Polar Stationary Phases Research Articles

Two-dimensional thin-layer chromatographic determination of phenolic antioxidants fromEupatorium cannabinumextracts on cyano-bonded polar stationary phases

Two-dimensional thin layer chromatography on cyano-bonded polar stationary phase was performed to optimize the separation of some antioxidant phenolic compounds from Eupatorium cannabinum extracts. Propan-2-ol mixed with n-heptane and ethyl acetate mixed with n-heptane were used as non-aqueous mobile phases in normal phase separations (1st direction of development in 2-dimensional high-performance thin-layer chromatography (2D-HPTLC mode)) and methanol mixed with water was used as a mobile phase in reversed phase (2nd direction of development in 2D-HPTLC mode). The plates were sprayed by use of Merck TLC sprayer using 2-(diphenylboryoxy)-ethylamine and PEG4000 (Merck, Darmstadt, Germany) or DPPH and photographed in CAMAG Cabinet UV lamp at 254 nm and 365 nm by use of Fuji 8 mpx camera. The plots RF non-aqueous mobile phase vs RF aqueous mobile phase were prepared to find optimal orthogonal 2D-TLC systems for the separation of investigated test compounds and then extracts from Eupatorium cannabinum. Satisf...

Lc–Ms Metabolomics of Polar Compounds

The metabolome is the complete set of small molecules coming from protein activity (anabolism and catabolism) in living systems. They have a broad range of chemical structures and physicochemical properties and therefore different analytical methodologies are necessary. Highly polar metabolites, such as sugars and most amino acids are not retained by conventional reversed-phase LC columns. Without sufficient retention, coelution may result in identification problems while the detection of compounds by MS at low concentrations may also be problematic due to ion suppression. In order to retain compounds based on their hydrophilicity, polar stationary phases and hydrophilic-interaction LC provide a complementary tool to reversed-phase LC for untargeted comprehensive metabolite fingerprinting. However, robustness of the methods is still limiting their applications. This review focuses on sample pretreatment, stationary phases, analytical methods and applications for polar compound analysis in biological matrices.

Determination of nitrosamines and caffeine metabolites in wastewaters using gas chromatography mass spectrometry and ionic liquid stationary phases

Recently, the interest to assess the environmental and human health effects of a wide group of emerging contaminants is growing worldwide. However, one of the main problems associated to their exposure is their determination in environmental matrices. It is hindered by the high polarity of most of these analytes, the poor selectivity obtained with low polarity stationary phases and the high background obtained with polar columns commonly used in GC–MS. Accordingly, this study examines the suitability of ionic liquid (IL) (e.g. SLB-IL59, SLB-IL61, SLB-IL82 and SLB-IL111) as stationary phases for GC–MS and their application to the determination of nitrosamines and caffeine metabolites in wastewater samples. Different chromatographic conditions were evaluated and results discussed in terms of resolution and peak symmetry. The SLB-IL111 column enabled the baseline separation and quantification of 7 nitrosamines in a shorter analysis time compared with cyanopropylphenyl polysiloxane commonly used. On the other hand, the SLB-IL59 column provided the best results for caffeine metabolites.

Characterization and use of hydrophilic interaction liquid chromatography type stationary phases in supercritical fluid chromatography

All stationary phase chemistries are useful to achiral packed-column supercritical fluid chromatography (pSFC), but the majority of recent applications are based on polar stationary phases of the type used in normal-phase HPLC. Some manufacturers have recently introduced pSFC-tailored stationary phases, while others simply advocate the use of selected HPLC columns among their brands for SFC use. Indeed, any column developed for HPLC use can be used with supercritical fluids. Besides, hydrophilic interaction liquid chromatography (HILIC) is facing an increasing interest. Consequently, a number of HILIC-devoted stationary phases are now commercialized by most column manufacturers. As HILIC stationary phases are polar, their possible use in pSFC seems obvious, although literature examples are not numerous. However, whether they provide acceptable peak shapes in SFC conditions is a serious concern for them to find applicability. Indeed, columns optimized for HILIC mobile phases may not be optimum for SFC mobile phases. We present the characterization of eleven HILIC-type stationary phases used with carbon dioxide–methanol mobile phases in the isocratic mode. The columns are compared in terms of their retention and separation characteristics assessed by the solvation parameter model, and based on peak shapes. For this purpose, hundred and forty-six low molecular weight molecules, comprising neutral, basic and acidic compounds, were eluted on each column. Data analysis is carried out with hierarchical cluster analysis and principal component analysis in order to define three clusters of columns with similar selectivity: the first cluster comprises neutral stationary phases like amide and diol phases; the second one comprises basic stationary phases like aminopropyl-bonded silica; the last cluster comprises bare silica stationary phases. Sample applications with three different test mixtures relevant to pharmaceutical applications (barbiturates, benzodiazepines and propionic acids) are presented to assess the complementarity of some selected columns.

