Headspace Technique Research Articles

Determination of halogenated solvents content in olive oil by two completely automated headspace techniques coupled to gas chromatography–mass spectrometry

Two different methods have been developed and compared for determining the halogenated solvents content of olive oils. The optimal parameters for isolation and preconcentration of relevant halogenated solvents (bromodichloromethane, dibromochloromethane, chloroform, bromoform, tetrachloroethene, trichloroethene, ethylenedichloride, and vinyl chloride) were established. These proposed procedures are completely automated and do not require reagents because both methods are based on headspace techniques, conventional headspace (HS) and headspace solid-phase microextraction (HS-SPME), both techniques on-line coupled to a gas chromatograph–mass spectrometer (GC–MS) operated in selected ion monitoring (SIM) mode. The methods were validated and compared their figures of merit. In general, both extraction techniques presented similar extraction efficiency at the studied concentrations. However, average relative standard deviation (R.S.D.) obtained at low concentration levels was slightly better for HS (8.6%) than for HS-SPME (11.8%) technique. It was due to the lower limits of detection (LOD) and quantification (LOQ) values obtained for HS, especially for the less volatile vinyl chloride, chloroform and ethylene dichloride compounds. Finally, the HS-GC–MS method was applied to the analysis of real olive oil and olive-pomace oil samples. None content of halogenated solvents was found above the LOD in the studied samples. The proposed methods are faster, simpler and easier than the official methods proposed by the European Union and the International Olive Oil Council.

Limonene, linalool, α-terpineol, and terpinen-4-ol as quality control parameters in mandarin juice processing

Consumers demand commercial citrus juices resembling fresh juices; however, citrus juice elaboration is quite delicate due to the formation of off-flavors during heat treatment and storage. Four volatile compounds, d-limonene, linalool, α-terpineol, and terpinen-4-ol were extracted using the dynamic headspace technique and were identified and quantified by GC-MS in mandarin juices from two Spanish varieties, Fortuna and Clemenules. Our results clearly demonstrated that both the pasteurization and storage steps significantly affected concentrations of these four aroma compounds. Formation of off-flavors components, α-terpineol and terpinen-4-ol, and simultaneous decomposition of d-limonene and linalool were observed in mandarin juices. Therefore, measurements of the stability of d-limonene and linalool, and formation of α-terpineol and terpinen-4-ol will help mandarin juice producers in analyzing the quality of their products.

Volatile organohalogen compounds in human urine: The effect of environmental exposure

The paper presents the results of determination of volatile organohalogen compounds (VOX) in urine samples from subjects exposed to these compounds in their workplaces and through consumption of chlorinated tap water. The analytes were isolated and preconcentrated from the complex urine samples using the thin layer headspace (TLHS) technique with autogenous generation of the liquid sorbent. Final gas chromatographic determination was carried out by direct aqueous injection with electron capture detection (DAI-ECD). The results indicate that only a small fraction (<4%) of the VOX input is excreted with urine in the non-metabolized form. A positive correlation was found between the occupational levels of VOX in the workplace and their levels in urine. VOX levels in the urine of subjects not exposed to them in the workplace were significantly lower. Their presence in the organisms was most probably related to consumption of tap water produced by chlorination of surface waters.

Adsorption Equilibria of C8 Aromatic Liquid Mixtures on Y Zeolites Using Headspace Chromatography

Liquid phase adsorptive separations are found in several industrial applications such as the recovery of p‐xylene from its isomers. In this study, the headspace experimental technique was used to measure pure and multicomponent adsorption equilibria of liquid xylenes in Y zeolite. Data for pure‐component equilibrium were determined at temperatures between 80 and 120°C and correlated using the Extended Langmuir model. The parameters for pure components estimated from the correlated data showed good agreement with data reported in previous studies and relatively low deviations when compared to the experimental data dispersion. Using the pure‐component data, two models were tested for multicomponent (binary and quaternary) equilibrium correlation: Ideal Adsorbed Solution (IAS) model and Extended Langmuir Multicomponent model. The results from the IAS model did not conform well to the experimental results, indicating the existence of significant nonidealities in the system. The Extended Langmuir model predicted values generally in good agreement with the binary and quaternary experimental data measured using the Headspace technique.

