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PubMed2002

Determination of total cholesterol content in food by flow injection analysis with immobilized cholesterol oxidase enzyme reactor.

A new analytical method has been developed--including a new sample preparation procedure--for the automatic determination of total (free and bound) cholesterol in food by flow injection analysis (FIA) with immobilized (cholesterol oxidase) enzyme reactor (IMMER). A suitable sample preparation procedure has been applied to eliminate the problems derived from sensitivity of FIA equipment to common organic solvents used for dissolving of cholesterol: after direct saponification the non-saponificable fraction was dissolved in water phase detergent (sodium cholate) solution. The analytical method is based on the oxidation by cholesterol oxidase followed by the photometric determination of hydrogen peroxide (at 500 nm) using the indicator reaction with peroxidase. The new FIA method was tested for commercial food samples such as whole egg powder and dried pasta. The results were compared with data obtained by GC-determination. It was found that this new procedure is suitable for rapid automated measurement of total cholesterol content in foodstuff and consequently, the FIA technique with immobilized enzyme reactor could be an alternative to the widely used gas-chromatographic (GC) method.

Cholesterol↗

PubMed2000

Separation of naphthalene-2,3-dicarboxaldehyde-derivatized-substance P and its metabolites by micellar electrokinetic chromatography.

This paper describes the development of analytical methodology for the separation of naphthalene-2,3-dicarboxaldehyde (NDA)-derivatized substance P (CBI-SP) and five lysine-containing metabolites by micellar electrokinetic chromatography (MEKC). The effect of surfactant composition and organic modifiers on the separation was investigated. The final separation buffer consisted of 80 mM sodium cholate in 50 mM N-tris (hydroxymethyl)methyl-2-aminoethanesulfonic acid (TES), pH 7. All six lysine-containing peptides were separated under these conditions.

Amino Acid Sequence↗

PubMed2001

Separation of neutral compounds by microemulsion electrokinetic chromatography: fundamental studies on selectivity.

The selectivity of microemulsion electrokinetic chromatography (MEEKC) was studied utilizing some uncharged model compounds like aromatic amides, steroids, and esters of nicotinic acid. The cosurfactant of the microemulsion was found to be the most important factor affecting the selectivity, and alteration between 6.6% of 1-propanol, 1-butanol, tetrahydrofuran, and 2-ethoxyethanol caused several substantial changes in the migration order. In addition, the nature of the surfactant was found to significantly affect the selectivity. In this case, changes in order of migration was observed by replacement of half the content of sodium dodecyl sulfate (SDS) with either sodium dioctyl sulfosuccinate (SDOSS), 3-(N,N-dimethylmyristylammonio) propanesulfonate (MAPS), polyoxyethylene sorbitan monolaurate (Tween 21), and polyoxyethylene 23 lauryl ether (Brij 35). MEEKC was also accomplished with 3.3% of the anionic surfactant sodium cholate and with the cationic surfactant N-cetyl-N,N,N-trimethylammonium bromide (CTMA). Both provided substantial differences in selectivity as compared to the SDS-based systems. With SDS as surfacant, the concentration was varied within 1.0-4.5%. Minor selectivity changes were observed as the concentration of the surfacant was reduced, but the major effect was a reduction in the total migration time. The organic solvent of the microemulsion droplets was found only to have minor impact on the selectivity.

Chromatography↗

PubMed2002

Chiral separation of benzoporphyrin derivative mono- and diacids by laser induced fluorescence-capillary electrophoresis.

A method for the separation of benzoporphyrin derivative mono- and diacid (BPDMA, BPDDA) enantiomers by laser induced fluorescence-capillary electrophoresis (LIF-CE) has been developed. By using 300 mM borate buffer, pH 9.2, 25 mM sodium cholate and 10% acetronitrile as electrolyte, +10 kV electrokinetic sampling injection of 2 s and an applied +20 kV voltage across the ends of a 37 cm capillary (30 cm to the detector, 50 microm ID), all six BPD stereoisomers were baseline-separated within 20 min. Formation constants, free electrophoretic and complexation mobilities with borate and cholate were determined based on dynamic complexation capillary electrophoresis theory. The BPD enantiomers can be quantitatively determined in the range of 10(-2)-10(-5) mg mL(-1). The correlation coefficients (r2) of the least-squares linear regression analysis of the BPD enantiomers are in the range of 0.9914-0.9997. Their limits of detection are 2.18-3.5 x 10(-3) mg mL(-1). The relative standard deviations for the separation were 2.90-4.64% (n = 10). In comparison with high-performance liquid chromatography (HPLC), CE has better resolution and efficiency. This separation method was successfully applied to the BPD enantiomers obtained from a matrix of bovine serum and from liposomally formulated material as well as from studies with rat, dog and human microsomes.

