Yada Nolvachai

Two-Dimensional Retention Indices Improve Component Identification in Comprehensive Two-Dimensional Gas Chromatography of Saffron

Comprehensive two-dimensional gas chromatography hyphenated with accurate mass time-of-flight mass spectrometry (GC × GC-accTOFMS) was applied for improved analytical accuracy of saffron analysis, by using retention indices in the two-dimensional separation. This constitutes 3 dimensions of identification. In addition to accTOFMS specificity, and first dimension retention indices ((1)I), a simple method involving direct multiple injections with stepwise isothermal temperature programming is described for construction of isovolatility curves for reference alkane series in GC × GC. This gives access to calculated second dimension retention indices ((2)I). Reliability of the calculated (2)I was evaluated by using a Grob test mixture, and saturated alkanes, revealing good correlation between previously reported I values from the literature, with R(2) correlation being 0.9997. This essentially recognizes the retention property of peaks in the GC × GC 2D space as being reducible to a retention index in each dimension, which should be a valuable tool supporting identification. The benefit of (2)I data, in supplementing (1)I and MS library matching, was clearly demonstrated by the progressive reduction of the number of possible compound matches for peaks observed in saffron. 114 analytes were assessed according to (1)I and (2)I values within ±20 index unit of reference values, and by MS spectrum matching above a match statistic of 750 (including mass accuracy of the molecular ion <20 ppm) and their possible identities derived. The described method provides a new avenue to utilize the full capability of the two-dimensional separation (GC × GC), in combination with MS library matching in complex sample analysis, to provide improved component identification.

GC for flavonoids analysis: Past, current, and prospective trends

Flavonoids represent one of the more abundant classes of phytochemicals. They are renowned for their health benefits against age-related ailments and diseases. Several chromatography techniques have underpinned many chemical analysis methods, developed for superior flavonoid separation and identification. Among these, GC is one of the most powerful tools in separation science, providing precise measurement of a wide range of flavonoids. Combined with various detectors - most commonly MS-GC offers a sensitive and accurate tool for quantitative and qualitative flavonoids analysis. This review features developments in the application of GC and MS for flavonoids determination during past decades, progressing to recent developments and considering future trends. The review will highlight the state-of-the-art of GC, with opportunities for multidimensional GC analysis also briefly discussed.

Thermally Sensitive Behavior Explanation for Unusual Orthogonality Observed in Comprehensive Two-Dimensional Gas Chromatography Comprising a Single Ionic Liquid Stationary Phase

In this study, a theoretical concept and method to achieve a degree of orthogonality in comprehensive two-dimensional gas chromatography (GC × GC) for separation of fatty acid methyl esters (FAME) by using a single ionic liquid (IL) stationary phase (1-phase-GC × GC) were established. The 1-phase system comprises a long IL column and shorter IL column of the same phase before and after the modulation region, operated under temperature-programmed conditions. Initial isothermal experiments employing six commercial IL columns were conducted at different temperatures. On the basis of the temperature-dependent linear solvation energy relationship (LSER) concept, SLB-IL111 exhibited the greatest thermal sensitivity and degree of difference over the tested temperature (T) range, so it was selected for investigation of the 1-phase-GC × GC mode. With the same temperature program, a significantly high degree of orthogonality was observed for the experiment, varied with column lengths. The switchable separation result, which inverts the retention of saturated and unsaturated FAME on the downstream column ((2)D), was achieved by varying column diameters and surface thicknesses of the IL-coated layers. These results were explained according to the corresponding LSER principles. Also, the time summation model was applied for the simulation of the observed 1-phase-GC × GC results.

