Controlled ultraviolet (UV) photoinitiated fabrication of monolithic porous layer open tubular (monoPLOT) capillary columns for chromatographic applications

An automated column fabrication technique that is based on a ultraviolet (UV) light-emitting diode (LED) array oven, and provides precisely controlled "in-capillary" ultraviolet (UV) initiated polymerization at 365 nm, is presented for the production of open tubular monolithic porous polymer layer capillary (monoPLOT) columns of varying length, inner diameter (ID), and porous layer thickness. The developed approach allows the preparation of columns of varying length, because of an automated capillary delivery approach, with precisely controlled and uniform layer thickness and monolith morphology, from controlled UV power and exposure time. The relationships between direct exposure times, intensity, and layer thickness were determined, as were the effects of capillary delivery rate (indirect exposure rate), and multiple exposures on the layer thickness and axial distribution. Layer thickness measurements were taken by scanning electron microscopy (SEM), with the longitudinal homogeneity of the stationary phase confirmed using scanning capacitively coupled contactless conductivity detection (sC(4)D). The new automated UV polymerization technique presented in this work allows the fabrication of monoPLOT columns with a very high column-to-column production reproducibility, displaying a longitudinal phase thickness variation within ±0.8% RSD (relative standard deviation).     

High-efficiency solvating gas chromatography using packed capillaries

In this study, column efficiency in packed capillary column solvating gas chromatography (SGC) was investigated. Long (>3 m) fused silica capillaries with an inner diameter of 250 μm were packed with 10 and 15 μm spherical porous (300 ?) octadecyl bonded silica particles using a CO(2) slurry packing method. A 336 cm × 250 μm i.d. fused silica capillary containing 10 μm particles provided a total column efficiency of 264?000 plates (k = 0.41), corresponding to a reduced plate height of 1.27, using CO(2) as the mobile phase at a column inlet pressure of 260 atm. A minimum plate height of 12.7 μm and a maximum plate number per unit time of 813 plates/s were obtained using packed capillary SGC. Retention factors were dependent on the column inlet pressure but independent of the pressure gradient along the column. Gasoline and diesel samples were separated under SGC conditions, and the results were comparable to those obtained using typical open tubular column gas chromatography.     

On-line 1D and 2D porous layer open tubular/LC-ESI-MS using 10-microm-i.d. poly(styrene-divinylbenzene) columns for ultrasensitive proteomic analysis

Following on our recent work, on-line one-dimensional (1D) and two-dimensional (2D) porous layer open tubular/liquid chromatography-electrospray ionization-mass spectrometry (PLOT/LC-ESI-MS) platforms using 3.2 mx10 microm i.d. poly(styrene-divinylbenzene) (PS-DVB) PLOT columns have been developed to provide robust, high-performance, and ultrasensitive proteomic analysis. With the use of a PicoClear tee, the dead volume connection between a 50 microm i.d. PS-DVB monolithic micro-SPE column and the PLOT column was minimized. The micro-SPE/PLOT column assembly provided a separation performance similar to that obtained with direct injection onto the PLOT column at a mobile phase flow rate of 20 nL/min. The trace analysis potential of the platform was evaluated using an in-gel tryptic digest sample of a gel fraction (15-40 kDa) of a cervical cancer (SiHa) cell line. As an example of the sensitivity of the system, approximately 2.5 ng of protein in 2 microL of solution, an amount corresponding to 20 SiHa cells, was subjected to on-line micro-SPE-PLOT/LC-ESI-MS/MS analysis using a linear ion trap MS. A total of 237 peptides associated with 163 unique proteins were identified from a single analysis when using stringent criteria associated with a false positive rate of less than 1%. The number of identified peptides and proteins increased to 638 and 343, respectively, as the injection amount was raised to approximately 45 ng of protein, an amount corresponding to 350 SiHa cells. In comparison, only 338 peptides and 231 unique proteins were identified (false positive rate again less than 1%) from 750 ng of protein from the identical gel fraction, an amount corresponding to 6000 SiHa cells, using a typical 15 cmx75 microm i.d. packed capillary column. The greater sensitivity, higher recovery, and higher resolving power of the PLOT column resulted in the increased number of identifications from only approximately 5% of the injected sample amount. The resolving power of the micro-SPE/PLOT assembly was further extended by 2D chromatography via combination of the high-efficiency reversed-phase PLOT column with strong cation-exchange chromatography (SCX). As an example, 1071 peptides associated with 536 unique proteins were identified from 75 ng of protein from the same gel fraction, an amount corresponding to 600 cells, using five ion-exchange fractions in on-line 2D SCX-PLOT/LC-MS. The 2D system, implemented in an automated format, led to simple and robust operation for proteomic analysis. These promising results demonstrate the potential of the PLOT column for ultratrace analysis.     

