Use of vancomycin silica stationary phase in packed capillary electrochromatography I. Enantiomer separation of basic compounds

Chiral separation of basic compounds was achieved by using 75 or 100 microm ID fused-silica capillaries packed with a vanoomycin-modified diol silica stationary phase. The capillary was firstly packed for about 12 cm with a slurry mixture composed of diolsilica (3:1) then with the vancomycin modified diol-silica (3:1) (23 cm), and finally with diol-silica (3:1) for about 2 cm. Frits were prepared by a heating wire at the two ends of the capillary; the detector window was prepared at 8.5 cm from the end of the capillary where vancomycin was not present. The influence of the mobile phase composition (pH and concentration, organic modifier type and concentration) on the velocity of the electroosmotic flow, chiral resolution and enantioselectivity was studied. Good enantiomeric resolution was achieved for atenolol, oxprenolol, propranolol, and venlafaxine using a mobile phase composition of 100 mM ammonium acetate solution (pH 6)/water/acetonitrile (5:5:90 v/v/v) while for terbutaline a mixture of 5:15:80 v/v/v provided the best separations. The use of methanol instead of acetonitrile caused a general increase of enantiomer resolution of the studied compounds together with a reduction of efficiency and detector response. However, the combination of acetonitrile and methanol in the mobile phase (as, e.g., 10% methanol and 80% acetonitrile) allowed to improve the enantiomer resolution with satisfactory detector response.

Separation of multicomponent mixtures of 2,4-dinitrophenyl labelled amino acids and their enantiomers by capillary zone electrophoresis

The use of capillary zone electrophoresis (CZE) for the separation of a group of 33 2,4-dinitrophenyl labeled amino acids (DNP-AA), including DNP-AA racemates, DNP-L-AA enantiomers and achiral DNP-AAs, was investigated. Alpha-, beta- and gamma-cyclodextrins (CDs) and their derivatives (hydroxypropyl derivatives of alpha-, beta- and gamma-CDs, polymeric beta-CD and 6A-methylamino-beta-cyclodextrin (MA-beta-CD)) served as complexing agents and chiral selectors in this investigation. Although native alpha- and gamma-CDs and their derivatives influenced the effective mobilities of the studied DNP-AAs in different ways, they generally failed to resolve enantiomers of the individual DNP-AAs. On the other hand, beta-CD and all of its derivatives were found to be effective in this respect. Of these, the best results were achieved with a positively charged MA-beta-CD and this chiral selector resolved enantiomers of ten DNP-AA racemates available for this study. However, a complete resolution of these enantiomers in one CZE run required that the effect of the chiral selector be complemented by complexing effects of polyvinyl pyrrolidone (PVP) or gamma-CD. Complexing and chiral recognition capabilities of MA-beta-CD combined with complexing effects of gamma-CD and PVP provided separating conditions suitable for the CZE separations of multicomponent mixtures of DNP-AAs with preserved resolutions of the enantiomers. For example, a mixture consisting of 43 DNP-AA constituents was resolved using an MA-beta-CD/gamma-CD combination with three peak overlaps.

Capillary electrochromatography and capillary electrochromatography-electrospray mass spectrometry for the separation of non-steroidal anti-inflammatory drugs

In this study capillary electrochromatography (CEC) was utilized for the separation of ten non-steroidal anti-inflammatory drugs (NSAIDs). Experiments were carried out in a commercially available CE instrument using a packed capillary with RP-18 silica particles where the stationary phase completely filled the capillary. The mobile phase consisted of a mixture of ammonium formate buffer pH 2.5 and acetonitrile. Selectivity and resolution were studied changing the pH and the concentration of the buffer, the acetonitrile content mobile phase and the capillary temperature. The optimum experimental conditions for CEC separation of the studied drug mixture were found using 50 mM ammonium formate pH 2.5-acetonitrile (40:60) at 25 degrees C. The CEC capillary was coupled to an electrospray mass spectrometer for the characterization of the NSAIDs. A mobile phase composed by the same buffer but with a higher concentration of acetonitrile (90%) was used in order to speed up the separation of analytes.

