Polar Stationary Phases Research Articles

Chromatographic Study of Novel Heteronuclear Complexes with Schiff Base as Main Ligand.

The properties of 12 new heterodi- and heterotrinuclear complexes having general formulae [Cu2Ln(L)2(NO3)(H2O)2](NO3)2·3H2O [where Ln = Pr (1), Nd (2), Sm (3) and Eu (4)], and [CuLn(L)(NO3)2(H2O)3MeOH]NO3·MeOH [where Ln = Gd (5), Tb (6), Dy (7), Ho (8), Ef (9), Tm (10), Yb (11) and Lu (12)], and their main ligand [L = C19H18N2O4Br2 = N,N’-bis(5-bromo-3-methoxysalicylidene)propylene-1,3-diamine] have been characterized by chromatographic analyses. The parameter of relative lipophilicity (R M0) of the tested compounds was determined experimentally by reversed-phase high-performance thin layer chromatography method with mixtures of methanol and water as a mobile phase. We also described interactions between chromatographed substances and various surfaces (silica—SiO2 and modified by hydrocarbon chains—RP-2, RP-8, RP-18 phases). This study also investigates the effect of pH of the mobile phase on the retention on the polar stationary phase. Thin layer chromatography combined with magnetic and electric field has been proposed as a complementary method for the determination of physicochemical properties of the investigated compounds. The chromatograms in the field and outside of it were developed simultaneously in three identical chromatographic chambers. One of them was placed in external magnetic field of 0.4 T inductivity, and the second in external electrical field. In magnetic and electric fields, retention of some complexes changed, which indicated that the presence of these fields influenced physicochemical properties of the compounds and their interactions with the stationary phase.

Stationary Phases for the Separation of Reducing Sugars by Normal-Phase Partition Chromatography

High-performance liquid chromatography (HPLC) has great contribution in the analysis of the carbohydrates. Various separation modes such as ion exchange chromatography, size exclusion chromatography and partition chromatography have been applied to HPLC of mono- and oligosaccharides. Among them, partition chromatography with a polar stationary phase and aqueous mobile phase, called aqueous normal phase partition (ANP) chromatography, has been used in various fields, and is widely used for the separation of reducing sugars. Currently, this separation mode is considered to be a type of "hydrophilic interaction chromatography (HILIC)". As the use of HILIC mode increases, many novel stationary phases being available for the separation of reducing sugars have been developed. This article focuses on the separation of reducing sugars by ANP (HILIC) mode, and summarizes the traditional and/or recent stationary phases for the separation of reducing sugars. The applicability of various kinds of stationary phases to solid-phase extraction (SPE) of saccharides is also described.

The Cyclization of Alkyl Side Chains of Naphthalenes: The GC/Potential Energies/FTIR Approach

Gas chromatographic measurements of the retention times of alkyl naphthalenes on packed columns with polar and non-polar stationary phases have proven that the logarithm of the relative retention time increases bi-linearly (not linearly) with the number of carbon atoms in a molecule. This is caused by a strong inclination of alkyl side chains toward intramolecular cyclization. A FTIR spectral analysis has shown that longer alkyl side chains of alkyl naphthalenes are cyclized through an interaction between the terminal CH3 group and the aromatic ring. Conventional aromatic-aliphatic molecules thus become new molecules with quasi-alicyclic rings. This, however, alters the effect of non-covalent van der Waals attractive forces both inside and outside the molecules, which is reflected in an exponential increase of the retention times of alkyl naphthalenes with a side chain longer than propyl and in the bi-linearity of the logarithmic dependence of the relative retention times on the number of carbons in the molecule.

Hydrophilic interaction chromatographic analysis of anthocyanins

Hydrophilic interaction chromatography (HILIC) provides an alternative separation mode for the analysis of phenolic compounds, in which aqueous-organic mobile phases with polar stationary phases are used. This paper reports the evaluation of HILIC for the analysis of the natural pigments anthocyanins, which are of importance because of their chromophoric properties and a range of health benefits associated with their consumption. Several HILIC stationary phases (silica, diol, amine, cyanopropyl and amide) and mobile phase combinations were evaluated, with the latter proving particularly important due to the distinctive chromatographic behaviour of anthocyanins. Diode array detection was used for selective detection of anthocyanins, while high resolution quadrupole-time-of-flight mass spectrometry (Q-TOF-MS) was used for compound identification. The potential of HILIC separation is demonstrated for a range of anthocyanins varying in glycosylation and acylation patterns found in blueberries, grape skins, black beans, red cabbage and red radish. HILIC is shown to be a complementary separation method to reversed phase liquid chromatography (RP-LC) due to the alternative retention mechanism.

