Determination of petitgrain oils landmark parameters by using gas chromatography-combustion-isotope ratio mass spectrometry and enantioselective multidimensional gas chromatography.

Gas chromatography-combustion-isotope mass spectrometry was employed for the assessment of the Carbon isotope ratios of volatiles in Italian mandarin and lemon petitgrain oils. In addition, the composition of the whole oil and the enantiomeric distribution of selected chiral compounds were determined for all the samples by using gas chromatography and by multidimensional and conventional enantioselective gas chromatography. The composition of the oils was compared with previous studies. The enantiomeric distribution of lemon petitgrain oils is here reported for the first time. On the composition of mandarin petitgrain oil, the information available in literature, to date, is relative only to one sample from Egypt. Carbon isotope ratio of several terpene hydrocarbons and of their oxygenated derivatives contained in petitgrains was compared with the δ (13)C(VPDB) values of the same compounds present in the corresponding genuine Italian Citrus peel oil. The results prove that the isotopic values obtained for lemon and mandarin petitgrain oils are very close to those relative to the corresponding peel oils determined in previous studies.

Evaluation of a medium-polarity ionic liquid stationary phase in the analysis of flavor and fragrance compounds.

The present research is focused on the evaluation, in terms of efficiency and polarity, of a recently introduced gas chromatography (GC) column, coated with a 1,12-di(tripropylphosphonium) dodecane bis(trifluoromethansulfonyl) amide ionic-liquid stationary phase (SLB-IL59) and its application to the analysis of a complex essential oil. The ionic liquid column demonstrated very good efficiency, in terms of plate number, and a polarity close to that of the 100% poly(ethyleneglycol) stationary phase. In this preliminary evaluation, the SLB-IL59 30 m column was subjected to bleeding measurements, by means of conventional gas chromatography/mass spectrometry (GC/MS) and, in addition, of comprehensive 2D GC. The SLB-IL59 column (30 m × 0.20 µm d(f), 0.25 mm i.d.) was then evaluated in the analysis of typical essential oil constituents, in the form of pure standard compounds. Resolution toward several analytes was measured and the results were compared to those obtained with both apolar [silphenylene polymer, equivalent to poly(5% diphenyl/95% dimethylsiloxane)] and medium-polarity [100% poly(ethyleneglycol)] stationary phases, namely, the most common columns employed in the analysis of essential oils; peak symmetry, for different essential oil constituents, was also measured and expressed through tailing factors (at 10% of peak height). The final part of the investigation was devoted to the GC/MS analysis of lemon essential oil, with GC-flame ionization detection (FID) used for quantification. Linear retention indices of all the identified compounds were determined, and the data obtained were compared to those attained on the apolar and "wax" columns. The results obtained in the present investigation reveal the great potential of this novel stationary phase, as a medium-polarity alternative, in the analysis of essential oils.

Comprehensive two-dimensional liquid chromatography with evaporative light-scattering detection for the analysis of triacylglycerols in Borago officinalis.

An optimized 2-D liquid chromatography (LC×LC) set-up, based on the different selectivities of a silver ion (Ag) and a non-aqueous reversed phase (NARP), employed in the first (D1) and the second dimension (D2), respectively, in combination with evaporative light-scattering detection (ELSD), has been developed for the analysis of the triacylglycerol (TAG) fraction in a Borago officinalis oil. The 2-D set-up, thanks to the complementary separation selectivity provided by the two columns, allowed to distribute 78 TAGs throughout the 2-D LC retention plane otherwise unachievable by 1-D LC.

Performance evaluation of a rapid-scanning quadrupole mass spectrometer in the comprehensive two-dimensional gas chromatography analysis of pesticides in water.

The performance of a novel rapid-scanning (20,000 amu/s) quadrupole mass spectrometer (qMS) has been evaluated in the comprehensive 2-D gas chromatography (GC×GC) analysis of pesticides contained in water. Analyte extraction was performed by using direct solid-phase microextraction (SPME). The MS system was operated using a rather wide m/z 50-450 mass range and a 33 Hz spectral production rate, a frequency which was found sufficient for reliable quantification. The qMS performance was evaluated considering: (i) number of data points per peak, (ii) mass spectral quality, (iii) extent of peak skewing, and (iv) consistency of retention times. Seven-point calibration curves (external calibration) were constructed for 28 pesticides over the limit of quantification range of 100 µg/L (1, 5, 10, 25, 50, and 100 µg/L). The solid-phase microextraction-GC×GC-qMS method was validated by calculating limits of detection and quantification, intraday peak area precision, accuracy, and intraday retention-time precision. A series of tap water samples were subjected to analysis, fortunately giving negative results.

