Direct screening of olive oil samples for residual benzene hydrocarbon compounds by headspace-mass spectrometry

Gas chromatography-mass spectrometry using microvial insert thermal desorption for the determination of BTEX in edible oils

A rapid analytical procedure for BTEX determination involving minimum sample handling.

Independent components analysis coupled with 3D-front-face fluorescence spectroscopy to study the interaction between plastic food packaging and olive oil

Olive oil is one of the most valued sources of fats in the Mediterranean diet. Its storage was generally done using glass or metallic packaging materials. Nowadays, plastic packaging has gained worldwide spread for the storage of olive oil. However, plastics are not inert and interaction phenomena may occur between packaging materials and olive oil. In this study, extra virgin olive oil samples were submitted to accelerated interaction conditions, in contact with polypropylene (PP) and polylactide (PLA) plastic packaging materials. 3D-front-face fluorescence spectroscopy, being a simple, fast and non destructive analytical technique, was used to study this interaction. Independent components analysis (ICA) was used to analyze raw 3D-front-face fluorescence spectra of olive oil. ICA was able to highlight a probable effect of a migration of substances with antioxidant activity. The signals extracted by ICA corresponded to natural olive oil fluorophores (tocopherols and polyphenols) as well as newly formed ones which were tentatively identified as fluorescent oxidation products. Based on the extracted fluorescent signals, olive oil in contact with plastics had slower aging rates in comparison with reference oils. Peroxide and free acidity values validated the results obtained by ICA, related to olive oil oxidation rates. Sorbed olive oil in plastic was also quantified given that this sorption could induce a swelling of the polymer thus promoting migration.

Chemometric tools to highlight possible migration of compounds from packaging to sunflower oils

Polyethylene terephthalate (PET) could be considered for the packaging of vegetable oils taking into account the impact of its oxygen permeability on the oxidation of the oil and the migration of volatile organic compounds (VOC) from the polymer matrix. After accelerated aging tests at 40 °C for 10, 20, and 30 days, the headspace of three sunflower oils packed in PET with high density polyethylene caps was carried out using solid phase microextraction. VOCs such as benzene hydrocarbons, ethylbenzene, xylene isomers and diethyl phthalate were identified in vegetable oils by gas chromatography coupled to mass spectrometry. Chemometric tools such as principal components analysis (PCA), independent components analysis (ICA), and a multiblocks analysis, common components and specific weight analysis (CCSWA) applied to analytical data were revealed to be very efficient to discriminate between samples according to oil oxidation products (hexanal, heptanal, 2-pentenal) and to the migration of packaging contaminants (xylene).

Quantification of the intensity of virgin olive oil sensory attributes by direct coupling headspace-mass spectrometry and multivariate calibration techniques

The main sensory defects of virgin olive oils (rancid, vinegary, winey, muddy sediment, musty and vegetable water) and one positive attribute (fruity) characteristic of three monovarietal extra virgin olive oils (Arbequina, Picual and Frantoio) have been quantified using the direct coupling headspace-mass spectrometry. The results obtained were compared with those provided by the panel test for the same samples. Taking into account that no chromatographic separation exists, multivariate calibration techniques (partial least squares, PLS, and principal components regression, PCR) were used to create the appropriate models. The best results, in terms of standard error of prediction and prediction residual error sum of squares were obtained by PLS and therefore it was used for the prediction of a new set of samples with the above-mentioned positive and negative attributes at different concentration levels. The samples were also assessed by the panel test and good correlations were obtained in all cases. In order to extend the applicability of the model with the time, a multiplicative calibration transfer was used. The benefit of this approach was found to be more marked for the negative than the positive attributes.

The color space of foods: virgin olive oil

The CIE 1976 (L*, a*, and b*) color space for virgin olive oil was determined. Such a space encompasses any acceptable sample of this type of oil irrespective of the agronomic treatment that the olives have undergone because its color is due to two types of pigments, a systematic combination of which provides the whole range of theoretically possible colors. Color is quantified from the visible spectra for pure samples. Therefore, the pigment spectra, which were the averages of those for several samples, were determined in a medium highly similar to the source oil following application of a photochemical method. A combination of the pigment spectra provided 651 spectra for virtual samples, the colors of which spanned the entire color space for virgin olive oil. The positions of more than 100 Spanish olive oil samples of diverse origins in the color space were also determined, and the results were examined in relation to oil type and quality. Similar color spaces can be obtained for other foods, which can thus be characterized in terms of an additional physical property.

Enhancing Sensitivity in Headspace-Mass Spectrometric Determination of BTEX in Drinking Water

A way to extract useful chemical information from the volatile profile provided by a headspace-mass spectrometer (HS-MS) is developed in order to improve sensitivity in HS-MS analysis. The methodology is based on the selection of a narrow window in the volatile profile where the signal-to-noise ratio was maximal by combining the data acquisition time and scan rate. To test this approach, benzene, toluene, ethylbenzene, and p-xylene (BTEX) as well as their mixtures were quantified in drinking waters. Individual hydrocarbons were determined between 1 and 30 microg/L (mean RSD, 4.0% for 10 microg/L) while mixtures were quantified at a microgram per liter level by using the partial least-squares multivariate algorithm with a relative standard prediction error of under 3.5%. These results indicate that the method proposed is useful as a sensitive and selective tool for the determination of BTEX and surpasses other reported HS-MS alternatives. In addition, the proposed methodology can be extended to others that insert analytes from a sample directly into a MS, such as membrane introduction mass spectrometry among others.

