Capillary electrophoretic separation of tricyclic antidepressants using charged carboxymethyl-beta-cyclodextrin as a buffer additive.

Charged carboxymethyl-beta-cyclodextrin was successful in the capillary electrophoretic separation of a series of tricyclic antidepressants. The cyclodextrin alone was successful in the separation of carbamazepine, protriptyline, desipramine, clomipramine, and opipramol using a 3-(trimethoxysilyl)propyl methacrylate capillary coating to reduce the electroosmotic flow. The ideal buffer pH was found to be in the range of 6-7 and the ideal cyclodextrin concentration to be 10 mM. All nine antidepressants were resolved using the charged cyclodextrin in the micellar electrokinetic chromatography (MEKC) mode with sodium dodecyl sulfate as the surfactant. Neither the cyclodextrin nor the surfactant alone were successful in resolving the whole series of compounds under investigation but a combination of both produced the separation. Separations were performed on a linear polyacrylamide coated capillary. The ideal pH of the buffer was in the range of 5-7.

Bile acid measurements using a cholestyramine-coated TSM acoustic wave sensor.

A novel chemical sensor for bile acids is described. A 10-MHz piezoelectric crystal operating in the thickness-shear mode (TSM) is coated on one side with cholestyramine resin and mounted in a batch-mode sensor block which exposes the coating to solution. After sample injection, the binding process is observed in real time as a drop in frequency as the bile salt binds to the coating, reaching > 90% completion within 10 min with most of the binding occurring within the first minute. Linear calibration curves are generated with sensitivity increasing in the order cholate approximately glycocholate < taurocholate < < taurodeoxycholate. Detection limits in water are in the range 0.2-9 nmol and are better than those observed in phosphate buffer. A multistep regeneration protocol allows the coating to be reused more than 400 times over a period of several months. Precision for replicate injections is approximately 10% RSD and depends on the reproducibility of the regeneration and injection steps. In terms of the binding process, hydrophobic interactions are observed to be of importance in the ability of bile salts to displace other counterions. However, anions with greater charge density also appear to compete effectively for binding sites on the resin. In particular, at equimolar concentrations of citrate and bile salt, the trivalent citrate anion reduces the amount of bile salt binding by approximately 40%. This suggests that the efficiency of cholestyramine-based bile salt sequestering drugs used in the reduction of hypercholesterolemia may be improved by eliminating citric acid as an excipient and avoiding the use of fruit juices during ingestion.

Chromatographic techniques for the isolation and purification of lipoproteins.

Various modes of chromatography are available for lipoprotein separation. Gel permeation and affinity chromatography are used for preparative purposes and to separate lipoproteins according to size and apolipoprotein content, respectively. Development of rigid supports for gel permeation has led to large improvements in speed and resolution. Reversed-phase high-performance liquid chromatography (HPLC) of apolipoproteins offers the best performance in terms of speed and resolution of structural variants. Due to its high speed and superior resolving power, the recently developed technique of capillary electrophoresis should emerge as an important method for lipoprotein analysis.

Capillary electrophoretic resolution of phosphorylated peptide isomers using micellar solutions and coated capillaries.

The addition of sodium dodecyl sulfate (SDS) micelles in the running buffer can be used to resolve mono- and diphosphorylated isomers of the insulin receptor peptide by capillary electrophoresis. The effect of SDS on peptide resolution is very dependent on pH. Complete resolution of three monophosphorylated isomers is achieved in uncoated capillaries filled with phosphate buffer containing 25 mM SDS and buffered at pH 6.1. Resolution of the diphosphorylated isomers can be significantly improved by using polyacrylamide coated capillaries. In coated capillaries electroosmotic flow is negligible and the migration order of the isomers is reversed. This allows for a longer period of interaction between the diphosphorylated isomers and the micelle and therefore selectivity is improved. Efficiency of all peptide isomers was also improved in coated capillaries due to reduced adsorption to the capillary wall.

Capillary electrophoretic separation of nucleotide isomers via complexation with cyclodextrin and borate.