Fabrication of 1-dimensional porous hydroxyapatite and evaluation of its osteoconductivity

Porous HA ceramics with 1-dimensional pore channels were fabricated to obtain controllable microstructure. 1-dimensional porous HA was objected to find out the optimum condition of bone ingrowth and also to facilitate the observation of osteocondutive behavior in porous HA. The porous structure was formed by burnt-out of polymeric fibers and the size of pores was determined by the diameter of polymeric fibers. The porosity could be varied by the thickness of HA slurry coated on polymeric fiber and by the thickness of HA tapes inserted between fiber layers. As result, 1-dimensional porous HA ceramics of this study have the uniform interconnection size (50-500 microm) and the linearly open pore structure. The compressive strength of 1-dimensional porous HA was 6-10 MPa similar to that of human cancellous bone. On the in vivo test, oteon-like osteoconduction in pore channel of 1-dimensional porous HA was observed, like what had been found in cortical bones. This osteon-like new bone grew from the surface to the center of pore channels. The 1-dimensional porous HA ceramics prepared in this study were very useful as a model system to observe bone ingrowth in the porous HA implants.     

Analysis of inorganic species by capillary electrophoresis-mass spectrometry and ion exchange chromatography-mass spectrometry using an ion spray source

Mixtures of inorganic ions separated by capillary electrophoresis (CE) and ion exchange chromatography (IC) are detected by mass spectrometry (MS) using an ion spray atmospheric pressure ionization source. The selectable degree of ion-adduct declustering and molecular fragmentation in the MS interface region allows the system to be operated as an elemental analyzer or as a molecular detector suitable for oxidation state determinations. Both inorganic anions and cations (including alkalis, alkaline earths, transition metals, and lanthanides) are analyzed by CE-MS. A variety of CE separation buffers are evaluated for the cation analyses (e.g., creatinine, ammonium acetate, and tris[hydroxymethyl]aminomethane). Only one of the buffers (i.e., creatinine) can be used for CE-indirect UV detection. A CE capillary permanently coated with strong anion exchange sites and a pyromellitic acid buffer (suitable for indirect UV detection) is used for the inorganic anion separations. The coated column eliminates the need for buffer modifiers to reverse the flow in the capillary, which then reduces background noise and mass spectral complexity. The separation and detection of 13 inorganic anions are also accomplished by IC using an anion exchange column with a carbonate-bicarbonate mobile phase, on-line suppressed conductivity detection, and mass spectrometric detection.     

Sol-gel open tubular ODS columns with reversed electroosmotic flow for capillary electrochromatography

Sol-gel chemistry was successfully used for the fabrication of open tubular columns with surface-bonded octadecylsilane (ODS) stationary-phase coating for capillary electrochromatography (OT-CEC). Following column preparations, a series of experiments were performed to investigate the performance of the sol-gel coated ODS columns in OT-CEC. The incorporation of N-octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride as one of the sol-gel precursors played an important role in the electrochromatographic performance of the prepared columns. This chemical reagent possesses a chromatographically favorable, bonded ODS moiety, in conjunction with three methoxy groups allowing for sol-gel reactivity. In addition, a positively charged nitrogen atom is present in the molecular structure of this reagent and provides a positively charged capillary surface responsible for the reversed electroosmotic flow (EOF) in the columns during CEC operation. Comparative studies involving the EOF within such sol-gel ODS coated and uncoated capillaries were performed using acetonitrile and methanol as the organic modifiers in the mobile phase. The use of a deactivating reagent, phenyldimethylsilane, in the sol-gel solution was evaluated. Efficiency values of over 400,000 theoretical plates per meter were achieved in CEC on a 64 cm x 25 microm i.d. sol-gel ODS open tubular column. Test mixtures of polycyclic aromatic hydrocarbons, benzene derivatives, and aromatic aldehydes and ketones were used to evaluate the CEC performances of both nondeactivated and deactivated open tubular sol-gel columns. The effects of mobile-phase organic modifier contents and pH on EOF in such columns were evaluated. The prepared sol-gel ODS columns are characterized by switchable electroosmotic flow. A pH value of approximately 8.5 was found correspond to the isoelectric point for the prepared sol-gel ODS coatings.     