Usefulness of the direct coupling headspace–mass spectrometry for sensory quality characterization of virgin olive oil samples

The applicability of the headspace coupled to mass spectrometry for evaluation of the sensory quality of virgin olive oil samples is presented. The volatiles of the oil are directly transferred from the sample vial to the detector without chromatographic separation. The mass spectrum obtained can be considered as a fingerprint of the oil sample and can be used for classification purposes. After a training step with samples previously qualified following the official method, a classification model was created using the supervised technique soft independent modeling of class analogy (SIMCA). Eight negative (rancid, winey-vinegary, muddy sediment, hay-wood, vegetable water, earthy, fusty and musty-humidity) and three principal positive attributes (fruity, bitter and pungent) have been included in this study. With them, a classification model consisting of two main classes (extra- and lampante-virgin olive oil) was constructed. In addition, the unsupervised technique cluster analysis permitted the discrimination among oils with different negative attributes. The proposed procedure has been applied to the classification of commercial samples (as extra- or lampante-virgin olive oils) and the results were compared with those provided by the expert's panel with acceptable correlation.

Direct screening and confirmation of priority volatile organic pollutants in drinking water

A screening tool was proposed for the rapid detection of eight priority volatile organic pollutants according to European standards in drinking water. The method is based on the direct coupling of a headspace sampler with a mass spectrometer, using a chromatographic column heated to 175 degrees C as an interface. The water sample was subjected to the headspace extraction process and the volatile fraction was introduced directly into the mass spectrometer, without prior chromatographic separation, achieving low detection limits (0.6-1.2 ng/ml) for all compounds. The mass spectrum resulting from the simultaneous ionization and fragmentation of the mixture of molecules constitutes the volatile profile of each sample. An appropriate chemometric treatment of these signals permitted them to be classified, on the basis of their volatile composition, as contaminated or uncontaminated with respect to the legally established concentration levels for these compounds in drinking water, and providing no false negatives. A conventional confirmation method was carried out to analyze positive water samples by using the same instrumental setup as in the screening method, but using an appropriate temperature program in the chromatographic column to separate, identify and quantify each analyte.

Surfactant-coated carbon nanotubes as pseudophases in liquid–liquid extraction

The advantages of surfactant-coated carbon nanotubes (CNTs) as coadjutants in liquid-liquid extraction are systematically considered. The effect of the CNT state (dispersed or suspended in an aqueous medium) is characterized by the single-component solid-liquid isotherms exemplified for benzene. Adsorption isotherms are obtained by means of a headspace-GC-MS method, the recommended instrumental combination when very volatile compounds are involved. Adsorption studies are completed using toluene and n-undecane as model analytes of aromatic and linear hydrocarbons, respectively. The potential of using dispersed carbon nanotubes to improve liquid-liquid extraction is finally evaluated. The liquid-liquid distribution of the two model analytes between an organic phase (n-heptane) and the aqueous dispersion of CNTs is studied via batch extraction and subsequent analysis of the organic phase by GC-MS. A prospective application of this methodology is also given.

Direct olive oil authentication: Detection of adulteration of olive oil with hazelnut oil by direct coupling of headspace and mass spectrometry, and multivariate regression techniques

Control of adulteration of olive oil, together with authentication and contamination, is one of the main aspects in the quality control of olive oil. Adulteration with hazelnut oil is one of the most difficult to detect due to the similar composition of hazelnut and olive oils; both virgin olive oil and olive oil are subjected to that kind of adulteration. The main objective of this work was to develop an analytical method able to detect adulteration of virgin olive oils and olive oils with hazelnut oil by means of its analysis by a headspace autosampler directly coupled to a mass spectrometer used as detector (ChemSensor). As no chromatographic separation of the individual components of the samples exists, a global signal of the sample is obtained and employed for its characterization by means of chemometric techniques. Four different crude hazelnut oils from Turkey were employed for the development of the method. Multivariate regression techniques (partial least squares and principal components analysis) were applied to generate adequate regression models. Good values were obtained in both techniques for the parameters employed (standard errors of prediction (SEP) and prediction residual error sum of squares (PRESS)) to evaluate its goodness. With the proposed method, minimum adulteration levels of 7 and 15% can be detected in refined and virgin olive oils, respectively. Once validated, the method was applied to the detection of such adulteration in commercial olive oil and virgin olive oil samples.

Factors affecting signal intensity in headspace mass spectrometry for the determination of hydrocarbon pollution in beach sands

One of the main limitations to the use of direct coupling of headspace mass spectrometry (HS-MS) for the quantitative determination of analytes in a sample is related to factors affecting the signal intensity. The importance of strategies aimed at compensating this problem is considerable in the case of classification, and is indeed critical as regards the problems involved in quantification. This paper reports the effects of the different factors affecting HS-MS signal intensity in the quantification of the pollution of beach sands by hydrocarbons--the matrix effect, signal instability over time and nature of the different pollutants present in the polluted sands--and proposes possible solutions. Signal instability was solved by using a multiplicative calibration transfer algorithm. A three-factor Box-Behnken experimental design was used to study the matrix effect, mainly as regards the moisture of the samples, and the results are discussed.