Gas chromatography/mass spectrometry analysis of the six‐ring regioisomeric dimethoxybenzyl‐N‐methylpiperazines (DMBMPs)

Piperazine-based designer drugs represent a novel class of substances found in illicit drug samples in the US and abroad. The clandestine production of these substances often makes use of piperazine as a key commercially available precursor substance. The commercial availability of 1-methylpiperazine suggests additional designer modification based on this additional precursor material. This study focuses on the electron ionization mass spectrometric (EI-MS) fragmentation of the dimethoxybenzyl-N-methylpiperazines as potential designer modifications of the general benzylpiperazine drug skeleton and explores the gas chromatography (GC)/MS properties of all six of these regioisomeric substances. Fragmentation of the bond between the benzylic carbon and the adjacent piperazine nitrogen provides the base peak in all six spectra. The internal fragmentation within the piperazine ring produces a number of unique ions in the mass spectra of these dimethoxybenzyl-N-methylpiperazines. The migration of methyl groups from nitrogen and oxygen were confirmed by deuterium-labeling experiments. The six regioisomeric dimethoxybenzyl-N-methylpiperazines yield equivalent fragment ions and deuterium labeling confirmed the elemental composition of the characteristic fragments in their mass spectra. Mixtures of the dimethoxybenzyl-N-methylpiperazines were successfully resolved via capillary gas chromatography using a relatively polar stationary phase and temperature-programming conditions. Copyright © 2013 John Wiley & Sons, Ltd.

Gas chromatographic vapor pressure determination of atmospherically relevant oxidation products of β-caryophyllene and α-pinene

Vapor pressures (subcooled liquid, pliquid) of atmospherically relevant oxidation products of β-caryophyllene (β-caryophyllene aldehyde 0.18 ± 0.03 Pa and β-nocaryophyllene aldehyde 0.17 ± 0.03 Pa), and α-pinene (pinonaldehyde 16.8 ± 0.20 Pa, cis-pinic acid 0.12 ± 0.06 Pa, and cis-pinonic acid 0.99 ± 0.19 Pa) at 298 K were obtained by gas chromatography with flame ionization detection (FID) and mass spectrometric (MS) detection. The effects of stationary phase polarity and column film thickness on the vapor pressure values were investigated. Increase in stationary phase polarity provided smaller values, while increase in film thickness gave slightly higher values. Values for vapor pressure were at least two orders of magnitude lower when obtained by a method utilizing vaporization enthalpy (determined by gas chromatography–mass spectrometry) than by retention index method. Finally, the results were compared with values calculated by group contribution theory. For the β-caryophyllene oxidation products, the values measured by gas chromatography were slightly lower than those obtained by theoretical calculations. The opposite trend was observed for the α-pinene oxidation products. The methods based on gas chromatography are concluded to be highly useful for the determination of vapor pressures of semi-volatile compounds. Except for the most polar pinic and pinonic acids, differences between vapor pressure values obtained by GC–FID and GC–MS were small. Since GC–MS provides structural information simultaneously, the use of GC–MS is recommended.

Water uptake on polar stationary phases under conditions for hydrophilic interaction chromatography and its relation to solute retention

Since water associated with the stationary phase surface appears to be the essence of the retention mechanism in hydrophilic interaction chromatography (HILIC), we developed a method to characterize the water-absorbing capabilities of twelve different HILIC stationary phases. Adsorption isotherms for non-modified and monomerically functionalized silica phases adhered to a pattern of monolayer formation followed by multilayer adsorption, whereas water uptake on polymerically functionalized silica stationary phases showed the characteristics of formation and swelling of hydrogels. Water accumulation was affected by adding ammonium acetate as buffer electrolyte and by replacing 5% of the acetonitrile with tertiary solvents capable of hydrogen bonding such as methanol or tetrahydrofuran. The relationship between water uptake and retention mechanism was investigated by studying the correlations between retention factors of neutral analytes and the phase ratios of HILIC columns, calculated either from the surface area (adsorption) or the volume of the water layer enriched from the acetonitrile/water eluent (partitioning). These studies made it evident that adsorption and partitioning actually coexist as retention promoters for neutral solutes in the water concentration regime normally encountered in HILIC. Which factors that dominates is dependent on the nature of the solute, the stationary phase, and the eluting conditions.