Medium effect on electrochemical behaviour of anodized aluminium

The effect of some anions on the growth of the oxide film on aluminium was studied in acid and neutral media, as well as the effect of pH in presence of the same anion. In all the cases studied an inner barrier layer is formed adjacent to the metal and is covered on top with a porous layer. This latter outer layer differentiates into two regions, the one adjacent to the solution being characterized by a more open structure and a higher degree of anion incorporation as compared to the region embedded between it and the inner barrier layer. The rate of dissolution of the barrier layer is not affected by pH or anion type prevailing in the formation medium, since this layer is formed of pure alumina. The dissolution of the outer porous layer, on the other hand, is affected by both pH and anion type.     

Introducing Enantioselective Ultrahigh-Pressure Liquid Chromatography (eUHPLC): Theoretical Inspections and Ultrafast Separations on a New Sub-2-μm Whelk-O1 Stationary Phase

A new chiral stationary phase for ultrahigh-pressure liquid chromatography (UHPLC) applications was prepared by covalent attachment of the Whelk-O1 selector to spherical, high-surface-area 1.7-μm porous silica particles. Columns of varying dimensions (lengths of 50, 75, 100, and 150 mm and internal diameters of 3.0 or 4.6 mm) were packed and characterized in terms of permeability, efficiency, retention, and enantioselectivity, using both organic and water-rich mobile phases. A conventional HPLC Whelk-O1 column based on 5.0-μm porous silica particles and packed in a 250 mm × 4.6 mm column was used as a reference. Van Deemter curves, generated with low-molecular-weight solutes on a 100 mm × 4.6 mm column packed with the 1.7-μm particles, showed H(min) (μm) and μ(opt) (mm/s) values of 4.10 and 5.22 under normal-phase and 3.74 and 4.34 under reversed-phase elution conditions. The flat C term of the van Deemter curves observed with the 1.7-μm particles allowed the use of higher-than-optimal flow rates without significant efficiency loss. Kinetic plots constructed from van Deemter data confirmed the ability of the column packed with the 1.7-μm particles to afford subminute separations with good efficiency and its superior performances in the high-speed regime, compared to the column packed with 5.0-μm particles. Resolutions in the time scale of seconds were obtained using a 50-mm-long column in the normal phase or polar organic mode. The intrinsic kinetic performances of 1.7-μm silica particles are retained in the Whelk-O1 chiral stationary phase, clearly demonstrating the potentials of enantioselective UHPLC in terms of high speed, throughput, and resolution.     

High-efficiency nanoscale liquid chromatography coupled on-line with mass spectrometry using nanoelectrospray ionization for proteomics

We describe high-efficiency (peak capacities of approximately 10(3)) nanoscale (using column inner diameters down to 15 microm) liquid chromatography (nanoLC)/low flow rate electrospray (nanoESI) mass spectrometry (MS) for the sensitive analysis of complex global cellular protein enzymatic digests (i.e., proteomics). Using a liquid slurry packing method with carefully selected packing solvents, 87-cm-length capillaries having inner diameters of 14.9-74.5 microm were successfully packed with 3-microm C18-bonded porous (300-A pores) silica particles at a pressure of 18,000 psi. With a mobile-phase delivery pressure of 10,000 psi, these packed capillaries provided mobile-phase flow rates as low as approximately 20 nL/min at LC linear velocities of approximately 0.2 cm/s, which is near optimal for separation efficiency. To maintain chromatographic efficiency, unions with internal channel diameters as small as 10 microm were specially produced for connecting packed capillaries to replaceable nanoESI emitters having orifice diameters of 2-10 microm (depending on the packed capillary dimensions). Coupled on-line with a hybrid-quadrupole time-of-flight MS through the nanoESI interface, the nanoLC separations provided peak capacities of approximately 10(3) for proteome proteolytic polypeptide mixtures when a positive feedback switching valve was used for quantitatively introducing samples. Over a relatively large range of sample loadings (e.g., 5-100 ng, and 50-500 ng of cellular proteolytic peptides for 14.9- and 29.7-microm-i.d. packed capillaries, respectively), the nanoLC/nanoESI MS response for low-abundance components of the complex mixtures was found to increase linearly with sample loading. The nanoLC/nanoESI-MS sensitivity also increased linearly with decreasing flow rate (or approximately inversely proportional to the square of the capillary inner diameter) in the flow range of 20-400 nL/min. Thus, except at the lower loadings, decreasing the separation capillary inner diameter has an effect equivalent to increasing sample loading, which is important for sample-limited proteomic applications. No significant effects on recovery of eluting polypeptides were observed using porous C18 particles with surface pores of 300-A versus nonporous particles. Tandem MS analyses were also demonstrated using the high-efficiency nanoLC separations. Chromatographic elution time, MS response intensity, and mass measurement accuracy was examined between runs with a single column (with a single nanoESI emitter), between different columns (same and different inner diameters with different nanoESI emitters), and for different samples (various concentrations of cellular proteolytic peptides) and demonstrated robust and reproducible sensitive analyses for complex proteomic samples.     

