Simultaneous determination of semivolatile organic compounds in indoor air by gas chromatography-mass spectrometry after solid-phase extraction

A method is described for simultaneous determination of semivolatile organic compounds (SVOCs) in indoor air by gas chromatography-mass spectrometry (GC-MS). The selected 73 SVOCs were collected using combined adsorbents (quartz fiber filter disk and Empore disk) for 24 h at a 5.0 l/min flow rate. The SVOCs collected were extracted with acetone, concentrated, then analyzed by an internal standard method. Forty compounds (19 plasticizers and flame retardants; 19 insecticides; 1 synergist; and 1 fungicide) among the target SVOCs were determined accurately and precisely. The method of detection limits for these compounds were approximately 0.5 ng/m3 for most of the SVOCs. The collected SVOC samples could be stored for up to 1 month at 4 C in the refrigerator.     

Thermal-desorption gas chromatographic procedure for screening coal fly ash for volatile organic compounds

Thermal desorption of coal fly ash in a flowing stream of helium liberates volatile compounds which are collected on Tenax resin. A chemical “fingerprint” of these components collected from the fly ash is obtained by using thermal desorption of the material collected on the Tenax resin and capillary-column gas chromatography. Compounds ranging in volatility from that of benzene (b.p. 80°C) through C₁-phenanthrene (b.p. ca. 360°C) are detected, but recoveries of components only through naphthalene (b.p. 218°C) are suitable for quantitative work. The method provides chemical information on volatile organic compounds complementary to that achieved by procedures based on solvent extraction.     

Polymer-coated hollow fiber microextraction combined with on-column stacking in capillary electrophoresis

In this work, a novel microextraction method termed polymer-coated hollow fiber microextraction (PC-HFME) was developed in combination with capillary electrophoresis (CE). Polar dihydroxylated polymethylmethacrylate polymer was coated onto a porous propylene hollow fiber membrane and used as an adsorbent and that was placed in a stirred aqueous sample solution. Tumbling of the extraction device within the sample solution facilitated extraction. The amino alcohols (2-amino-1-phenylethanol, norephedrine, alprenolol and atenolol which are beta-blocker drugs), were used as model compounds to investigate the extraction performance. No organic solvent was used in this procedure. The extract was then further concentrated through on-column stacking (normal stacking mode) during CE analysis. The detection limits ranged from 0.9 to 7 ng ml(-1). Relative standard deviations (n=6) ranged from 4 to 6%. The extraction of the amino alcohols in spiked wastewater effluent (representing a complex matrix) was evaluated using the developed procedure.     

Evaluation of a valveless thermal desorption system for organic aerosols and vapors. Transfer lines and preconcentration module

Semivolatile organic compounds (SVOCs) are distributed in the atmosphere between the gas- and aerosol-phases. The low vapor pressures of some SVOCs makes thermal extraction and transfer through gas chromatographic (GC) systems difficult. We evaluated a programmable temperature vaporization (PTV) GC inlet, which served as the preconcentration module, and four open-tubular capillaries (Silcosteel- and Siltek-treated stainless steel, Silcosteel-treated stainless steel coated with 100% dimethylpolysiloxane, and deactivated fused silica) as transfer lines in a valveless, whole-sample analytic system. Thermal extraction of C(9)-C(36)n-alkanes at 300 and 320 degrees C from fused silica and quartz wool in the PTV inlet was equally efficient. Adsorptive losses of C(22)-C(36)n-alkanes to stainless steel surfaces that protruded into the PTV inlet were suspected. Thus, treatment of the outer surfaces of transfer lines is recommended for effective thermal transfer of SVOCs. Transfer efficiencies began to decline after n-C(24), n-C(28), and n-C(30) in Silcosteel-treated stainless steel, deactivated fused silica, and Siltek-treated stainless steel transfer lines, respectively. Thus, quantitative recovery at 320 degrees C of compounds with vapor pressures less than about 3 x 10(-8)Pa is not expected in valveless SVOC thermal desorption systems that use Siltek-treated stainless steel transfer lines and fused silica or quartz wool as preconcentration substrates.     

Isolation and Determination of Volatile Organic Compounds from Water by Dynamic Purge-and-Trap Technique Coupled with Capillary Gas Chromatography

The preconcentration technique of purge-and-trap has been investigated in the present work for quantitative adsorption of volatile organic pollutants purged from water samples. A dynamic purging device with variable volume size has been constructed and tested to purge different concentrations of organic compounds. With Tenax GR as the adsorbent, a dynamic purge-and-trap technique was developed combining on-column preconcentration procedures using ambient trapping/thermal desorption/cryogenic focusing/back-flash injection prior to separation and determination using capillary gas chromatography. Various aromatic compounds in water were determined, giving linear working ranges over five orders of magnitude from 0.02 to 5000 µg/L. The analytical procedures were optimized under the assistance of ultrasonication with results validated for the determination of organic contaminants in underground water and tap water, giving over 93% recoveries and a detection limit of 0.01 µg/L, two orders of magnitude lower than those obtained using commercial available instruments with on-line configuration to minimize cross-contamination. The technique provides a potential automated method for in situ monitoring of volatile organic compounds in water.     

