Evaluation of multi-walled carbon nanotubes as gas chromatographic column packing

Purified multi-walled carbon nanotubes (PMWCNTs), activated charcoal and graphitized carbon black (Carbopack B) were used as column packing materials to compare their separation ability and other gas chromatographic behavior for aromatic hydrocarbons, alkanes, halogenated hydrocarbons, alcohols, ketones, esters, and ethers. The results show that PMWCNTs can be an excellent gas chromatographic packing material. Compared to Carbopack B with the same surface area, PMWCNTs had a stronger retention ability, a more homogenous surface and smaller theoretical plate numbers. Polar compounds can present symmetric peaks on PMWCNTs. PMWCNTs were found to be an interesting alternative adsorbent to activated charcoal and Carbopack B as gas chromatographic column packing material for volatile compounds, especially those with relatively low boiling points.     

Oral malodor,assessed by closed-loop,gas chromatography,and ion-trap technology

A method is described for the analysis of volatile organic compounds in saliva and tongue coating samples. The techniue is based on an off-line preconcentration step by means of a closed-loop trapping system followed by gas chromatography-ion trap detection. With the closed-loop technique, the volatile organic compounds(VOCs) are released from the matrix and trapped on an adsorbent without interference of water. The VOCs are released from the adsorbent into the gas chromatograph by thermdesorption. After separation, identification of the compounds is performed by ion trap technology. By this technique 82 compounds could be demonstrated in saliva and tongue coating samples. The technique is also used to demonstrate the formation of volatile bacterial fermentation compounds when a protein substrate is added to tongue coating samples. It is considered a very promising tool in further research on oral malodor.     

Novel adsorbent based on multi-walled carbon nanotubes bonding on the external surface of porous silica gel particulates for trapping volatile organic compounds

A novel adsorbent, 3-amino-propylsilica gel-multi-walled carbon nanotubes (APSG-MW), was prepared by chemical bonding multi-walled carbon nanotubes on silica gel. The surface area of APSG-MW was 98 m²/g, and the particle size was between 60 and 80 mesh with the average size of 215.0 μm. The adsorption capability of the new adsorbent to volatile organic compounds (VOCs) was measured. The effect of water to the adsorbent and its stability during storage were also investigated. Duplicate precision (DP) and distributed volume pair (DVP) on the basis of the EPA TO-17 criteria were estimated. The results showed that the sampling precision of the adsorbent was more superior compared to the MWCNTs because of the better air permeability. The new adsorbent was successfully applied in the determination of VOCs in ambient indoor air.     

Adsorption of water vapour from humid air in carbon molecular sieves: carbosieve S-III and carboxens 569, 1000 and 1001

The adsorption of water vapour in carbon molecular sieves (CMS) used to determine volatile organic compounds (VOCs) in air was investigated. The CMS mass in the trap was found not to affect the mass of retained water under conditions of incomplete saturation of the adsorbent bed with water. Thus, the restrictions commonly imposed on the CMS mass are not necessary. The usefulness of four different CMSs to sample large volumes of humid air was estimated. Carboxen 1000 exhibited the best performance. To assess the magnitude of CMS mass in the trap in dependence on the volume, the relative humidity and the temperature of the sample, the use of a novel parameter, called the water vapour interference factor, was suggested.     

Fast volatile organic compound recovery from soil standards for analysis by thermal desorption gas chromatography

The development of high-throughput environmental screening assays are needed to meet high-specification data quality objectives (DQOs) that require large numbers of samples to be taken and analysed rapidly. The acquisition and stabilisation of the sample is a key technical and operational challenge in analytical sequences associated with the determination of volatile organic compound (VOC) contamination of soils. Further the development of miniaturised and embedded analytical systems for environmental conditioning monitoring requires the development of new sampling techniques. A proof-of-concept study is described that shows how pressurised gas, in this case carbon dioxide, may be used to recover reversibly-bound VOCs from soil into an adsorbent sampler, and then analysed by thermal desorption-gas chromatography. The effects of the volume of the pressurised gas, the gas flow rate and the mass of the soil sample on the recovery efficiency and breakthrough from the adsorbent trap were investigated in a preliminary characterisation study. Two distinct approaches were identified. The first involved ventilation of the voids within the soil matrix to displace the soil-gas headspace, a rapid screening approach. The second involved a more prolonged purge of the matrix to strip reversibly bound species into the gas phase and hence pass them into the adsorbent trap, a purge and trap approach. The shortest possible sample processing time required to yield analytically useful responses was 5 s with the use of the headspace approach. In this case n-octane, benzene and toluene were recovered from conditioned spiked soil samples at concentrations in the range 42 to 1690 mg kg(-1). The limit of detection for the system was estimated to be no greater than 1.2 mg kg(-1). Using the purge and trap variant enabled recovery efficiencies greater than 93% to be achieved with liquid spikes of n-octane onto soil samples. These preliminary studies showed that a system based on this approach would need to balance recovery efficiency, time and analyte breakthrough from the adsorbent trap.     