Fused-core silica column high-performance liquid chromatography/tandem mass spectrometric determination of rimonabant in mouse plasma

A high-performance liquid chromatography (HPLC) method using a fused-core silica particle packing was evaluated to allow fast and efficient separation for the analysis of pharmaceutical compounds. Fused-core particles are produced by "fusing" a porous silica layer onto a solid silica particle. The efficiencies of columns packed with 2.7 microm "fused-core" particles (a 0.5 microm porous shell fused to a solid 1.7 microm silica core particle) and 1.7 microm porous particles were compared in reversed-phase HPLC using rimonabant as an analyte. The fused-core silica materials providing the shorter diffusional mass transfer path for solutes are less affected in resolving power by increases in mobile-phase velocity than the sub-2 microm porous silica packings resulting in faster separations and higher sample throughput. This fast HPLC technology is comparable with ultrahigh-pressure liquid chromatography (UHPLC) in terms of chromatographic performance but demands neither expensive ultra-high-pressure instrumentation nor new laboratory protocols. The column effluent was directly connected to the atmospheric pressure chemical ionization (APCI) source prior to tandem mass spectrometric detection. In this work, the described fast HPLC-MS/MS and UHPLC-MS/MS approaches requiring approximately 1.5 min per sample were applied and compared for the determination of the rimonabant in mouse plasma samples at the low nanograms per milliliter region in support of a pharmacodynamic study.     

R.F. magnetron sputtering of multilayered c-BN films on cemented carbide tool

A c-BN thin film was deposited using a B4C target in a r.f. magnetron sputtering system. The c-BN layer was coated with a TiAIN adhesion layer (approximately 2 microm), boron carbide (approximately 1 microm) and BCN (10 approximately 15 nm) nano-gradient layer system. The c-BN layers with thicknesses of more than 0.5 microm were successfully deposited onto cemented carbide substrates. The high resolution XPS spectra analysis of B1s and N1s revealed that the c-BN film was mainly composed of sp3 BN bonds.     

Electroosmotic flow-based pump for liquid chromatography on a planar microchip

An electroosmotic flow (EOF)-based pump, integrated with a sol-gel stationary phase located in the electric field-free region of a microchip, enabled the separation of six nitroaromatic and nitramine explosives and their degradation products via liquid chromatography (LC). The integrated pump and LC system were fabricated within a single quartz substrate. The pump region consisted of a straight channel (3.0 cm x 230 microm x 100 microm) packed with 5-microm porous silica beads. The sol-gel stationary phase was derived from a precursor mixture of methyltrimethoxy- and phenethyltrimethoxysilanes and was synthesized in the downstream, field-free region of the microchip, resulting in a stationary-phase monolith with dimensions of 2.6 cm x 230 microm x 100 microm. Fluid dynamic design considerations are discussed, especially as they relate to integrating the EOF pump with the LC system. Pump and separation performance, as characterized by flow rate measurements, injection, elution, separation, and detection, point to a viable analytical chemistry platform that encompasses all of the benefits expected of portable, laboratory-on-chip systems, including reduced sample requirements and small packaging.     

