Supercritical Fluid Chromatography Mobile Phase Research Articles

Characterization of a solventless injection interface for supercritical fluid chromatography

Packed column supercritical fluid chromatography (SFC) is capable of highly efficient separations of drug-like molecules with les solvent consumption than HPLC. However, solute peaks in SFC are susceptible to broadening and distortion due to mismatch between the elution strength and viscosity of the injection solvent and the SFC mobile phase. The magnitude of solvent-induced band broadening increases as the elution strength and viscosity of the sample and mobile phase become more dissimilar and varies with the type of stationary phase used and the nature of the solute injected. A number of researchers have coupled supercritical fluid extraction with supercritical fluid chromatography in an attempt to remove solvent from injected samples, and thereby reduce peak broadening and distortion during SFC chromatography. While solventless injection is effective in overcoming solvent-induced band broadening in SFC, there have been few reports dealing with the optimization of the solvent removal process of this technique. In this work, we describe the influence of temperature, purge time, purging gas flow rate, stationary phase used in the sample precolumn, and injection solvent composition on solvent elimination and solute recovery.

Packed Column Supercritical Fluid Chromatography/Mass Spectrometry for High-Throughput Analysis

A supercritical fluid chromatograph was interfaced to a mass spectrometer, and the system was evaluated for applications requiring high sample throughput. Experiments presented demonstrate the high-speed separation capability of supercritical fluid chromatography (SFC) and the effectiveness of supercritical fluid chromatography/mass spectrometry (SFC/MS) for fast, accurate determinations of multicomponent mixtures. A high-throughput liquid chromatography/mass spectrometry (LC/MS) analysis cycle time is reduced 3-fold using our general SFC/MS high-throughput method, resulting in substantial time saving for large numbers of samples. Unknown mixture characterization is improved due to the increased selectivity of SFC/MS compared to LC/MS. This was demonstrated with sample mixtures from a 96-well combinatorial library plate. In this paper, we report a negative mode atmospheric pressure chemical ionization (APCI) method for SFC/MS suitable for most of the components in library production mixtures. Flow injection analysis (FIA) also benefits from this SFC/MS system. A broader range of solvents is amenable to the SFC mobile phase compared with standard LC/MS solvents, and solutes elute more rapidly from the SFC/MS system, reducing sample carryover and cycle time. Finally, our instrumental setup allows for facile conversion between LC/MS and SFC/MS modes of operation.

The plasma emission detector (PED) as an element-selective detector for supercritical fluid chromatography

The plasma emission detector (PED) has been shown to be an element specific detector for supercritical fluid chromatography (SFC). The commonly used eluents (CO2 and N2O) tend to disturb the He plasma; two different discharge tubes were tested in an attempt to overcome this problem. Promising results were obtained with a concentric dual flow torch design for the element specific detection of Cl, H, and C containing analytes using N2O as SFC mobile phase.

Improved Supercritical Fluid Chromatography Mobile-Phase Tolerance with a Moderate-Power Helium Microwave-Induced Plasma

Studies comparing the use of moderate (500 W) and low (60–150 W) power helium microwave-induced plasmas (MIPs) for packed-column supercritical fluid chromatography (SFC) are presented. In the 100 to 220 atm SFC pressure range, the low-power plasma exhibits greater signal reduction due to the SFC mobile phase. Plasma characteristics such as helium line intensities and electron densities remain unaltered in the 0 to 120 mL/min (atmospheric pressure volumes) flow rate range with the 500-W helium MIP. As well, Cl(II) emission intensity at 479.45 nm is not affected in this flow rate range. Finally, it is shown that the SFC peak area is not affected as the chromatographic pressure is increased from 150 to 250 atmospheres.

Characterization of N-linked glycans by supercritical fluid chromatography—mass spectrometry

N-Linked glycans have been characterized by supercritical fluid chromatography (SFC) and SFC-MS using positive- and negative-ion chemical ionization. Four common oligosaccharide derivatives have been prepared and their chromatographic properties assessed on three SFC columns of varying polarity. Carbon dioxide has been used as the SFC mobile phase, with ammonia or CO 2 added to the ion source for positive-and negative-ion chemical ionization, respectively. Direct SFC-MS interfacing allows the analytical manipulations of single-ion monitoring, total-ion plots, background subtraction, library searches, and spectral reconstruction algorithms. Positive ammonia chemical ionization yields abundant molecular-weight information, (MH) +, and (MNH 4) + with little or no fragmentation. To capitalize on sensitivity, samples were prepared with the pentafluorobenzyl aminobenzoate reagent, acetylated, and analyzed by SFC-NICI-MS. This modification improves column efficiency and resolution and greatly enhances detecting sensitivity. These “soft” ionization conditions provide abundant molecular-weight-related anions for collision-induced dissociation and subpicogram detection.

Simulated Supercritical Fluid Chromatography Mobile Phase Introduction to a Helium Microwave-Induced Plasma: Effects on Nonmetal Emission and Spectral Behavior

The effects of the introduction of capillary supercritical fluid chromatography mobile phases, CO2 and N2O, into a helium microwave-induced plasma (He-MIP) are investigated. The plasma and mobile-phase flow rates are maintained at conditions comparable to those typically used for these systems. Spectral characteristics are monitored in both the ultraviolet-visible and near-infrared regions. Molecular bands from these “foreign” gases are assigned and their relative intensities are noted as a function of the doping gas flow rate. Possible molecular band interferences are noted for nonmetal atomic emission determinations with He-MIPs. Nonmetal atomic emission reduction by these gases is studied with the use of chlorine atom and ion lines as test signals. Decreases in chlorine atom and ion emission are seen as CO2 and N2O flow rates are increased. It is found that ion line emission intensity is reduced more significantly than atom line emission. Reduction of both atom and ion line emission is more pronounced with CO2 than with N2O. The electron density of the plasma does not change as the CO2 flow rate is increased from 0 to 0.25 mL (STP)/min.