Single-walled carbon nanohorns immobilized on a microporous hollow polypropylene fiber as a sorbent for the extraction of volatile organic compounds from water samples

We have evaluated the behavior of single-walled carbon nanohorns as a sorbent for headspace and direct immersion (micro)solid phase extraction using volatile organic compounds (VOCs) as model analytes. The conical carbon nanohorns were first oxidized in order to increase their solubility in water and organic solvents. A microporous hollow polypropylene fiber served as a mechanical support that provides a high surface area for nanoparticle retention. The extraction unit was directly placed in the liquid sample or the headspace of an aqueous standard or a water sample to extract and preconcentrate the VOCs. The variables affecting extraction have been optimized. The VOCs were then identified and quantified by GC/MS. We conclude that direct immersion of the fiber is the most adequate method for the extraction of VOCs from both liquid samples and headspace. Detection limits range from 3.5 to 4.3 ng L^?1 (excepted for toluene with 25 ng L^?1), and the precision (expressed as relative standard deviation) is between 3.9 and 9.6 %. The method was applied to the determination of toluene, ethylbenzene, various xylene isomers and styrene in bottled, river and tap waters, and the respective average recoveries of spiked samples are 95.6, 98.2 and 86.0 %.

Evaluation of graphene as an advantageous adsorbent for solid-phase extraction with chlorophenols as model analytes

Graphene, a novel class of carbon nanostructures, possesses an ultrahigh specific surface area, and thus has great potentials for the use as sorbent materials. We herein demonstrate the use of graphene as a novel adsorbent for solid-phase extraction (SPE). Eight chlorophenols (CPs) as model analytes were extracted on a graphene-packed SPE cartridge, and then eluted with alkaline methanol. The concentrations in the eluate were determined by HPLC with multi-wavelength UV detection. Under the optimized conditions, high sensitivity (detection limits 0.1-0.4 ng/mL) and good reproducibility of CPs (RSDs 2.2-7.7% for run-to-run assays) were achieved. Comparative studies showed that graphene was superior to other adsorbents including C18 silica, graphitic carbon, single- and multi-walled carbon nanotubes for the extraction of CPs. Some other advantages of graphene as SPE adsorbent, such as good compatibility with various organic solvents, good reusability and no impact of sorbent drying, have also been demonstrated. The proposed method was successfully applied to the analysis of tap and river water samples with recoveries ranging from 77.2 to 116.6%. This work not only proposes a useful method for environmental water sample pretreatment, but also reveals great potentials of graphene as an excellent sorbent material in analytical processes.     

Magnetic spherical carbon as an efficient adsorbent for the magnetic extraction of phthalate esters from lake water and milk samples

Magnetic spherical carbon was synthesized by a facile hydrothermal carbonization procedure with biomass glucose as the carbon precursor and nanoclusters iron colloid as magnetic precursor. The textures of the as‐prepared magnetic spherical carbon were characterized by nitrogen adsorption–desorption isotherms, X‐ray diffraction, transmission electron microscopy, scanning electron microscopy and vibration sample magnetometry. Results indicated that the magnetic spherical carbon possessed high surface area as well as strong magnetism, which endows the material with good adsorption capability and easy separation properties. To assess its absorption performance, the magnetic spherical carbon was employed as adsorbent for the extraction and preconcentration of phthalate esters from lake water and milk samples before high‐performance liquid chromatographic analysis. Some key parameters that could influence the enrichment efficiency were investigated. Under the optimum conditions, a good linearity was achieved with the linear correlation coefficients higher than 0.9973. The limits of detection (S/N = 3) were 0.05–0.08 ng/mL for lake water and 0.1–0.2 ng/mL for milk samples. The recoveries of the analytes for the method were in the range 80.1–112.6%.     

