Stationary Phases Of Different Polarity Research Articles

The leaf essential oil of Ecuadorian Ophryosporus peruvianus (J.F. Gmel.) R.M. King & H. Rob: chemical composition, enantioselective analysis, and in vitro enzymatic inhibitory activity

ABSTRACT An Ecuadorian specimen of Ophryosporus peruvianus produced an essential oil with a yield of 0.4% of the weight of the fresh plant material. A total of thirty-two compounds were detected and quantified. The chemical composition showed the predominance of monoterpene hydrocarbons, with sabinene (22.5%), β-pinene (15.1%), limonene (8.3%), β-phellandrene (29.7%), δ-elemene (2.1%), and epi-α-cadinol (2.7%) being the main components, expressed as mean values on two stationary phases of different polarity. This composition was very different from that reported in the literature for the essential oil of a Peruvian specimen, which was dominated by sesquiterpene hydrocarbons. These results indicate the existence of different chemotypes of O. peruvianus. Moreover, an enantioselective analysis of the major chiral constituents was performed, which revealed (R)-(-)-β-phellandrene, (R)-(-)-β-phellandrene and (1R,9R,E)-(-)-β-caryophylleneas enantiomerically pure compounds. On the other hand, β-thujene, β-pinene, β-pinene, sabinene, limonene, and terpinen-4-ol were scalemic mixtures. Finally, a preliminary screening of enzymatic inhibitory activity was performedin vitro, showing modest but interesting inhibition of both butyrylcholinesterase and lipase.

In-Column Dehydration Benzyl Alcohols and Their Chromatographic Behavior on Pyridinium-Based Ionic Liquids as Gas Stationary Phases.

At present, stationary phases based on ionic liquids are a promising and widely used technique in gas chromatography, yet they remain poorly studied. Unfortunately, testing of "new" stationary phases is often carried out on a limited set of test compounds (about 10 compounds) of relatively simple structures. This study represents the first investigation into the physicochemical patterns of retention of substituted (including polysubstituted) aromatic alcohols on two stationary phases of different polarities: one based on pyridinium-based ionic liquids and the other on a standard polar phase. The retention order of the studied compounds on such stationary phases compared to the standard polar phase, polyethylene glycol (SH-Stabilwax), was compared and studied. It was shown that pyridinium-based ionic liquids stationary phase has a different selectivity compared to the SH-Stabilwax. Using a quantitative structure-retention relationships (QSRR) study, the differences in selectivity of the two stationary phases were interpreted. Using CHERESHNYA software, the importance of descriptors on different stationary phases was evaluated for the same data set. Different selectivity of the stationary phases correlates with different contributions of descriptors for the analytes under study. For the first time, we show that in-column dehydration is observed for some compounds (mostly substituted benzyl alcohols). This effect is worthy of further investigation and requires attention when analyzing complex mixtures. It suggests that when testing "new" stationary phases, it is necessary to conduct tests on a large set of different classes of compounds. This is because, in the case of using ionic liquids as an stationary phase, a reaction between the analyte and the stationary phase is possible.

A new leaf essential oil from the Andean species Gynoxys szyszylowiczii Hieron. of southern Ecuador: chemical and enantioselective analyses

The essential oil obtained from the dry leaves of Gynoxys szyszylowiczii Hieron. was described in this study for the first time. The chemical analysis, conducted on two stationary phases of different polarity, permitted to identify sixty-four compounds, that were quantified with at least one column. The main components, on a non-polar and polar stationary phase respectively, were germacrene D (21.6–19.2%), α-pinene (4.4–4.9%), n-tricosane (4.3% on both columns), (E)-β-caryophyllene (3.3–4.3%), 1-docosene (3.2–2.8%), α-cadinol (2.8–3.1%), and cis-β-guaiene (2.6–3.0%). This investigation was complemented by the enantioselective analysis of some major chiral compounds, carried out on two chiral selectors based on β-cyclodextrines. As a result, (S)-( +)-α-phellandrene, (S)-( +)-β-phellandrene, and (1S,2R,6R,7R,8R)-( +)-α-copaene appeared enantiomerically pure, whereas α-pinene, β-pinene, terpinen-4-ol, and germacrene D were detected as scalemic mixtures. Finally, linalool was practically racemic. The distillation yield, analytically calculated by weight of dry plant material, was 0.03%.

