Use of experimental design to optimize the analysis of volatile compounds by dynamic headspace extraction followed by cold trapping and capillary GC

A central composite design has been used to improve the extraction performance of a dynamic headspace method; extraction yield was evaluated on a homogeneous sample of cheese powder. The volatile compounds were stripped from the sample with nitrogen and adsorbed on a Tenax trap, analysis being performed with a thermal cold trapping injector connected directly to a capillary GC. Three variables (sample temperature, extraction time, and nitrogen flow rate) were investigated, and a quadratic model with interactions was postulated. Twenty experiments was performed, each producing five responses. It was shown that the best conditions for the extraction procedure were those characterized by the highest values of the three variables investigated.     

AMicro-sized headspace GC technique for determination of organic volatile impurities in water-insoluble pharmaceuticals

Summary A micro-sized headspace technique is presented for determination of organic volatile impurities (OVIs) in water-insoluble pharmaceuticals. Its main features include reduction of the amounts of sample of drug and sample dissolution medium, from 100–200 mg and 1–5 mL, respectively, in the traditional headspace method to 5–30 mg and 100 μL in the micro-sized headspace method, and shortening the headspace equilibration time from 45–60 min to 5–10 min. The validity of method has been examined both experimentally and theoretically. The relative standard deviation of the analysis and the linearity of method satisfied the requirements of the United States Pharmacopoeia. It was found that headspace equilibrium conditions have little influence on the sensitivity of the method, and that the presence of different amounts of drug substance in the sampling solution has little effect on the analytical results, in contrast with the traditional headspace GC method.     

Possibilities of dynamic headspace analysis coupled with capillary GC for the investigation of solid samples

The advantages of the dynamic headspace method for the analysis of solid samples, as compared with the static head space method, are discussed. Examples of dynamic headspace analyses are given to illustrate its possibilities.     

顶空固相微萃取-气相色谱-质谱联用分析纺织品中挥发性有机物

建立了顶空固相微萃取（HSSPME）-气相色谱（GC）-质谱（MS）联用测定纺织品中甲苯、4-乙烯基环己烯、苯乙烯、萘和1-苯基环己烯5种挥发性有机物（VOCs）的分析方法。选择聚二甲基硅氧烷（PDMS）作为萃取涂层,优化了SPME的萃取条件,包括平衡时间、萃取时间、萃取温度、顶空体积、离子强度、搅拌速度、解吸温度和时间以及GC—MS仪器条件。对于甲苯、4-乙烯基环己烯、苯乙烯、萘和1-苯基环己烯方法线性范围分别为0．087～870、3．32～3320、2．28～2280、0．015～150和0．050～50．0ng／g;检出限分别为0．005、0．042、0．670、0．008和0．011ng／g。实际样品加标回收率在80．1％～122％之间,RSD在0．8％～8．6％之间。方法符合纺织品中痕量VOCs的快速分析要求。     

Validation of a headspace trap gas chromatography and mass spectrometry method for the quantitative analysis of volatile compounds from degraded rapeseed oil

Due to lipid oxidation, off‐flavors, characterized by a fishy odor, are emitted during the heating of rapeseed oil in a fryer and affect the flavor of rapeseed oil even at low concentrations. Thus, there is a need for analytical methods to identify and quantify these products. To study the headspace composition of degraded rapeseed oil, and more specifically the compounds responsible for the fishy odor, a headspace trap gas chromatography with mass spectrometry method was developed and validated. Six volatile compounds formed during the degradation of rapeseed oil were quantified: 1‐penten‐3‐one, (Z)‐4‐heptenal, hexanal, nonanal, (E,E)‐heptadienal, and (E)‐2‐heptenal. Validation using accuracy profiles allowed us to determine the valid ranges of concentrations for each compound, with acceptance limits of 40% and tolerance limits of 80%. This method was then successfully applied to real samples of degraded oils.     