新型单壁碳纳米管采样吸附剂性能的评价

研究了单壁碳纳米管(SWCNTs)作为新型采样吸附剂的性能和效果,并应用于空气中挥发性有机化合物的分析测定。结果表明,单壁碳纳米管具有较大的比表面积,与经典Tenax TA吸附剂相比,对低碳数挥发性强的有机化合物回收率高,有更强的吸附能力;空白实验表明,SWCNTs易获得较低本底,具有化学惰性和疏水特性,采样时水的干扰小。当湿度增加时在误差允许的范围内准确度不受影响;实验测定具有较大的穿透容量和安全采样体积。将单壁碳纳米管吸附剂实际应用于大气中挥发性有机化合物的测定,通过与经典吸附剂Tenax TA相比,更适于采集大气中的挥发性有机化合物。     

Determination of organophosphorus pesticides by gas chromatography with mass spectrometry using a large‐volume injection technique after magnetic extraction

A fast and efficient method was developed for the extraction and determination of organophosphorus pesticides in water samples. Organophosphorus pesticides were extracted by solid‐phase extraction using magnetic multi‐walled carbon nanotubes and determined by gas chromatography with ion‐trap mass spectrometry. Parameters affecting the extraction were investigated. Under optimum conditions of the method, 10 mg magnetic multi‐walled carbon nanotubes were added into 10 mL sample. After 2 min, adsorbent particles settled at the bottom of test tube with a magnet. After removing aqueous supernatant, the analytes were desorbed with acetonitrile. Then, 70 μL of acetonitrile phase was injected into the gas chromatography and mass spectrometry system that had an ion‐trap analyzer. To achieve high sensitivity, the large‐volume‐injection technique was used with a programmed temperature vaporization inlet, and the ion‐trap mass spectrometer was operated in single ion storage mode. Under the best conditions, the enrichment factors and extraction recoveries were in the range of 113–124 and 74–103%, respectively. The limits of detection were between 3 and 15 ng/L, and the relative standard deviations were < 10%. This method was successfully used for the determination of organophosphorus pesticides in dam water, lagoon water, and river water samples with good reproducibility and recovery.     

Sensitive determination of polycyclic aromatic hydrocarbons in water samples by HPLC coupled with SPE based on graphene functionalized with triethoxysilane

The graphene functionalized with (3‐aminopropyl) triethoxysilane was synthesized by a simple hydrothermal reaction and applied as SPE sorbents to extract trace polycyclic aromatic hydrocarbons (PAHs) from environmental water samples. These sorbents possess high adsorption capacity and extraction efficiency due to strong adsorption ability of carbon materials and large specific surface area of nanoparticles, and only 10 mg of sorbents are required to extract PAHs from 100 mL water samples. Several condition parameters, such as eluent and its volume, adsorbent amount, sample volume, sample pH, and sample flow rate, were optimized to achieve good sensitivity and precision. Under the optimized extraction conditions, the method showed good linearity in the range of 1–100 μg/L, repeatability of the extraction (the RSDs were between 1.8 and 2.9%, n = 6), and satisfactory detection limits of 0.029–0.1 μg/L. The recoveries of PAHs spiked in environmental water samples ranged from 84.6 to 109.5%. All these results demonstrated that this new SPE technique was a viable alternative to conventional enrichment techniques for the extraction and analysis of PAHs in complex samples.     

Preparation of a magnetic porous carbon with hierarchical structures from waste biomass for the extraction of some carbamates

In this study, corn stalk was used to synthesize a magnetic adsorbent by pyrolysis together with KHCO₃ as the chemical activator and iron(III) salt as the magnetic reagent. The characterization by scanning electron microscopy, transmission electron microscopy and N₂ adsorption–desorption analysis showed that the magnetic carbon adsorbent had a structure of hierarchical pores with a high specific surface area. To evaluate its adsorption performance, the adsorbent was used for the extraction of carbamates pesticides (propoxur, isoprocarb and fenobucarb) from water and zucchini samples before high‐performance liquid chromatography analysis. The result showed that the adsorbent had a good adsorption capability for the analytes. Under the optimized conditions, a good linearity for the analytes existed in the range of 0.1–100.0 ng/mL for water samples and 0.5–100.0 ng/g for zucchini samples with the correlation coefficients of 0.9992–0.9998. The limits of detection for the analytes at a signal to noise ratio of 3 were 0.03 ng/mL for water samples and 0.20–0.50 ng/g for zucchini samples.     

