A novel headspace solid-phase microextraction arrow method employing comprehensive two-dimensional gas chromatography-mass spectrometry combined with chemometric tools for the investigation of wine aging

BACKGROUND

Omics is used as an analytical tool to investigate wine authenticity issues. Aging authentication ensures that the wine has undergone the necessary maturation and developed its desired organoleptic characteristics. Considering that aged wines constitute valuable commodities, the development of advanced omics techniques that guarantee aging authenticity and prevent fraud is essential.

RESULTS

Α solid phase microextraction Arrow method combined with comprehensive two-dimensional gas chromatography-mass spectrometry was developed to identify volatiles in red wines and investigate how aging affects their volatile fingerprint. The method was optimized by examining the critical parameters that affect the solid phase microextraction Arrow extraction (stirring rate, extraction time) process. Under optimized conditions, extraction took place within 45 min under stirring at 1000 rpm. In all, 24 monovarietal red wine samples belonging to the Xinomavro variety from Naoussa (Imathia regional unit of Macedonia, Greece) produced during four different vintage years (1998, 2005, 2008 and 2015) were analyzed. Overall, 237 volatile compounds were tentatively identified and were treated with chemometric tools. Four major groups, one for each vintage year were revealed using the Hierarchical Clustering Analysis. The first two Principal Components of Principal Component Analysis explained 86.1% of the total variance, showing appropriate grouping of the wine samples produced in the same crop year. A two-way orthogonal partial least square - discriminant analysis model was developed and successfully classified all the samples to the proper class according to the vintage age, establishing 17 volatile markers as the most important features responsible for the classification, with an explained total variance of 88.5%. The developed prediction model was validated and the analyzed samples were classified with 100% accuracy according to the vintage age, based on their volatile fingerprint.

SIGNIFICANCE

The developed methodology in combination with chemometric techniques allows to trace back and confirm the vintage year, and is proposed as a novel authenticity tool which opens completely new and hitherto unexplored possibilities for wine authenticity testing and confirmation.

Flow-modulation comprehensive two-dimensional enantio-gas chromatography: A valid and flexible alternative to heart-cutting multidimensional enantio-gas chromatography

The present research is focused on the proposal of use of flow-modulation comprehensive two-dimensional enantio-gas chromatography (FM eGC × GC) as a valid, flexible, and possibly superior alternative to heart-cutting multidimensional enantio-GC (eMDGC). The latter, a technique of demonstrated utility, is used specifically for the targeted separation of chiral compounds, whereas FM eGC × GC can produce both targeted and high-resolution untargeted information in a single run. It is clearly possible to use eMDGC for untargeted analysis, often with a flame ionization detector (stand-by analysis), to monitor a first-dimension (1D) separation, of much lower peak capacity compared to FM eGC × GC. If eMDGC is used with mass spectrometry (MS), it is normally exploited to monitor the second-dimension (2D) separation. The analytical instrument consisted of automated solid-phase microextraction (SPME), and a low duty-cycle FM eGC × GC system (with time-of-flight MS), equipped with an enantioselective 1D column (2,3-di-O-methyl-6-t-butyl silyl β-cyclodextrin derivative) and a 2D polyethylene glycol one. Ten Marsala wines were subjected to analysis, for the determination of chiral lactones (many at the low ppb level, due to the high concentration capacity of SPME) and for general analyte profiling. In many instances, highly complex chromatograms were attained, with statistical analysis (ANOVA-simultaneous component analysis and partial least squares discriminant analysis) used for sample differentiation.