Evaluation of a rapid-scanning quadrupole mass spectrometer in an apolar × ionic-liquid comprehensive two-dimensional gas chromatography system.

Comprehensive two-dimensional gas chromatography (GC×GC) is a powerful technique which can enable a great increase in GC peak capacities. However, since secondary-column separations are very rapid, detectors with a fast acquisition rate are mandatory. Such a requirement has certainly limited the use of the quadrupole mass spectrometer in the GC×GC field. The present research is focused on the evaluation of a novel rapid-scanning quadrupole mass spectrometry (qMS) detector, characterized by a 20,000 amu/s scan speed and a 50 Hz scan frequency, using a 290 amu mass range (40-330 m/z). The performance of the MS system was assessed by analyzing mixtures of 24 allergens, as well as a perfume sample, through GC×GC/qMS. The MS parameters evaluated at different acquisition rates (50, 33, and 25 Hz), as well as in the (simultaneous) scan/selected ion monitoring (SIM) mode, were the number of data points per peak, mass spectrum quality, peak skewing, and sensitivity. Two GC×GC/qMS methods, using the 50 Hz acquisition rate and the scan/SIM mode, were validated. Both methods provided similar results in terms of repeatability, accuracy, and linearity, while a great increase in sensitivity was observed (ca. a factor of 10) under scan/SIM conditions. The validated method proved to be suitable for the analysis of perfume allergens, according to the requirements of Directive 2003/15/EC.

Accurate quadrupole MS peak reconstruction in optimized gas-flow comprehensive two-dimensional gas chromatography.

In the present research, a split-flow comprehensive 2-D GC-quadrupole MS (qMS) method was developed using: a primary apolar 30 m×0.25 mm id×0.25 µm d(f) capillary linked, via a T-union, to a secondary polar 1.0 m×0.05 mm id×0.05 µm d(f) capillary and to a 0.10 m×0.05 mm id×0.05 µm d(f) uncoated column segment. The GC×GC-qMS instrument was equipped with two GC ovens and a loop-type modulator. The polar column was connected to the MS, whereas the uncoated column directed most of the first-dimension effluent to waste and enabled the generation of optimum gas velocities in both dimensions, namely circa 20 and 80 cm/s in the first and second dimensions, respectively. The rapid-scanning qMS was operated at a scan speed of 10,000 amu/s, a 25-Hz data acquisition frequency (scan time+interscan time: 40 ms), and with a normal GC mass range (m/z 40-360). Chromatography bands at the second-dimension outlet were never less than 360 ms wide (6σ), enabling the acquisition of at least 10 spectra/peak.

Genuineness assessment of mandarin essential oils employing gas chromatography-combustion-isotope ratio MS (GC-C-IRMS).

Cold-pressed mandarin essential oils are products of great economic importance in many parts of the world and are used in perfumery, as well as in food products. Reconstituted mandarin oils are easy to find on the market; useful information on essential oil authenticity, quality, extraction technique, geographic origin and biogenesis can be attained through high-resolution GC of the volatile fraction, or enantioselective GC, using different chiral stationary phases. Stable isotope ratio analysis has gained considerable interest for the unveiling of citrus oil adulteration, detecting small differences in the isotopic carbon composition and providing plenty of information concerning the discrimination among products of different geographical origin and the adulteration of natural essential oils with synthetic or natural compounds. In the present research, the authenticity of several mandarin essential oils was assessed through the employment of GC hyphenated to isotope ratio MS, conventional GC flame ionization detector, enantioselective GC and HPLC. Commercial mandarin oils and industrial natural (declared as such) mandarin essential oils, characterized by different harvest periods and geographic origins, were subjected to analysis. The results attained were compared with those of genuine cold-pressed Italian mandarin oils, obtained during the 2008-2009 harvest season.

Optimized use of a 50 microm internal diameter secondary column in a comprehensive two-dimensional gas chromatography system.