Pesticides Analysis: Advantages of Increased Dimensionality in Gas Chromatography and Mass Spectrometry

For a century, pesticides have been an integral component of the environmental system of the world. There has been increasing attention paid to the regulation and analysis of these compounds. Gas chromatography (GC) and mass spectrometry (MS) are two of the most important analytical techniques employed for high throughput pesticide analysis. This review features applications, advantages, and comparison of different GC and MS techniques based on applied separation dimensionalities related to column and/or mass analyzers. A brief historical perspective, a primary focus on recent developments, and a view to future trends will be highlighted here. Multidimensional analysis, employing novel types of stationary phases for GC, will be considered, along with the role of hyphenation with emerging MS technologies.

Enantiomeric separation in comprehensive two-dimensional gas chromatography with accurate mass analysis.

Chiral comprehensive two-dimensional gas chromatography (eGC×GC) coupled to quadrupole-accurate mass time-of-flight mass spectrometry (QTOFMS) was evaluated for its capability to report the chiral composition of several monoterpenes, namely, α-pinene, β-pinene, and limonene in cardamom oil. Enantiomers in a standard mixture were fully resolved by direct enantiomeric-GC analysis with a 2,3-di-O-methyl-6-t-butylsilyl derivatized β-cyclodextrin phase; however, the (+)-(R)-limonene enantiomer in cardamom oil was overlapped with other background components including cymene and cineole. Verification of (+)-(R)-limonene components based on characteristic ions at m/z 136, 121, and 107 acquired by chiral single-dimension GC-QTOFMS in the alternate MS/MSMS mode of operation was unsuccessful due to similar parent/daughter ions generated by interfering or co-eluting cymene and cineole. Column phases SUPELCOWAX, SLB-IL111, HP-88, and SLB-IL59, were incorporated as the second dimension column ((2)D) in chiral GC×GC analysis; the SLB-IL59 offered the best resolution for the tested monoterpene enantiomers from the matrix background. Enantiomeric ratios for α-pinene, β-pinene, and limonene were determined to be 1.325, 2.703, and 1.040, respectively, in the cardamom oil sample based on relative peak area data.

Insights into the origin of the separation selectivity with silica hydride adsorbents.

In this study, the surface properties of type-B silica have been compared with an unmodified silica hydride phase, a diamond hydride phase and silica hydride phases modified with bidentate anchored octyl (BDC8), bidentate anchored octadecyl (BDC18), phenyl and cholesteryl groups. Atomic distributions of the surface elemental composition of each type of stationary phase were determined using energy-dispersive X-ray spectroscopy. For the type-B silica, unmodified silica hydride, diamond hydride as well as BDC18 and cholesteryl silica hydride phases, the increase in carbon contents correlated with more negative surface ζ potential values (R(2) = 0.92). The origin of these more negative ζ potentials has been evaluated with mobile phases up to 100% (v/v) methanol content, with this property attributed to either an increase in the amount of adsorbed hydroxide ions or a decrease in the amount of adsorbed protons on the surfaces modified silica hydride phases of higher carbon content. This property of chemically modified silica hydride phases is in accordance with the unique propensity for hydroxide ions to be preferentially adsorbed onto hydrophobic surfaces of low permittivity and effects due to the specific accumulated water molecules associated with the electrical interfacial double layer of the adsorbent.

Miniaturized molecularly imprinted polymer extraction method for the gas chromatographic analysis of flavonoids

In this study, the use of monolithic molecularly imprinted polymers in a micropipette tip format allowing the simple and fast extraction of flavonoids from standard solutions and a black tea sample is demonstrated. The imprinted polymer employed quercetin, methacrylic acid or 4-vinylpyridine, and ethylene glycol dimethacrylate as template, functional monomer, and cross-linker, respectively. Surface morphologies of the quercetin-imprinted polymers and the corresponding nonimprinted polymers were characterized by SEM. Extraction of flavonoid standards was performed to evaluate the selectivity and recovery with these imprinted and nonimprinted polymers. Flavonoid compositions in aliquots eluted from the tips were identified using fast GC with flame ionization detection. Maximum specific capacities of 0.2, 5.7, and 16.0 mg/g for catechin, morin, and quercetin, respectively, were obtained with the imprinted polymer prepared with methacrylic acid, with the corresponding recoveries of 99.8, 98.8, and 95.4%, respectively. Efficient extraction by the quercetin-imprinted polymer of epicatechin, catechin, and quercetin from an apple-flavored black tea sample was achieved, with GC-MS employed for compound identification for both the tea and extracted samples.