Gas–liquid chromatography-obtained differences in the dissolution enthalpy between two positional isomers in a polar stationary phase: A measure of the inter- or intramolecular hydrogen bond energy?

Previous GLC work with several 2- and 4-substituted phenols and anilines, as well as with a pyrrolizidine alcohol, had determined the difference between the heats of dissolution of two positional isomers in a strong polar stationary liquid phase; one of these isomers forms an intramolecular hydrogen bond (intra-HB) and the other has no such bond for steric reasons. The energies of the intermolecular hydrogen bonds (inter-HBs), ΔHinter-HB, formed by the 1,2- and 1,4-isomers with the molecules of a polar phase had been assumed approximately equal, so the difference between them could be ignored. The same assumption had been made for the energies of nonspecific interactions (NSIs), ΔHNSI. It had been concluded that the found difference can be considered as an intra-HB energy (enthalpy), ΔHintra-HB, when the energies (enthalpies) of inter-HBs formed by the 1,2- and 1,4-isomers under study with the molecules of a polar phase are much greater in absolute value than ΔHintra-HB. And, conversely, when |ΔHintra-HB|>|ΔHinter-HB|, an inter-HB enthalpy will result. With the same assumptions, we here obtained an extended thermodynamic equation and corrected this above conclusion on the basis of a general consideration of the dissolution thermodynamics for two isomers of a molecule in a polar phase. Account was taken of the coefficients of isomer partitioning between the liquid and the gaseous phase at the experimental temperature. The conclusion made previously was adjusted for ΔHNSI and formulated as follows: The GLC method determines the intra-HB energy at |ΔHintra-HB|≤|ΔHinter-HB+ΔHNSI|. If |ΔHintra-HB|>|ΔHinter-HB+ΔHNSI|, the method yields the values of ΔHinter-HB+ΔHNSI. This new conclusion was illustrated with virtual (numerical) experiments in which various ΔHintra-HB, ΔHinter-HB, and ΔHNSI values were postulated and results were obtained that would have been achieved by GLC if it had been done. Using a capillary column with the PEG 20M stationary phase, we measured the differences between the heats of dissolution for six pairs of isomers of phenolic compounds and for seven pairs of disubstituted benzene derivatives, which have similar structures but cannot form an intra-HB. The benzene derivatives served to make an approximate experimental estimate of the difference between the energies of NSIs of the isomers under study with a polar phase, ΔHNSI.

Fruit Volatile Analysis Using an Electronic Nose

Numerous and diverse physiological changes occur during fruit ripening, including the development of a specific volatile blend that characterizes fruit aroma. Maturity at harvest is one of the key factors influencing the flavor quality of fruits and vegetables1. The validation of robust methods that rapidly assess fruit maturity and aroma quality would allow improved management of advanced breeding programs, production practices and postharvest handling. Over the last three decades, much research has been conducted to develop so-called electronic noses, which are devices able to rapidly detect odors and flavors2-4. Currently there are several commercially available electronic noses able to perform volatile analysis, based on different technologies. The electronic nose used in our work (zNose, EST, Newbury Park, CA, USA), consists of ultra-fast gas chromatography coupled with a surface acoustic wave sensor (UFGC-SAW). This technology has already been tested for its ability to monitor quality of various commodities, including detection of deterioration in apple5; ripeness and rot evaluation in mango6; aroma profiling of thymus species7; C6 volatile compounds in grape berries8; characterization of vegetable oil9 and detection of adulterants in virgin coconut oil10. This system can perform the three major steps of aroma analysis: headspace sampling, separation of volatile compounds, and detection. In about one minute, the output, a chromatogram, is produced and, after a purging cycle, the instrument is ready for further analysis. The results obtained with the zNose can be compared to those of other gas-chromatographic systems by calculation of Kovats Indices (KI). Once the instrument has been tuned with an alkane standard solution, the retention times are automatically converted into KIs. However, slight changes in temperature and flow rate are expected to occur over time, causing retention times to drift. Also, depending on the polarity of the column stationary phase, the reproducibility of KI calculations can vary by several index units11. A series of programs and graphical interfaces were therefore developed to compare calculated KIs among samples in a semi-automated fashion. These programs reduce the time required for chromatogram analysis of large data sets and minimize the potential for misinterpretation of the data when chromatograms are not perfectly aligned.We present a method for rapid volatile compound analysis in fruit. Sample preparation, data acquisition and handling procedures are also discussed.