Comprehensive profiling of 136 tetra- to octa-polychlorinated dibenzo-p-dioxins and dibenzofurans using ionic liquid columns and column combinations

The orders of elution of all 136 tetra- to octa-chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were determined on six gas chromatography (GC) columns. Three of these columns had ionic liquid stationary phases (SLB-IL111, SLB-IL76 and SLB-IL61; Supelco), one a liquid crystal phase (LC-50; Restek), one a chiral phase (βDEXcst; Restek) and one a low bleed non-polar phase (DB-XLB; J&W/Agilent). According to our results, the high polarity and multiple solvation interactions of the ionic liquid stationary phases offered superior resolving power to that achieved with previously evaluated columns. The SLB-IL61 and SLB-IL111 columns resolved or partially separated 106 and 100 congeners, respectively, of the 136 PCDD/Fs. The SLB-IL61 also resolved 15 and partially separated one of the seventeen 2,3,7,8-substituted PCDD/Fs. Additional congeners can be separated by complementary analyses using additional columns in a dual- or triple-column approach. For example, using a combination of the SLB-IL61 and SLB-IL111 columns all but 8 congeners would be separated, including all 2,3,7,8-substituted PCDD/Fs. Two more congeners would be separated using a combination of SLB-IL76 and a liquid crystal (SB-Smectic) column, but in this case the 2,3,7,8-TeCDF would not be resolved. Three-column combinations would give even better separation: the DB-17/Smectic/SLB-IL76 and DB-225/Smectic/SLB-IL111 combinations would separate all but 1 of the 136 PCDD/F congeners. Unfortunately, the smectic column is no longer in production. If only commercially available columns are considered, combinations of SLB-IL61 and SLB-IL111 with DB-XLB, LC-50, or DB-225 offer the best performance, with 4, 4, and 3 unresolved congeners, respectively. Moreover, in each of these cases, one of the congeners in each unresolved pair is resolved on at least one of the other columns and so a reasonable estimate of the unresolved congeners’ concentrations can be obtained by subtraction. The profiling of all 136 PCDD/Fs is thus greatly facilitated by using ionic liquid columns or combinations including such columns. However, there is room for improvement in the technical performance of the evaluated ionic liquid columns: their long-term retention time stability was poor and some highly chlorinated and sterically hindered congeners underwent dehalogenation during separation.

Properties of columns with several pyridinium and imidazolium ionic liquid stationary phases

Recent advances in the development of new liquid phases (ILs) made it possible to use some classes of ILs as polar stationary liquid phases (SLP). In our days only alkylimidazolium- and alkylphosphonium-based ILs are widely used as polar SLP. In present work some other types of ILs – pyridinium and cyanopropyl/hydroxypropyl imidazolium were investigated as SLP. Columns with efficiencies 2000–2500 plates/m by high-pressure static method were prepared. Polarity and selectivity of these phases were measured. Selectivity was described in terms of intermolecular interactions by using Abraham solvatation parameter model. The set of the regularities between cation structure of ionic liquid and selectivity has been shown. The number and position of methyl groups in ionic liquid pyridinium ring were shown to have the sufficient influence on all type of molecular interactions. Finally the resolutions of test mixture for the several ionic liquid SLP were obtained. For columns with some ionic liquids the dependencies of the height equivalent to a theoretical plate (HETP) and sample loading capacity were obtained and compared with the conventional phases. It was found that the optimal efficiency for the IL columns is attained at lower carrier gas velocities in comparison with traditional phases. Nevetheless sample loading capacity of IL phases is comparable to those of conventional GC phases.

