-phase flow on a microfluidic device using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (commercial name, PC-88A) as an extractant. The extraction conditions (contact time of the two phases, pH, extractant concentration) in the microfluidic device were examined. These investigations demonstrated that the conventional methodology for solvent extraction of metal ions is applicable to solvent extraction in a microchannel. Finally, we employed the three-phase flow in the microchannel as a liquid membrane and observed the selective transport of Y ion through the liquid membrane. In the present study, we succeeded, for the first time, in the selective separation of a targeted metal ion from an aqueous feed solution to a receiving phase within a few seconds by employing a liquid membrane formed in a microfluidic device.     

HPLC-MS/MS法测定食品接触材料中6种邻苯二甲酸酯的含量

建立了测定食品接触材料中6种邻苯二甲酸酯的含量的高效液相色谱-串联质谱法(HPLC-MS/MS)。实验以Agilent ZORBAX SB-C18色谱柱为分析柱,以甲醇-0.1%的甲酸水为流动相,采用梯度模式洗脱。质谱离子源的工作模式为正离子电离模式(ESI+),流速为0.35 mL/min,采用多反应监测离子模式(MRM)进行检测定量。实验样品前处理采用了加速溶剂萃取法,明显提高了食品接触材料中邻苯二甲酸酯的提取效率。结果表明:6种邻苯二甲酸酯在其线性范围内线性关系良好(R2>0.999),DPRP和BBP的定量限为1.0 ng/mL,DCHP,DNHP,DHP,DBEP的定量限为0.2 ng/mL,DPRP和BBP的检测限为0.2 ng/mL,DCHP,DNHP,DHP,DBEP的检测限为0.05 ng/mL。该方法的加标回收率为89.2%～107.5%,相对标准偏差均小于5.0%。实验表明,所建立的方法简单、灵敏度高,适用于食品接触材料中的6种邻苯二甲酸酯类增塑剂的分析检测。     

Hot phosphate-buffered water extraction coupled on-line with liquid chromatography/mass spectrometry for analyzing contaminants in soil

We evaluated the feasibility of analyzing rapidly traces of polar and medium polar contaminants in soil by coupling on-line a hot phosphate-buffered water extraction apparatus to a liquid chromatography/mass spectrometer system. Coupling was accomplished by using a small C-18 sorbent trap for collecting analytes and two six-port valves. The efficiency of this device was evaluated by extracting 13 selected pesticides from 200 mg of laboratory-aged soils by varying the extraction temperature, the extractant volume, and the flow rate at which the extractant passed through the extraction cell and the sorbent trap. In terms of extraction efficiency, robustness of the method, and extraction time, the best compromise was that of using 8 mL of extractant at 90 degrees C and 0.5 mL/min flow rate. Under these conditions, recoveries of 11 out of 13 analytes ranged between 82 and 103%, while those of the least hydrophilic pesticides, i.e., neburon and prochloraz, were 73 and 63%, respectively. By increasing the extractant volume to 60 mL, additional amounts of the two latter compounds could be recovered. Under this condition, however, the most hydrophilic analytes were in part no more retained by the C-18 sorbent trap. From a naturally 1.5-year aged soil, hot phosphate-buffered water removed larger amounts of three herbicides and hydroxyterbuthylazine (a terbuthylazine degradation product) than pure water and Soxhlet extraction. This result seems to confirm that hot phosphate buffer is also able to remove from soil those fractions of contaminants that, on aging, are sequestered into the humic acid framework.     

Pressurized hot water extraction with on-line fluorescence monitoring: a comparison of the static,dynamic, and static-dynamic modes for the removal of polycyclic aromatic hydrocarbons from environmental solid samples

A comparison of the feasibility of the three operational modes of pressurized hot solvent extraction (PHSE) (namely, static, where a fixed extractant volume is used; dynamic, where the extractant continually flows through the sample; and static-dynamic mode, which consists of a combination of the two previous modes) for the extraction of polycyclic aromatic hydrocarbons (PAHs) from environmental solid samples (such as soil, sediment, trout, and sardine) has been performed. In all cases, a sodium dodecyl sulfate (SDS) aqueous solution was used as leaching agent. The use of a flow injection manifold between the extractor and a molecular fluorescence detector allowed real-time on-line fluorescence monitoring of the PAHs extracted from the samples, thus working as a screening system and providing qualitative and semiquantitative information on the target analytes extracted from both natural and spiked samples. The on-line monitoring option allowed the extraction kinetics to be monitored and the end of the leaching step to be determined independently of the sample matrix, thereby reducing extraction times. Efficiencies close to 100% have been provided by the three modes, which differ in the extraction time required for total removal of the target compounds. The time needed for the dynamic mode was shorter than that for the static mode. However, the establishment of a static extraction step prior to dynamic extraction was the key to shorten the time required for complete extraction. The method has been applied to a certified reference material (CRM 524, BCR, industrial soil/organics) for quality assurance/validation.     