Fruit Volatile Analysis Using an Electronic Nose

Numerous and diverse physiological changes occur during fruit ripening, including the development of a specific volatile blend that characterizes fruit aroma. Maturity at harvest is one of the key factors influencing the flavor quality of fruits and vegetables1. The validation of robust methods that rapidly assess fruit maturity and aroma quality would allow improved management of advanced breeding programs, production practices and postharvest handling. Over the last three decades, much research has been conducted to develop so-called electronic noses, which are devices able to rapidly detect odors and flavors2-4. Currently there are several commercially available electronic noses able to perform volatile analysis, based on different technologies. The electronic nose used in our work (zNose, EST, Newbury Park, CA, USA), consists of ultra-fast gas chromatography coupled with a surface acoustic wave sensor (UFGC-SAW). This technology has already been tested for its ability to monitor quality of various commodities, including detection of deterioration in apple5; ripeness and rot evaluation in mango6; aroma profiling of thymus species7; C6 volatile compounds in grape berries8; characterization of vegetable oil9 and detection of adulterants in virgin coconut oil10. This system can perform the three major steps of aroma analysis: headspace sampling, separation of volatile compounds, and detection. In about one minute, the output, a chromatogram, is produced and, after a purging cycle, the instrument is ready for further analysis. The results obtained with the zNose can be compared to those of other gas-chromatographic systems by calculation of Kovats Indices (KI). Once the instrument has been tuned with an alkane standard solution, the retention times are automatically converted into KIs. However, slight changes in temperature and flow rate are expected to occur over time, causing retention times to drift. Also, depending on the polarity of the column stationary phase, the reproducibility of KI calculations can vary by several index units11. A series of programs and graphical interfaces were therefore developed to compare calculated KIs among samples in a semi-automated fashion. These programs reduce the time required for chromatogram analysis of large data sets and minimize the potential for misinterpretation of the data when chromatograms are not perfectly aligned. We present a method for rapid volatile compound analysis in fruit. Sample preparation, data acquisition and handling procedures are also discussed.

Separation and Identification of Volatile Compounds from Liquid Cultures of Trichoderma harzianum by GC-MS using Three Different Capillary Columns

A simple, fast, repeatable and less laborious sample preparation protocol was developed and applied for the analysis of biocontrol fungus Trichoderma harzianum strain FA1132 by using gas chromatography-mass spectrometry. The match factors for sample spectra with respect to the mass spectra library of fungal volatile compounds were determined and used to study the complex hydrocarbons and other volatile compounds, which were separated by using different capillary columns with nonpolar, medium polar and high polar stationary phases. To date, more than 278 volatile compounds (with spectral match factor at least 90%) such as normal saturated hydrocarbons (C7-C30), cyclohexane, cyclopentane, fatty acids, alcohols, esters, sulfur-containing compounds, simple pyrane and benzene derivatives have been identified. Most of these compounds have not previously been reported. The method described in this paper is a more convenient research tool for the detection of volatile compounds from the cultures of T. harzianum.

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.

Prefractionation and separation by C8 stationary phase: Effective strategies for integral membrane proteins analysis

Analysis of integral membrane proteins (IMPs) presents great challenges due to their hydrophobic nature. Recently, much attention has been paid to improve the solubilization of IMPs. However, besides that, the separation of hydrophobic peptides with high recovery is also a dominating factor, but with rare report. Here, the prefractionation of the digests by reverse phase trap column during desalting was presented to efficiently decrease the complexity of samples, with the identified hydrophobic peptides and IMPs increased by more than 43%. Furthermore, the effect of C18 and C8 stationary phases on the separation of membrane protein digests was studied. A total of 301 proteins (536 peptides) with C18 stationary phase and 398 proteins (703 peptides) with C8 stationary phase were identified by μRPLC–ESI-MS/MS using an LCQ instrument in duplicate runs, with false discovery rate (FDR) less than 5% at peptide level. In addition, with C8 stationary phase, the number of identified hydrophobic peptides and IMPs was obviously improved by 29% and 20%, respectively, compared with that identified by C18 stationary phase, indicating that the polarity of stationary phase has evident effect on the analysis of membrane protein digests. All these results show that the prefractionation by reverse phase trap column during desalting and the separation by C8 stationary phases could facilitate the efficient identification of IMPs.