多壁碳纳米管作为气相色谱固定相的性能研究

将甲烷催化裂解法生产的经过纯化的多壁碳纳米管(PMWCNTs)、活性炭、石墨 化碳黑(Carbopack B)分别填装成气相色谱填充柱,比较它们分离烷烃、芳香烃、 卤代烃、醇、酮、醚、酯类的性能。分别在PMWCNTs和Carbopack B上涂清5%(w/w) 的Carbowax 20M,填装成气相色谱填充柱后,比较它们分离醇、酮、醚、酯、有机 酸类的性能。结果表明,PMWCNTs是一种性能优异的气相色谱固定相。与相同比表 面积的Carbopack B石墨化碳黑相比较,它有更强的保留能力,适合于分析沸点相 对较低的化合物;具有更均匀的表面,表现为极性化合物亦可得到对称的峰形;理 论塔板数较小。此外,和Carbopack B一样,PMWCNTs涂清5% (w/w) Carbowax 20M 后可用来分离极性化合物,甚至是强极性的小分子有机酸。     

Nanoporous carbon derived from a metal organic framework as a new kind of adsorbent for dispersive solid phase extraction of benzoylurea insecticides

We describe the preparation of nanoporous carbon using a metal-organic framework (MOF) as a template and furfuryl alcohol as the source for carbon. The MOF consists of a zeolitic framework (ZIF-8) that was obtained from 2-methylimidazole and Zn(II) ions. ZIF-8 was soaked with furfuryl alcohol which then was carbonized at 900 °C. The resulting nanoporous carbon (MOF-C) exhibits a high specific surface area and a large pore volume. It was used as a dispersive solid-phase adsorbent for the preconcentration of the benzoylurea insecticides diflubenzuron, triflumuron, hexaflumuron and teflubenzuron from water and tangerine samples. Under optimized conditions, the methods exhibits excellent extraction performance. The insecticides can be quantified via HPLC with UV detection in the 0.5 to 100 ng mL⁻¹ concentration range in case of spiked tap water, and in the 2.0 to 200 ng g⁻¹ concentration range in case of tangerines. The limits of detection range from 0.10 to 0.23 ng mL⁻¹ in case of water samples, and from 0.34 to 0.71 ng g⁻¹ for tangerine sample (at an S/N ratio of 3). Mean recoveries range from 91.7 to 107.9 %, with relative standard deviations of <7.1 %. The results indicate that the method was efficient for the preconcentration of trace levels of benzoylurea insecticides from water and tangerine samples. Conceivably, this new adsorbent has a large potential with respect to the enrichment of other organic pollutants from various kinds of samples.

Nanoporous carbon was prepared using metal-organic framework (zeolitic imidazolate framework, ZIF-8) as template with furfuryl alcohol as carbon precursor, and was used as dispersive solid phase extraction adsorbent for the enrichment of some benzoylurea insecticides from water and tangerine samples.

     

荧光衍生化-磁分散固相萃取/高效液相色谱检测池塘水与蔬菜中3种挥发性异味物质

以6-碳酰氯左氧氟沙星(LFC-Cl)为衍生试剂,磁性氧化石墨烯(MGO)为吸附剂,建立了2-甲基异莰醇(2-MIB)、土臭素(GSM)和3-甲基-1-丁醇(3-MB)的高效液相色谱荧光检测(HPLC-FLD)分析方法。在浓度为0.05 mol/L的4-二甲氨基吡啶(DMAP)乙腈溶液中,衍生温度60℃,反应时间90 min,超声波辅助条件下,可完成上述3种醇类挥发性异味物质(VOCs)的衍生化。在吸附剂用量20 mg、萃取时间20 min、解吸剂为乙腈(含1%甲酸)、解吸时间3 min条件下,能实现3种异味物质衍生物的富集和净化。在优化的HPLC条件下,15 min内可实现3种衍生物的基线分离和高灵敏检测。方法检出限(LOD)为0.020~0.95 ng/L,定量下限(LOQ)为0.10~3.3 ng/L,线性、精密度和回收率良好。与已报道的方法相比,该方法具有灵敏度高、样品前处理简单、仪器普适性好等优势,可用于池塘水、蔬菜中VOCs的快速、定量测定,为食品和环境水样监测提供了一种新方法。     

An Improved Method for Testing Weak VOCs in Dry Plants with a Purge and Trap Concentrator Coupled to GC-MS