Kinetic calibration for automated headspace liquid-phase microextraction

The kinetics of the absorption and desorption of analytes for headspace liquid-phase microextraction (HS-LPME) were studied. It was found that the desorption of analytes from the extraction phase into the sample matrix is isotropic to the absorption of the analytes from the sample matrix into the extraction phase under the same conditions. This therefore allows for the calibration of absorption using desorption. Calibration was accomplished by exposing the extraction phase, which contained a standard, to the sample matrix. The information from the desorption of the standard, such as time constant a, could be directly used to estimate the concentration of the target analyte in the sample matrix. This new kinetic calibration method for headspace LPME was successfully used to correct the matrix effects in the BTEX analysis of an orange juice sample. In this study, the headspace LPME techniques were successfully fully automated, for both static and dynamic methods, with the CTC CombiPal autosampler. All operations of headspace LPME, including sample transfer and agitation, filling of extraction solvent, exposing the solvent in the headspace, withdrawing the solvent to syringe and introducing the extraction phase into injector, were autoperformed by the CTC autosampler. The fully automated headspace LPME technique is more convenient and improved the precision and sensitivity of the method. This automated dynamic headspace LPME technique can be also used to obtain the distribution coefficient between the sample matrix (aqueous or another solution) and the extraction phase (1-octanol or another solvent). The distribution coefficient between 1-octanol and orange juice, at 25 degrees C, was obtained with this technique.     

Solvent bar microextraction

In this work, a new and simple microextraction method termed solvent bar microextraction (SBME) was developed. In this method, the organic extractant solvent (1-octanol) was confined within a short length of a hollow fiber membrane (sealed at both ends) that was placed in a stirred aqueous sample solution. Tumbling of the extraction device within the sample solution facilitated extraction. Pentachlorobenzene (PCB) and hexachlorobenzene (HCB) were used as model compounds to investigate the extraction performance. Analysis was carried out by gas chromatography/electron capture detection. This new method provided very high enrichment (approximately 110-fold for PCB and approximately 70-fold for HCB) in 10 min and good reproducibility (<4%, n = 6). Since the hollow fiber membrane was sealed, it could be used for extraction from "dirty" samples, such soil slurries. This novel microextraction method was compared with single-drop microextraction and static hollow fiber membrane microextraction in which the extractant solvent was also held within a hollow fiber but with the latter fixed to a syringe needle (i.e., there was no tumbling effect). Comparison between SBME and conventional solid-phase microextraction in a soil slurry sample was also investigated.     

Continuous ultrasound-assisted extraction coupled to flow injection-pervaporation, derivatization, and spectrophotometric detection for the determination of ammonia in cigarettes

A dynamic system for the continuous removal of ammonia from cigarettes with ultrasound assistance and iterative change of the flow direction of the extractant through the sample cell has been developed. A 0.1-g sample of cigarette was subjected to 7 min of ultrasound-assisted extraction (application and duration of pulse 0.7 s, output amplitude 85% of the converter nominal amplitude), and 1 M NaOH solution was used both as extractant and as carrier in the dynamic system. The ultrasound-assisted extractor was coupled to a pervaporation unit through a flow injection interface in order to develop a fully automated method. In arriving at the pervaporator, the ammonia is transferred from the donor-carrier stream to an acceptor stream, where the classical Berthelot reaction takes place--thus favoring pervaporation. The blue complex formed is spectrophotometrically monitored at 655 nm. The method was applied to the determination of ammonia in a selection of 10 European cigarette brands and Kentucky Reference 2R4F cigarettes.     