Classification of white wine aromas with an electronic nose

This paper reports the use of a tin dioxide multisensor array based electronic nose for recognition of 29 typical aromas in white wine. Headspace technique has been used to extract aroma of the wine. Multivariate analysis, including principal component analysis (PCA) as well as probabilistic neural networks (PNNs), has been used to identify the main aroma added to the wine. The results showed that in spite of the strong influence of ethanol and other majority compounds of wine, the system could discriminate correctly the aromatic compounds added to the wine with a minimum accuracy of 97.2%.

Determination of dichloroacetic acid and trichloroacetic acid in drinking water by acidic methanol esterification and headspace gas chromatography

A simple and rapid headspace method for gas chromatographic determination of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) in drinking water was developed. Acidic methanol esterification followed by a headspace technique using a capillary column gas chromatograph (GC) equipped with an electron capture detector (ECD) was applied to determine the levels of DCAA and TCAA in drinking water. The major advantages of this method are the use of acidic methanol as the derivatization agent instead of the hazardous diazomethane, and esterification is carried out in water instead of organic solvent. DCAA and TCAA methyl esters produced in the reaction were determined directly by a headspace GC/ECD method. The linear correlation coefficients at concentrations ranging from 0 to 60 μg/L were 0.992 and 0.996 for DCAA and TCAA, respectively. The relative standard deviations (RSD, %) for the determination of DCAA and TCAA in drinking water were 15 and 21.3%, respectively ( n = 3 ). The detection limits of this method were 3 and 0.5 μg/L for DCAA and TCAA, respectively, and the recovery was 68–103.2% for DCAA and TCAA.

A relative headspace method for Henry's constants of volatile organic compounds

A relative headspace gas chromatographic method is described for the measurement of Henry's constants of volatile organic compounds (VOCs) in aqueous salt solutions. The method requires the Henry's constant of the VOC in pure water, and employs larger liquid samples than conventional headspace techniques in order to minimize errors arising from solute mass loss from the liquid phase. Henry's constants of five methyl ketones (2-propanone, 2-butanone, 2-pentanone, 2-hexanone, and 2-heptanone) in 0.2 M (molal) to 1.0 M sodium sulfate solutions were measured using the relative method at temperatures between 50 and 80 °C. Reference values of Henry's constants of the five methyl ketones in pure water were measured using a differential headspace technique. The entire data set was correlated using an equation containing three parameters (obtained from VOC + water data) and a single salt parameter. The equation was able to successfully extrapolate Henry's constant data over the entire range of salt concentrations.

Determination of the Vapor Density of Triacetone Triperoxide (TATP) Using a Gas Chromatography Headspace Technique

AbstractUsing a GC headspace measurement technique, the vapor pressure of TATP was determined over the temperature range 12 to 60 °C. As a check on the experimental method, TNT vapor pressure was likewise computed. Values for TNT are in excellent agreement with previous published ones. For TATP the vapor pressure was found to be ~ 7 Pa at ambient conditions. This value translates to a factor of 104 more molecules of TATP in air than TNT at room temperature. The dependence of TATP vapor pressure on temperature can be described by the equation log10P(Pa)=19.791−5708/T(K). Its heat of sublimation has been calculated as 109 kJ/mol.

Determination of Acetonitrile and Cyanide in Rat Blood: Application to an Experimental Study

Methods were developed for the analysis of acetonitrile and its metabolite cyanide in the blood of rats exposed to acetonitrile. Acetonitrile was analyzed by the headspace technique coupled to gas chromatography with detection by flame ionization, and cyanide was analyzed by high-performance liquid chromatography with fluorescence detection (lambdaex = 418 nm and lambdaem = 460 nm) after derivatization of the ion with naphthalene 2,3-dicarboxyaldehyde and taurine. The quantitation limits of the methods for the analysis of acetonitrile and cyanide were 4.875 microg/mL and 0.025 microg/mL, respectively. The coefficients of variation of 10% or less obtained for intra- and interassay precision indicate the precision of these analytical methods and the systematic errors, all less than 5%, indicate that the methods are quite accurate. The methods were applied to an experimental study after the animals received acetonitrile at the doses of 2 mmol/kg or 5 mmol/kg.