Characterisation of capillary ionic liquid columns for gas chromatography–mass spectrometry analysis of fatty acid methyl esters

Due to their distinct chemical properties, the application of ionic liquid (IL) compounds as gas chromatography (GC) stationary phases offer unique GC separation especially in the analysis of geometric and positional fatty acid methyl ester (FAME) isomers. Elution behaviour of FAME on several commercialised IL capillary columns including phosphonium based SLB-IL59, SLB-IL60, SLB-IL61 and SLB-IL76 and imidazolium based SLB-IL82, SLB-IL100, and SLB-IL111 as well as a general purpose column SLB-5ms, were evaluated in gas chromatography–mass spectrometry (GC–MS) analysis. The phases were further characterised by using a linear solvation energy relationship (LSER) approach according to the equivalent chain length (ECL) index of FAME. Among all tested IL columns, elution temperatures of saturated FAME increased as their McReynolds’ polarity value decreased, except for IL60. ECL values increased markedly as the stationary phase polarity increased, particularly for the polyunsaturated FAME. The LSER study indicated a lowest l/e value at 0.864 for IL111, displaying phase selectivity towards unsaturated FAME, with higher peak capacity within a carbon number isomer group. s and e descriptors calculated from LSER were validated by excellent correlation with dipole moments and lowest unoccupied molecular orbital (LUMO) energies, with R2 values of 0.99 and 0.92 respectively, calculated using GAUSSIAN.

Comparison of GC stationary phases for the separation of fatty acid methyl esters in biodiesel fuels

The fatty acid methyl ester (FAME) content of biodiesel fuels has traditionally been determined using gas chromatography with a polar stationary phase. In this study, a direct comparison of the separation of FAMEs present in various biodiesel samples on three polar stationary phases and one moderately polar stationary phase (with comparable column dimensions) was performed. Retention on each column was based on solubility in and polarity of the phase. Quantitative metrics describing the resolution of important FAME pairs indicate high resolution on all polar columns, yet the best resolution, particularly of geometric isomers, is achieved on the cyanopropyl column. In addition, the separation of four C18 monounsaturated isomers was optimized and the elution order determined on each column. FAME composition of various biodiesel fuel types was determined on each column to illustrate (1) chemical differences in biodiesels produced from different feedstocks and (2) chemical similarities in biodiesels of the same feedstock type produced in different locations and harvest seasons.

Fatty acid composition of <i>Tilia</i> spp. seed oils

As part of a study of the seed oil fatty acid composition of Malvaceae plants, the seeds of seven Tilia species (lime or linden trees) were evaluated for their fatty acid profiles. Seeds were obtained from the Germplasm Research Information Network and from various commercial sources. After extraction of the seed oil with hexane, the glycerides were trans-methylated and analyzed by gas chromatography on two polar stationary phases. All of the seed oils analyzed were composed primarily of linoleic acid (49-60%) with lesser amounts of oleic (16-22%) and palmitic (8-10%) acids. The usual secondary components were also found. In addition, cyclopropenoid acids (i.e., sterculic and malvalic acids) were present at levels between 6 and 17%. In all samples, the level of malvalic acid was approximately twice the level of sterculic acid, indicating that considerable a-oxidation of sterculic acid had occurred in these seeds. Two additional a-oxidation products, 8-heptadecenoic acid and 8,11-heptadecadienoic acid were also detected. Combined, the level of these fatty acids was between 1.3 and 2.3%, roughly comparable to the levels of these acids recently reported in the seed oil of Thespesia populnea.

Selectivity differences of water‐soluble vitamins separated on hydrophilic interaction stationary phases

In this study, the retention behavior and selectivity differences of water-soluble vitamins were evaluated with three types of polar stationary phases (i.e. an underivatized silica phase, an amide phase, and an amino phase) operated in the hydrophilic interaction chromatographic mode with ESI mass spectrometric detection. The effects of mobile phase composition, including buffer pH and concentration, on the retention and selectivity of the vitamins were investigated. In all stationary phases, the neutral or weakly charged vitamins exhibited very weak retention under each of the pH conditions, while the acidic and more basic vitamins showed diverse retention behaviors. With the underivatized silica phase, increasing the salt concentration of the mobile phase resulted in enhanced retention of the acidic vitamins, but decreased retention of the basic vitamins. These observations thus signify the involvement of secondary mechanisms, such as electrostatic interaction in the retention of these analytes. Under optimized conditions, a baseline separation of all vitamins was achieved with excellent peak efficiency. In addition, the effects of water content in the sample on retention and peak efficiency were examined, with sample stacking effects observed when the injected sample contained a high amount of water.