Microwave-assisted steam distillation for simple determination of polychlorinated biphenyls and organochlorine pesticides in sediments

A novel sample extraction technique for polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) analysis using microwave-heating device is developed. In this study, microwave-assisted extraction (MAE) and steam distillation techniques were combined. Desorption of the anatytes from solid matrixes was accelerated with water vapor which was generated by microwave irradiation. A sample holder in a commercial microwave extraction cell kept the sample from direct contact with the organic solvent for analytes trapping during the treatment process. Therefore, relatively clean extracts were obtained with small amount of solvents. Without any cleanup steps, the obtained extract could be analyzed with gas chromatograph/mass spectrometers (GC/MS). Six PCB congeners (PCB15, 28, 70, 101, 180, 194, 209) and three OCPs (gamma-HCH, 4,4'-DDE, 4,4'-DDD) in two marine sediment samples (a sediment collected from a bay of Kyusyu Island, Japan, and a certified reference material NIST SRM1944) were analyzed by using this microwave-assisted steam distillation (MASD) technique and another extraction method (exhaustive steam distillation, MAE, and Soxhlet extraction); and comparisons of the results are shown in this report. Although recovery yields of highly chlorinated biphenyls (PCB180, 194, 209) and relatively polar OCPs (gamma-HCH, 4,4'-DDD) were low (30-60%) compared with other analytes (PCB15, 28, 70, 101, 4,4'-DDE; recovery, 80-100%), use of isotope labeled internal standards for the MASD technique gave comparable results with the values obtained by other extraction methods and the certified values in the samples.     

Microwave accelerated selective Soxhlet extraction for the determination of organophosphorus and carbamate pesticides in ginseng with gas chromatography/mass spectrometry

Microwave accelerated selective Soxhlet extraction (MA-SSE), a novel selective extraction technique, was investigated in this study. A Soxhlet extraction system containing a glass filter was designed as an extractor. During the procedure of MA-SSE, both the target analytes and the interfering components were extracted from the sample into the extraction solvent enhanced by microwave irradiation. After the solvent flowed though the sorbent, the interfering components were adsorbed by the sorbent, and the target analytes remaining in the solvent were collected in the extraction bottle. No cleanup or filtration was required after extraction. The efficiency of the MA-SSE approach was demonstrated in the determination of organophosphorus and carbamate pesticide residues in ginseng by gas chromatography/mass spectrometry (GC/MS). Under the optimized conditions, low limits of detection (0.050-0.50 μg/kg) were obtained. The recoveries were in the range of 72.0-110.1% with relative standard deviations less than 7.1%. Because of the effect of microwave irradiation, MA-SSE showed significant advantage compared with other extraction techniques. The sorbent used in this study showed good cleanup ability. The mechanism of MA-SSE was demonstrated to be based on the rupture of the cell walls according to the structural changes of ginseng samples. On the basis of the results, MA-SSE as a simple and effective sample preparation technique for the analysis of pesticide residues in complex matrixes shows great promise.     

Nanoliter solvent extraction combined with microspot MALDI TOF mass spectrometry for the analysis of hydrophobic biomolecules

A nanoliter solvent extraction technique combined with microspot matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is presented. This method involves the use of a nanoliter droplet containing organic solvents at the tip of a small capillary for extraction. The droplet is formed inside a microliter aqueous sample containing the analyte of interest. After extraction, the droplet is deposited onto a MALDI target precoated with a thin matrix layer. Since the nanoliter droplet never touches the sample container wall, any possible extraction of contaminants adsorbed on the plastic or glassware is avoided. In addition, there is no need to concentrate the organic phase after the extraction, thus avoiding any possible loss during the concentration step. The nanoliter volume can be readily deposited onto a MALDI target, producing a high analyte concentration within a microspot. Combined with microspot MALDI, this technique allows for very sensitive analysis of the extracted analyte. The performance of this technique is illustrated in several applications involving the detection of hydrophobic peptides or phospholipids. It is shown that very hydrophobic analytes can be extracted from small-volume samples containing a large amount of salts and/or more hydrophilic analytes, which tend to give dominant signals in conventional MALDI experiments. Nanoliter extraction of analyte from samples containing less than 100 nM hydrophobic analyte and over 1 microM easily ionized hydrophilic species is demonstrated. Finally, using the analysis of the ionophore valinomycin as an example, it is demonstrated that the technique is a more reliable tool for probing metal-peptide complexes than regular MALDI sample preparations.     