Animals↗

PubMed1993

On the interaction of polypeptides with bile salts or bilirubin-IX alpha.

Aqueous solutions formed by polypeptides, simple models of proteins, and bile salts (sodium cholate and deoxycholate, NaC and NaDC, respectively) or bilirubin-IX alpha (BR) have been studied by CD measurements. They could mimic more complicated biliary systems, thus supplying a possible interpretation of the behavior of some amino acid residues in the biliary proteins. The aggregation of NaDC and NaC in water can be monitored by CD measurements. Bile salts, in submicellar and micellar form, stabilize poly(L-Lys) (PLL) in alpha-helical conformation. The alpha-helix content increases with increasing bile salt concentration and ionic strength. NaDC seems to be a slightly better stabilizing agent of the alpha-helix conformation than NaC. Models characterized by hydrogen bonds between bile salts and PLL are proposed, also resorting to previous data available on the systems formed by NaDC and poly(L-Leu-L-Leu-L-Lys) (PLLL) or poly(L-Leu-L-Leu-L-Asp) (PLLA). Binding of BR to PLL, poly(D-Lys), poly(L-Glu), PLLL, and PLLA in water has been investigated by CD spectra in order to clarify the nature of the association complexes and the mechanism of the BR enantioselective complexation. Potential energy calculations provide binding models capable of explaining the enantioselective ability of the PLL and PLLL alpha-helices toward the left- and right-handed enantiomer of BR, respectively. BR is bound to -NH2 groups of PLL and PLLL lying on a right- and left-handed spiral, respectively. These results, together with those formerly obtained for some bile salts-BR systems, indicate that the selectivity originates from a binding that involves large regions of the BR molecule and gives rise, very probably, to moderate conformational changes from the "ridge tile" structure observed in the crystals. In some cases van der Waals forces can play a crucial role in the chiral recognition of bilirubin. Moreover, possible interaction models of BR with human serum albumin are proposed on the basis of a recent x-ray crystal structure of the protein.

Amino Acid Sequence↗

PubMed1979

In vitro dissolution of human gallstones: the efficacy of heparinized solutions.

The use of heparinized solutions to dissolve or fragment stones retained in the biliary tree after surgery is still controversial. In this in vitro study heparin in concentrations of up to 100,000 mu/l did not dissolve or fragment the stones examined, nor did it enhance the dissolution properties of the bile salt, sodium cholate.

Cholelithiasis↗

PubMed2005

Separation and determination of active components in Schisandra chinensis Baill. and its medicinal preparations by non-aqueous capillary electrophoresis.

A simple, economical and effective non-aqueous capillary electrophoresis separation and detection method was developed for the quantification of deoxyschizandrin and gamma-schizandrin in Schisandra chinensis Baill. and its medicinal preparations for the first time. After optimization of separation conditions, a buffer of 140 mmol/L sodium cholate in methanol was selected for separating the two analytes, but baseline separation of SA and SB in real samples was not obtained. Therefore second-order derivative electropherograms were applied for resolving overlapping peaks. Regression equations revealed good linear relationships (correlation coefficients 0.9975--0.9988) between peak heights in second-order derivative electropherograms and concentrations of the two analytes. The relative standard deviations (RSD) of the migration times and the peak height of the two constituents were in the ranges 0.62--0.79% and 0.25--2.17% (intra-day) and 1.43--2.06 and 4.08--5.72% (inter-day), respectively. The recoveries of the two constituents ranged from 93.2 to 103.0%. The results indicated that baseline separation of the analytes was sometimes hard to obtain in real samples and second-order derivative electropherograms were applicable for the resolution and analysis of overlapping peaks.

Cyclooctanes↗

PubMed1997

Separation of fungicides by micellar electrokinetic capillary chromatography.

Capillary electrophoresis with ultraviolet detection (CE/UV) of selected fungicides (carbendazim, metalaxyl, propiconazole, and vinclozolin) using different buffer compositions was investigated. Capillary zone electrophoresis (CZE) with 10 mM sodium phosphate (pH 7.0) was not useful in separating the four fungicides used in this study. However, the four fungicides were well resolved by employing micellar electrokinetic capillary chromatography (MEKC). Among the two surfactants tested in MEKC, bile salts provided better separation compared to sodium dodecyl sulfate (SDS). A buffer consisting of 10 mM sodium phosphate with 100 mM sodium cholate and 10% methanol (pH 7.0) gave best results; excellent separation of the four compounds was achieved in less than 15 min. The CE/UV method was validated by analyzing deionized and lake-water samples fortified with known concentrations for the four fungicides. Average recoveries of the fungicides in lake water of 4 micrograms/L level ranged from 42 to 87%.