On-column micro gas chromatography detection with capillary-based optical ring resonators

We developed a novel on-column micro gas chromatography (microGC) detector using capillary based optical ring resonators (CBORRs). The CBORR is a thin-walled fused silica capillary with an inner diameter ranging from a few tens to a few hundreds of micrometers. The interior surface of the CBORR is coated with a layer of stationary phase for gas separation. The circular cross section of the CBORR forms a ring resonator and supports whispering gallery modes (WGMs) that circulate along the ring resonator circumference hundreds of times. The evanescent field extends into the core and is sensitive to the refractive index change induced by the interaction between the gas sample and the stationary phase. The WGM can be excited and monitored at any location along the CBORR by placing a tapered optical fiber against the CBORR, thus enabling on-column real-time detection. Rapid separation of both polar and nonpolar samples was demonstrated with subsecond detection speed. Theoretical work was also established to explain the CBORR detection mechanism. While low-nanogram detection limits are observed in these preliminary tests, many methods for improvements are under investigation. The CBORR is directly compatible with traditional capillary GC columns without any dead volumes. Therefore, the CBORR-based muGC is a very promising technology platform for rapid, sensitive, and portable analytical devices.     

Single-walled carbon nanotubes used as stationary phase in GC

Single-walled carbon nanotubes (SWNTs) have high surface area, high adsorption ability, and nanoscale interactions. In this study, capillary columns including SWNTs, ionic liquid (IL), and IL + SWNTs for GC were prepared. The separation results showed that SWNTs possessed a wide selectivity toward alkanes, alcohols, aromatic compounds, and ketones, and a SWNT capillary column was a very useful GC column for the separation of gas samples. Coating the IL stationary phase on the SWNT capillary column, the SWNTs were able to improve chromatographic characteristic of ionic liquid. Comparing the IL coated on three graphite carbon black capillary columns, which were prepared by dynamic coating, static coating, and chemical bonding the Carbopack C with on SWNTs capillary column, the capacity factors were much higher on the SWNT column. The SEM showed that SWNTs could be bonded to the inner surface of capillary tubing, and most of them were linked end-to-end to form a layer of network structure of skeletons resulting in a high surface area, which increased the interactions between stationary phase and analytes. This is the first single-wall carbon nanotubes bonded to the fused-silica capillary tubing. In the first approach, SWNTs assist ionic liquid with enhanced chromatographic characteristic in GC. This work indicates that SWNTs make it possible to extend the application range on the newly prepared chromatographic stationary phases for GC.     

Detection of G-quartet structure in a DNA aptamer stationary phase using a fluorescent dye

The fluorescent porphyrin dye N-methylmesoporphyrin IX (NMM) was used to provide direct evidence of intramolecular G-quartet formation by an oligonucleotide immobilized at the inner surface of a fused silica capillary. The oligonucleotide is the thrombin-binding DNA aptamer, which has been used in several analytical applications, including a stationary phase for open tubular capillary electrochromatography. Spectroscopic studies of the dye in batch solutions of the aptamer and of an oligonucleotide with the same base composition, but in a different, "scrambled" sequence that does not form an intramolecular G-quartet, provided evidence of selective fluorescence enhancement of NMM by the aptamer in the intramolecular G-quartet structure. On-column experiments compared results for injections of NMM onto an aptamer-coated capillary, a capillary coated with the scrambled sequence oligonucleotide, and a bare fused silica capillary. Results show that while NMM adsorbs to both coated capillaries, the selective fluorescence enhancement provides evidence of the intramolecular G-quartet structure on the aptamer-coated capillary.     

Gas chromatography on self-assembled, single-walled carbon nanotubes

High-performance stationary phases, which provide high resolutions and are stable at high temperatures, are of significant importance in gas chromatographic analysis. Carbon nanotubes are nanosized carbon-based sorbents that have a high surface area and a large aspect ratio and are known to be stable at high temperatures. It is, therefore, conceivable that gas chromatography can benefit from their unique properties. This paper reports gas chromatography separations in an open tubular format on self-assembled, single-walled carbon nanotubes (SWNTs) inside silica-lined steel capillary tubing. A SWNT film with an average thickness of 300 nm was self-assembled by a unique, single-step, catalytic chemical vapor deposition (CVD) process consisting of dissolved cobalt and molybdenum salts in ethanol. A variety of organic compounds with varying polarity were separated at high resolution, and the column efficiency demonstrated approximately 1000 theoretical plates/m. Comparison of capacity factors' and isosteric heats of adsorption with a packed column containing a commercial sorbent (Carbopack C) showed comparable results. This demonstrated high capacity and strong sorbate-sorbent interactions on the SWNT phase. Evaluation of the McReynolds constants suggested that the SWNT was a nonpolar phase.     