Analysis of nicotine and its oxidation products in nicotine chewing gum by a molecularly imprinted solid-phase extraction

Chromatographic stationary phases showing exceptional selectivity for nicotine can be prepared by the technique of molecular imprinting. Such phases were used in the search for a rapid cleanup step for nicotine and some of its oxidation products in chewing gum formulations. Thus, using an organic mobile phase, the nicotine analytes from chewing gums dissolved in nonpolar solvent were retained, whereas the nonpolar matrix eluted close to the void peak. A subsequent switch to an acidic mobile phase resulted in elution of the analytes as one sharp peak. Due to weak binding of the less basic oxidation products, other imprinted polymers were tested, and the solid-phase extraction procedure was optimized. Polymers were prepared using various functional and cross-linking monomers, templates, porogens and thermal treatments. This resulted in phases that, when compared with a nonimprinted or a C18 reversed-phase column, showed significantly higher recoveries of the analytes. Furthermore, no bleeding of template from the phases could be detected. The cleanup step was coupled off-line to reversed-phase HPLC, and the efficiency of the analysis was compared with and without the cleanup step. Three out of four analytes were quantitatively recovered using the imprinted phase, whereas, using the nonimprinted phase, only nicotine was recovered. Without the cleanup step, none of the analytes could be determined using the reversed-phase HPLC method.     

Solvent extraction applied to the recovery of heavy metals from galvanic sludge

In this study, a hydrometallurgical treatment involving the solvent extraction and recovery of some heavy metals from a sulphuric acid leach solution of galvanic sludge, using di-(2-ethylhexyl)-phosphoric acid (D2EHPA) and bis-(2,4,4-trimethylpentyl)-phosphinic acid (Cyanex 272), both diluted in kerosene, has been investigated.

The preliminary tests revealed the necessity to remove other metal species than zinc and nickel, contained in the leach solution, and therefore, processes to cement copper and precipitate chromium were then applied to finally obtain a Zn and Ni pregnant solution prior to solvent extraction. For the experimental conditions studied, Cyanex 272 showed a good recovery of Zn after the stripping stage using H₂SO₄, but D2EHPA effectively promoted a higher Zn extraction than Cyanex 272 did. The dependence of the solvent extraction method on variables such as pH, contact time and concentration of extractant, as well as the effect of different concentrations of sulphuric acid on stripping, are discussed.

The discussion also includes the previous conditions developed to separate the main interfering metallic species from the leach solution in order to improve the extraction and recovery of zinc by solvent extraction. The final objective has been to achieve a solution as pure as possible to recover nickel sulphate.     

Liquid-phase microextraction of phenolic compounds combined with on-line preconcentration by field-amplified sample injection at low pH in micellar electrokinetic chromatography.

This paper describes a novel method that applies field-amplified sample injection (FASI) in micellar electrokinetic chromatography (MEKC) with a low pH background electrolyte (BGE). Six phenolic compounds prepared in water or NaOH solution were used as the test analytes. Sample was injected electrokinetically after the introduction of a plug of water. During the injection, the water plug was pumped out of the capillary inlet by the electroosmotic flow, and the phenolic anions migrated very quickly in the direction of the outlet. When the anions reached the boundary between the water plug and BGE, they were neutralized and ceased moving. Thereafter, MEKC was initiated for the separation. This on-line preconcentration method could be conveniently coupled with a liquid-liquid-liquid microextraction procedure, in which a hollow fiber was used as an extraction solvent support to extract the analytes from the water sample. The acceptor phase consisted of 8 mM NaOH. After extraction, the extract was analyzed directly by MEKC, as described.     

Hybrid field-assisted solid-liquid-solid dispersive extraction for the determination of organochlorine pesticides in tobacco with gas chromatography

A novel one-step sample preparation technique termed hybrid field-assisted solid-liquid-solid dispersive extraction (HF-SLSDE) was developed in this study. A simple glass system equipped with a condenser was designed as an extraction vessel. The HF-SLSDE technique was a three-phase dispersive extraction approach. Target analytes were extracted from the sample into the extraction solvent enhanced by the hybrid field. Meanwhile, the interfering components were adsorbed by dispersing sorbent. No cleanup step preceded chromatographic analysis. The efficiency of the HF-SLSDE approach was demonstrated in the determination of organochlorine pesticide (OCP) residues in tobacco with a gas chromatography-electron capture detector (GC-ECD). Various operation conditions were studied systematically. Low detection limits (0.3-1.6 μg/kg) and low quantification limits (1.0-4.5 μg/kg) were achieved under the optimized conditions. The recoveries of OCPs ranged from 70.2% to 118.2%, with relative standard deviations of <9.6%, except for the lowest fortification level. Because of the effect of the hybrid field, HF-SLSDE showed significant predominance compared with other extraction techniques. The dispersing sorbent with good cleanup ability used in this study was also found to be a microwave absorption medium, which could heat the nonpolar extraction solvent under microwave irradiation. Different microstructures of tobacco samples before and after extractions demonstrated the mechanism of HF-SLSDE was based on an explosion at the cell level. According to the results, HF-SLSDE was proved to be a simple and effective sample preparation method for the analysis of pesticide residues in solid samples and could potentially be extended to other nonpolar target analytes in a complex matrix.     