Alanine↗

PubMed1997

Capillary electrophoretic detection of metabolites in the urine of patients receiving hypoglycemic drug therapy.

Micellar electrokinetic chromatography (MEKC) in tandem with diode array detection (DAD) has been exploited as an analytical method for the separation and detection of sulfonylurea drugs. The ultimate goal is the development of an assay to detect these drugs or their metabolites in urine as a means of diagnosing sulfonylurea drug abuse. Using a separation buffer consisting of 5 mM borate/5 mM phosphate/75 mM sodium cholate, separation of both the second and third generation sulfonylurea drugs can be achieved. The characteristic absorbance spectra associated with each of the third generation drugs, glipizide and glyburide, allow for their identification in mixtures. Coinjection of glyburide, its primary metabolite, hydroxy glyburide, and glipizide demonstrated that the metabolite was resolved from the parent drug but shared its absorbance spectral properties. MEKC analysis of a series of solid phase-extracted urine samples from patients prescribed glipizide or glyburide, as well as from control patients not ingesting the drug, showed that the parent compounds were difficult to detect in the urine. However, the use of DAD allowed for detection of metabolites in the urine of these patients. With glyburide patients, only primary metabolites were detected, while urine from patients on glipizide showed a series of peaks whose absorbance spectra was consistent with the presence of both primary and secondary metabolites. In addition, the intensity of the metabolite peaks corresponded reasonably well with the respective dose and in vivo time interval associated with the urine collection. This study shows that MEKC with DAD has potential for further exploration as a clinical assay for detecting surreptitious abuse of sulfonylurea drugs.

Electrophoresis, Capillary↗

PubMed1998

On-line partial filling micellar electrokinetic capillary chromatography-electrospray ionization-mass spectrometry of corticosteroids.

The one-line combination of micellar electrokinetic chromatography (MECC) with electrospray ionization-mass spectrometry (ESI-MS) was investigated using some corticosteroids as model components. The on-line technique is difficult because the micelles in the electrolyte solution tend to soil the mass spectrometer and lower the sensitivity of the spectrometer. To prevent the micelles from reaching the mass spectrometer, several techniques have been developed among which is the partial filling (PF) technique. In this study the PF-MECC technique was investigated in an on-line MECC-ESI-MS study of mixtures of corticosteroids. Because the compounds are uncharged, partitioning or interaction with micelles is required to achieve separation. Surfactant solutions of sodium dodecyl sulfate (SDS), sodium cholate (SC), and SDS/SC mixtures were used as micellar phase. Good MECC separation was achieved after optimization of the surfactant concentrations and the length of the injected micellar plug. Both hydrodynamic and electrokinetic injections of the micellar solutions were tested. A basic ammonium acetate solution was used as the CE electrolyte solution. The ESI-MS analysis of the compounds was performed in the positive ionization mode, using an acidic sheath liquid. Because of the low MS intensities of the corticosteroids, the peaks were isolated during the MS runs. MS-MS and MS-MS-MS data on the corticosteroids were obtained by off-line injection of the compounds.

Adrenal Cortex Hormones↗

PubMed2004

Separation and determination of biphenyl nitrile compounds by microemulsion electrokinetic chromatography with mixed surfactants.

A mixture of six biphenyl nitrile compounds and three related substances with high hydrophobicity and similar structures was successfully separated by microemulsion electrokinetic chromatography (MEEKC) within 30 min. The microemulsion system contained 100 mM sodium dodecyl sulfate (SDS), 80 mM sodium cholate (SC), 0.81% v/v heptane, 7.5% v/v n-butanol, 10% v/v acetonitrile, and 10 mM borate. The addition of SC, organic modifiers, sample preparation, and temperature all showed remarkable effects on the separation. The capacity factor (k) was calculated by using dodecyl benzene as the marker for microemulsion, and the calculated partition coefficient log P(o/w) of the solutes was in the range of 3.35-7.38. The log k values matched well with the log P(o/w) with a correlation coefficient of 0.96. In addition, the linear correlation coefficients of each compound between peak area and concentration were from 0.996 to 0.998 with the repeatability RSD value < 1.2% for migration time and < 4.8% for peak area, and the highest theoretic plate number was > 586000. MEEKC was compared with micellar electrokinetic chromatography (MEKC) indicating that the former method is more suitable for this separation and can be used for the quality control of biphenyl nitrile compounds in the synthesis of liquid crystals.