A volatilomics analytical protocol employing solid phase microextraction coupled to GC × GC-MS analysis and combined with multivariate chemometrics for the detection of pomegranate juice adulteration

In this work, a solid-phase microextraction (SPME) method combined with two-dimensional gas chromatography coupled to mass spectrometry (GC × GC-MS) was optimized and used to assess the authenticity of pomegranate juice to prevent fraudulent practices. A divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber was used for the extraction of the volatiles. The critical parameters that affect the extraction process, such as the sample volume, and the extraction time were studied. The optimized protocol involved the addition of 15 mL of juice in 50 mL vial and saturation with 30% w/v NaCl.The extraction was carried out within 45 min under 1000 rpm stirring and was applied in the analysis of real juice samples to assess authenticity and detect low levels of pomegranate juice adulteration with grape and apple juice down to 1%. Commercially available pomegranate juice samples were acquired (n1 = 6) and adulterated with 1% of apple juice (n2 = 6), 1% of grape juice (n3 = 6), and a mixture of 1% apple juice and 1% grape juice (n4 = 6). Authentic pomegranate juice samples and adulterated mixtures were analyzed by SPME-GC × GC-MS. The analysis resulted in the identification of 123 volatile compounds that were further processed with chemometric tools. Principal component analysis (PCA) was employed to visualize the clustering of the samples, and a two-way orthogonal partial least squares discriminant analysis (O2PLS-DA) chemometric model was developed and successfully classified the samples to authentic pomegranate juice or adulterated with an explained total variance of 87.4%. The O2PLS-DA prediction model revealed characteristic volatile markers that could be used to detect pomegranate juice fraud.

Dual sorbent coating based magnet-integrated fabric phase sorptive extraction as a front-end to gas chromatography-mass spectrometry for multi-class pesticide determination in water samples

Magnet-integrated fabric phase sorptive extraction (MI-FPSE) is a sample preparation technique that has proved to be a powerful tool for environmental analysis. The fabrication and application of magnet-integrated dual sorbent-based FPSE membrane prepared by combining two different sol-gel sorbent-coated disks of different polarities together with a magnetic bar inserted between the two membranes to allow the stirring, was examined as novel preparation technique that not required samples pretreatments. The dual sorbent-based sample preparation platforms (made up of poly(tetrahydrofuran) and Carbowax 20M) were used for the extraction of seven classes of pesticides from ambient surface water samples prior to their determination by gas chromatography-mass spectrometry. Initially, different single and dual sol-gel sorbent-based MI-FPSE membranes were evaluated in terms of their extraction efficiency. The MI-FPSE with dual sol-gel sorbents were found to be superior to the single-materials MI-FPSE devices in terms of extraction recovery. The main parameters affecting the MI-FPSE extraction protocol (e.g., adsorption time, sample volume, stirring rate, salt addition, eluent type, desorption time and elution volume) were investigated. The selected extraction protocol enabled detection limits in the range between 0.001 and 0.16 ng mL-1. Furthermore, good relative standard deviation values for the intra-day and inter-day repeatability studies were obtained and were lower than 5.9 and 9.9 %, respectively. The proposed method was successfully used for the multi-class analysis of environmental surface water samples.

Determination of mineral oil hydrocarbon contamination in Citrus essential oils by using on-line liquid-gas chromatography: critical aspects

The present manuscript reports and discusses critical issues related to the determination of mineral oil hydrocarbon contamination in Citrus essential oils (EOs); an on-line liquid-gas chromatography system equipped with a Y-interface was used (with no additional off-line step for pre-concentration). In total, eighteen samples were analyzed, specifically eleven cold-pressed (CP) and seven distilled EOs. With regard to the CP EOs, various degrees of mineral oil saturated hydrocarbon (MOSH) contamination were detected, ranging between 10.7 and 338.4 mg kg-1 (only one sample was MOSH-free); different MOSH sub-fractions were determined, with the  > C25- ≤ C35 sub-fraction always present, with an average concentration of 74.5 mg kg-1. Based on the EO composition, different sample amounts were injected to avoid the overloading of the LC column and consequently the GC one, thus leading to different limits of quantification (LoQ), which were either 2 mg kg-1 (for bergamot EO) or 5 mg kg-1 (for all the other investigated samples). For all samples, the mineral oil aromatic hydrocarbon level was always lower than the LoQ.