Ultrasonic extraction of total particulate aromatic hydrocarbons (TpAH) from airborne particles at room temperature.

A superior enrichment procedure for the extraction of TpAH from airborne particles collected on glass fiber filter paper is described. The sample is suspended in a solvent and subjected to ultrasonic waves at room temperature with glass powder to adsorb polar coextractives. The TpAH in the filtered extracts are separated from other compounds by high speed liquid chromatography. Sensitivity is in the nanogram range, and the procedure is highly reproducible. Significantly larger amounts of TpAH are recovered than with Soxhlet extraction for 6 to 8 hours, and the percentage of pAH in the extracts is much higher. The entire procedure requires approximately 40 minutes, most of which is waiting time.     

Application of central composite design in the optimisation of thermal desorption parameters for the trace level determination of the chemical warfare agent chloropicrin

A quantitative trace-level thermal desorption gas chromatography mass spectrometry method was developed for chloropicrin CCl3NO2 using central composite design. Factors influencing the thermal decomposition were elucidated and optimum conditions for maximum response deduced. Four factors were investigated: desorption time, desorption temperature, valve temperature and line temperature. Only valve and line temperature influenced the response. The storage stability of chloropicrin on Tenax TA was investigated. Only the storage conditions affected recovery: no significant loss of chloropicrin was observed for spiked tubes stored in a refrigerator for up to 30 days. The application of central composite design to study thermal degradation of chloropicrin has not been described in the literature. The benefits in adopting this approach are reflected in the limit of detection, 22 ng on the sorbent tube (equivalent to 3.2 ppbv), the lowest atmospheric detection limit reported to date.     

The determination of nitrite and nitrate by the ring-oven technique

Determinations of nanogram amounts of nitrite and nitrate individually and together, based on a variation of the ring-oven technique, are described. In the “segment technique” used, a stable standard scale is not necessary. Interferences have been studied. Nitrite in sausages can be determined.     

Multi-layer cartridges filled with multi-walled carbon nanotubes for the determination of volatile organic compounds in indoor air.

A kind of new multi-layer adsorbent including Tenax TA/multi-walled carbon nanotubes (MWCNTs)/Carboxen 564 was developed for collecting volatile organic compounds. The adsorption and desorption efficiencies of 11 kinds of adsorbents (including Activated charcoal, Tenax TA, Carboxen 564, Chromosorb 101, Chromosorb 102, Chromosorb 103, Chromosorb 105, Porapak Q, GDX 301, XAD-2, and MWCNTs) were compared. By combining the advantages of Tenax TA, MWCNTs, and Carboxen 564, new type of multi-layer adsorbents was developed. The adsorption and desorption efficiency, the sampling reproducibility, and the effect of water were improved using multi-layer adsorbents, Tenax TA/MWCNTs/Carboxen 564. New multi-layer adsorbents were successfully applied to the determination of volatile organic compounds (VOCs) in ambient air.     

Considerations on Static and Dynamic Sorptive and Adsorptive Sampling to Monitor Volatiles Emitted by Living Plants

Static and dynamic headspace sampling have been applied for the enrichment of volatiles emitted by living plants. For solid phase microextraction (SPME) the sorptive fibers polydimethylsiloxane (PDMS) and polyacrylate (PA) have been compared and, in accordance with the like‐like principle, polar compounds exhibit more affinity for the PA fiber while apolar solutes favor the PDMS fiber. For dynamic sampling, tubes packed with PDMS particles show greater inertness than Tenax; some Tenax decomposition products, e.g. benzaldehyde and acetophenone, interfere with the analyses. With PDMS particles operated in the breakthrough mode, the obtained profiles are similar to those obtained by SPME on the PA fiber. Recoveries relative to a packed PDMS bed are 85% for Tenax, 2.4% for SPME‐PDMS, and 6.2% for SPME‐PA.     

A study of the aroma profiles of non-alcohol beer by thermal desorption and GC-MS

The aroma profiles of different types of low alcohol and non-alcohol beer have been compared by collection of volatile headspace compounds on Tenax resin and GC-MS analysis following thermal desorption. Some aroma compounds have been tentatively identified by NBS library search.     