Biphenyl Compounds↗

PubMed2003

Mixed micellar electrokinetic capillary chromatography separation of depolymerized grape procyanidins.

Oligomeric procyanidins are potent antioxidant polyphenols of potential interest as disease-preventing agents. Their efficiency depends on the size and composition of their oligomeric structures. The mean degree of polymerization of these compounds is usually estimated by thiolysis with thiol-alpha-toluene followed by analysis using high-performance liquid chromatography (HPLC). We show the development of a mixed micellar electrokinetic chromatography (MEKC) method for the separation of the major components obtained after thiolysis with cysteamine (catechins and their cysteamine conjugates). MEKC studies using sodium dodecyl sulfate (SDS as pseudostationary phase led to long migration times, e.g., with 100 mM SDS, at pH 7, the solutes were separated in about 40 min), while the use of sodium cholate (SC) produced an elution window relatively short. Using a mixed micellar SC-SDS system (50 mM phosphate at pH 7 containing 40 mM SC and 10 mM SDS), it is possible to separate these compounds in less than 15 min. The proposed method is useful to separate the major components of the thiolysate in effluents from food processing (e.g., skins and seeds from grape and apple) considered as potential procyanidin sources.

Biflavonoids↗

PubMed2003

Comparison of the retention characteristics of different pseudostationary phases for microemulsion and micellar electrokinetic chromatography of betamethasone and derivatives.

Five electrokinetic chromatography systems were compared concerning retention behavior and lipophilicity. Comparison was based on capacity (retention) factors of some steroidal drugs, and on log P(OW) values derived by the aid of reference substances. In all systems the aqueous buffer consisted of phosphate (20 mM, pH 7.5). Two systems had micelles, three systems microdroplets as negatively charged pseudostationary phases. The micelles were formed by sodium dodecyl sulfate (SDS) and sodium cholate, respectively. One microemulsion consisted (as usual) from octane as oil, butanol as cosurfactant and SDS as charged tenside. Two microemulsions were made from biosurfactants (phosphatidylcholine, isopropylmyristate) to better simulate biopartitioning of the drugs. Even for noncharged analytes a change in migration sequence and thus in log P(OW) was observed for the systems consisting of the biosurfactants, compared to the others. For the former systems, log P(OW) derived from the capacity factors agree for all analytes with those obtained from calculation by computer software based on the structure of the drugs, and with experimental data directly obtained from octanol/water partitioning.

Betamethasone↗

PubMed2005

Microemulsion and micellar electrokinetic chromatography of Hematoporphyrin D: a starting material of hematoporphyrin derivative.

An investigation of the basic factors which govern the microemulsion electrokinetic chromatography (MEEKC) and micellar electrokinetic chromatography (MEKC) separation of Hematoporphyrin D and its base hydrolysis product, hematoporphyrin derivative (HpD), was performed. These model compounds contain a complex mixture of porphyrin monomers, dimers and/or oligomers, and were utilized to gain insights into the MEEKC/micellar electrokinetic chromatography (MEKC) separation of samples containing highly lipophilic substances. For example, the organic modifier/cosurfactant (1-butanol) and/or oil phase (e.g., 1-octanol in comparison to ethyl acetate) were found to have an apparent influence on the separation selectivity of Hematoporphyrin D, the extent of which was dependent on the chemical nature of the surfactant employed (e.g., sodium dodecyl sulfate vs. sodium cholate). An interesting and important finding was that the presence of an organic modifier (methanol or acetonitrile at a concentration of 20% or higher) in the sample matrix as well as in the run buffer was essential for the optimal MEEKC or MEKC separation of a number of porphyrin monomers (including hematoporphyrin IX and its acetates, most likely hydroxyacetate, diacetate, and vinyl acetate, as well as its dehydration products, hydroxyethylvinyldeuteroporphyrin and protoporphyrin) contained in Hematoporphyrin D. On the other hand, the use of these optimized conditions for the MEEKC or MEKC separation of various oligomeric porphyrin species in HpD were unsatisfactory. As HpD is a well-known and effective photosensitizing agent in photodynamic therapy (a new approach for cancer treatment), the improved separation and characterization of various monomeric and oligomeric porphyrin species in HpD and its starting material, such as Hematoporphyrin D, is a challenging and important task.