The purge and trap (P&T) technique was improved for measuring the release of organic compounds with weak volatility (weak VOCs) from dry plant materials. Using distilled water as a dispersant, the plant tissues were mulled and placed in the purge tube of a P&T concentrator. Then the sample-containing purge tube was heated to 80 °C with helium as the carrier gas, and the purged volatiles were preconcentrated in the trap prior to analysis with GC-MS. The VOCs in Chinese herbal medicinal plants Swertia tetraptera, Saussurea involucrate and S. lacostei, which had been stored dry for 1–2.5 years were assayed with this improved method and conventional P&T techniques. Our results show this new P&T method had great promise for determining the VOCs in dry plant materials. Using this new technique, we identified 38 weak VOCs with a large peak area from the dry samples. In contrast, less than five VOCs were detected by the conventional P&T method. So the improved heat-purge and trap system showed to be more efficient for measuring the release of the weak VOCs from dry plant materials.     

吹扫捕集-气相色谱/质谱法分析汉江有机污染物

采用恒温水浴吹扫捕集-气相色谱/质谱(P&T-GC/MS)法分析汉江水中挥发性有机物,提高了挥发性有机物分析的灵敏度;选用低空白的纯净水,降低了分析的干扰。采用避光的方法以及将水样直接过柱,提高了半挥发性有机物的回收率。用改进了的方法分析汉江水共检出有机物36种。此方法同样适用于其它地表水中有机物的分析。     

Comparison of multiwalled carbon nanotubes and a conventional absorbent on the enrichment of sulfonylurea herbicides in water samples.

Recently, multiwalled carbon nanotubes (MWCNTs) have been at the center of attention because of their applications in many fields. Efforts to investigate the possibility of MWCNTs as SPE absorbents for the enrichment of environmental pollutants yielded positive results. The goal of the present work was to compare the enrichment power of MWCNTs with that of regular adsorbents, such as C18 silica for SPE of five sulfonylurea herbicides. The results indicated that multiwalled carbon nanotubes were very suitable for the preconcentration of sulfonylurea herbicides in complex water samples, yielding better recoveries. C18 gave a lightly lower enrichment performance, and could not enrich nicosulfuron in complex samples. All of these experimental results indicated that multiwalled carbon nanotubes could be used as a valuable alternative adsorbent for the SPE of sulfonylurea herbicides in many real water samples.     

Inside-tube solid-phase microextraction as an interlink between solid-phase microextraction and needle device for n-hexane evaluation in air and urine headspace

Monitoring the trace amount of chemicals in various samples remains a challenge. This study was conducted to develop a new solid-phase microextraction (SPME) system (inside-tube SPME) for trace analysis of n-hexane in air and urine matrix. The inside-tube SPME system was prepared based on the phase separation technique. A mixture of carbon aerogel and polystyrene was loaded inside the needle using methanol as the anti-solvent. The air matrix of n-hexane was prepared in a Tedlar bag, and n-hexane vapor was sampled at a flow rate of 0.1 L/min. Urine samples spiked with n-hexane were used to simulate the sampling method. The limit of detection using the inside-tube SPME was 0.0003 μg/sample with 2.5 mg of adsorbent, whereas that using the packed needle was 0.004 μg/sample with 5 mg of carbon aerogel. For n-hexane analysis, the day-to-day and within-day coefficient variation were lower than 1.37%, with recoveries over 98.41% achieved. The inside-tube SPME is an inter-link device between two sample preparation methods, namely, a needle trap device and an SPME system. The result of this study suggested the use of the inside-tube SPME containing carbon aerogel (adsorbent) as a simple and fast method with low cost for n-hexane evaluation.     

Magnetic nanoporous carbon as an adsorbent for the extraction of phthalate esters in environmental water and aloe juice samples

In this work, magnetic nanoporous carbon with high surface area and ordered structure was synthesized using cheap commercial silica gel as template and sucrose as the carbon source. The prepared magnetic nanoporous carbon was firstly used as an adsorbent for the extraction of phthalate esters, including diethyl phthalate, diallyl phthalate, and di‐n‐propyl‐phthalate, from lake water and aloe juice samples. Several parameters that could affect the extraction efficiency were optimized. Under the optimum conditions, the limit of detection of the method (S/N = 3) was 0.10 ng/mL for water sample and 0.20 ng/mL for aloe juice sample. The linearity was observed over the concentration range of 0.50–150.0 and 1.0–200.0 ng/mL for water and aloe juice samples, respectively. The results showed that the magnetic nanoporous carbon has a high adsorptive capability toward the target phthalate esters in water and aloe juice samples.