Direct extraction with acetonitrile of hemp seed oil for the analysis of pesticides by using comprehensive two-dimensional gas chromatography-triple quadrupole mass spectrometry

The method herein described involves a rapid and limited-volume (0.5 mL of acetonitrile) solvent-extraction sample preparation process, for pesticide determination in hemp seed oil. The extraction method was characterized by the absence of both clean-up or pre-concentration steps. The extracts were directly analyzed through cryogenic-modulation comprehensive two-dimensional gas chromatography coupled to triple quadrupole mass spectrometry. The novelty characterizing the present research [compared to a previous one (Arena et al., 2023)] is related to the extension of the number of pesticides (97), and to the investigation of a more challenging matrix, contained in a vegetable oil of increasing interest among consumers. Linearity, limits of detection and quantification, accuracy, precision, recovery, and matrix effect were measured. Particular emphasis was devoted to the matrix effect, with the co-extracted matrix amount defined. Three international regulations (Canada, California, Europe) were considered, and the obtained limits of quantification were found to be too high in five (Canada) and twelve (Europe) cases, for a total number of 15 pesticides. The analysis of ten commercial samples showed the presence of seven pesticide residues in four of them, at concentration levels ranging from 0.02 to 0.98 mg kg-1, with most over the regulation residue limits.

A dilute-and-inject low-pressure gas chromatography-tandem mass spectrometry method for phthalate determination in extra virgin olive oil

The goal of this study was to develop a method for the determination of nine phthalic acid esters in extra virgin olive oils using low-pressure gas chromatography-triple-quadrupole mass spectrometry. Sample preparation was simple, environmental friendly, and rapid inasmuch that it involved only dilution (< 1 mL of hexane). The low-pressure gas chromatography analyses were performed by using a 5 m wide-bore column. The limit of quantification for the phthalates ranged from 0.06 to 1.14 mg kg-1 . Both intra- and interday precisions were measured, with coefficient of variation values ranging from 0.2% to 11.7%. The trueness of the method was measured by evaluating accuracy at the initial stage of the work and after 2 months, with values ranging between -8.7% and 12.1%. Moreover, blind accuracy was comprised between -11.6% and 14.2%. The method involves the use of simplified instrumentation and reduced analysis times (nearly two times faster) compared to a previously published comprehensive two-dimensional gas chromatography-triple-quadrupole mass spectrometry method, leading to a reduction of energy and helium consumption. The approaches were compared in analytical terms and for the environmental impact. In total, 23 olive oil samples were analyzed, with at least one phthalate detected in all but one sample.

Design and development of second-generation fabric phase sorptive extraction membranes: Proof-of-concept for the extraction of organophosphorus pesticides from apple juice prior to GC-MS analysis

In this work, different sol-gel sorbent-coated second-generation fabric phase sorptive extraction (FPSE) membranes were synthesized using titania-based sol-gel precursors. The proposed membranes were tested for their efficiency to extract eleven selected organophosphorus pesticides (OPPs) from apple juice samples. Among the examined materials, sol-gel C₁₈ coated titania-based FPSE membranes showed the highest extraction efficiency. These membranes were used for the optimization and validation of an FPSE method prior to analysis by gas chromatography-mass spectrometry. The detection limits for OPPs ranged between 0.03 and 0.08 ng mL^-1. Moreover, the relative standard deviation was < 8.2% and 8.4% for intra-day and inter-day studies, respectively. The relative recoveries were 91-110% (intra-day study) and 90-106% (inter-day study) for all the target analytes, demonstrating good overall method accuracy. Moreover, the novel membranes were reusable at least 5 times. The titania-based membranes were compared to the conventional silica-based membranes and their utilization resulted in higher extraction recoveries.