A new essential oil from the native Ecuadorian species Steiractinia sodiroi (Hieron.) S.F. Blake (Asteraceae): chemical and enantioselective analyses

In the present study, the essential oil from dry leaves of Steiractinia sodiroi (Hieron.) S.F. Blake is described for the first time. The plant material, collected in the Province of Loja (Ecuador), was analytically steam-distilled in a Marcusson-type apparatus, affording an essential oil with a 0.2 ± 0.12% yield. The volatile fraction was submitted to GC–MS and GC–FID analyses, on two stationary phases of different polarity. A total of sixty-seven compounds, corresponding to 95.6–91.2% by weight of the whole oil mass, on the two columns respectively, were detected and quantified with at least one column. The quantification was carried out calculating the relative response factors of each constituent according to their combustion enthalpy. The major components were limonene (25.6–24.9%), sabinene (11.7–12.4%), germacrene D (7.7–7.0%), α-pinene (7.8–6.9%), δ-cadinene (7.3–7.0%), (E)-β-caryophyllene (4.8–4.5%), and bicyclogermacrene (3.6–3.0%). The chemical composition was complemented with the enantioselective analysis of some major chiral compounds, conducted by means of two β-cyclodextrin-based capillary columns. Three constituents, (S)-(+)-α-phellandrene, (R)-(−)-1-octen-3-ol, and (S)-(−)-limonene were enantiomerically pure, whereas (1R,5R)-(+)-β-pinene, (1S,5S)-(−)-sabinene, (R)-(−)-terpinen-4-ol, (R)-(+)-α-terpineol, and (R)-(+)-germacrene D presented an enantiomeric excess. Finally, α-pinene was present as a racemic mixture.

Effect of position of deuterium atoms on gas chromatographic isotope effects

Deuterium substitution provides various benefits in drug molecules, including improvement in pharmacokinetic properties, reduction of toxicity, reduction of epimerization, etc. Also, it has been shown that the position of deuterium substitution affects the properties of drug molecules. Therefore, it is important to study low molecular weight deuterated isotopologues which constitute the deuterated pool and are building blocks of larger deuterated molecules. The effect of the position and number of deuterium atoms on the retention of 23 deuterated isotopologues on two gas chromatography stationary phases of different polarities was evaluated. It was observed that the ratio of calculated chromatographic isotope effects resulting from a deuterium atom connected to an sp2 vs. an sp3 hybridized carbon was more on the polar IL-111i stationary phase compared to the nonpolar PDMS-5, for each group of isotopologues. Also, a compound with a deuterium atom connected to an sp2 hybridized carbon always had greater retention than the analogous compound where deuterium was connected to an sp3 hybridized carbon. The van't Hoff plots for all analytes showed that the effect of entropy was almost negligible in the separation of deuterated vs. protiated isotopologues, thus these separations were mainly enthalpy driven.

EFFECT OF TEMPERATURE ON THE PARAMETERS OF FLUORESCENCE SPECTRA OF SOLVATOCROMIC INDICATOR SOLUTIONS IN STATIONARY PHASES FOR GAS-LIQUID CHROMATOGRAPHY

The luminescence spectra of several polarity indicators at temperatures of 20 and 120°C, including previously studied at room temperature Coumarin 153 and coronene and also Nile Red and Pigment Red 179 are registered in solutions of liquid stationary phases of different polarity. The effect of temperature on the spectral parameters sensitive to the polarity of the stationary phases is estimated for the indicators. The prospects for estimating the polarity of stationary liquid phases using luminescent methods at high temperatures are demonstrated.