The electrophoretic behaviour of monophosphorylated nucleotide isomers can be manipulated using complex-forming reactions with beta-cyclodextrin (beta-CD) and borate. Resolution of the 2'- and 3'-isomers of nucleotides is possible when the electrophoresis buffer contains 10 mM CD. The effect of beta-CD concentration on electrophoretic mobility is used to calculate the formation constant, K, of beta-CD-nucleotide complexes. The 3'-isomer of adenosine monophosphate (AMP) forms the strongest complex with beta-CD probably as a result of hydrogen bonding between the phosphate group of AMP and hydroxyls of beta-CD. In addition, complexation of 5'-nucleotides with borate increases the migration time window and leads to better separation. Complex-forming reactions of guanosine monophosphate and uridine monophosphate are shown to be strongly dependent on buffer pH. A mixture of 12 monophosphorylated nucleotides can be separated in less than 15 min using a buffer of 20 mM borate-10 mM beta-CD.

Effect of detergents on the electrophoretic behaviour of plasma apolipoproteins in capillary electrophoresis.

The influence of various detergents on the capillary electrophoretic behaviour of plasma apolipoproteins was studied. Electrophoretic mobility increased in the presence of anionic detergents sodium deoxycholate (DOC) and sodium dodecyl sulfate (SDS), and decreased in the presence of non-ionic Triton X-100. Apolipoproteins from plasma low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs) exhibited different affinities for DOC and SDS. Optimal separation and reproducibility of HDL and LDL apolipoproteins was obtained using high-pH buffers containing SDS. Good resolution of very-low-density lipoprotein (VLDL) apolipoproteins was obtained on addition of either SDS or cetyl trimethylammonium bromide to the running buffer. For VLDL apolipoproteins the use of polyacrylamide coated capillaries yielded better results.

Characterization of plasma apolipoproteins by capillary electrophoresis.

The main apolipoproteins of plasma high-density lipoproteins (HDL) and low-density lipoproteins (LDL) were analyzed by capillary electrophoresis. Where possible the results were compared with slab sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Addition of the detergent SDS to the running buffer was essential for separation. Separations were carried out in bare silica and polyacrylamide-coated capillaries. The main apolipoproteins of HDL could be separated in an uncoated capillary filled with borax buffer containing 0.1% SDS. Using the coated capillary, a mixture of HDL and LDL apolipoproteins was resolved in less than 12 min. These preliminary studies indicate that capillary electrophoresis is a promising technique for screening plasma apolipoproteins.

A rapid separation of alpha- and beta-lipoproteins by affinity chromatography.

A rapid and inexpensive separation of alpha- and beta-lipoproteins has been achieved using sulfated dextran beads as an affinity chromatography medium. The separation is completed in less than 15 min and the cholesterol content of the lipoprotein fractions can then be determined in a separate procedure.

Preparation of heparin-glyceryl controlled-pore glass affinity media for the separation of alpha- and beta-lipoproteins.

The preparation of a stable affinity medium with heparin as the affinity ligand has been investigated. Glyceryl controlled-pore glass (CPG) was activated with 1-cyano-4-dimethylaminopyridinium tetrafluoroborate and coupled with heparin. This affinity medium was used to separate some simple proteins, trypsinogen and lysozyme, in a high-performance liquid chromatographic configuration. The heparin-glyceryl-CPG was also used to separate alpha- and beta-lipoproteins in human serum. The effectiveness of the separation is confirmed by radial immunodiffusion and the determination of the cholesterol content of each of the separated fractions.

Liquid chromatographic separation of phenothiazines and structurally-related drugs using a beta-cyclodextrin bonded phase column.

The retention behaviour of 16 phenothiazines and structurally-related drugs on a beta-cyclodextrin bonded phase column is examined with respect to pH, methanol and TEAA concentrations in the mobile phase, and column temperature. The results are utilized to optimize the separation of these compounds. Both isocratic and gradient-elution separation of the 16 phenothiazine derivatives on the beta-cyclodextrin bonded phase column are investigated. The successful separation of all of the compounds is achieved in the gradient-elution mode.

Liquid chromatographic retention behavior and separation of chlorophenols on a beta-cyclodextrin bonded-phase column, Part I. Monoaromatic chlorophenols: retention behavior.

The liquid chromatographic retention behavior of nineteen monoaromatic chlorophenols on a beta-cyclodextrin bonded-phase column is investigated with respect to mobile phase composition, pH, temperature, and ionic strength. The mechanistic aspects of retention of these compounds on the beta-cyclodextrin column are studied and compared to other reversed-phase columns. Most of the evidence suggests that the unique selectivity of this column is due to inclusion complex formation, which provides the physical basis for the resolution of positional isomers. Under certain chromatographic conditions, however, the more highly chlorinated congeners appear to be excluded from the cyclodextrin cavity; in such cases a normal-phase chromatographic mechanism is postulated, based on the interaction of the substrates with the secondary hydroxyls on the periphery of the cyclodextrin moieties.