Solid-phase microextraction Arrow combined with comprehensive two-dimensional gas chromatography-mass spectrometry for the elucidation of the volatile composition of honey samples

In this work, a solid-phase microextraction (SPME) Arrow method combined with comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC-MS) was developed for the elucidation of the volatile composition of honey samples. The sample preparation protocol was optimized to ensure high extraction efficiency of the volatile organic compounds (VOCs) which are directly associated with the organoleptic properties of honey and its acceptance by the consumers. Following its optimization, SPME Arrow was compared to conventional SPME in terms of sensitivity, precision, and number of extracted VOCs. The utilization of SPME Arrow fibers enabled the determination of 203, 147, and 149 compounds in honeydew honey, flower honey, and pine honey, respectively, while a significantly lower number of compounds (124, 94, and 111 for honeydew honey, flower honey, and pine honey, respectively) was determined using conventional SPME. At the same time, the utilization of SPME Arrow resulted in enhanced sensitivity and precision. All things considered, SPME Arrow and GC × GC-MS can be considered as highly suitable for the elucidation of the volatile composition of complex food samples resulting in high sensitivity and separation efficiency.

Direct analysis of phthalate esters in vegetable oils by means of comprehensive two-dimensional gas chromatography combined with triple quadrupole mass spectrometry

Phthalic acid esters (PAEs), known as phthalates, have a variety of industrial applications, mainly related to their ability to increase plastic softness,flexibility, and durability. With regard to toxicological aspects, several studies suggest that phthalates would act as endocrine-disrupting chemicals, and they have been correlated to several forms of cancer. Since the analysis of PAEs in food is challenging, the aim of this study was the development of a simple and direct method, with no sample preparation (only dilution withsolvent), for the analysis of targeted phthalates in vegetable oils, by using cryogenic-modulation comprehensive two-dimensional gas chromatography combined with triple quadrupole mass spectrometry. The method was characterized by good repeatability values, limit of quantification values ranging between 0.06 and 2.10 mg/kg, accuracy values ranging from -9.2 to 10.4%, and a matrix effectranging from -4 to 78%.The developed technique was used for the analysis of 27 vegetable oils.

Exploring the volatile profile of whiskey samples using solid-phase microextraction Arrow and comprehensive two-dimensional gas chromatography-mass spectrometry

We present a novel sample preparation method for the extraction and preconcentration of volatile organic compounds from whiskey samples prior to their determination by comprehensive two-dimensional gas chromatography (GC × GC) coupled to mass spectrometry (MS). Sample preparation of the volatile compounds, important for the organoleptic characteristics of different whiskeys and their acceptance and liking by the consumers, is based on the use of the solid-phase microextraction (SPME) Arrow. After optimization, the proposed method was compared with conventional SPME regarding the analysis of different types of whiskey (i.e., Irish whiskey, single malt Scotch whiskey and blended Scotch whiskey) and was shown to exhibit an up to a factor of six higher sensitivity and better repeatability by a factor of up to five, depending on the compound class. A total of 167 volatile organic compounds, including terpenes, alcohols, esters, carboxylic acids, ketones, were tentatively-identified using the SPME Arrow technique, while a significantly lower number of compounds (126) were determined by means of conventional SPME. SPME Arrow combined with GC × GC-MS was demonstrated to be a powerful analytical tool for the exploration of the volatile profile of complex samples, allowing to identify differences in important flavour compounds for the three different types of whiskey investigated.

Flow-modulated comprehensive two-dimensional gas chromatography combined with time-of-flight mass spectrometry: use of hydrogen as a more sustainable alternative to helium

The present research is focused on the use and evaluation of hydrogen, as a more sustainable alternative to helium, within the context of fast flow modulation comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry. In such a respect, a comparison was made between the two mobile phases in terms of speed and overall chromatography performance. All experiments were carried out by using the following column set: low polarity with dimensions 10 m × 0.25 mm ID × 0.25 µm d_f and medium polarity with dimensions 2 m × 0.10 mm ID × 0.10 µm d_f. Fundamental gas chromatography parameters (efficiency, resolution) were measured under different experimental conditions, using the two carrier gases. Efficiency was measured in both the first and second dimensions, using a probe compound under isothermal conditions; after defining the optimum carrier gas conditions, a mixture containing 20 pesticides was analyzed to measure resolution, again in the first and second dimensions, using a temperature program. It was found (as expected) that a similar chromatography performance could be attained when using hydrogen, albeit with a circa 25% reduction in analysis time. Signal-to-noise ratios of the pesticides were calculated, using both carrier gases, with such values generally reduced (on average by 14%) when using hydrogen. Finally, a comparison was made between mass spectral profiles obtained analyzing the pesticides and fatty acid methyl esters using the two mobile phases. Even though mass spectral differences were observed, the ion profiles could be considered generally similar.