The focus of the present research is directed toward the development of a comprehensive two-dimensional gas chromatography (GC x GC) method, characterized by a greatly increased separation power, if compared with GC x GC approaches using classical column combinations. The analytical objective was achieved by using a 0.05 mm internal diameter (i.d.) capillary as second dimension, a split-flow approach reported in previous research (Tranchida, P. Q., Casilli, A., Dugo, P., Dugo, G. and Mondello, L. Anal. Chem. 2007, 79, 2266-2275), and a twin-oven GC x GC instrument. The column combination employed was an orthogonal one: an apolar 30 m x 0.25 mm i.d. column was linked, by means of a Y-union, to a flame ionization detector (FID)-connected high-resolution 1 m x 0.05 mm i.d. polar one and to a 0.20 m x 0.05 mm i.d. uncoated capillary segment; the latter was connected to a manually operated split valve, located on top of the second GC. As previously shown, the generation of optimum gas linear velocities in both dimensions can be attained by splitting gas flows at the outlet of the first dimension (Tranchida, P. Q., Casilli, A., Dugo, P., Dugo, G. and Mondello, L. Anal. Chem. 2007, 79, 2266-2275). An optimized GC x GC method was developed and exploited for the analysis of a complex petrochemical sample. The satisfactory results attained were directly compared with those observed using the same instrumentation, equipped with what can be defined as a classical GC x GC split-flow column set: the same primary column was connected to an FID-linked 1 m x 0.10 mm i.d. polar one and to a 0.30 m x 0.10 mm i.d. uncoated capillary. It will be herein illustrated that there is still room for significant progress in the GC x GC field.

Evaluation of use of a dicationic liquid stationary phase in the fast and conventional gas chromatographic analysis of health-hazardous C18 cis/trans fatty acids.

The present research is focused on the evaluation of one 0.10 mm i.d. and two 0.25 mm i.d., ionic liquid (IL) stationary phase [1,9-di(3-vinyl-imidazolium) nonane bis(trifluoromethyl) sulfonyl imidate] columns, with lengths of 12 (the microbore capillary), 30 and 100 m, in the GC analysis of cis/trans fatty acid methyl esters (FAMEs). The selectivity of the IL columns toward a series of standard C(18:1), C(18:2), and C(18:3) geometric isomers (a group of 22 compounds was subjected to GC analysis) was compared to the performance of a widely used column in the cis/trans FAMEs analysis field, viz., a 100 m x 0.25 mm i.d. capillary with a 0.20 microm stationary phase film of bis-cyanopropyl polysiloxane (SP-2560). The selectivity provided by the IL phase was superior if compared to that of the other well-established capillary. An optimized IL method, using the longer column, was subjected to validation: retention time and peak area intraday precision (n = 5) were good, with RSD values lower than 0.07% and 6.6%, respectively; LODs (considering a S/N of 3) for C(18:1Delta)(9tr) and C(18:2Delta)(9tr,12tr) were 0.15 (7.3 ppm) and 0.18 ng (9.1 ppm) on-column, respectively, while LOQs (considering a S/N of 10) were 0.49 (24.3 ppm) and 0.60 ng (30.2 ppm), respectively; the method was found to be linear, for both trans FAMEs, in the 10-2000 ppm range. For the evaluation of accuracy, a hydrogenated margarine, spiked with known amounts of C(18:3Delta)(9c,12c,15c), was subjected to analysis using C(13:0) as an internal standard.

High peak capacity separation of peptides through the serial connection of LC shell-packed columns.

High peak capacity was obtained for the separation of a HSA tryptic digest through the serial connection of three LC columns packed with shell material (C18, 15 cmx4.6 mm, 2.7 mum particle size). A major benefit of these particles, consisting of a 1.7 mum solid core and a 0.5 mum porous shell, is the small diffusion path, which reduces axial dispersion of solutes and minimizes peak broadening allowing for higher resolving power to be obtained. Increase in the temperature decreases the viscosity and the backpressure on the columns and in this way allowed to couple multiple columns. Single and multicolumn systems were first evaluated for the separation of a standard sample mixture in the isocratic mode; afterwards three columns could be coupled at 60 degrees C, generating more than 90,000 effective plates (200,000 plates/meter) for the separation of HSA in gradient mode on a conventional HPLC instrument. Peak capacity ratios were found in good accordance with the theoretical gain in resolution, i.e. values of 1.37 and 1.67 were measured, when doubling and tripling the length of stationary phases, respectively (the highest measured peak capacity on three coupled columns was 367).

Characterization of the yerba mate (Ilex paraguariensis) volatile fraction using solid-phase microextraction-comprehensive 2-D GC-MS.