The human multidrug resistance gene (MDR-1): immunocytochemical detection of its expression in oral SCC

A large number of oral cancer patients show poor or partial response to chemotherapy and the mechanisms are poorly understood. At present, an MDR-1 product, the P-170 glycoprotein, is the best known of the P-170 family and is involved in resistance to natural product-based chemotherapeutics, including taxanes, anthracyclines, vinca alkaloids, podophyllotoxins and camptothecins. Although several reports suggest that P-170 is clinically relevant in haematological malignancies, its role in solid tumours is not well understood. Its overexpression has been found to be correlated with the poor outcome observed in patients treated with chemotherapy and presenting drug resistance. The aim of this study was to detect the protein expression patterns of MDR-1 product by immunohistochemistry in formalin-fixed-paraffin-embedded tissues. For these reasons, 30 oral SCC and 6 healthy oral mucosa specimens were tested with anti-P-170 antibodies using standard streptavidin-biotin-peroxide technique. Immunohistochemistry demonstrated that 4 cases (66.6%) of normal oral mucosa and 24 cases (80%) of oral SCC showed positivity. Four cases (13.4%) showed strong positivity in tumour areas and complete negativity in normal epithelial cells adjacent to the tumour. No staining was observed in stromal structures, with the exception of the lymphocytic compartment that showed a strong staining as reported in literature for CD56+ and CD8+ cells. Four G1 tumours (33%) and 2 G3 tumour (33%) showed strong positivity in areas with a higher degree of differentiation. P-170 positivity in normal epithelial cells of smoker patients, in differentiated area of neoplasia and negativity or zonal positivity in undifferentiated area of tumour suggested that activation of the MDR-1 gene or selection of intrinsically multidrug resistance neoplastic cells may occur at early stages of tumorigenesis of oral cancers, before the real evidence of cellular transformation. Thus the contact with possible chemical carcinogens, such as those of tobacco smoke, may induce activation of MDR-1 gene. This study was conducted only on untreated carcinomas so for this reason it cannot indicate the real incidence of acquired multidrug resistance. The data of MDR-1 product expression by immunohistochemistry in oral SCC might suggest that an overexpression of this protein could constitute a hallmark of potential more aggressive phenotype for this type of neoplasia and a rapid method for pre-screening tumours for a constitutive multidrug resistance in order to orientate the cancer treatment.

Enantiomeric separation of dihydroxyphenylalanine (DOPA), methyldihydroxyphenylalanine (MDOPA) and hydrazinomethyldihydroxyphenylalanine (CDOPA) by using capillary electrophoresis with sulfobutyl ether-beta-cyclodextrin as a chiral selector

Capillary electrophoresis (CE) was successfully applied to the enantiomer resolution of racemic structurally related compounds, namely dihydroxyphenylalanine (DOPA), methyldihydroxyphenylalanine (MDOPA) and hydrazinomethyldihydroxyphenylalanine (CDOPA). The chiral resolution was performed in an untreated fused-silica capillary by using a phosphate buffer at pH 2.5 or 3.0 supplemented with sulfobutylated beta-cyclodextrin (SBE-CD). Resolution was strongly influenced by the concentration of the chiral selector added to the background electrolyte. In fact, 2-5 mM of SBE-CD enabled the resolution of DOPA and MDOPA enantiomers, while CDOPA optical isomers were resolved by using either 0.5 mM or 6-20 mM of SBE-CD. The latter separation conditions (reversed polarity mode) made it possible to obtain inversion of migration order.

Simultaneous stereoselective analysis of venlafaxine and O-desmethylvenlafaxine enantiomers in clinical samples by capillary electrophoresis using charged cyclodextrins

Capillary electrophoresis (CE) was used for the simultaneous chiral determination of venlafaxine (Vx), a new antidepressant drug and its main active metabolite. O-desmethyl venlafaxine (ODV). Among the charged cyclodextrins (CD) tested, phosphated gamma-CD was the most appropriate. Resolution of Vx and ODV was obtained with 50 mM phosphate buffer (pH 2.5) containing 20 mg/ml of phosphated gamma-CD. After optimisation of the method (including robustness), validation was carried out. Vx and ODV concentrations, as well as the enantiomeric ratio, were investigated in clinical samples. Chiral determination of Vx and ODV was performed after a simple liquid-liquid extraction (LLE). In the tested concentration range (25-500 ng/ml), coefficients of correlation were superior to 0.996. Within-day and between-day accuracy and precision were determined at three different concentrations for each enantiomer. Analyses of clinical samples (n = 16) exhibited non-racemic ratios for Vx and ODV, which suggests a stereoselective metabolism in humans.