Mixed-Mode Hydrophilic Interactions/Reversed-Phase Retention Mechanism in Thin-Layer Chromatography.

We investigated the dual retention mechanism in thin-layer chromatography taking place on three stationary phases of different polarity (C-18, plain silica gel and DIOL) and using binary mobile phases composed of acetonitrile as the main component and water, or methanol as a modifier. As the test analytes, we selected a set of 12 compounds of pharmaceutical importance and considerably different chemical structure, i.e. the imidazoline and serotonin receptor ligands, and their related compounds. Retention of each analyte in each investigated chromatographic system was determined in a wide enough range of the mobile phase composition, with volume fraction of the mobile phase modifier ranging from 0.10 to 0.90. Calculation of the exact turning point values as a proof of occurrence of the reversed-phase hydrophilic interaction chromatography (HILIC/RP) retention mechanism was based on the multimodal retention model. The dual retention mode was described with the use of the volume fraction of the mobile phase modifier, the total polarity and the total solubility models. For the DIOL, C-18 and silica gel stationary phase, the dual (HILIC/RP) retention mechanism was confirmed. In the case of the DIOL stationary phase and acetonitrile/methanol mobile phase, the observed retention mechanism was more complicated than the dual HILIC/RP one.

Specificities of using differential characteristics of organic compounds for their group identification

The possibility of group identification of organic compounds, specifically their assignment to the corresponding homologous series) on the basis of differential quantities, such as differences in their physicochemical characteristics or analytical parameters, is considered. The first example of using difference in the refractive indices at different wavelengths for the determination of the overall concentration of aromatic hydrocarbons in gasoline fractions is described. Various methods for the assignment of unknown compounds to homologous series are analyzed, in particular those based on the limiting values of refractive indices and relative densities, differences in gas chromatographic retention indices on stationary phases of different polarities, combinations of gas chromatographic retention indices with partition coefficients for heterogeneous organic solvent systems, and two versions of combinations of mass spectrometric and GC parameters, namely molecular retention indices and homologous increments of retention indices. The latter version (as the most important) is illustrated in detail by a particular example.

Investigation of Antioxidant Activity of M.comminus L. from Turkey due to its Essential Oil Composition and Polyphenolic Content

In this study, it is aimed to investigate the chemical composition of the essential oils, antioxidant activity, and polyphenol content of methanol extracts of M.comminus L. leaves and berries. M.comminus L. Plant was collected from Yalova, Marmara region of Turkey. Its essential oil was prepared by hydrodistillation in a Clevenger-type apparatus in 0.5%. The chemical composition of the essential oil was analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC–MS), using two columns with stationary phases of different polarity (polar ZB-WaxMS/apolar ZB-5MS). On both columns monoterpenes were determined to be the dominant compounds. The myrtenyl acetate, α-pinene, 1,8-cineole, linalool, and limonene were the remarkable substances. As polyphenol compounds, the flavanoids and anthocyanidins in leaves and berries were detected by HPLC and furthermore, their antioxidant activities were studied with DPPH, Cuprac and Folin – Ciocalteu method of the methanolic extracts.

Factors Influencing the Isothermal Retention Indices of 51 Solutes on 12 Stationary Phases of Different Polarity: Applicability of the Solvation Parameter Model

Isothermal retention indices (I) at 333–413 K on 12 stationary phases (SPs) covering a wide polarity range of a variety of volatile solutes belonging to 7 one-heteroatom chemical function series and 10 non-series solutes have been determined. The I values were computed with a method (LQG method) which does not require the determination of holdup times of the chromatographic column. I values of some compounds never before studied are reported. The influence on the retention indices of the column temperature, methylene number, and polarity of both the stationary phase and the solute has been studied. The solvation parameter model (SPM) as a function of I has been used for predicting I values, and for unraveling the influence of the polarity of stationary phase and solute on the retention indices. Seeley et al.’s formulation of the SPM has been used for quantifying the influence of polar and non-polar interactions on the I, and for checking the agreement between calculated and experimental values. According to our results, the I values obtained by the modified SPM can be considered equal to the experimental I values at the 99 % confidence level.

