Capillary electrophoresis (CE) has been combined with atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) for mass spectrometric (MS) detection. Separation conditions using potassium phosphate buffer and ammonium formate buffer have been compared for analysis of eleven pharmaceutical bases. The results showed improvements in separation efficiency and peak symmetry when phosphate buffer was used. The low flow in CE may enable utilization of these advances with MS detection. Compared with ESI, the APPI technique provided a cluster-free background. The enhanced signal-to-noise ratio in the total ion current (TIC) and the reduced spectral background indicated that the APPI process is less affected by non-volatile salts in the CE buffers. This results in a wider range of choice of CE buffers in CE/MS analysis when APPI is the ionization method.

Porous graphitic carbon has been successfully used for the separation of L-DOPA and four metabolites (dopamine, 3,4-dihydroxy-phenyl-acetic acid, homovanillic acid and 3-O-methyl-L-DOPA) and with a volatile mobile phase of relatively high percentage organic modifier (methanol-ammonium formate pH 2.9, 60∶40, v/v). The substances were analysed in plasma. Ultrafiltration was used to remove the proteins from the sample and a coupled column system to enrich and perform on-line sample clean up. Both precolumn and separation column of i. d. 0.2 mm were packed with porous graphitic carbon.

Fixed-size moving window evolving factor analysis and base peak chromatograms have been used for peak purity detection in data generated with LC–MS. The two methods were evaluated with both real and simulated data and were found to be fast and complementary to each other. When a possibly impure peak is detected, it is suggested that further information can be obtained from local principal component analysis modelling and comparative mass chromatogram plots.

A simple and very mild approach for the application of a conductive layer for sheathless electrospray has been developed. A modified 'fairy dust' method is employed in which 2 microm gold particles are applied by a thin layer of silicone on shaped tips. This novel approach comprises fabrications at room temperature, under atmospheric pressure, and involves no etching, extensive cleaning or otherwise harsh conditions. With this approach, sheathless electrospray emitters have been fabricated from fused silica capillaries with chemically pre-modified inner walls and from heat-sensitive polypropylene hollow fibres. Long term stability for more than two weeks of continuous spraying has been achieved. Capillary zone electrophoresis/time-of-flight mass spectrometry demonstrates attomole sensitivity and no detectable band broadening. A comparison with a chromium-gold coated emitter in terms of chemical noise is made with continuous infusion experiments, showing no significant increase in background from the polymer involved.

Selected pesticides are spiked in an empty extraction thimble for use as a model system to study the solvating power of supercritical carbon dioxide and spiked in solid-phase sorbent materials to study the influences of matrix effects on the recoveries. Results from this study show that it is possible to identify supercritical fluid extraction conditions where the molecular structure of the analytes affect the extraction efficiency. The results also indicate that parameters other than solubility (e.g., volatility) have a marked influence on the extraction process, even under simplistic conditions (extraction from empty thimble).

Supercritical carbon dioxide exhibits solvating power comparable to hexane and has been primarily utilized as a fluid for the separation of relatively non-polar compounds. 8 For this reason, many SFC methods have been developed as substitutes for normal-phase HPLC methods. Commonly used normal-phase HPLC mobile phases consist generally of chlorinated solvents such as chloroform and methylene chloride. Traces of water in these mobile phases cause retention times to fluctuate in the normal-phase mode. These solvents also present an environmental hazard, which can be eliminated in part by using a mobile phase of carbon dioxide which may or may not have been modified with a small percentage of organic solvent. Additionally, the quantity of solvent required and the high disposal costs commonly encountered with many normal-phase HPLC solvents may be dramatically reduced by employing carbon dioxide based mobile phases.

Estimations of concentration of the labile sodium pump inhibitor isolated from human peritoneal dialysate were made using supercritical fluid chromatography coupled to flame ionization detection to determine the quantity of this factor in half of a purified preparation of the factor compared to the bioactivity of the other half in different assays. Ouabain was used for comparison. The labile factor appeared to be 30 times more effective than ouabain against canine renal [Na,K]ATPase. Moreover, this same factor appeared to be similar to 1,000 times more potent than ouabain in causing vascular smooth muscle contraction. The differences between this labile sodium pump inhibitor and ouabain most likely reflect their respective binding affinities. The assay differences in half maximal response to the labile sodium pump inhibitor may be due to differences in sodium pump alpha isoform sensitivity.

Enantiomers of disopyramide display different biological actions, and therefore chiral selective analysis is necessary. Fifteen different cyclodextrins (CDs) and CD derivatives were tested as capillary electrophoresis (CE) additives for the chiral separation of disopyramide. Eleven types of CDs showed chiral recognition features and four types had a baseline or close to baseline separation. The best resolution (Rs = 3.0) was with 15 mM carboxymethylated β‐CD (pH 4.9). A sharp decrease in the selectivity of γ‐phosphate (γ‐PhoCD) was observed in the pH range of 2–3, indicating a structural change of γ‐PhoCD. The enantiomers of disopyramide were separated in its ionized as well as neutral forms using acidic substituted CDs. The results show that the size of the CD cavity can not be used as a guide to estimate chiral separations, suggesting a more complex separation mechanism of these CDs towars disopyramide.