Separation and identification of etodolac and its urinary phase I metabolites using capillary electrochromatography and on-line capillary electrochromatography-electrospray ionisation mass spectrometry coupling

Capillary high-performance liquid chromatography (capillary HPLC), pressure-assisted capillary electrochromatography (pCEC) and capillary electrochromatography (CEC) were performed in the same capillary packed with 5 microm octadecylsilica (C18) as stationary phase. These three separation modes were compared from the viewpoint of peak efficiency and separation selectivity in order to critically evaluate the advantages which CEC may offer compared to capillary HPLC for the solution of practical biomedical problems. The separation of the non-steroidal anti-inflammatory drug etodolac (ET, 1) and its phase I metabolites, 6-hydroxy etodolac (6-OH-ET, 2), 7-hydroxy etodolac (7-OH-ET, 3) and 8-(1'-hydroxyethyl) etodolac (8-OH-ET, 4) was selected as an example. Baseline separation of all compounds was achieved in different modes and conditions. The effect of pure electrophoretic separation mechanism on the overall separation selectivity observed in CEC has been shown. A high electroosmotic flow (EOF) was observed in C18 packed capillary even at pH 2.5 in various buffers. Furthermore, these separations were coupled on-line with electrospray ionisation mass spectrometry (ESI-MS) and the parent drug and its metabolites were identified in urine. For the coupling of CEC with ESI-MS a laboratory-made electrophoretic device was used in order to overcome some technical disadvantages of commercial instrumentation.

Analysis of hydroquinone and some of its ethers by using capillary electrochromatography

Capillary electrochromatography (CEC) was used for the analysis of relevant compounds in cosmetic preparation. Hydroquinone (HQ) and some of its ethers (methyl-, dimethyl-, benzyl-, phenyl-, propyl-HQ derivatives) were analyzed by using an octadecylsilica (ODS) stationary phase packed in fused-silica capillary (100 microm I.D.; 30 cm and 21.5 cm total and effective lengths, respectively). 20 mM Ammonium acetate pH 6-acetonitrile (50-70%) were the mobile phases used for the experiments. The acetonitrile (ACN) content strongly influenced the resolution of the studied compounds as well as the efficiency and the retention factor. Baseline resolution for the studied analytes was achieved at both the lowest and the highest percentage of ACN, the last one providing the shortest analysis time. Mobile phase containing 70% of ACN was therefore used for the analysis of an extract of skin-toning cream declared to contain HQ. Good repeatability of both retention times, peak areas and peak areas ratio (Asample/Ainternational standard) was found. The calibration graphs were linear in the concentration range studied (5-90 microg/ml) with correlation coefficients between 0.9975 and 09991. The analysis of the cosmetic preparation revealed the presence of HQ (1.72%, w/w) and of two additional peaks (not identified).

Quality control of benserazide-levodopa and carbidopa-levodopa tablets by capillary zone electrophoresis

In modern practice, the treatment of Parkinson's disease and syndrome is carried out using pharmaceutical formulations containing a combination of levodopa and a decarboxylation inhibitor (carbidopa or benserazide). Two pharmaceutical formulations were quantified by capillary zone electrophoresis using two procedures which differed only in the kind of background electrolyte used. One procedure used a 25 mM phosphate buffer, pH 2.5, while the second one used a 25 mM borate buffer, pH 8.5. The electrophoretic analysis was carried out using an uncoated fused- silica capillary, a separation voltage of 20 kV with currents typically less than 60 microA, and spectrophotometric detection at 205 nm. Calibration curves were performed for levodopa (concentration range 1-100 microg/mL), for carbidopa and benserazide (1-50 microg/mL), and the plots of the peak area versus concentration were found to be linear with a correlation coefficient better than 0.9990. Satisfactory results were obtained when commercial tablets were analyzed in terms of accuracy (98-102%), repeatability (0.6-2.0%), and intermediate precision (1.1-2.6%).

Enantioselective determination by capillary electrophoresis with cyclodextrins as chiral selectors

This review surveys the separation of enantiomers by capillary electrophoresis using cyclodextrins as chiral selector. Cyclodextrins or their derivatives have been widely employed for the direct chiral resolution of a wide number of enantiomers, mainly of pharmaceutical interest, selected examples are reported in the tables. For method optimisation, several parameters influencing the enantioresolution, e.g., cyclodextrin type and concentration, buffer pH and composition, presence of organic solvents or complexing additives in the buffer were considered and discussed. Finally, selected applications to real samples such as pharmaceutical formulations, biological and medical samples are also discussed.

Immunocytochemical detection of hMSH2 and hMLH1 expression in oral melanoma

BACKGROUND

The DNA mismatch repair system (MMR) plays an important role in the maintenance of genomic stability. To date few studies have been performed on hMSH2 and hMLH1 expression and melanoma of the head and neck region. A study of two cases revealed no mutations of the mismatch repair genes hMSH2 and hMLH1.