The full evaporation technique: A promising alternative for residual solvents analysis in solid samples

The static headspace technique is the most common approach to residual solvent analysis in pharmaceutical and environmental matrices. This paper presents an alternative tool where the volatile impurities are released from the matrix by working directly on a small amount of sample at a high equilibration temperature: the so-called Full Evaporation Technique (FET). The capability of this method was evaluated on a mixture of nine solvents, which belong to Class 3 in the classification of the European Pharmacopoeia Agency for residual solvents, at various levels of concentration: ethanol, acetone, 2-propanol, methyl acetate, 2-butanone, ethyl acetate, tetrahydrofuran, 2-methyl-1-propanol, 1-butanol. Data on linearity, accuracy, precision and sensitivity are reported. Use of an internal standard proved to be necessary when using such a method. The method is then successfully applied to the analysis of solvent traces in permethylated beta-cyclodextrin.

The relationship between sensory quality and volatile compounds in raw juice processed from elderberries (Sambucus nigra L.)

Elderberry juice was processed by pressing of 101 samples of elderberries (Sambucus nigra L.) picked in Austria, England and Denmark at optimum maturity. Taste panels trained in determination of elderberry flavour evaluated the juices and the results from the sensory evaluation were correlated to the content of volatile compounds. The volatile compounds were isolated from elderberry juices by dynamic headspace technique and analysed by GC-FID and GC-MS. A total of 59 volatile compounds were identified, 9 of which have not previously been detected in elderberry products. A total of 53 compounds occurred in quantifiable amounts and significant differences among the investigated elderberry samples were observed for 50 compounds. The importance of the isolated volatile compounds to elderberry flavour was determined by classical factor analysis using the results from the sensory evaluation and information on the odour of the individual volatile compounds. Classical factor analysis were used including determination of eigenvalues, factor loadings and factor scores by varimax rotation of standardised variables for extraction of four non correlated factors (principal components) explaining approximately 73% of the variation in elderberry flavour. Twenty-eight volatile compounds and sensory quality were included in the four factors. Using the compounds with highest numerical values (loadings) the four factors were named: fresh-elderberry-elder flower (35.2%), fresh-fruity-sweet (17.3%), fresh-fruity (13.7%) and green-floral-fruity (6.7%). Three compounds with characteristic elderberry odour (β-damascenone, nonanal, dihydroedulan) were closely correlated with the sensory quality of elderberry together with compounds with fruity, floral, green and/or miscellaneous odours.

Stir Bar Sorptive Extraction: A New Quantitative and Comprehensive Sampling Technique for Determination of Chemical Signal Profiles from Biological Media

Various applications of a novel sampling procedure in chemical ecology are outlined. The stir bar extraction method features the analytical reproducibility needed in recording the analytical profiles of volatile and semivolatile components of biological mixtures. This methodology has been demonstrated here through the examples of small volume urine samples, glandular tissue volatiles, and the air blown through animal cages. Its analytical merits are compared with those of the previously established purge-and-trap (dynamic headspace) technique.

Comparison of Terpene Composition in Engelmann Spruce (Picea engelmannii) Using Hydrodistillation, SPME and PLE

Terpenes emitted by conifer trees are generally determined by analysing plant extracts or essential oils, prepared from foliage and cones using steam distillation. The application of these procedures limits experiments to cut plant materials. Recently headspace techniques have been adopted to examine terpene emission by living plants. This paper deals with the application of solid-phase micro-extraction (SPME) for the analysis of terpenes emitted by conifers foliage of Engelmann spruce (Picea engelmannii), including its seedlings. The compositions of SPME extracts obtained for destroyed and non-destroyed old and juvenile spruce needles were compared with the compositions of essential oils and pressurised liquid extraction (PLE) extracts corresponding to the same plant materials. No substantial differences have been found in the qualitative terpene composition estimated by analysing essential oil and PLE and SPME extracts from non-destroyed old and juvenile foliage. The disintegration of spruce needles results in the formation of a significant amount of myrcene in the case of the old conifer foliage and non-terpenoic compounds in the case of juvenile conifer foliage. This phenomenon can be attributed to enzymatic reactions occurring in the destroyed plant cells.