Detection of volatile organic sulfur compounds in water by headspace gas chromatography and membrane inlet mass spectrometry

Two gas chromatographic methods, GC-FID (flame ionization detection) and GC-ELCD (electrolytic conductivity detector) are compared in tlie analysis of volatile organic sulfur compounds (VOSCs) in water samples with a membrane inlet mass spectrometry (MIMS) technique. Carbon disulfide, ethanethiol, dimethyl sulfide, ethyl-methyl sulfide, thiophene, and dimethyl disulfide were used as test compounds. Linear dynamic ranges were found to be two decades with the GC-ELCD method and four decades with the GC-FID and MIMS methods. Detection limits were at low (μg/1 levels with the two gas chromatographic methods and clearly below μg/1 level with the MIMS method. Analysis of one sample takes 40 min with the gas chromatographic methods and five minutes with the MIMS method. The selectivity was good, especially with the GC-ELCD and the MIMS method. In addition, quantitative results obtained with spiked water samples by the three methods are compared.     

Cooled internal reflection element for infrared chemical sensing of volatile to semi-volatile organic compounds in the headspace of aqueous solutions

In this study, the cooling effect was applied to an evanescent wave type infrared (IR) chemical sensing method to effectively trap volatile organic compounds (VOCs), which have been absorbed in the hydrophobic film coated around the internal reflection element (IRE). The detection of VOCs in aqueous solutions was taken in the headspace of the aqueous solution. This method eliminates the long-term instability of hydrophobic film soaked in an aqueous solution and the potential spectral interference caused by the matrix of the aqueous solution. Thermal energy has been applied to the aqueous solution to assist in the evaporation of VOCs out of the aqueous matrix. By applying a cooling system to the IRE, the excess thermal energy can be removed leading to more stable IR signals. After examination of organic compounds with vapour pressure (P_v) ranging from 0.017 to 150 Torr, significant differences were found between IR signals from cooled and un-cooled systems. Because the thermal conductivity of the IRE used in IR detection is typically low; the efficiency in removing the thermal energy is limited. By heating the aqueous solutions to different temperatures, the IR signals showed that the sample temperature was limited to around 80 °C. The IR signal determination results for five different volatility organic compounds indicated that the optimal heating temperature was not necessary to match with the volatilities of organic compounds in cooling system. The linear regression coefficient (R²) of the standard curve for sample concentrations in the range 5-200 μg ml⁻¹ was generally higher than 0.991 and the detection limit was around a few hundred ng ml⁻¹, which was two to three times lower than that of un-cooled system.     

Application of headspace solid phase microextraction and gas chromatography to the screening of volatile compounds from some Brazilian aromatic plants

Summary An HS-SPME method was developed and applied for the isolation of volatile organic compounds from plants native or acclimatized to Brazil. Method optimization was performed using typical analytes from the target samples; fibers coated with 100 μm PDMS and 75 μm Carboxen/PDMS were tested. Using PDMS 100 μm fibers and GC-MS for separation and identification, up to 99.9% of the peak area in the chromatograms from plants were identified. The method was also applied to quantify the major volatile components of one of the samples (Aloysia gratissima) with results comparable to those from the conventional steam distillation method.     

Static headspace versus head space solid-phase microextraction (HS-SPME) for the determination of volatile organochlorine compounds in landfill leachates by gas chromatography

The determination of five volatile organochlorine compounds, VOX (chloroform, 1,1,1-trichloroethane, carbon tetrachloride, trichloroethene and tetrachloroethene) in raw landfill leachates and biologically cleansed leachates by GC-MS is investigated. Two extraction and preconcentration procedures were evaluated for recovery of such analies from the samples, including static headspace (HS) and solid phase microextraction by sampling the headspace above the sample (HS-SPME). Optimisation of operating parameters for the best performance of both, sampling and preconcentration techniques was described. Detection limits, time of analysis, precision and linear ranges of both introduction techniques have been established. Application of proposed methods to the determination of the five VOX under study in the above referred samples revealed the absence of such analytes in both leachates. Then both methods were applied to the determination to the five organochlorine compounds under study on spiked leachates samples. While HS-GC-MS offered better analytical precision than HS-SPME-GC-MS, this last technique gave a faster analytical response because no dilution must be done for a reliable VOX determination in landfill leachates. In any case, both sample introduction techniques tested provides excellent recoveries and good analytical precision (ranged from 1 to 3%).     