QSRR Study on Flavor Compounds of Diverse Structures on Different Columns with the Help of New Chemometric Methods

A quantitative structure–retention relationship study was performed for 286 flavor compounds with highly structural diversity on different stationary phases of different polarities. Firstly, the structure–retention relationship was statistically explored using constitutional, topological, molecular properties, charge descriptors and quantum chemical descriptors. Some recently developed chemometric methods, such as the ones for robust analysis and variable selection were firstly employed to predict accurately the gas chromatographic retention indices. The stability and validity of models have been tested by internal and external validation, and good robustness and predictive ability were obtained. The resulting QSRR models were well correlated, with the square of correlation coefficient for cross validation, Q 2, values of 0.9847, 0.9838, 0.9745 and 0.9646 on stationary phase DB5, OV101, OV17 and C20M, respectively. The molecular properties known to be relevant for GC retention index, such as molecular size, branching, electron density distribution and hydrogen bond effect were well covered by generated descriptors. The descriptors used in models on four stationary phases were compared, and some reasonable explanations about gas chromatographic retention mechanism were obtained. The developed model may be useful for the prediction of flavor compounds while experimental data are unavailable.

Liquid Chromatography Study on Atenolol--Cyclodextrin Inclusion Complex

Inclusion complex formation of atenolol with -cyclodextrin (-CD) has been investigated by HPLC on different stationary phases, by varying pH and concentration of -CD added as an additive in the mobile phase over a wide range of column temperature. Stationary phases of different polarity and hydrophobicity were evaluated to find the best conditions for complex formation. The optimum conditions for inclusion complexation were achieved on YMC ODS-AQ C18 ( mm, 5 μ) analytical column. The apparent formation constant () of the complex as evaluated by liquid chromatography using retention factors () was M−1 at 25°C. The stoichiometry of the complex was 1 : 1 as is evident from the straight line plot of 1/ versus -CD concentration. The formation of inclusion complex was essentially enthalpy (−42.12 kJ/mol) driven and the binding forces included hydrophobic, van der Waals-London dispersion interactions. The enthalpy-entropy compensation criterion was used to prove the inclusion phenomena.

Comparison of quantitative structure–retention relationship models on four stationary phases with different polarity for a diverse set of flavor compounds

A quantitative structure–retention relationship study was performed for 656 flavor compounds with highly structural diversity on four stationary phases of different polarities, using topological, constitutional, quantum chemical and geometrical descriptors. Statistical methods were employed to find an informative subset that can accurately predict the gas chromatographic retention indices (RIs). Multivariable linear regression (MLR) was used to map the descriptors to the RIs. The stability and validity of models have been tested by internal and external validation, and good stability and predictive ability were obtained. The resulting QSRR models were well-correlated, with the square of correlation coefficients for cross validation, Q 2, values of 0.9595, 0.9528, 0.9595 and 0.9223 on stationary phase OV101, DB5, OV17 and C20M, respectively. The molecular properties known to be relevant for GC retention index, such as molecular size, branching, electron density distribution and hydrogen bond effect were well covered by generated descriptors. The descriptors used in models on four stationary phases were compared, and some reasonable explanations about gas chromatographic retention mechanism were obtained. The model may be useful for the prediction of flavor compounds while experimental data is unavailable.