Hydrophilic interaction chromatography of seized drugs and related compounds with sub 2μm particle columns

The use of hydrophilic interaction chromatography (HILIC) with sub 2 μm particle columns for the analysis of drugs and related compounds of forensic interest is described. This technique uses a high organic/low aqueous buffered mobile phase with a polar stationary phase, and is excellent for the separation of many of the charged solutes that are found in forensic drug exhibits. In this study, HILIC is investigated for 11 solutes of forensic interest, including weak bases, weak acids, and a neutral solute. In addition, for columns containing either ethylene bridged hybrid particles with or without an amide bonded phase, the effects of acetonitrile concentration, buffer type, buffer concentration, linear velocity, and sample concentration were studied. Based on these studies, HILIC with sub 2 μm particle columns can offer highly efficient, selective, and rapid isocratic separations of drugs and related compounds of forensic interest, with excellent peak shapes and low back pressures. This is in contrast to reverse phase chromatography (RPLC), where gradient elution is usually required, which can result in extensive overlap between acidic, neutral, and basic solutes. In addition, since HILIC exhibits a much greater loading capacity than RPLC, it could be a preferred technique for drug profiling. Furthermore, because high organic content mobile phases are highly amenable to mass spectrometric detection, the use of HILIC with tandem mass spectrometric detection for the analysis of seized drugs is described.

Establishment and Application of a Metabolomics Workflow for Identification and Profiling of Volatiles from Leaves of Vitis vinifera by HS‐SPME‐GC‐MS

Volatile organic compounds (VOCs) occurring in leaves of plants carry information about the physiological state of the plant. Monitoring of VOCs assists in detecting plant stress before visible signs are present. To establish and apply a simple workflow for the automated extraction, measurement and annotation/identification of Vitis vinifera cv. Pinot Noir leaf metabolites. Leaf samples were harvested, cooled with liquid nitrogen and homogenised under cooled conditions. VOCs were extracted and enriched by solid phase microextraction (SPME) and analysed by GC-MS. Samples were measured on two columns with different polarity of stationary phases. Mass spectral deconvolution and identification was done by AMDIS software. Strict identification criteria were applied: match factor ≥ 90; relative retention index deviation ≤ 2% from reference value on both columns. Data of two sampling dates were analysed with multivariate statistics. We found ~600 components in a single chromatogram. Applying the mentioned criteria resulted in annotation of 63 metabolites of which 47 were confirmed with authentic standards. For the majority of the compounds technical variability was < < 40% (RSD), biological variability among plants was 7-119%. Principal component analysis (PCA) scores plot of leaf samples from two different sampling dates showed two clearly separated clusters. The presented workflow enabled for the first time the detection and identification of 19 metabolites that have so far not been described for Vitis spp. The developed workflow enabled the identification of grapevine leaf metabolites, which allowed the separation of leaves from two sampling dates by PCA.

Cross-column prediction of gas-chromatographic retention of polychlorinated biphenyls by artificial neural networks