The study describes the use of α, β, and γ phosphated cyclodextrins (CDs) for chiral separation by capillary electrophoresis (CE). A systematic study was performed to establish the effect of such variables as the type and concentration of chiral selectors as well as the pH and ionic strength of buffer and organic modifiers. It was found that CDs with acidic character offer high chiral selectivity toward basic compounds. These CDs can give chiral recognition features toward molecules in their ionized as well as in their undissociated form. The phosphated cyclodextrins were also found to have adsorptive properties resulting in mixed-migration mechanism, and some guidelines are given to avoid this side effect. A number of racemic drug molecules were used as model compounds to demonstrate optimization procedures of the competing parameters in the analysis. © 1997 John Wiley & Sons, Inc. J Micro Sep 9: 581–589, 1997

Six different cyclodextrins with varying cavity size and rim substitution were used as chiral agents for the enantiomeric separation of eight chromane compounds or analogues using capillary electrophoresis. It is shown that the cyclodextrin type and concentration have a large influence on the enantiomeric separation obtained for these compounds. A chiral resolution of 1.4 or better could be obtained for all the substances with either substituted heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin or unsubstituted γ-cyclodextrin as the chiral selector. The influence of the γ-cyclodextrin concentration, ionic strength and pH on the chiral separations was also investigated with a multivariate screening design. The detection limit and resolution of the present method allow determinations of the investigated compounds down to a chiral impurity of less than 0.1 % (area/area).

The acidic, phosphate substituted cyclodextrins (CD)s are excellent chiral selective agents for several neutral and positively charged molecules in CE. They are multimodal chiral selectors, and useful in a broad pH (2-9) range. Organic modifiers can drastically influence their selectivity in various ways. A good chiral separation is a result of compromise among various analysis parameters.

Summary  In this paper, polymeric hollow fibers prepared from pH-stable polypropylene were used as columns for micellar electrokinetic capillary chromatography (MECC). The electroosmotic flow (EOF) for polypropylene hollow fibers was evaluated in the pH range of 5.0–12.0. With untreated polypropylene hollow fibers a stabilized but enhanced EOF was achieved when SDS was used in the buffer, decreasing the separation window for uncharged substances in MECC to impractical levels. Uncharged acrylamide and charged 2-acryloylamido-2-methylpropane sulfonic acid surface modifications were used to lower the strength of the EOF, increase the separation window and prevent local overheating that could melt the column wall.

Supercritical fluid chromatography is an attractive alternative for chiral separations of compounds which are not readily analyzed by gas chromatography. It offers fast separations, high-efficiency, low-temperature analysis and access to a wide range of detectors including the “universal’ flame ionization detector. In this article the state of the art is reviewed. The technique is compared with other chromatographic techniques and the applicability of different chiral stationary phases as well as the choice of experimental conditions is discussed.

In this study, several new stationary phases were characterized by principal component analysis. Fourteen new stationary phases, including substituted phenyl and oligoethyleneoxide functionalities on polysiloxane polymers, were tested and compared to three well known stationary phases. The main features of these phases were studied using a series of test solutes of varying chemical characteristics representing the data set for principal component analysis. Two principal compounds were found to account for 99.20% of the variance (the first accounted for 94.96% and the second for 4.24%). The data were represented as a two-dimensional map for visual representation of the characteristics of these stationary phases. The first principal component represented a selectivity based on polarity (r2=0.998), while the second showed Lewis acid-base characteristics of the phases. Polarizable and amphoteric characteristics of these phases also became evident using this evaluation method.

Carboranylalanine, the o-carborane analogue of phenylalanine, is a potential candidate for boron neutron capture therapy of cancer. In this paper a method is described for the determination of enantiomeric purity of (S)-carboranylalanine as the (N-trifluoroacetyl)propylester using open tubular column supercritical fluid chromatography with a chiral stationary phase consisting of permethyl-beta-cyclodextrin methyloctylsiloxane.

A new UV-absorption detector cell for on-column detection in open tubular column liquid chromatography was evaluated. Optical fibers and quick-fit connections were employed for flexibility and ease in alignment and mounting in an oven for high temperature detection. Different optical fiber diameters were evaluated for 50 mum i.d. capillary columns. The best combination of optical fibers (200 mum source and collector) resulted in a detection limit of 2 x 10(-6) M for acetophenone. No dramatic change in the signal-to-noise ratio was found when the temperature was raised to 150-degrees-C.