MATERIALS AND METHODS

To verify the possibility of implication of hMSH2 and hMLH1 alterations in melanocytic cancerogenesis, the authors examined the protein expression pattern of hMSH2 and hMLH1 by immunohistochemistry in 9 paraffin-embedded oral melanoma.

RESULTS

One case (11%) showed nuclear positivity for hMSH2, 3 cases (33%) showed cytoplasmic positivity, and five cases (55%) showed no staining in the tumoral cells, even if normal squamous epithelium available in this section showed a nuclear positivity. Four cases (44%) showed no hMLH1 staining in the tumoral cells, even if normal squamous epithelium available in this section showed a nuclear positivity. Two cases (22%) showed nuclear positivity, and three cases (33%) showed cytoplasmic positivity.

CONCLUSIONS

The analysis of mismatch repair genes can be a new molecular diagnostic tools for the detection of patients at high risk of developing melanoma and other neoplasia, or metastasis and recurrences.

[Glutathione-S-transferase expression in oral squamous cell carcinoma]

BACKGROUND

A large number of oral cancer patients shows poor or partial response to chemotherapy and the mechanisms are poorly understood. Glutathione-S-transferase (GST) is one of the molecules involved in resistance to natural product-based chemotherapeutics. It is an enzyme able to conjugate several substances (metabolites, drugs) to reduct glutathione. Today several isoenzymes of GST are known: GST-alpha, GST-mu, GST-pi, GST-theta. Over-expression of glutathione S-transferase-pi class isozyme is often associated with malignant transformation. Several studies reported that GST-pi staining patterns and their distribution may be helpful in identifying high-risk oral lesions. However, GST is surely involved in resistance to alchilant agents.

OBJECTIVE

To verify the possibility of implication of GST in oral cancerogenesis and in natural chemioresistance, the authors examined the protein expression patterns by immunohistochemistry in paraffin-embedded specimens of primary untreated oral cancers (OSCC).

METHODS

GST-a and GST-pi expression in 17 cases of OSCC at different degree of cellular differentiation have been evaluated by immunohistochemistry.

RESULTS

The GST-pi expression in primary tumours predominantly varied from mild to moderate levels. The GST-a expression was often quite similar to GST-pi expression with a few exceptions.

CONCLUSIONS

Expression of GST enzymes is an important signal for multidrug resistance: positive staining for both GST-pi and GST-a could constitute a hallmark of chemoresistant groups of OSSC.

Tissue reactions, fluids, and bacterial infiltration in implants retrieved at autopsy: a case report

A 72-year-old patient underwent the placement of 2 screw-type implants. After 5 months the patient died of a massive stroke, and a block section of the portion of the mandible containing the implants was done. The specimen was treated to obtain thin ground sections. A 1- to 5-micron gap was present between the implant and the healing cover screw, and this space was filled by bacteria and calculus; bacteria were also present in the most apical portion of the hollow part of the implant. An inflammatory infiltrate was present in the connective peri-implant tissues. The spaces between all implant components (implant, abutment, and healing screw) can act as conduits and reservoirs for bacteria, which could cause inflammation of the peri-implant soft tissues. In conclusion, the histologic data from this autopsy case may help to confirm the penetration by fluids and bacteria into the internal portion of the implants, obtained from previous in vitro and in vivo studies.

Simultaneous stereoselective analysis of tramadol and its main phase I metabolites by on-line capillary zone electrophoresis-electrospray ionization mass spectrometry

On-line combination of partial filling capillary electrophoresis and electrospray ionization mass spectrometry was demonstrated for the simultaneous enantioseparation of tramadol and its main phase I metabolites. The partial filling technique was efficient at avoiding MS contamination by the chiral selector. Different experimental factors were investigated, including the chiral selector nature and concentration, plug length as well as the separation temperature. The best enantioseparation of the investigated compounds was achieved with a coated polyvinyl alcohol capillary and a 40 mM ammonium acetate buffer, pH 4.0, adding sulfobutyl ether beta-cyclodextrin (2.5 mg/ml) as the chiral selector. The charged cyclodextrin not only allowed enantioseparation of tramadol and its metabolites, but also improved the selectivity of compounds with the same molecular mass. Finally, CE-electrospray ionisation-MS was successfully applied to the stereoselective analysis of tramadol and its main metabolites in plasma after a simple liquid-liquid extraction.