Untargeted profiling and differentiation of geographical variants of wine samples using headspace solid-phase microextraction flow-modulated comprehensive two-dimensional gas chromatography with the support of tile-based Fisher ratio analysis

The volatile fraction of food, also called the food volatilome, is increasingly used to develop new fingerprinting approaches. The characterization of the food volatilome is important to achieve desired flavor profiles in food production processes, or to differentiate different products, with winemaking being one popular area of interest. In the present research, headspace solid-phase microextraction (HS SPME) coupled to flow-modulated comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (FM GC×GC-TOFMS) was used to characterize geographical-based differences in the volatilome of five white "Grillo" wines (of Sicilian origin), comprising the five sample classes. All wines were produced with the same vinification method in 2019. To minimize the influence of minor bottle-to-bottle differences, three bottles of the same wine were randomly selected, and three samples were collected per bottle, resulting in nine sample replicates per wine. Particular emphasis was devoted to the operational conditions of a novel low duty cycle flow modulator. A fast FM GC×GC-TOFMS method with a modulation period of 700 ms and a re-injection period of 80 ms was developed. Following, the instrumental software was exploited to identify class-distinguishing analytes in the dataset via tile-based Fisher ratio analysis (i.e., ChromaTOF Tile). A tile size of 10 modulations (7 s) on the first dimension and 45 spectra (300 ms) on the second dimension was used to encompass average peak widths and to account for minor retention time shifting. Off-line software was used to apply an ANOVA test. A p-value of 0.01 was applied in order to select the most important class-distinguishing analytes, which were input to principal component analysis (PCA). The PCA scores plot showed distinct clustering of the wines according to geographical origin, although the loadings revealed that only a few analytes were necessary to differentiate the wines. However, a comprehensive flavor profile assessment underscored the importance of all the information output by the ChromaTOF Tile software.

Occurrence of Mineral Oil Hydrocarbons in Omega-3 Fatty Acid Dietary Supplements

Omega-3 fatty acid dietary supplements have become increasingly popular with consumers due to their multiple health benefits. In this study, the presence of mineral oil hydrocarbons (MOH) was investigated in seventeen commercial samples of such supplements, characterized by different formulations. The analyses were performed using on-line liquid chromatography–gas chromatography (with flame ionization detection), which is considered the most efficient method for the determination of MOH in foodstuffs. Analyte transfer was performed by using the retention gap technique, with partially concurrent solvent evaporation. Various degrees of mineral oil saturated hydrocarbon contamination (from 2.4 ppm to 375.7 ppm) were found, with an average value of 49.9 ppm. Different C-number range contaminations were determined, with the >C₂₅–≤C₃₅ range always found with an average value of 26.9 ppm. All samples resulted free of mineral oil aromatic hydrocarbons, except for two samples in which a contamination was found at the 9.9 and 6.6 ppm levels, respectively.

Use of a low-cost, lab-made Y-interface for liquid-gas chromatography coupling for the analysis of mineral oils in food samples