Behaviour of the isothermal retention indices of n-alkylbenzenes on stationary phases of different polarity

Isothermal retention indices ( I) of benzene, toluene, ethylbenzene, n-propylbenzene and n-butylbenzene were determined at 323–423 K on twelve WCOT capillary columns covering a broad stationary phase polarity spectrum. These I values have been tested carrying out a comparison with the NIST database values. The effect of the stationary phase polarity on I values was studied. But for the poly(3,3,3-trifluoropropylmethyl siloxane) column, a good linear correlation was found. At each temperature, the dependence on I of the alkyl chain length ( z) attached to the ring of the n-alkylbenzenes was linear and of similar magnitude for the stationary phases of low to middle polarity, but lower for the more polar ones. Moreover, an important influence of the column temperature on the slope of the I vs. z plots was observed for the only non polysiloxane-type stationary phase studied, i.e., poly(ethylene glycol), due to its higher chain stiffness. Finally, different expressions describing the effect of the temperature on the retention index have been compared. I values of the n-alkylbenzenes in the 323–423 K range increase with increasing column temperature according to the Antoine-type ( I = α + β( γ + T) −1) and the extended ( I = a + bT −1 + c ln T) models. No significant differences were observed between them, except for the poly[70% bis(3-cyanopropyl) 30% dimethyl silphenylene-siloxane] column, for which the Antoine-type model was slightly better.

Modeling of retention behaviors of most frequent components of essential oils in polar and non‐polar stationary phases

The gas chromatography retention indices of 100 different components of essential oils, on three columns with stationary phases of different polarities, were used to develop robust quantitative structure-retention relationship (QSRR) models. Two linear models with only one variable, i.e. solvation entropy, were developed, which explain 95 and 94% of variances of the test set for dimethyl silicone and dimethyl silicone with 5% phenyl group columns, respectively. These models are extremely simple and easy to interpret, but they show higher errors compared with more robust models such as partial least square (PLS) and ridge regressions. For the third column (polyethylene glycol (PEG)), 24 hydrogen bonding descriptors were calculated and were used for modeling. Kernel orthogonal projection to latent structure (KOPLS), as a non-linear technique, was applied for the modeling of the retention indices of the compounds on the PEG column. R(2) values for the test set established by Monte Carlo cross-validation and SPXY (sample set partitioning based on joint x-y distances) test set of the KOPLS were 0.92 and 0.94, respectively. y-Randomization indicated that chance plays no role in constructing the KOPLS model.

Orthogonal analytical screening for liquid chromatography–mass spectrometry method development and preparative scale-up

An analytical HPLC–MS screening methodology has been developed to improve preparative RP-HPLC–MS purifications in medicinal chemistry laboratories. Although several approaches have been previously described to optimize analytical separations, none of them met our needs for the optimization of preparative conditions. Our screening protocol is based on searching among several orthogonal conditions to find the optimum preparative separation. Five different buffer conditions, from low to high pH, two organic solvents, acetonitrile and methanol, and five stationary phases of different polarities and characteristics were used. The orthogonality of the system was demonstrated using both, a standard mixture and mixtures from synthesis. To carry out the screening one of the analytical “open access” HPLC–MS systems was modified to perform the analytical screening while maintaining the open-access functionality for synthesis reaction monitoring. A software tool for automated sample programming and data reporting was also developed.

Lipophilicity of Some Preservatives Estimated by RP-TLC Using Stationary Phases with Different Polarity

Lipophilcity of some preservatives was determined by reversed phase high performance thin layer chromatography (RP-HPTLC) using methanol–water mixtures in different volume proportions as mobile phase on three stationary phases of different polarity: RP-18F254s, RP-18WF254s and CNF254s plates. The R M values decreased linearly with increasing methanol concentration in the mobile phase in all cases. The regression determination coefficients obtained for all stationary phases were excellent (higher than 0.98 in most cases). The chromatographic behavior of the preservatives on the RP-HPTLC plates used in this study is similar and in a very good agreement with their polarity. Good chromatographic regularities found for retention factors and by applying principal component analysis for all three types of stationary phases indicate that the same lipophilic interactions are dominants in all cases. The relationships between different RP-HPTLC retention parameters (R M0 , b, scores of R F -PC1/R F and scores of R M -PC1/R M ) and various calculated log P values of the same preservatives show highly significant correlations for all types of stationary phases.