Enantioresolution of pharmaceutical compounds by capillary electrophoresis. Use of cyclodextrins and antibiotics

Capillary electrophoresis (CE) is a powerful tool for the analysis of chiral compounds of pharmaceutical interest. The separation of enantiomers can be achieved using a chiral environment responsible for the diastereoisomers formation (stable or labile in the indirect or direct separation method, respectively). A wide number of chiral selectors have been employed in CE and among them cyclodextrins or their derivatives and antibiotics are the most used stereoselective agents. The review surveys the chiral separation of drugs using the above mentioned chiral selectors by CE. The main parameters influencing the enantioresolution, e.g., chiral selector type and concentration, buffer type, concentration, pH, organic modifier as well as the capillary temperature are discussed. Finally some selected applications to real samples such as pharmaceutical formulations, serum, urine are also discussed.

Enantiomeric separation of fluoxetine and norfluoxetine in plasma and serum samples with high detection sensitivity capillary electrophoresis

A capillary electrophoresis method was optimized for the stereoselective analysis of the antidepressant drug fluoxetine and its main demethylated metabolite norfluoxetine using a cyclodextrin-modified sodium phosphate buffer at pH 2.5. The combination of a neutral and a negatively charged cyclodextrin, dimethylated-beta- and phosphated-gamma-respectively, provided the baseline enantiomeric separation of the two compounds. The very low concentrations of chiral selectors employed together with the use of a high sensitivity detection cell of special design (zeta-shaped) in a diode array UV detector allowed us to reach a limit of detection of 0.005 and 0.01 microg/mL for fluoxetine and norfluoxetine, respectively. Analysis of fluoxetine and norfluoxetine standard mixtures showed a reproducibility of migration times and peak area and linearity in the concentration range of 0.1-2.0 microg/mL. The optimized method was applied to the analysis of clinical serum and plasma samples of patients under depression therapy. In all the analyzed samples the enantiomeric forms of fluoxetine and norfluoxetine were easily identified. The fluoxetine and metabolite enantiomeric ratio confirmed the stereoselectivity of the metabolic process of the fluoxetine drug in accordance with the literature data.

Stereoselective analysis of acid herbicides in natural waters by capillary electrophoresis

A capillary electrophoretic method for the stereoselective analysis of aryloxypropionic and aryloxyphenoxypropionic acidic herbicides in ground water and river water was performed. Vancomycin and gamma-cyclodextrin were added to the background electrolyte (BGE) as chiral selectors. Water sample preconcentration was accomplished by solid-phase extraction on styrene-divinylbenzene packed cartridges (2 L of ground water and 1 L of river water). The analytical method allowed for the resolution of mecoprop, fenoprop, fluazifop and haloxyfop racemic mixtures in natural water samples spiked with enantiomer concentration levels in the range 0.1-0.13 ppb for ground water and 0.4-0.54 ppb for river water.

Optical isomer separation of potential analgesic drug candidates by using capillary electrophoresis

Using cyclodextrin capillary zone electrophoresis (CD-CZE), baseline separation of synthetic potential analgesic drug diastereoisomer candidates 6,11-dimethyl-1,2,3,4,5,6-hexahydro-3-[(2'-methoxycarbonyl-2'-phenylc yclopropyl)methyl]-2,6-methano-3-benzazocin-8-ol (MPCB) and 6,11-dimethyl-1,2,3,4,5,6-hexahydro-3-[[2'-methoxycarbonyl-2'(4-chloroph enyl)cyclopropyl]methyl]-2,6-methano-3-benzazocin-8-ol (CCB) was achieved. Among the cyclodextrins tested (hydroxypropyl-, carboxymethyl- and sulfobutyl-beta-cyclodextrin (HP-beta-CD, CM-beta-CD and SBE-beta-CD)) SBE-beta-CD was found to be the most effective complexing agent, allowing good optical isomer separation. Resolution was also influenced by the CD concentration, pH of the buffer and presence of organic modifier in the background electrolyte. The optimum experimental conditions for the separation of studied analgesic drugs were found using 25 mM borate buffer at pH 9 containing 40 mM of SBE-beta-CD and 20% v/v of methanol. Using the above-mentioned background electrolyte, it was also possible to separate, in the same run, the enantiomers of normetazocine (NMZ) as well as the optical isomers of (+/-)-cis-2-chloromethyl-1-phenyl cyclopropancarboxylic acid methyl ester (PCE) or (+/-)-cis-2-chloromethyl-1-(4-chlorophenyl)cyclopropancarboxylic acid methyl ester (CPCE) reagents used in the synthesis of the studied analgesic drugs).