All-hydrocarbon liquid crystalline polysiloxane polymer as stationary phase in gas chromatography capillary column for separation of isomeric compounds of polynuclear aromatic hydrocarbons

Two new and high-purity all-hydrocarbon side-chain liquid crystalline polysiloxane polymers were synthesized by grafting all-hydrocarbon liquid crystal monomers onto a polymethylhydrosiloxane backbone. The two polysiloxane polymers show both smectic B and E mesophases which were characterized by (differential scanning calorimetry and X-ray analysis. As stationary phases, these liquid crystalline polysiloxane polymers were coated on the inner surface of a capillary column (i.d. = 0.32 mm, film thickness d(f) ≈ 0.25 μm) using the static coating method. The capillary column was installed on a GC/MS instrument. We used a standard commercial mixture of 21 species of polynuclear aromatic hydrocarbons (purchased from Supelco Co. and Merck Co.) to test the chromatographic behavior of the coated stationary phase. Test results of the isomeric pair compounds show a better separation resolution than identical tests using the commercial HP-5 capillary column, which is a standard and state-of-the-art analytical tool for the chromatographic resolution of PAHs.     

Fabrication of nano- and micro-scale UV imprint stamp using diamond-like carbon coating technology

Two-dimensional (2-D) and three-dimensional (3-D) diamond-like carbon (DLC) stamps for ultraviolet nanoimprint lithography were fabricated with two methods: namely, a DLC coating process, followed by focused ion beam lithography; and two-photon polymerization patterning, followed by nanoscale-thick DLC coating. We used focused ion beam lithography to fabricate 70 nm deep lines with a width of 100 nm, as well as 70 nm deep lines with a width of 150 nm, on 100 nm thick DLC layers coated on quartz substrates. We also used two-photon polymerization patterning and a DLC coating process to successfully fabricate 200 nm wide lines, as well as 3-D rings with a diameter of 1.35 microm and a height of 1.97 microm, and a 3-D cone with a bottom diameter of 2.88 microm and a height of 1.97 microm. The wafers were successfully printed on an UV-NIL using the DLC stamps without an anti-adhesive layer. The correlation between the dimensions of the stamp's features and the corresponding imprinted features was excellent.     

Chromatography on self-assembled carbon nanotubes

Stationary phases that provide high resolutions and are stable at high temperatures are of significant importance in chromatographic analysis. Carbon nanotubes (CNTs) are known to have high thermal and mechanical stability and have the potential to be high-performance separation media that utilize the nanoscale interactions. Here, we report the first application of self-assembled CNTs in long capillary tubes for the development of gas chromatography columns. A film of CNTs was deposited by chemical vapor deposition (CVD) to form the stationary phase in the open tubular format. High-resolution separation of a number of compounds has been achieved. Altering the CVD conditions can vary the thickness and the morphology of the CNT film, which opens the possibility of selectivity tuning. The ability to fabricate long tubes coated with CNTs can be readily employed in other gas- and liquid-phase separations as well.     

Examination of ionic liquids and their interaction with molecules, when used as stationary phases in gas chromatography.

Stable room-temperature ionic liquids (RTILs) have been used as novel reaction solvents. They can solubilize complex polar molecules such as cyclodextrins and glycopeptides. Their wetting ability and viscosity allow them to be coated onto fused silica capillaries. Thus, 1-butyl-3-methylimidazolium hexafluorophosphate and the analogous chloride salt can be used as stationary phases for gas chromatography (GC). Using inverse GC, one can examine the nature of these ionic liquids via their interactions with a variety of compounds. The Rohrschneider-McReynolds constants were determined for both ionic liquids and a popular commercial polysiloxane stationary phase. Ionic liquid stationary phases seem to have a dual nature. They appear to act as a low-polarity stationary phase to nonpolar compounds. However, molecules with strong proton donor groups, in particular, are tenaciously retained. The nature of the anion can have a significant effect on both the solubilizing ability and the selectivity of ionic liquid stationary phases. It appears that the unusual properties of ionic liquids could make them beneficial in many areas of separation science.