Consumers are daily exposed to a range of mineral oil hydrocarbons via food consumption. Major sources of MOH in food are packaging and additives, processing aids, and lubricants. In 2019, an EU guidance was released covering specific directions for sampling and analysis of mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH) in food and food contact materials within the frame of Recommendation (EU) 2017/84 for the monitoring of mineral oils. The parameters required by the guide are increasingly stringent, and coping with this type of analysis is now very challenging. It is within such a context that the present research is confined, inasmuch that it is focused on the construction of a low-cost, lab-made Y-interface for liquid-gas chromatography coupling used for the determination of MOSH and MOAH in foodstuffs. The response ratios of alkanes comprised between C₁₀ and C₅₀ were measured and were comprised between 0.9 and 1.1, with a maximum coefficient of variation of 4% (n = 5). Intermediate precision was evaluated for the fat/oil category during a period of 48 days obtaining a value of 10%. Qualitative and quantitative analysis of both MOSH and MOAH were performed in a single run and in a fully-automated manner. Seventeen different foods were analyzed in order to cover the categories reported in the EU guide. Saturated hydrocarbon contamination was detected only in a few samples (in the range 1-153 ppm); MOAH contamination was found only in one sample (sunflower oil: 15 ppm).

Determination of multi-pesticide residues in vegetable products using a "reduced-scale" Quechers method and flow-modulated comprehensive two-dimensional gas chromatography-triple quadrupole mass spectrometry

The aim of the present research was the development of an analytical method for the determination of multi-pesticide residues (88 target analytes) in four vegetable products (tomatoes, cucumbers, sweet red peppers and iceberg lettuce) using a "reduced-scale" QuEChERS (quick, easy, cheap, effective, rugged, and safe) extraction method and flow-modulated comprehensive two-dimensional gas chromatography-triple quadrupole mass spectrometry. In particular, the suitability of flow modulation [with relatively high second-dimension gas flow conditions (8 mL min^-1)] for trace analyte determination was evaluated. The samples were prepared according to the QuEChERS procedure as reported by the official European Union method, namely EN 15662:2018, based on the use of 3 g of vegetable product. Matrix-matched calibration processes were carried out for all the samples. The figures-of-merit determined were recovery, linearity, precision, limits of detection (LoDs), and limits of quantification (LoQs). Specifically, recoveries were in the 53-160% range, regression coefficients were between 0.9156 and 0.9999, the LoDs were in the 0.1-6.3 μg kg^-1 range, the LoQs were in the 3.0-21.0 μg kg^-1 range, and coefficients of variation were between 1 and 28% (at the 50 μg kg^-1 level).

Preliminary observations on the use of a novel low duty cycle flow modulator for comprehensive two-dimensional gas chromatography

The present research is focused on the preliminary evaluation, in particular in relation to the advisable operational conditions, of a novel low duty cycle flow modulator. In such a respect, a fast comprehensive two-dimensional gas chromatography-mass spectrometry method is herein proposed. Applications on a C₇-C₃₀ series of alkanes, 64 fragrance allergens (plus 2 internal standards), and 5 perfumes, were carried out by using two different column sets, low-polarity + medium-polarity and low-polarity + low-polarity. In both cases, the first column was of dimensions 10 m × 0.25 mm ID × 0.25 µm d_f, while the second one was of dimensions 1 m × 0.10 mm ID × 0.10 µm d_f. A modulation period of 700 ms, with a re-injection period of 80 ms, was used in order to obtain a higher duty cycle (measured to be approx. 0.04). Absolute quantification of the allergens was carried out by using two internal standards, namely 1,4-dibromobenzene and 4,4'-dibromobiphenyl. In terms of limits of quantification the instrumental response was characterized by a wide variability, ranging between 9 ppb and 5.4 ppm for both column sets. A total number of 97 fragrance allergens were identified and quantified in five commercial perfumes.

Evaluation of different internal diameter coated modulation columns within the context of solid-state modulation