Preparation and evaluation of a hydrophilic poly(2‐hydroxyethyl methacrylate‐co‐N,N′‐methylene bisacrylamide) monolithic column for pressurized capillary electrochromatography

A polar polymethacrylate-based monolithic column was introduced and evaluated as a hydrophilic interaction CEC stationary phase. The monolithic stationary phase was prepared by in situ copolymerization of a neutral monomer 2-hydroxyethyl methacrylate and a polar cross-linker N,N'-methylene bisacrylamide in a binary porogenic solvent consisting of dodecyl alcohol and toluene. The hydroxyl and amino groups at the surface of the monolithic stationary phase provided polar sites which were responsible for hydrophilic interactions. The composition and proportion of the polymerization mixture was investigated in detail. The mechanical stability and reproducibility of the obtained monolithic column preformed was satisfied. The effects of pH and organic solvent content on the EOF and the separation of amines, nucleosides, and narcotics on the optimized monolithic column were investigated. A typical hydrophilic interaction CEC was observed on the neutral polar stationary phase. The optimized monolithic column can obtain high-column efficiencies with 62,000-126,000 theoretical plates/m and the RSDs of column-to-column (n = 9), run-to-run (n = 5), and day-to-day (n = 3) reproducibility were less than 6.3%. The calibration curves of these five narcotics exhibited good linearity with R in the range of 0.9959-0.9970 and linear ranges of 1.0-200.0 μg/mL. The detection limits at S/N = 3 were between 0.2 and 1.2 μg/mL. The recoveries of the separation of narcotics on the column were in the range of 84.0-108.6%. The good mechanical stability, reproducibility, and quantitation capacity was suitable for pressure-assisted CEC applications.

Application of hydrophilic interaction chromatography in phytochemical analysis

Summary Hydrophilic interaction chromatography (HILIC) is a liquid chromatography technique when a polar stationary phases — silica or polar bonded phases and aqueous mobile phase containing amount of a less polar solvent (often acetonitrile) is applied. HILIC is important for the separation of highly polar substances including biologically active compounds, such as drugs, amino acids, peptides, proteins, nucleosides, neurotransmitters, etc. HILIC is also the appropriate method for analysis of plant extract polar components such as carbohydrates, amino acids, peptides, phenolic acids, flavonoids and some alkaloids. Plant extracts are usually multicomponent mixtures of compounds of wide polarity range, which often cannot be analyzed by use of a single separation and detection method because of the high chemical diversity. Good results are obtained by use of coupled method, e.g., reversed-phase liquid chromatography (RP-LC) and HILIC mode separation. The elution order in HILIC is usually opposite to that in RP separations. This orthogonality determines one of the advantages of HILIC — the possibility of creating multidimensional separations. An important feature of HILIC is the improved sensitivity with electrospray mass spectrometry. This is significant for the analysis of components existing in small concentration in multicomponent mixtures. The high acetonitrile content also gives additional advantage of HILIC — faster separations due to the lower viscosity of HILIC eluents compared to standard RP ones. The presented review deals with the optimization of HILIC separations and application of the method for analysis of plant extracts components.

Hydrophilic interaction chromatography with aerosol-based detectors (ELSD, CAD, NQAD) for polar compounds lacking a UV chromophore in an intravenous formulation

In this work, a high performance liquid chromatography (HPLC) method is reported for the separation and quantitation of a drug substance that is highly polar and lacking a chromophore in a mannitol intravenous (IV) formulation. Three polar stationary phases operated in hydrophilic interaction chromatography (HILIC) mode were evaluated in conjunction with an Alltech 800 ELSD detector. These columns were evaluated with respect to chromatographic properties such as buffer, pH and organic concentrations to identify the best stationary phase. The chromatographic method was then validated for the determination of mGlu2/3 receptor agonist (−)-(1R, 4S, 5S, 6S)-4-Amino-2-sulfonylbicyclo [3.1.0] hexane-4,6-dicarboxylic acid (LY404039) content in a mannitol IV formulation with respect to linearity (R2 of 0.9997), repeatability (%RSD of 0.36%), accuracy, solution stability (99.56% after 24h), specificity, intra-assay precision (%RSD 0.48%) and limit of detection (LOD, ∼50μg/mL). In addition to the Alltech 800 ELSD detector, several other aerosol-based detectors were investigated for reproducibility, linearity and LOD. These additional detectors consisted of an Alltech 3300 evaporative light scattering detector (ELSD), a nano quantity analyte detector (NQAD) and a charged aerosol detector (CAD). Based on the data from this report, a feasible isocratic LC method was achieved using a TSKgel Amide-80 column with mobile phase conditions of 30% water with 0.2% trifluoroacetic acid (TFA) and 70% acetonitrile (ACN) using any of the four aerosol-based detectors for detection and quantitation.