Monitoring and analytics of semivolatile organic compounds (SVOCs) in indoor air

This paper reviews literature information on the behaviour of semivolatile organic compounds (SVOCs) in the indoor environment, as well as the most likely emission sources. The consecutive stages of analytical procedures used for monitoring SVOCs in indoor environments are described. The most common approaches used for collecting samples from the gas and particulate phases are mentioned. The paper discusses and compares various types of sorbents and filters applied in dynamic, passive and denudational techniques, as well as the techniques used to liberate the SVOCs, including Soxhlet, sonication and microwave extraction. The main advantages and disadvantages of each technique are discussed, together with possible future trends. The approaches commonly used during the final determination step, such as gas chromatography and liquid chromatography, are presented together with their possible drawbacks, and ways of eliminating them are suggested. The review makes brief reference to the effects of human exposure to SVOCs in house dust and discusses the main aspects of the analytical procedures used to monitor the presence of SVOCs in this medium.     

Multiwalled Carbon Nanotube Coated on Stainless Steel Wire for Solid-Phase Microextraction of Organochlorine Pesticides in Water

A novel solid-phase microextraction (SPME) fiber was prepared by coating multiwalled carbon nanotube (MWCNTs) on a stainless steel wire, and its characteristics were studied. To evaluate the MWCNTs coating, the fiber was used for the extraction of some organochlorine pesticides (OCPs) from water samples by Headspace SPME (HS-SPME) mode. Potential factors affecting the extraction efficiency such as extraction time, extraction temperature, agitation, ionic strength, desorption temperature, and time were also optimized. Several experiments were carried out by water spiked with target compounds to evaluate the analytical characteristics of the proposed method under optimized conditions. The linearity was from 0.1 to 10 ug/L with the linear correlation coefficients (r) ranging from 0.9956 to 0.9995. The limits of detection (LOD, S/N = 3) for these pesticides were between 0.43 and 2.13 ng/L and the precision (RSD, n = 5) was 2.53–12.25%. When this method was applied for the spiked real river sample, the relative recoveries ranged from 72.4% to 134.7% for the tested OCPs.     

Growth of cedar-like Au nanoparticles coating on an etched stainless steel wire and its application for selective solid-phase microextraction

A novel cedar-like Au nanoparticles (AuNPs) coating was fabricated on an etched stainless steel (SS) wire by direct chemical deposition and used as an efficient and unbreakable solid phase microextraction (SPME) fiber. The etched SS wire offers a rough surface structure for subsequent growth of AuNPs in chloroauric acid solution. As a result, the uniform cedar-like AuNPs coating with larger surface area was tightly attached to the etched SS wire substrate. The AuNPs coated etched SS fiber (AuNPs/SS) was examined for SPME of ultraviolet (UV) filters, phthalate esters and aromatic hydrocarbons coupled to high-performance liquid chromatography with UV detection. The fabricated fiber exclusively exhibited excellent extraction efficiency and selectivity for some aromatic hydrocarbons. Influential parameters of extraction and desorption time, temperature, stirring rate and ionic strength were investigated and optimized. The limits of detection ranged from 0.008 μg L⁻¹ to 0.037 μg L⁻¹. The single fiber repeatability varied from 3.90% to 4.50% and the fiber-to-fiber reproducibility ranged from 5.15% to 6.87%. The recovery of aromatic hydrocarbons in real water samples spiked at 2.0 μg L⁻¹ and 20 μg L⁻¹ ranged from 94.38% to 106.2% with the relative standard deviations below 6.44%. Furthermore the growth of the cedar-like AuNPs coating can be performed in a highly reproducible manner. This fabricated fiber exhibits good stability and withstands at least 200 extraction and desorption replicates.     

Highly porous silica-polyaniline nanocomposite as a novel solid-phase microextraction fiber coating

A highly porous fiber-coated SBA-15/polyaniline material was prepared for solid-phase microextraction (SPME). The SBA-15/polyaniline nanocomposite was synthesized via chemical polymerization. The prepared SBA-15/polyaniline particles were analyzed by scanning electron microscopy 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). In optimum conditions (extraction temperature 60°C, extraction time 40 min, ionic strength 20%, stirring rate: 500 rpm, desorption temperature 260°C, desorption time 2 min), the repeatability for one fiber (n=3), expressed as relative standard deviation (RSD%), was between 5.3 and 8.6% for the test compounds. For deionized water, spiked with selected PAHs, the detection limits for the studied compounds were between 2 and 20 pg/mL.     