In this paper, we build a multiple-column retention model able to predict the behaviour of polychlorinated biphenyls (PCBs) in capillary gas-chromatography (GC) within a wide range of separation conditions. To this end, GC retention is related to both chemical structure of PCBs, encoded by selected theoretical molecular descriptors, and the kind of stationary phase, represented by the relative retention time (RRT) of a suitable small number of analytes. The model was generated using the retention data of 70 PCBs extracted from the pool of the 209 possible congeners collected on 17 different capillary columns featured by non-polar or moderately polar stationary phases, reported in the literature. Multilinear regression combined with genetic algorithm variable selection was preliminarily applied to generate a four-dimensional quantitative structure-retention relationship (QSRR) for each of the 17 columns, based on theoretical molecular descriptors extracted from the large set provided by the software Dragon. 33 molecular descriptors obtained by merging the non-common descriptors of various single-column QSRRs, combined with RRTs values of the less and the most retained PCB, were considered as the starting independent variables of the multiple-column retention model. A multi-layer artificial neural network (ANN), optimised on a validation set extracted from the calibration data, was applied to generate the multi-column retention model. The influence of starting inputs on the network output was evaluated by a sensitivity analysis and model complexity was reduced through a step-wise elimination of redundant molecular descriptors, while RRTs of further PCBs were included to improve description of the stationary phase. Nine molecular descriptors and RRTs of eight selected PCBs are considered as the independent variables of the final ANN-based model, whose predictive performance was tested on the 139 PCBs excluded from calibration and on six external columns and/or temperature programs.

Retention Characteristics of Four Different HILIC Stationary Phases in the Analysis of Meat Polar Compounds

Hydrophilic interaction chromatography has been used to investigate the retention characteristics of a group of polar compounds typically present in meat like carnosine (Car), anserine (Ans), creatine (Cr), creatinine (Cn), glutathione oxidised (GSSG), glutathione reduced (GSH) and nicotinamide adenine dinucleotide (NADH). These compounds were separated using four polar stationary phases composed by bare silica, amide and zwitterionic groups bound to porous silica and zwitterionic groups attached to a polymeric bead. Ammonium acetate salt used in the mobile phase was found to provide the best results in selectivity and reproducibility. The effect of salt concentration together with pH and acetonitrile (ACN) content of the eluent on the retention of the different polar stationary phases was also studied. A linear gradient of ACN from 80% to 30% with 10 mM ammonium acetate at neutral pH values (pH 6.0 and pH 7.8) offered retention factors k ≤ 10 while keeping a resolution higher than 1.5 for all the assayed compounds in bare silica and amide columns. The separation of NADH from GSSG was not possible under the studied conditions at any salt concentration using zwitterionic columns.

Hydrophilic interaction liquid chromatography (HILIC)—a powerful separation technique

Hydrophilic interaction liquid chromatography (HILIC) provides an alternative approach to effectively separate small polar compounds on polar stationary phases. The purpose of this work was to review the options for the characterization of HILIC stationary phases and their applications for separations of polar compounds in complex matrices. The characteristics of the hydrophilic stationary phase may affect and in some cases limit the choices of mobile phase composition, ion strength or buffer pH value available, since mechanisms other than hydrophilic partitioning could potentially occur. Enhancing our understanding of retention behavior in HILIC increases the scope of possible applications of liquid chromatography. One interesting option may also be to use HILIC in orthogonal and/or two-dimensional separations. Bioapplications of HILIC systems are also presented. Figure

Considerations on Orthogonality Duality in Comprehensive Two-Dimensional Gas Chromatography

The term "orthogonal" in comprehensive two-dimensional gas chromatography (GC × GC) has a double sided meaning as it stands for a separation resulting from the combination of two independent retention mechanisms (Giddings, J. C. J. High Resolut. Chromatogr. 1987, 10, 319) but also for a 2D separation where the components are evenly distributed over the entire 2D space. It is shown in the present study that a nonorthogonal GC × GC system associating a polar stationary phase in the first dimension (poly(ethylene glycol)) to a nonpolar one in the second dimension (poly(dimethyl siloxane)) leads to a structured chromatogram, a high peak capacity, and a great 2D space occupation. This idea is demonstrated through the characterization of oxygenated compounds in a coal-derived middle distillate. Results show a clear separation between oxygenated species and hydrocarbons which are classified into linear alkanes, cyclic alkanes, and aromatics. A breakthrough configuration combining a polar poly(ethylene glycol) first dimension and a trifluoropropyl methyl stationary phase in the second dimension enabled a unique identification and quantification of linear, cyclic, and aromatic alcohols. This configuration which could be considered as nonorthogonal still involves two different retention mechanisms: polarity and boiling point in the first dimension and electronic interactions in the second dimension. It is selective toward electronegative poles of alcohols and phenols. The contributions of these two configurations compared to a conventional orthogonal system as well as their roles for oxygenated compounds speciation are highlighted. This contribution is measured through three 2D space occupation factors. It appears through these two examples that orthogonality is intimately linked to analyte properties, and a general concept of dimensionality must be considered.