1-Butanol↗

PubMed2005

Amino acid analysis by micellar electrokinetic chromatography with laser-induced fluorescence detection: application to nanolitre-volume biological samples from Arabidopsis thaliana and Myzus persicae.

Amino acids were derivatised with 4-fluoro-7-nitrobenzo-2,1,3-oxadiazol (NBD-F), separated by micellar electrokinetic chromatography (MEKC), and detected by argon-ion (488 nm) laser-induced fluorescence. The optimised MEKC background electrolyte conditions were: 40 mM sodium cholate, 5 mM beta-cyclodextrin in 20 mM aqueous borate buffer, pH 9.1, with 7% v/v acetonitrile. Using these conditions, 19 amino acids were separated within 17 min. The limits of detection were in the range of 7.6-42.2 pmol/mL and limits of quantitation from 0.05-0.14 nmol/mL. The method was systematically validated for injection volume error, migration time variation, calibration linearity, accuracy, precision, and recovery. Nanolitre volume samples of phloem sap of individual sieve element cells from the plant Arabidopsis thaliana and honeydew from the aphid Myzus persicae were directly analysed with this method. Quantitative amino acid concentrations in these two biological matrices were profiled for the first time. This method is particularly important because it allows the complete profile of the amino acids obtained from individual phloem elements, allowing cell to cell and plant to plant variation to be quantified, which to date has not been possible with Arabidopsis thaliana.

4-Chloro-7-nitrobenzofurazan↗

PubMed2007

A dynamic molecular probe to investigate catalytic effects and Joule heating in enantioselective MEKC.

Enantiomerization of ferroin [tris(1,10-phenanthroline)-iron(II)-complex] was investigated by enantioselective dynamic micellar EKC. The enantiomer separation was performed in an aqueous 50 mM sodium borate/sodium dihydrogenphosphate buffer at pH 8.0 in the presence of the chiral surfactant sodium cholate. The unified equation of dynamic chromatography was employed to determine reaction rate constants from the electropherograms featured with distinct plateau formation. Activation parameters DeltaH( not equal) = 124.0 +/- 0.5 kJ/mol and DeltaS( not equal) = 121 +/- 1 J.K(-1)mol(-1) were calculated from temperature-dependent measurements between 10.0 and 27.5 degrees C in 2.5 K steps. Considering the data obtained by polarimetry of enantiomeric pure ferroin in water, it was found that enantiomerization rate in the micelle is accelerated by a factor of 12. Because of the highly positive activation entropy DeltaS( not equal), ferroin was used as a temperature-sensitive dynamic molecular probe to determine temperature deviations caused by Joule heating.

Catalysis↗

PubMedDate not supplied

Kinetics and thermodynamics of dissolution of lecithin by bile salts.

The kinetics of dissolution of dispersions of egg phosphatidylcholine (lecithin) by bile salts was studied by observing the decrease in turbidity as mixed micelles of lecithin and bile salts were formed. The rate of dissolution of lecithin corresponding to formation of mixed micelles was studied in the presence of dihydroxy bile salts, sodium deoxycholate, sodium chenodeoxycholate, sodium ursodeoxycholate and one trihydroxy bile salt, sodium cholate. The rate of dissolution of lecithin and mixed micelle formation decreased in the order: chenodeoxycholate greater than deoxycholate greater than cholate greater than ursodeoxycholate. Kinetic solvent isotope studies in D2O, along with measurement of enthalpies of mixed micelle formation both in H2O and D2O, suggest that formation and stabilization of mixed micelles are related to "hydrophobicity" as estimated by high performance liquid chromatography retention factors.

Bile Acids and Salts↗

PubMedDate not supplied

Liquid crystalline phase formation by cholesterol in aqueous fatty acid salt solutions.

The interaction of cholesterol with fatty acid salt solutions was investigated as a potential method for gallstone dissolution. In the presence of sodium oleate or laurate, crystalline cholesterol was rapidly converted into a lamellar liquid crystalline phase. Analysis of the mesophase showed that it contained approximately equimolar amounts of the lipid components, although water was the major constituent. The rate of conversion of cholesterol to mesophase was determined from a compressed disc immersed in a stirred solution, as if it were a simple dissolution process. The apparent rate of solubilization was independent of oleate concentration in the 2.5 to 10% range and was approximately 200 times faster than micellar dissolution of cholesterol in 5% sodium cholate. A mechanism is proposed in which the rate-limiting step in mesophase formation is dispersion of liquid crystalline fragments into the bulk medium.

Cholesterol↗