Testing of microencapsulated flavours by electronic nose and SPME–GC

The present study deals with the use of metal oxide gas sensors and the headspace techniques for microencapsulated essential oils of thyme, oregano and cassia. The volatile compounds released from the microencapsulated flavours were tested by an array of the gas sensors. The features of individual odours were described using an analysis of the transient responses of the sensors to the aroma. The coating materials were graded with respect to the leakage of volatile components. The volatile compounds leaking from the microencapsulated flavours were collected by the headspace SPME technique and analysed by GC–MS. Based on the results, the Hi Cap 100 was considered to be the least emitting coating material while the Encapsul 855 was the most leaking matrix in our study.

Correlation between emitted and total amount of 2-cyclopentyl-cyclopentanone in polyamide 6.6 allows rapid assessment by HS and HS-SPME under non-equilibrium conditions

A correlation was found between the emitted and total amount of 2-cyclopentyl-cyclopentanone in polyamide 6.6. The emitted amounts were measured by GC–MS after headspace (HS) or headspace solid-phase microextraction (HS-SPME) and the total content was determined after microwave-assisted extraction (MAE). The correlation was valid also under non-equilibrium conditions, which allows rapid assessment of 2-cyclopentyl-cyclopentanone content in polyamide 6.6 by headspace techniques. The incubation time needed for non-equilibrium headspace analysis could be reduced from 5 h to 45 min if the PA66 granules were milled to powder prior to extraction. However, to reach equilibrium between the analyte in the solid sample and the headspace still required 12 h of incubation at 80 °C. The long incubation time is explained by slow diffusion rate due to the strong hydrogen bonding between analyte and matrix and the relatively high crystallinity of polyamide 6.6. The headspace extraction profile showed several equilibrium-like patterns that are easily mistaken for the real equilibrium.

Early detection of fungal growth in bakery products by use of an electronic nose based on mass spectrometry.

This paper presents the design, optimization, and evaluation of a mass spectrometry-based electronic nose (MS e-nose) for early detection of unwanted fungal growth in bakery products. Seven fungal species (Aspergillus flavus, Aspergillus niger, Eurotium amstelodami, Eurotium herbariorum, Eurotium rubrum, Eurotium repens, and Penicillium corylophillum) were isolated from bakery products and used for the study. Two sampling headspace techniques were tested: static headspace (SH) and solid-phase microextraction (SPME). Cross-validated models based on principal component analysis (PCA), coupled to discriminant function analysis (DFA) and fuzzy ARTMAP, were used as data treatment. When attempting to discriminate between inoculated and blank control vials or between genera or species of in vitro growing cultures, sampling based on SPME showed better results than those based on static headspace. The SPME-MS-based e-nose was able to predict fungal growth with 88% success after 24 h of inoculation and 98% success after 48 h when changes were monitored in the headspace of fungal cultures growing on bakery product analogues. Prediction of the right fungal genus reached 78% and 88% after 24 and 96 h, respectively.