The use of headspace solid phase microextraction for the characterization of volatile compounds in olive oil matrices

Two different fibre coatings, for solid phase microextraction (SPME) sampling, poly(dimethylsiloxane) (PDMS) and poly(acrylate) (PA), were studied in order to test, for olive oil matrixes, two mathematical models that relate the directly proportional relationship between the amount of analyte absorbed by a SPME fibre and its initial concentration in the sample matrices. Although the PA fibre was able to absorb higher amounts of compounds from the olive oil sample, the equilibrium was reached later then with the PDMS fibre. In both cases, the amount of analyte present affected the time profile or the equilibrium time in two of the concentrations studied, 0.256 μL/kg, 2.56 μL/kg and for 2-ethylfuran, pentan-3-one, pent-1-en-3-one, hexanal, trans,trans-non-2,4-dienal and in the four concentrations studied, 0.256 μL/kg, 2.56 μL/kg, 6.25 μL/kg and 400 μL/kg, for 4-methyl-pent-3-en-2-one, 2-methylbutan-1-ol, methoxybenzene, hexan-1-ol, cis-hex-3-en-1-ol, trans-hex-2-en-1-ol, 2-ethyl-hexan-1-ol and trans,trans-dec-2,4-dienal. Comparing the mathematical models of both fibres, the PA-coated fibre showed direct proportionality between the initial concentration and amount extracted, that allows the possibility of relative quantification in a non-equilibrium state in non-aqueous media. The same was not observed for the PDMS fibre.     

The performance of various capillary columns for the analysis of volatile flavor compounds in dairy products by dynamic headspace gas chromatography

The aim of this study was to test the suitability and performance of various stationary phases and column dimensions for dynamic headspace gas chromatography of food aromas. The trials were performed using an aqueous test mixture containing thirty seven volatile flavor components of intense aroma, and a sample of ripe Swiss Emmental cheese. The best performance with both samples was obtained with a capillary column coated with a thick film of polydimethylsiloxane. This column resolved the greatest number of compounds in the cheese sample and resulted in the overlapping of one pair of peaks only from the test mixture. Because of its other advantages, i. e. high capacity owing to its film thickness, and insensitivity to the high moisture content of some samples or traces of oxygen in the carrier gas, the polydimethylsiloxane column appears suitable for the analysis of the volatile and highly polar compounds present in complex mixtures such as food aroma.     

Analysis of volatile aromatic compounds in gasoline-contaminated ground water samples by static headspace sampling and high speed gas chromatography

A 15 second, high speed, gas chromatographic determination has been performed on the volatile aromatic compounds in gasoline-contaminated ground water following manual, static headspace sampling. Retention time reproducibility of the seven peaks studied ranged from 0.25 to 0.67 per cent (average relative standard deviation). Excellent linear correlations were obtained for plots of either peak height or peak area against the concentration of the compounds. Comparison was made between the results obtained from the analysis of three replicate samples of gasoline-contaminated ground water by the high speed GC, by two field-portable GCs, and by a laboratorybased GC. It is worthy of note that all the high speed GC analyses required for this study were accomplished in one day.     

Review: The usefulness of the headspace analysis-gas chromatography technique for the investigation of solid samples

The scope of the headspace sampling technique for the analysis of solid samples is discussed, and the static and the dynamic headspace methods compared. Theoretical aspects relating to quantification are discussed. The paper considers both instrumental requirements and applications.     

Separation and identification of volatile and non-volatile compounds of wine by sorbent extraction and capillary gas chromatography

Sorbent extraction technology was used to separate the volatile and non-volatile components of wine. The extracts were analyzed by capillary gas chromatography.     

Alysis of the volatile constituents of food by headspace GC-MS with reversal of the carrier gas flow during sampling

A technique has been developed for performing headspace GC-MS analysis of volatile components of food, in which the carrier gas flow is reversed during sampling in order to overcome problems caused by the diffusion of substances not retained by the cold trap. Chromatographic profiles of volatile compounds from cheeses, obtained at room temperature, provide confirmation of the validity of the reversed flow technique, and the versatility of the system is evidenced by its successful application to both solid and liquid matrixes: the absence of any discrimination against the various components reveals its efficacy for compounds with a wide range of volatility. Addition of internal standards to the sample enables the use of the technique for quantitative analysis.     

Application of solid-phase microextraction to the analysis of volatile compounds in virgin olive oils

Solid-phase microextraction was used as a technique for headspace sampling of extra virgin olive oil and virgin olive oil samples with different off-flavours. A 100 microm coated polydimethylsiloxane fiber was used to extract volatile aldehydes, the sampling temperature was 45 degrees C and the fiber has been exposed to the headspace for 15 min. Nonanal and 2-decenal were present in all the olive oils with extraction off-flavours but were not in extra virgin olive oil sample.