Application of hydrophilic interaction TLC systems for separation of highly polar glycosidic compounds from the flowers of selectedVerbascumspecies

Separation of highly polar compounds, for example, iridoids and triterpene saponins, present in natural samples is a challenging task. Because of their nonvolatility and the lack of chromophores, their analysis by means of gas chromatography or high-performance liquid chromatography (HPLC) is difficult. The use of normal as well as reversed-phase systems fails to resolve highly polar compounds that are strongly adsorbed on polar stationary phases and poorly retained on alkyl-bonded stationary phases usually used in HPLC. Because of these facts, separation has been performed in hydrophilic interaction systems by means of thin-layer chromatography (TLC). Planar chromatography offers also a possibility to use different derivatizing agents to visualize the resolved compounds. Another problem encountered in the analysis of such compounds present in plant extracts is that they occur as multicomponent mixtures. In this article, two-dimensional (2D) TLC systems were used for the resolution of compounds present in...

A Quantitative Structure-Property Relationship (QSPR) Study of Aliphatic Alcohols by the Method of Dividing the Molecular Structure into Substructure

A quantitative structure–property relationship (QSPR) analysis of aliphatic alcohols is presented. Four physicochemical properties were studied: boiling point (BP), n-octanol–water partition coefficient (lg POW), water solubility (lg W) and the chromatographic retention indices (RI) on different polar stationary phases. In order to investigate the quantitative structure–property relationship of aliphatic alcohols, the molecular structure ROH is divided into two parts, R and OH to generate structural parameter. It was proposed that the property is affected by three main factors for aliphatic alcohols, alkyl group R, substituted group OH, and interaction between R and OH. On the basis of the polarizability effect index (PEI), previously developed by Cao, the novel molecular polarizability effect index (MPEI) combined with odd-even index (OEI), the sum eigenvalues of bond-connecting matrix (SX1CH) previously developed in our team, were used to predict the property of aliphatic alcohols. The sets of molecular descriptors were derived directly from the structure of the compounds based on graph theory. QSPR models were generated using only calculated descriptors and multiple linear regression techniques. These QSPR models showed high values of multiple correlation coefficient (R > 0.99) and Fisher-ratio statistics. The leave-one-out cross-validation demonstrated the final models to be statistically significant and reliable.

Differentiation of methylenedioxybenzylpiperazines (MDBPs) and methoxymethylbenzylpiperazines (MMBPs) By GC-IRD and GC–MS

The substituted benzylpiperazines, 3,4-methylenedioxybenzylpiperazine (3,4-MDBP), its regioisomer 2,3-methylenedioxybenzylpiperazine (2,3-MDBP) and four isobaric ring substituted methoxymethylbenzylpiperazines (MMBP) have almost identical mass spectra. Perfluoroacylation of the secondary amine nitrogen of these isomeric piperazines gave mass spectra with differences in relative abundance of some fragment ions. However, the spectra did not yield any unique fragments for specific identification of one isomer to the exclusion of the other compounds. Gas chromatography coupled with infrared detection (GC-IRD) provides direct confirmatory data for the structural differentiation between the six isomers. The mass spectra in combination with the vapor phase infrared spectra provide for specific confirmation of each of the isomeric piperazines. The underivatized and perfluoroacyl derivative forms of the ring substituted benzylpiperazines were resolved on the polar stationary phase Rtx-200.

Evaluation of ionic liquid stationary phases for one dimensional gas chromatography–mass spectrometry and comprehensive two dimensional gas chromatographic analyses of fatty acids in marine biota

Ionic liquid stationary phases were tested for one dimensional gas chromatography–mass spectrometry (GC–MS) and comprehensive two dimensional gas chromatography (GC × GC) of fatty acid methyl esters from algae. In comparison with polyethylene glycol and cyanopropyl substituted polar stationary phases, ionic liquid stationary phases SLB-IL 82 and SLB-IL 100 showed comparable resolution, but lower column bleeding with MS detection, resulting in better sensitivity. The selectivity and polarity of the ionic liquid phases are similar to a highly polar biscyanopropyl-silicone phase (e.g. HP-88). In GC × GC, using an apolar polydimethyl siloxane × polar ionic liquid column combination, an excellent group-type separation of fatty acids with different carbon numbers and number of unsaturations was obtained, providing information that is complementary to GC–MS identification.