食品接触材料中邻苯二甲酸酯的LTQ-Orbitrap组合式高分辨质谱快速筛查和确证

建立了食品接触材料中邻苯二甲酸酯快速筛查确证的高效液相色谱-高分辨质谱法(HPLC-LTQ-Orbi-trap/MS)。实验中采用加速溶剂萃取(ASE)法为样品前处理手段,优化了萃取溶剂、萃取温度、静态萃取时间等实验参数,提高了食品接触材料中邻苯二甲酸酯的提取效率。采用高分辨质谱有效地去除了基体干扰,通过静电场轨道阱全扫描得到的精确相对分子质量进行了化合物的定量,用离子阱的二级质谱图对未知化合物进行了进一步确证。结果表明:邻苯二甲酸酯的检测限为1 ng/mL;该方法的加标回收率为89.8%～101.3%,相对标准偏差均小于8.0%;所建立的方法简单,灵敏度高,适用于食品接触材料中邻苯二甲酸酯类增塑剂的筛查和检测。     

Analysis of continuous solvent extraction of nickel from spent electroless nickel plating baths by a mixer-settler

It is urgent to develop an effective technique to treat the large amount of spent electroless nickel plating bath and recycle the high concentration nickel. In our previous study, high recycling efficiency of nickel from the model spent bath was obtained by continuous solvent extraction with 2-hydroxy-5-nonylacetophenone oxime (LIX84I) as the extractant and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) as the accelerator using a mixer-settler extractor. It was observed that the extraction efficiency was affected by the operation parameters such as the flow rates of the aqueous and organic phases and the total stage number. In the present study, the effects of the operation parameters on the extraction efficiency were quantitatively studied on the basis of the pseudo-first-order interfacial extraction rate equation together with the hydrodynamic properties in the mixer. The organic phase holdup, measured under varying conditions of the flow rates of both phases, was analyzed by the Takahashi-Takeuchi holdup model in order to estimate the specific interfacial area. The overall extraction rate coefficients defined by the product of the interfacial extraction rate constant and the specific interfacial area were evaluated using the experimental data and ranged from 3.5 x 10(-3) to 6.7 x 10(-3)s(-1), which was close to the value of 3.4 x 10(-3)s(-1) obtained by batch extraction. Finally, an engineering simulation method was established for assessing the extraction efficiency of nickel during a multistage operation.     

有机磷农药残留前处理技术的研究

本实验主要是利用固相萃取技术对食品中有机磷农药前处理方法进行了研究。对自制的固相萃取小柱的选择参数进行了优化,建立合适的样品提取、净化、浓缩的前处理方法,确保色谱分析测定时无样品基质的干扰,从而为测定的结果提供了保证,并延长色谱柱的寿命,降低了实验成本。茶叶样品以丙酮为提取剂,超声波30 min后,经florisil柱(1000mg)+活性炭(50mg)混合柱浓缩净化,用10 mL的乙酸乙酯淋洗后,经色谱分析验证,所得回收率在73.7%以上,RSD在4.1%以下,结果令人满意。     

Improved solvent trapping of volatiles in supercritical fluid extraction by pressurizing the collection vial

The high flow rates that result after decompression make the trapping of analytes one of the more difficult aspects of a supercritical extraction. By elevation of the pressure on the collection vial, the flow may be reduced and trapping efficiency improved, considerably. The effects of different collection vial pressures were evaluated. The best results were obtained at 25 atm. With the collection vial at 25 atm, the trapping efficiencies of different solvents were then investigated. Also considered were the effects of solvent volume, extraction flow rate, collection solvent geometry, and restrictor temperature. For a 30 min extraction--with the restrictor line at 200 degrees C--quantitative recoveries were obtained with analytes as volatile as chlorobenzene (approximately 90%) in 1 mL of solvent. Mild precooling of the collection vessel allowed quantitative recoveries to be obtained down to benzene (94.2%).