The present research is focused on the use of a solid-phase microextraction-comprehensive 2-D GC methodology, in the analysis of the volatile fraction of yerba mate. Yerba mate is used for the generation of a tea-like beverage, widely consumed in South America. A rapid-scanning quadrupole mass spectrometer (qMS), employed as a detection system and operated at a 25 Hz scanning frequency, supplied high-quality mass spectra. The effectiveness of the 3-D comprehensive 2-D GC-qMS experiment was compared to that of GC-qMS analysis on the same sample. Peak identification, in both applications, was achieved through MS library matching, with the support of linear retention index data. Apart from a great increase in the number of analytes separated (approx. by a factor of 5) and identified (approx. by a factor of 3.5), the comprehensive 2-D GC-qMS approach enabled the determination of a high number of hazardous contaminants (aliphatic hydrocarbons, polycyclic aromatic hydrocarbons, and plasticizers), barely visible in the GC-qMS analysis.

Quantification in comprehensive two-dimensional liquid chromatography.

Although the use of comprehensive two-dimensional liquid chromatography (LCxLC) as a powerful separation technique is continuously increasing, its employment in quantification experiments is rather limited. The present research is focused on the quantification of a series of standards, as well as real-world sample compounds, by using dedicated laboratory-constructed LCxLC software, developed through a novel approach. Moreover, the difficulties encountered during software operation, in various elution conditions, are described and discussed. The results attained were compared with those observed in conventional LC, and no statistically significant differences were observed in the determination of aurapten in grapefruit oil. However, a loss in sensitivity was observed when using LCxLC (limit of detection = 0.10 ppm) compared to conventional LC (limit of detection = 0.05 ppm) as a consequence of the sample dilution in comprehensive two-dimensional liquid chromatography.

Comprehensive multidimensional liquid chromatography: theory and applications.

Comprehensive two-dimensional (2D) liquid chromatographic (LC x LC) techniques can be considered innovative methods only recently developed and adopted in many configurations. The revolutionary aspect of comprehensive two-dimensional techniques, with respect to classical multidimensional (MD) chromatography, is that the entire sample is subjected to the 2D advantage. The major benefit is that the separation capacities of each dimension are multiplied, offering a high peak capacity to resolve samples of great complexity. The first part of the present review briefly describes the theoretical and practical aspects related to the development of a multidimensional comprehensive liquid chromatographic method. Applicational experiences in comprehensive liquid chromatography are then described, divided into four groups, according to the HPLC modes used in the two dimensions and to the nature of the samples analyzed.

Gas chromatography-olfactometry in food flavour analysis.

The application of gas chromatography-olfactometry (GC-O) in food flavour analysis represents to be a valuable technique to characterise odour-active, as well as character impact compounds, responsible for the characterizing odour of a food sample. The present article briefly reviews the use of GC-O in the flavour investigation of dairy products (milk and cheese), coffee, meat and fruits. Particular attention has been devoted to extraction techniques, GC-O hardware commonly utilised and olfactometric assessment methods, which can be applied to food analysis.

Reliable identification of pesticides using linear retention indices as an active tool in gas chromatographic-mass spectrometric analysis.

The present research is focused on the current development and employment of a dedicated pesticide mass spectral library, characterized by a double-filter search procedure: the first is based on the degree of spectral similarity and the second on chromatographic retention information (linear retention indices). The highly pure mass spectra contained in the library have been attained by subjecting mixtures of widely used pesticides to comprehensive GC-MS analysis. Linear retention indices for conventional GC-MS analyses were calculated by injecting the same compounds on a single-column GC-MS system. The effectiveness of this approach was verified by analysing a white wine sample spiked with 10 structurally similar pyrethroid compounds, through automated solid-phase microextraction-GC-MS.

Evaluation of use of a very short polar microbore column segment in high-speed gas chromatography analysis.

Very fast GC analyses are commonly carried out by using 10 m x 0.1 mm id capillaries. In order to achieve rapid elution times (1-3 min), the latter are operated under suboptimum conditions. The present research is focused on the evaluation of use of a 0.1 mm id polar column segment (2 m), operated under near-to-optimum conditions, in very fast GC analysis. The results attained are compared with those derived from using a 10 m microbore column in very fast GC experiments. Prior to method development, the effects of gas velocity, temperature program rate, and sample amounts on analytical performance were evaluated. Following these preliminary applications, a complex lipidic sample, cod liver oil, was subjected to rapid separation (approximately 2.1 min) on the 10 m capillary through the application of a 50 degrees C/min temperature rate and a 130 cm/s gas velocity. The same matrix was analyzed on the 2 m capillary using the same temperature program rate and range, but with a close-to-ideal linear velocity. The results observed were of interest, as the separation was achieved in less time (1.45 min) with improved peak resolution. Finally, both methods were validated in terms of retention time and peak area repeatability, LOQ, and linearity.