Quantitative structure–retention relationship modelling of esters on stationary phases of different polarity

The semi-empirical electrotopological index, I SET, used for QSRR models, was developed and optimized to describe the chromatographic retention of saturated esters on the five different stationary phases (SE-30, OV-7, DC-710, OV-225 and XE-60). The simple linear regressions between the retention indices and the proposed index were of good statistical quality, high internal stability and good predictive ability for external groups, especially for the stationary phase with low polarity, showing that the specific molecular interactions occur on highly polar phases. For the esters, the interactions between the molecules and the stationary phase are slowly increased relative to hydrocarbons due to the charge redistribution that occurs in the presence of the heteroatom. These facts were included in the calculation of I SET through a small increase in the SET i values for heteroatoms and the carbon atoms attached to them. The increase in the SET i values originates from the dipole moment of the whole molecule and an equivalent local dipole moment related to the net charges of the atoms belonging to the functional group and the carbon atoms attached to them. The polarity of the stationary phases, indicated by the retention polarity ( P R) given by Tarján, is reflected in the intercept of the equations obtained for each stationary phase. Thus, a single combined QSRR model was generated with a satisfactory predictive quality, including a parameter that represents the polarity retention of all stationary phases studied.

Mathematical Models of Solute Retention in Gas Chromatography as Sources of Thermodynamic Data. Part IV. Aliphatic Alcohols as the Test Analytes

This study is the fourth consecutive part belonging to the cycle devoted to an alternative approach to deriving certain thermodynamic magnitudes. The previous three papers were dedicated, respectively, to ketones, aldehydes, and alkylbenzenes. In our present study (similar to the previous ones) the following working procedure is adopted. With the aid of capillary gas chromatography, the retention times are obtained for a wide variety of the aliphatic alcohols. The analyses are carried out isothermally on stationary phases of different polarity and at five different measuring temperatures. These data constitute an experimental basis for further processing with the aid of the specially devised mathematical equations. The fitting parameters of these equations, due to their physicochemical meaning, enable determination of certain thermodynamic data. Nine equations used in this study are the relationships coupling the selected retention data [relative retention (r), non-reduced relative retention (rG), the retention factor (k), or the Kováts retention index (I)] and a variety of the physical magnitudes [the boiling point of the analyte (T(B)), its molar volume (Vm), or its molar refraction (Rm)]. These relationships are tested with respect to their performance to predict the molar enthalpy of vaporization (deltaHvap) of the analytes of interest (i.e., of aliphatic alcohols). Evaluation of the equations' performance is carried out through a comparison of the numerical values generated from this approach with those originating from the other methods, and a very good agreement was found between these two series of the data. The best molar enthalpy vaporization values (deltaHvap) are obtained from the retention data originating from the most polar of the three investigated stationary phases (i.e., DB-Wax). Models V and VIII proved the best performing ones among the nine models tested in this study.

Compound Identification: A Journal of Agricultural and Food Chemistry Perspective

This perspective is designed to summarize the standards that authors of manuscripts submitted to the Journal of Agricultural and Food Chemistry are expected to follow in establishing the structures of either new or unknown compounds identified in the course of a study. It is especially important that the molecular formulas of new compounds be determined by either high-resolution mass spectrometry or combustion analysis. All relevant physical, spectroscopic, and spectrometric data should also be reported, so that other research workers have criteria for comparison with compounds that may be isolated in the future. In the case of flavor and aroma constituents, it is not sufficient to depend upon mass spectrometric identifications based solely on comparison with commercial databases. Mass spectra and retention indices on GC stationary phases of different polarities must be determined and the results compared to data for reference compounds and with commercial standards, when available. If geometric or positional isomers may be present, or for chiral compounds, the retention indices of all isomers or enantiomers must be determined. Odor properties or odor thresholds determined by GC-olfactometry may also serve as appropriate tools for compound identification. Adherence to these standards will ensure that processing of manuscripts proceeds expeditiously and that the high standards of the Journal are maintained.