The solid-state-modulator is a consumable-free thermal modulator, used within the context of comprehensive two-dimensional gas chromatography. Its consumable-free nature is guaranteed by the presence of a thermal-electric cooler device located between two heated chambers, everything located outside the gas chrpmatograph oven. The aim of the present research is to evaluate the solid-state-modulator modulation performance in relationship to different modulation capillary geometries. For this purpose, two coated modulation capillaries with the same length, but with different internal diameters (0.25 and 0.18 mm) were used. The effects of gas linear velocity, modulator temperature, and modulation period were evaluated in several applications involving standard alkanes and a sample of diesel fuel. Fundamental gas chromatography parameters (peaks widths, resolution) were measured under the different experimental conditions. Detailed information is provided on gas flow optimization, with particular emphasis on the efficiency of chromatography band reinjection onto the second-dimension column. The results obtained from the present investigation highlight how the modulation capillary characteristics have a great impact on the overall comprehensive two-dimensional gas chromatography separation. Specifically, considering the results herein attained, the use of a 0.18 mm ID × 0.18 μm d_f modulation column is advisable compared to a 0.25 mm ID × 0.25 μm d_f one.

In-Depth Qualitative Analysis of Lime Essential Oils Using the Off-Line Combination of Normal Phase High Performance Liquid Chromatography and Comprehensive Two-Dimensional Gas Chromatography-Quadrupole Mass Spectrometry

The present research is focused on the in-depth qualitative analysis of three types of lime essential oil (EO), viz., Key (A and B) and Persian, using the off-line combination of normal phase high performance liquid chromatography (NP-HPLC) and comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC × GC-QMS). The first analytical dimension (NP-HPLC) was exploited for the isolation of the hydrocarbon constituents from the oxygenated ones. Each fraction was then reduced in volume and analyzed using (cryogenic modulation) GC × GC-QMS. Peak assignment was carried out through the combined use of mass spectral database and linear retention index matching processes. The powerful four-dimensional technology enabled the separation and identification of a very high number (153) of lime essential oil volatile compounds.

Study of the Lipid Profile of ATCC and Clinical Strains of Staphylococcus aureus in Relation to Their Antibiotic Resistance

A number of reports have indicated a relationship between bacterial resistance to antibiotics and their lipid composition. In the present study, we characterized the lipid profiles of American Type Culture Collection (ATCC) and clinical strains of Staphylococcus aureus and its correlation with antibiotic resistance and hydrophobicity. The following strains were used: S. aureus ATCC 6538P, S. aureus ATCC 43300 (MRSA), seven clinical strains from the pharynges, two strains from duodenal ulcers, four strains from hip prostheses, and one strain from the conjunctiva. Lipid-related differentiation was observed across the S. aureus strains: the higher abundance of anteiso-pentadecanoic acid (anteiso-C_15:0) and anteiso-heptadecanoic acid (anteiso-C_17:0), followed by iso-pentadecanoic acid (iso-C_15:0), suggested that these were common lipids. Iso-tridecanoic acid (iso-C_13:0) and anteiso-tridecanoic acid (anteiso-C_13:0), iso-hexadecanoic acid (iso-C_16:0) and anteiso-hexadecanoic acid (anteiso-C_16:0), and all forms of octadecanoic acid (C_18:0) were usually detected in low abundance. Strains isolated from pharynges showed the highest ratio of branched/straight chains. A distinction in two clusters based on the amount and type of bacterial lipids identified was obtained, which correlated to the antibiotic resistance, the strains origin, and the cell-surface hydrophobicity. We report a potential correlation between the lipid profile of S. aureus strains, site of infection, antibiotic resistance, and cell-surface hydrophobicity. These results, which still need further insights, could be a first step to identifying antibiotic resistance in response to environmental adaptation.

Comprehensive two-dimensional gas chromatography-mass spectrometry: Recent evolution and current trends

The present contribution is focused on the evolution and current trends of comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC-MS), with respect to a review that described this specific methodology published at the beginning of 2008 (Mondello et al., 2008). In fact, since then there has been considerable evolution in the MS field, certainly exceeding that observed in GC × GC. In particular, the present paper will cover the combination of novel MS machines [single quadrupole (Q) and triple quadrupole, isotope ratio, low- and high-resolution time-of-flight (ToF), hybrid (Q-ToF)] to GC × GC systems, and will position comprehensive two-dimensional gas chromatography within the wider context of separation science. © 2014 Wiley Periodicals, Inc. Mass Spec Rev 35:524-534, 2016.