Simultaneous stereoselective analysis by capillary electrophoresis of tramadol enantiomers and their main phase I metabolites in urine

Capillary zone electrophoresis was successfully applied to the enantiomeric resolution of racemic tramadol and its six phase I metabolites using carboxymethylated beta-cyclodextrin (CMB) added to the background electrolyte (BGE). Baseline resolution of tramadol and its metabolites was obtained in less than 30 min using a 50 mM phosphate buffer (pH 2.5) containing 5 mM of CMB. Chiral determinations of tramadol and its main three metabolites, O-demethyltramadol (M1), N-demethyltramadol (M2) and O-demethyl-N-demethyltramadol (M5), were performed in urine after a simple double liquid-liquid extraction of 200 microliters of biological material. In the tested concentration range (0.5-20 micrograms/ml, except for M2: 0.5-10 micrograms/ml) coefficients of correlation superior than 0.994 were obtained. Within-day variation determined on three different concentrations for each enantiomers showed accuracies ranging from 95.4% to 103.2%. The relative standard deviation (RSD) of these assays was determined to be less than 10.0%. Day-to-day variation presented accuracies ranging from 96.3% to 106.5% with a RSD less than 9.0%. After oral administration of 100 mg of tramadol hydrochloride to an healthy volunteer, the urinary excretion was monitored during 30 h. About 15% of the dose was excreted as unchanged tramadol. The enantiomeric ratios of all the excreted analytes, T, M1, M2 and M5, were found to be very different to 1.0, showing that a stereoselective metabolism of tramadol clearly occurred.

Capillary zone electrophoresis separations of enantiomers present in complex ionic matrices with on-line isotachophoretic sample pretreatment

Analytical capabilities of capillary zone electrophoresis (CZE) with on-line coupled capillary isotachophoresis (ITP) sample pretreatment in the column-coupling capillary electrophoresis equipment to separate and determine enantiomers present in multicomponent ionic matrices were studied. Tryptophan was used as a model analyte in the ITP-capillary zone electrophoresis experiments performed in this context while a 90-component model mixture of UV-light absorbing organic anions and urine served as multicomponent sample matrices. Various working modes in which the on-line coupled capillary isotachophoresis-capillary zone electrophoresis combination in the column-coupling separation system can operate were employed in the anionic regime of the separation with direct injections of the samples. Advantages and limitations of these working modes in the separations of enantiomers present in model and urine matrices were assessed. Experiments with model mixtures of tryptophan enantiomers revealed that the two were resolved in the capillary zone electrophoresis stage with the aid of alpha-cyclodextrin also when their concentration ratio in the sample was 1:200 while the concentration of L(-)-tryptophan was 25 nmol/l. The limits of detection for the enantiomers were at approximately 10 nmol/l (approximately 1.5 ng/ml) concentrations for a 220 nm detection wavelength of the UV detector employed in the capillary zone electrophoresis stage and for a 30 microliters sample load. A high sample load capacity of the on-line coupled capillary isotachophoresis stage was effective in separating the samples corresponding to 3-6 microliters volumes of undiluted urine. The results from the runs with urine samples showed that only the capillary isotachophoresis-capillary zone electrophoresis combination with a post-column on-line coupled capillary isotachophoresis sample clean-up (responsible for a removal of more than 99% of the sample anionic constituents migrating in the on-line coupled capillary isotachophoresis stack and detectable in the capillary zone electrophoresis stage) provided a universal alternative for the detection and quantitation of the model analyte (L(-)-tryptophan).

A new electrode chamber for stable performance in capillary electrophoresis

Prerequisite to running automated sequences of analyses in capillary electrophoresis is a stable performance of the system. The products of the electrode reaction with the running background electrolyte (BGE) may play an important role, since even the neutral products may be driven into the capillary by electroosmosis and may severely deteriorate the stability of the baseline. Here, a simple, inexpensive, and fast procedure is described for improving the stability of the performance of capillary electrophoresis using a modified vial serving as the electrode chamber for the running BGE. The modification is based on creating two separate rooms in the vial, one for the electrode and a second one for the capillary. These two rooms are connected by a cotton plug. When both rooms are filled with the running BGE, the electrolytic connection between the electrode and the capillary is ensured; however, the convective transport of the electrode reaction products into the capillary is practically eliminated.