The Nature of Rest Silanol Groups on the Surfaces of Silica Based Solid Phase Extraction Materials

Chemically bonded solid phase materials are very important in separation chemistry. The chemically modified silica gel contains rest silanol groups that can affect the retention properties when they are used for separation of compounds. Some commercially available solid phase extraction (SPE) materials based on silica gel were analysed for rest silanol groups by near infrared spectroscopy. The combination frequency of the water molecules in the 5500- 5000 cm -1 region was used in identifying the nature of water molecules on the surface and the information was used to identify the types of silanol groups on the surface. Second derivative technique was employed in the detailed analysis. Nine different SPE materials including C18, C8, C6H5, NH2, OH, CN, SiOH, SA (SCX) and SB (SAX) were examined by near infrared spectroscopy for rest silanol groups. The results show that the non-polar and polar stationary phases contain vicinal silanol groups and the ion exchange solid phase materials contain free, vicinal and geminal silanol groups.

Ionic liquids as novel stationary phases in gas liquid chromatography: Inverse or normal isotope effect?

The separation of deuterated and non-deuterated compounds in gas liquid partitioning chromatography (GLC) on silicone type stationary phase usually results in the inverse isotope effect. With ionic liquids (ILs) as stationary phase, however, this may show a totally different nature. The inverse isotope effect, in which heavier (deuterated) isotopic compounds (isotopologues) elute earlier, is to be expected when van der Waals (London) dispersion forces play a dominant role in the solute–stationary phase interaction. Such (apolar) interactions seem to play only a minor role when ILs are the stationary phases, leading to only a marginal inverse isotope effect, e.g. for the separation of 2,4,6-trichloroanisole and its [2H5]-isotopologue on 1,12-di(tripropylphosphonium) dodecane bis(trifluoromethansulfonyl) amide (commercialized as SLB-IL59, Supelco). Indeed, with the most polar stationary phase available (commercialized as SLB-IL111; Supelco), this separation showed a normal isotope effect. Further examples are presented and the nature of the isotope effect observed is discussed.

Room temperature ionic liquids: New GC stationary phases with a novel selectivity for flavor and fragrance analyses

Ionic liquids (ILs) are of great interest as moderately polar to polar stationary phases for GC, because their selectivity differs markedly from that of conventionally used phases. In the flavor, fragrance and essential oil fields, analysts often deal with complex mixtures of compounds having similar structural and physical characteristics (e.g., mono- and sesquiterpenoids), therefore requiring an interactive combination between chromatographic and mass spectral data for correct identification. New GC stationary phases with different selectivity must therefore be continually tested. Performance and evolution over time of commercially available IL columns versus those commonly used in these fields are here evaluated, mainly in view of their routine use. Chromatographic and separative properties (efficiency, separation capability, inertness and/or activity) of commercially available IL columns were compared to those of columns coated with 5% phenyl–95% methylpolysiloxane, 14% cyanopropyl–86% polysiloxane, and polyethylene glycol, on different complexity samples, including standard mixtures of volatile suspected allergens and pesticides, and cornmint and vetiver essential oils. The results show that IL columns can successfully be used for a wide range of applications characteristic of these fields, mainly because of their unusual selectivity, in particular when separations based on functional groups are required. Moreover, the latest generation of IL columns (IL61 and IL60) presents chromatographic performance comparable to or only slightly lower than that of the conventional columns routinely used in these fields.

Compounds for expanding the descriptor space for characterizing separation systems

A combination of gas chromatography and liquid–liquid partitions in totally organic biphasic systems is used to determine descriptor values for compounds of low volatility suitable for characterizing open tubular columns at high temperatures. The descriptor database of varied compounds includes several difficult to determine by conventional techniques due to their low water solubility or stability. The descriptor database facilitates an expansion of the descriptor space and compound variation for characterizing separation systems. As an application the descriptor database is used to determine the system constants for SPB-Octyl, HP-5, Rxi-5Sil MS, Rtx-440, and Rtx-OPP for the temperature range 200–300°C. As an example of the broader affect of temperature on column selectivity the variation of the system constants for Rtx-440 over the temperature range 60–300°C is described in detail. These studies demonstrate the persistence of polar interactions to the highest temperature studied and that at high temperatures selectivity differences persist for moderately polar stationary phases.