In Silico Modeling of Hundred Thousand Experiments for Effective Selection of Ionic Liquid Phase Combinations in Comprehensive Two-Dimensional Gas Chromatography

The selection of the best column sets is one of the most tedious processes in comprehensive two-dimensional gas chromatography (GC × GC) where a multitude of choices of column sets could be employed for an individual sample analysis. We demonstrate analyte/stationary phase dependent selection approaches based on the linear solvation energy relationship (LSER), which is a reliable concept for the study of interaction mechanisms and retention prediction with a large database pool of columns and compounds. Good correlations between our predicted results, with experimental results reported in the literature, were obtained. The developed approaches were applied to the simulation of 157 920 individual experiments in GC × GC, focusing on the application of 30 nonionic liquid and 111 ionic liquid (IL) stationary phases for separation of some example sets of model compounds present in practical samples. The best column sets for each sample separation could then be extracted according to maximizing orthogonality, which estimates the quality of separation.

Continuum in MDGC Technology: From Classical Multidimensional to Comprehensive Two-Dimensional Gas Chromatography

Recent advances in multidimensional gas chromatography (MDGC) comprise methods such as multiple heart-cut (H/C) analysis and comprehensive two-dimensional gas chromatography (GC × GC); however, clear approaches to evaluate the MDGC results, choice of the most appropriate method, and optimized separation remain of concern. In order to track the capability of these analytical techniques and select an effective experimental approach, a fundamental approach was developed utilizing a time summation model incorporating temperature-dependent linear solvation energy relationship (LSER). The approach allows prediction of optimized analyte distribution in the 2D space for various MDGC approaches employing different experimental variables such as column lengths, temperature programs, and stationary phase combinations in order to evaluate separation performance (apparent (1)D, (2)D, total number of separated peaks, and orthogonality) for simulated MDGC results. The methodology applied LSER to generate results for nonpolar-polar and polar-nonpolar 2D column configurations for separation of 678 compounds in an oxidized kerosene-based jet fuel sample. Three-dimensional plots were generated in order to illustrate the dependency of separation performance on (2)D column length and number of injections for different stationary phase combinations. With a given limit of analysis time, a MDGC approach to obtain an optimized total separated peak number for a particular column set was proposed depending on (1)D and (2)D analyte peak distribution. This study introduces fundamental concepts and establishes approaches to design effective GC × GC or multiple H/C systems for different column combinations, to provide the best overall separation outcomes with the highest separated peak number and/or orthogonality.

Comparison of the performance of different silica hydride particles for the solid-phase extraction of non-volatile analytes from dark chocolate with analysis by gas chromatography-quadrupole mass spectrometry

The extraction capabilities of a Diamond Hydride™ phase, as well as silica hydride phases modified with bidentate octadecyl (BDC(18)), phenyl or cholesteryl groups, were evaluated for the analysis of fatty acids, amino acids, sugars and sterols in a dark chocolate extract. These batch adsorption performances were investigated using either methanol or aqueous methanol as the solvent. The compositions of the extracted fractions were assessed by gas chromatography interfaced with quadrupole mass spectrometry (GC-qMS). The batch binding propensities of the various compound classes with silica hydride particles modified with immobilised phenyl groups or larger ligands followed trends predicted from linear solvation energy relationships. Both prediction and experiment revealed that better extraction results could be obtained with the phenyl, BDC(18) and cholesteryl hydride particles for the major chocolate components. Based on these results, separations in micro-pipette tip format with these three types of stationary phase particles have been undertaken.