A Survey on High-Concentration-Capability Headspace Sampling Techniques in the Analysis of Flavors and Fragrances

This survey critically discusses high-concentration-capacity (HCC) headspace (HS) techniques applied to sample the volatile fraction of matrices of interest in the flavors and fragrance fields. In particular, the advantages, limits, and fields of application of HS solid-phase microextraction (SPME), high-capacity HS sorptive extraction (HSSE) and HS solid-phase dynamic extraction (SPDE) are evaluated. These techniques are discussed in view of the peculiar characteristic of HCC-HS techniques, from the standpoint that these techniques are a bridge between static (S-HS) and dynamic HS (D-HS) because they are as simple, fast, easy to automate, and reliable as S-HS, yet afford analyte concentration factors comparable to those of D-HS. Moreover, the different degree of their development is a consequence of the different times in which they were introduced into the market, because the potential of HS-SPME is now well known, having been introduced approximately 12 years ago, but that of HSSE has still to be fully explored, and HS-SPDE still has to be investigated because it is very recent.

Compostos voláteis dos frutos de maracujá (Passiflora edulis forma Flavicarpa) e de cajá (Spondias mombin L.) obtidos pela técnica de headspace dinâmico

Entre as inúmeras frutas tropicais e subtropicais produzidas no Brasil, duas que se destacam do ponto de vista do aroma da polpa são maracujá amarelo (Passiflora edulis forma Flavicarpa) e cajá (Spondias mombin L.). Os voláteis da polpa destas frutas foram capturados pela técnica de headspace dinâmico e analisados no sistema de cromatografia gasosa de alta resolução e espectrometria de massa. Foram identificados 48 e 33 compostos voláteis na polpa de maracujá e cajá, respectivamente. Os compostos voláteis predominantes na polpa de maracujá pertenceram às classes de ésteres (59,24%), aldeídos (15,27%), cetonas (11,70%) e álcoois (6,56%), enquanto na polpa de cajá as principais classes de compostos foram de ésteres (48,76%), álcoois (21,69%), aldeídos (11,61%) e cetonas (4,19%). Outros compostos aromáticos característicos foram para maracujá: beta-ionona e linalol e para cajá: gama-octalactona e ácidos butírico e hexanóico.

Compostos voláteis de três cultivares de manga (Mangifera indica L.)

Os compostos voláteis de três cultivares de manga (Haden, Tommy-Atkins e Keitt) procedentes do Estado de São Paulo, foram isolados por uma técnica de headspace dinâmico, envolvendo sucção em polímero poroso. A separação da mistura complexa de voláteis foi efetuada por cromatografia gasosa de alta resolução. Alguns compostos voláteis foram identificados por cromatografia gasosa-espectrometria de massas e índices de Kovats. Os hidrocarbonetos monoterpênicos foram os compostos mais abundantes no headspace das amostras. Car-3-eno foi o componente majoritário dos cultivares Haden e Keitt, enquanto a Tommy-Atkins mostrou predominância de car-3-eno e alfa-pineno. Outros compostos identificados foram alfa-fencheno, alfa-canfeno, p-cimeno, beta-mirceno, beta-felandreno, limoneno, alfa-terpinoleno, beta-cariofileno e alfa-humuleno. Os três lotes analisados para cada cultivar mostraram grande homogeneidade, não havendo diferença significativa ao nível de 5%.

Solid‐phase aroma concentrate extraction (SPACE™ ): a new headspace technique for more sensitive analysis of volatiles

AbstractThe SPACE™ (solid‐phase aroma concentrate extraction) method is a modified version of the SPME (solid‐phase micro extraction) technique for headspace analysis, with increased area of the adsorbent to enable more sensitive analysis of volatiles. The SPACE™ rod used in the technique is fabricated from stainless steel coated with an adsorbent mixture, consisting mainly of a graphite carbon. Initially, the SPACE™ rod is fixed in the head of a closed flask, where it adsorbs the aroma. Next, the rod is thermally desorbed on‐line with a high‐resolution gas chromatography–mass spectrometer (HRGC–MS). In the present experiments, SPACE™ sampling reproducibility was determined by analysing a standard mixture and roasted coffee beans. The SPACE™ rod collected the analytes with good reproducibility, with the exception of high polar compounds. Similar analyses of coffee powder were performed by SPME and other methods for comparison with the SPACE™ method. The SPACE™ method proved to have superior capabilities with high concentrations, and it produced a well‐balanced chromatogram. Copyright © 2004 John Wiley &amp; Sons, Ltd.