聚苯胺/二氧化钛纳米管固相微萃取纤维的组装及应用

以钛丝表面原位阳极氧化生成的二氧化钛纳米管为基体,通过电聚合苯胺组装得到新型聚苯胺包覆二氧化钛复合纳米管阵列固相微萃取纤维。实验讨论了无机酸介质、苯胺浓度和氧化电压对电聚合苯胺的影响,经过对纤维表面形貌和元素成分的分析,得到最佳的纤维涂层条件：电解液组成为1 mol/L的H₂SO₄-0.5 mol/L的苯胺,聚合电压10 V,氧化时间60 min。采用所制备的纤维与高效液相色谱联用萃取水样中的紫外线吸收剂并优化萃取条件,固相微萃取条件如下：萃取时间40 min,解吸时间4 min,萃取温度40℃,搅拌速率600 r/min,样品溶液中不加NaCl。同时对环境水样中的目标物分析测定,并做加标试验,目标分析物的平均回收率为78.2%~118%,相对标准偏差为4.4%~8.9%。该方法简便、灵敏、准确,适用于环境水样中紫外线吸收剂的快速测定。     

Application of thermal desorption to the development of a gas chromatographic/mass spectrometric method for the determination of toluene,chlorinated aromatic hydrocarbons,and 2,3,7,8-tetrachlorodibenzo-p-dioxin in combustion emissions

A fast and accurate analytical method, which uses commercially available adsorbents (Tenax TA, Carbotrap B and C, and Carbosieve S-III), was developed for the sampling and determination of aromatic hydrocarbons, chloroaromatic compounds, and 2,3,7,8-tetrachlorodibenzo-p-dioxin. The breakthrough volume data show that Carbotrap C has a good capacity for compounds of high molecular weight, whereas Carbosieve S-III and Tenax TA are efficient for volatile compounds. The organic components are thermally desorbed and transferred to a gas chromatograph/mass spectrometer. Importantly, thermal desorption avoids conventional solvent extraction procedures and also allows reuse of adsorbent tubes. Preliminary results for recovery of analytes from tubes packed with single adsorbent prove that a single-adsorbent bed is not capable of sampling a wide range of compounds. The best method to obtain the desired collection and desorption properties is to use adsorbent tubes containing several different materials. The results of optimization studies are summarized.     

Investigation of adsorption of nanogram quantities of iron(II) tris-(1,10-phenanthrolinate) on glasses and silica by thermal lens spectrometry

Thermal lens spectrometry is used for studying adsorption equilibria in aqueous solutions at the level of nanogram quantities of iron(II) tris-(1,10-phenanthrolinate) as a model system. The kinetics of the sorption of the chelate on silica is studied and adsorption isotherms are built. Thermal lensing is used as a method for direct determination of the chelate concentration adsorbed on a quartz surface. The detected amount is 4.1×10⁻¹⁵ mol at the area irradiated by the excitation beam. The adsorption of iron(II) tris-(1,10-phenanthrolinate) on laboratory glassware at the nanogram level is characterised by measuring the residual concentration of the sorbate in solution. A procedure for handling and cleaning the laboratory glassware for determining nanogram amounts of iron in aqueous solutions is proposed. The sensitivity of thermal lensing both in measuring adsorption on silica and glass and quartz surfaces is 100-fold higher than diffuse-reflectance measurements under the same conditions.     

Gas-liquid chromatography of amino acids: Columns and methodology as a basis for routine amino acid analysis using glass capillary gas chromatography

A carefully Standardized technique is described for the preparation of glass capillary columns which can be used successfully for routine quantitative amino acid analysis. Comparison is made between two different modes of sample injection. Preliminary quantitative results from “split” injection and “on-column” injection techniques are evaluated statistically and it is concluded that the “on-column” system is a prerequisite for quantitative amino acid analysis by glass capillary gas chromatography. An analysis of fish muscle protein hydrolyzate illustrates an application of this technique and results are compared with those from a packed column analysis.     

Application of simplified desorption method to study on sorption of americium(III) on bentonite

To elucidate the sorption behavior of americium(III) on bentonite, which is a mixture of montmorillonite clay, quartz and other minerals, simplified desorption experiments were applied to the solid phases collected after the sorption experiments. The sorption–desorption behavior was examined in the final pH range from 2 to 8. The desorption experiments revealed that most of the Am was sorbed on the montmorillonite moiety of the bentonite. The sorption of Am on montmorillonite was divided into two types: one was the “exchangeable” sorption, in which the sorbed Am was desorbed with a 1 M KCl aqueous solution, and the rest was the “unexchangeable” sorption. The exchangeable sorption was ion exchange of mostly Am³⁺. The unexchangeable sorption was the strong sorption of Am hydroxides. An accessory iron mineral, pyrite, might be involved in the Am sorption on bentonite at neutral pH.