Application of capillary supercritical fluid chromatography–double focusing mass spectrometry under negative ion chemical ionization conditions

AbstractThe application of mass spectrometry in the negative ion mode with capillary column supercritical fluid chromatography is described. The supercritical fluid chromatography mobile phase (CO2) was used as the primary reagent gas to generate thermalized electrons and reagent anions (such as O− and CO2−). When trace amounts of CH4 or NH3 gas were also introduced into the chemical ionization source, the mass spectrometer sensitivity was increased. Detection limits (S/N = 5) for heptachlor were determined to be 20 pg and 200 fg for full scan and selected ion monitoring modes, respectively. Mass spectra of a cyclic peptide, valinomycin, obtained with these mixed reagents (CH4 + CO2 and NH3 + CO2) gave the molecular anion at m/z 1110 as the most abundant ion and additional fragment ions that yielded peptide sequence information.

Atomic emission detector for gas chromatography and supercritical fluid chromatography

A recently developed atomic emission source, the microwave plasma torch (MPT), is evaluated as an element-selective detector for gas chromatography (GC) and capillary supercritical fluid chromatography (SFC). The interfaces between the gas chromatograph or supercritical fluid chromatograph and the MPT are described. The effects of plasma and GC-SFC experimental conditions on the emission of analytes are studied. Two alternative types of MPT discharges are identified and their comparative utility in GC-SFC-MPT detection investigated. The introduction of an SFC mobile phase (in this instance CO2) has less of an effect on the He MPT discharge stability and sensitivity than on a surfatron-sustained He microwave-induced plasma. Either a He or an Ar MPT can be used as an SFC detector for ferrocene. However, a He MPT is necessary if chlorine is to be measured. Figures of merit are given and compared with those obtained from other atomic emission chromatographic detectors.

Supercritical fluid chromatography and microbore liquid chromatography for drug analysis.

Supercritical fluid and microbore liquid chromatography offer potential applications for drug analysis. In supercritical fluid chromatography (SFC), the mobile phase is a gas (e.g., carbon dioxide) maintained at its supercritical state--that is, above its critical temperature and pressure, above which it cannot be liquefied even with further increases in applied pressure. The SFC mobile phase has low viscosity, approximating that of a gas, and high diffusivity, between those of a gas and a liquid. These properties yield favorable column efficiency, between that of capillary gas chromatography (GC) and liquid chromatography (LC). SFC analysis may be performed by either packed or open tubular capillary columns and with GC and LC detectors. SFC, interfaced with mass spectrometry, may become a viable alternative to GC/MS for drug identification in clinical and forensic toxicology. Advantages of microbore liquid chromatography include enhanced mass sensitivity, reduced solvent consumption, and others. Microbore columns (internal diameters 1 to 2 mm) may be packed with 3-, 5-, or 10-micron particles. Potential applications include micro-sample analysis (5-200 microL) for neonatal and pediatric drug monitoring, and drug confirmation analysis for toxicology.

High-performance liquid chromatography and capillary supercritical-fluid chromatography separation of vegetable carotenoids and carotenoid isomers

Carotenoids from carrots and tomatoes were separated with high-performance liquid chromatography (HPLC) and capillary supercritical fluid chromatography (SFC). All trans alpha- and beta-carotene were separated from their respective cis-isomers with capillary SFC. Carotenoids extracted from tomatoes included xanthophyll, lycopene and beta-carotene, while alpha- and beta-carotene were extracted from carrots. The HPLC separations were accomplished isocratically with a 25-cm column containing 5-μm ODS and methanol-acetonitrile-chloroform (47:47:6) or acetonitrile-dichloromethane (80:20). beta-Carotene cis-isomers were separated with SFC with a SB-cyanopropyl-25-polymethylsiloxane column, while alpha-carotene isomers were separated with two SB-cyanopropyl-50-polymethyl-siloxane columns. Carotenoids from carrots and tomatoes were separated with a SB-phenyl-5-polymethylsiloxane column. Carbon dioxide with 1% ethanol was the SFC mobile phase. The eluent was monitored at 461 nm for HPLC and either 453 or 461 nm for SFC.

Sulfur hexafluoride as a mobile phase for supercritical fluid chromatography

The capabilities of sulfur hexafluoride as a mobile phase for supercritical-fluid chromatography are investigated. An evaluation of its overall utility on the basis of separations of standard aromatic hydrocarbon odel mixtures performed on a variety of bonded-phase, packed columns with UV detection is presented. The dependence of separation performance upon operational parameters is also examined. A comparative evaluation of the chroamtographic properties of supercitrical sulfur hexafluoride and those of supercritical carbon dioxide is developed from these separations under corresponding supercritical state conditions.

Computer-assisted retention prediction of polycyclic aromatic hydrocarbons in supercritical fluid chromatography using carbon dioxide as the mobile phase

The dependence of the capacity factor of polycyclic aromatic hydrocarbons on column temperature and on the density of the mobile phase in supercritical-fluid chromatography was investigated using carbon dioxide as the mobile phase. Logarithmic capacity factors of polycyclic aromatic hydrocarbons were obtained as a linear function of the reciprocal column temperature at a constant molar volume of carbon dioxide.