Liquid chromatographic retention behavior and separation of chlorophenols on a beta-cyclodextrin bonded-phase column, Part II. Monoaromatic chlorophenols: separation.

The liquid chromatographic separation of 19 monoaromatic chlorophenols on a beta-cyclodextrin bonded-phase column is investigated in both an isocratic and a gradient elution mode. Even though the isocratic mode can be employed for the separation of the member components of each category of chlorophenols (e.g., mono-, di-, etc.), significant overlaps between the retention times of the various categories prevent the separation of all chlorophenols on a single chromatogram. Gradient elution can be used, however, for the separation of 15 of the 19 chlorophenol isomers. The unique features of gradient elution as applied to beta-cyclodextrin bonded-phase columns are discussed. The detection of chlorophenols with UV and electrochemical methods is also discussed and the two are compared.

Investigation of materials for making a carbon-support zinc-selective electrode.

The usefulness of zinc orthophosphate and zinc mercuric thiocyanate to make a carbon-support electrode responsive to zinc was investigated. The best results were obtained with zinc orthophosphate, which produced a Nernstian response to zinc in the concentration range from 10(-5) to 10(-2)M. The electrode response was lowered by the formation of acidic oxides on the surface of the electrode. Different ways of minimizing this problem are discussed. Interference effects from copper(II) (K(pot)(Zn.Cu) = 1.0), cadmium (K(pot)(Zn.Cd) = 8.9) and lead (K(pot)(Zn.Pb) = 10) were observed.

The effect of carbidopa and benserazide on human plasma 5-hydroxytryptophan levels.

Peripheral aromatic amino acid decarboxylase inhibitors increase human plasma 5-hydroxytryptophan (5-HTP) levels. However the 5-HTP, which is synthesized in the intestine, is not present in a sufficient quantity to influence brain 5-HT to any significant degree. Thus, peripheral decarboxylase inhibitors are unlikely to affect brain 5-HT function via 5-HTP which is synthesized peripherally.

The AAS determination of copper and zinc levels in the serum of hemodialysis patients.

An electrothermal atomic absorption technique for the determination of subnanogram amounts of copper and zinc in aqueous and blood serum matrices has been evaluated. The technique has been utilized to study the effect of dialysis (artificial kidney) on the levels of these trace elements in the serum of hemodialysis patients. The present results confirm a previous study (1) which was conducted on representative samples that were taken from the continuous flow of the dialysis fluid (dialysate). Matrix effects have been minimized by using serum controls (obtained from a pool made of the tested serum samples), small sample size, and background correction. Before dialysis, values of copper for patients who were dialysed against tap water (tap-water patients) and distilled water (distilled-water patients) were: (mean +/- SD) 1297 +/- 59 and 1064 +/- 137 micrograms/L, respectively; after dialysis: 1539 +/- 98 and 1120 +/- 129 micrograms/L, respectively. Zinc levels were less affected by the dialysis process; before dialysis: tap-water patients, 952 +/- 131 micrograms/L; distilled-water patients, 932 +/- 119 micrograms/L; after dialysis: 1001 +/- 137 micrograms/L, and 934 +/- 121 micrograms/L, respectively. Because the method is sensitive, accurate, and precise, it can be utilized to study trace levels of copper and zinc in serum when limitations of sample volume exist as in the present case or with pediatric patients.

Tryptophan, 5-hydroxyindoleacetic acid and indoleacetic acid in human cerebrospinal fluid: interrelationships and the influence of age, sex, epilepsy and anticonvulsant drugs.

Tryptophan, 5-hydroxyindoleacetic acid and indoleacetic acid were measured in cerebrospinal fluid, taken during pneumoencephalography, from a large series of patients, the majority of whom were epileptics, most of them receiving anticonvulsants. CSF indoleacetic acid reflects CNS tyrptamine metabolism in the same way that CSF 5-hydroxyindoleacetic acid reflects CNS 5-hydroxytryptamine metabolism. Our data suggest that (i) the brain tryptophan content is an important factor in the control of both 5-hydroxytryptamine and tryptamine synthesis (ii) brain 5-hydroxytryptamine metabolism exhibits a U-shaped relationship with age (iii) the mean brain tryptophan content and rate of 5-hydroxytryptamine metabolism are greater for women than men (iv) indoleamine metabolism is unaffected in untreated epileptics compared with non-epileptics, but anticonvulsant drugs decrease the rate of 5-hydrosytryptamine metabolism.