Investigation of the in vitro biotransformation of R-(+)-thalidomide by HPLC, nano-HPLC, CEC and HPLC--APCI-MS

High-performance liquid chromatography (HPLC), nano-HPLC, capillary electrochromatography (CEC) and on-line HPLC-atmospheric pressure chemical ionization mass spectrometry (APCI-MS) techniques were used for the identification and detailed characterization of two new metabolites of the former sedative drug thalidomide (TD). The advantages of nano-HPLC and CEC are higher peak efficiency and a drastic decrease in the analysis time, which, together with lower sample dilution during the analyses, allowed to obtain a detection sensitivity that was comparable to HPLC with common-sized columns. Both, nano-HPLC and CEC could be realized in the commercially available capillary electrophoresis system HP3D. On-line HPLC-APCI-MS coupling is a very useful technique for the rapid identification of metabolites without any need for reference compounds.

Capillary electrophoretic analysis of synthetic short-chain oligoribonucleotides

Thirty synthetic oligoribonucleotides, 3 to 18 nucleotides (nt) long, were analyzed by capillary electrophoresis, under nondenaturing conditions, using a commercial kit. The migration time t(m) was dependent on nt length and composition, capillary length, operating temperature, and type of sieving polymer. Under fixed experimental conditions, the t(m) proved predictable by the equation: t(m) = [0.22(n-1) + 6.14A/n + 6.86G/n + 3.61 (C+U)/n] min, for n>3, where A/n, G/n, C/n, U/n is the frequency of each type of nt within the oligonucleotide (ONT). The equation accounts for the influence of charge-to-mass ratio on t(m), but not for structural effects, if present. This approximation is acceptable for short ONTs. The possibility of detecting n+1, n-1, n-2 impurities, having predicted the t(m), is of crucial importance in assessing the purity of synthetic ONTs dedicated to structural studies. This appears to be feasible. High resolution was shown among homologous series of ONTs of increasing length, and in some cases, even within groups of ONTs of the same length but different composition. The addition of 7 M urea to the buffer, as denaturing agent, accelerates the t(m) and significantly lowers the resolution for the shortest ONTs. It was also possible to monitor the state of association of mixtures of RNA and DNA sequence-complementary strands.

Use of cyclodextrins in capillary electrophoresis: resolution of tramadol enantiomers

Capillary zone electrophoresis was successfully applied to the enantiomeric resolution of racemic tramadol. Both uncoated and polyacrylamide-coated capillaries were tested for method optimization using either negatively charged or native cyclodextrins (CD) added to the background electrolyte (BGE). The resolution was strongly influenced by the CD type and concentration as well as by the pH and the concentration of the BGE. Among the CDs tested, carboxymethylated-beta-cyclodextrin allowed the baseline separation of tramadol enantiomers. After the method was optimized, it was validated in a coated capillary for enantiomeric analysis of tramadol enantiomers in pharmaceutical formulation, including specificity and elution order, linearity, accuracy and precision, determination of limit of detection (LOD) and quantification (LOQ), enantiomeric purity linearity, freedom from interference, and stability of sample solutions. Precision at the target concentration was less than 2%, with an accuracy higher than 99%. Furthermore, the method was able to detect 0.3% and to quantify 1% of the minor enantiomer in the presence of the major one at the target value.

Use of a Hepta-tyr glycopeptide antibiotic as chiral selector in capillary electrophoresis

A new glycopeptide antibiotic, MDL 63,246 (Hepta-tyr), of the teicoplanin family, has been evaluated in capillary electrophoresis for the resolution of chiral compounds of pharmaceutical and environmental interest. Electrophoretic separations were carried out in a polyacrylamide-coated capillary using the partial filling-counter current mode with aqueous-organic buffers in the pH range 4-6. Experimental parameters affecting resolution, such as antibiotic concentration, buffer pH, organic modifier type and capillary temperature, were studied. The Hepta-tyr antibiotic exhibited a high enantiorecognition capability towards the studied compounds at very low concentrations (1-2 mg/mL). The optimum experimental conditions were achieved by using a buffer at pH 5 containing acetonitrile at 25 degrees C.

Quantitative analysis of synthetic dyes in lipstick by micellar electrokinetic capillary chromatography

The separation of synthetic dyes, used as color additives in cosmetics, by micellar electrokinetic capillary chromatography (MEKC) is described in this study. The separation of seven dyes, namely eosine, erythrosine, cyanosine, rhodamine B, orange II, chromotrope FB and tartrazine has been achieved in about 3 min in an untreated fused silica capillary containing as background electrolyte a 25 mM tetraborate/phosphate buffer, pH 8.0, and 30 mM sodium dodecyl sulfate. The electrophoretic method exhibits precision and relatively high sensitivity. A detection limit (LOD, signal/noise = 3) in the range of 5-7.5 X 10(-7) M of standard compounds was recorded. Intra-day repeatability of all the studied dye determinations (8 runs) gave the following results (limit values), % standard deviation: 0.24-1.54% for migration time, 0.99-1.24% for corrected peak areas, 0.99-1.24% for corrected peak area ratio (analyte/internal standard) and 1.56-2.74% for peak areas. The optimized method was successfully applied to the analysis of a lipstick sample where eosine and cyanosine were present.