Elucidation of fatty acid profiles in vegetable oils exploiting group-type patterning and enhanced sensitivity of comprehensive two-dimensional gas chromatography.

The present research is focused on the use of comprehensive 2-D GC (GCxGC) for the thorough elucidation of fatty acid (FA) profiles contained in vegetable oils; the samples analysed consisted of extra-virgin olive oil and refined hazelnut oil. The enhanced sensitivity and the formation of group-type patterns provided by GCxGC enabled the identification and quantification of both well-known and rather unexpected FAs contained in the lipid matrices. Peak assignment was, in most cases, supported by using pure standard compounds. Of particular interest was the identification of a series of odd-numbered FAs in both samples. The results attained to demonstrate the usefulness of GCxGC also for the analysis of supposedly low-complex samples.

Acquisition of deeper knowledge on the human plasma fatty acid profile exploiting comprehensive 2-D GC.

The present research is focused on the use of comprehensive 2-D GC (GC x GC) for the elucidation of the human plasma fatty acid (FA) profile. The enhanced sensitivity, increased separation power and the formation of group-type patterns provided by GC x GC enabled the identification and quantification of a high number of both well known and unexpected FAs, for a total of 65 components. Peak assignment was, in most cases, supported by using pure standard compounds. The results attained demonstrated the usefulness of the multidimensional GC method in this fundamental field of research.

Offline LC-GC x GC in combination with rapid-scanning quadrupole mass spectrometry.

The present research is focused on the offline combination of normal-phase LC to double-oven GC x GC-quadrupole MS. Initially, a diesel sample was subjected to automated LC x GC in order to define the elution windows of four fractions, viz., saturated hydrocarbons, monocyclic aromatics, dicyclic aromatics, tri- + tetracyclic aromatics; each fraction was collected exploiting the LC system in a further analysis and subjected to large-volume-injection-GC x GC analysis using an apolar-polar column combination. The GC x GC operational conditions were tuned in relation to the specific separation requirements of each heart-cut. The main benefits of what can be defined as offline LC-GC x GC were: (i) the high first-dimension LC selectivity; (ii) the injection of high sample amounts in the GC x GC system, enabling the detection and quantification of a series of low-amount diesel constituents; (iii) improved GC x GC operational conditions for each heart-cut with respect to direct GC x GC.

Application of comprehensive two-dimensional liquid chromatography to elucidate the native carotenoid composition in red orange essential oil.

In the present work, the ability of a LC x LC-DAD/APCI-MS method developed at this laboratory to identify the native composition of carotenoid in an extremely complex matrix such as red orange essential oil was demonstrated. To carry out this task, two independent and orthogonal separation mechanisms were coupled through a 10-port switching valve that simultaneously collected the eluent from a microbore cyano column used as the first dimension in normal phase mode and injected it to a conventional reversed phase monolithic C(18) column in the second dimension separation. By using this novel analytical technique together with the use of DAD and APCI-MS detectors it was possible to identify in the sample, without the need of any pretreatment, 40 different carotenoids. Among them, 16 carotenoid monoesters were identified, mainly beta-cryptoxanthin palmitate (C(16:0)), myristate (C(14:0)), and laureate (C(12:0)) as well as several lutein, violaxanthin, antheraxanthin, and luteoxanthin monoesters. Moreover, 21 carotenoid diesters composed by several antheraxanthin, luteoxanthin, violaxanthin, and auroxanthin diesters were found in the native carotenoid composition of the orange oil. The main carotenoid diesters were the laureate palmitate (C(12:0), C(16:0)), myristate palmitate (C(14:0), C(16:0)), and dipalmitate (C(16:0), C(16:0)) diesters, although other diesters were also identified. Besides, two different free carotenes, zeta-carotene and phytofluene, and a xanthophyll, lutein, were also determined. To the authors' knowledge, this is the first time that carotenoid diesters are described and identified in orange essential oil. Likewise, it has been demonstrated that the LC x LC approach proposed in this study is capable of coping with the direct analysis and identification of a complex natural source of carotenoids such as the orange.