Chiral analysis by capillary electrophoresis using antibiotics as chiral selector

The separation of chiral compounds by capillary electrophoresis (CE) is a very interesting field of research in different areas such as pharmaceutical, environmental, agricultural analysis etc. The separation of two enantiomers can be achieved in CE using a chiral environment interacting with the two analytes on forming diastereoisomers with different stability constants and thus different mobilities. A wide number of chiral selectors have been employed in CE and among them glycopeptide antibiotics exhibited excellent enantioselective properties towards a wide number of racemic compounds. Vancomycin, ristocetin A, rifamycins, teicoplanin, kanamycin, streptomycin, fradiomycin, and two vancomycin analogues, added to the background electrolyte (BGE), are the antibiotics studied by CE running the separation in untreated and/or coated fused-silica capillary. Due to adsorption and absorption phenomena, some drawbacks can be expected when using bare fused-silica capillary, e.g., changes of electroosmotic flow (EOF), broaden peaks, reduced efficiency and low sensitivity. Coated capillary and counter current mode can be the solution to overcome the above mentioned problems. This review surveys the separation of enantiomers by CE when macrocyclic antibiotics are used as chiral selector. The enantioselectivity can be easily controlled modifying several parameters such as antibiotic type and concentration, pH, ionic strength and concentration of the background electrolyte, organic modifier etc. The paper also presents a list of the latest chiral separations achieved by CE where antibiotics were used as chiral selector.

"Schizophrenic" behavior of zones in capillary zone electrophoresis: explanation of an old problem

Background electrolyte (BGE) systems with two coions are frequently used in capillary zone electrophoresis (CZE), especially in cases where indirect optical detection is employed. This study investigates the behavior of analytes, which possess mobilities intermediate to those of the BGE coions used. Besides the expected behavior, where the analytes provide either tailing or fronting zones, unusual behavior with extraordinary zone broadening is also observed in some cases. The explanation for this effect is that binary BGE systems involve, as a physico-chemical rule, a region where the analytes are forced by one coion to give tailing zones and simultaneously by the other coion to give fronting zones. The result of this "schizophrenic" situation is extraordinary zone broadening and deterioration of the detection record. A series of experiments is presented showing in a telling way the electromigration behavior of the discussed type of zones as well as the ways to remedy the deterioration of the peak shape by a mere slight changing of the quantitative composition of the BGE used.

Controlling enantioselectivity in chiral capillary electrophoresis with inclusion-complexation

The separation of chiral compounds is of key importance in different fields of application, e.g., pharmaceutical, industrial, forensic, biological, clinical etc. Capillary electrophoresis (CE) is a powerful analytical method applied in chiral analysis and inclusion-complexation is one of the most frequently used mechanism to improve the selectivity of the enantiomeric separation. Cyclodextrins and their derivatives or modified crown-ethers have been successfully applied in CE for the enantiomeric separation of a wide number of analytes. This review surveys the separation of enantiomers by CE when chiral selectors, forming inclusion-complexation, are used. The control of enantioselectivity can be done carefully by considering several experimental parameters such as chiral selector type and concentration, pH, ionic strength and concentration of the background electrolyte, electroosmotic flow, organic modifier etc. The review presents a list of the latest separation of enantiomers by CE where inclusion-complexation plays a key role in the stereoselective separation mechanism.

Stereoselective analysis of herbicides by capillary electrophoresis using sulfobutyl ether beta-cyclodextrin as chiral selector

Capillary zone electrophoresis has been used for the enantiomeric separation of several herbicides. Different beta-cyclodextrin (CD) derivatives have been investigated for chiral separations and among them the negatively charged sulfobutyl ether beta-cyclodextrin (SBE-beta-CD) proved to be effective for the stereo-selective resolutions of the investigated herbicides. The effect of CD concentration, buffer pH and organic modifier on effective mobilities, resolution and selectivity of the analytes have been studied. Addition of SBE-beta-CD (5-50 mg/mL) to the buffer at pH 9 resulted in a general increase of migration times as well as resolution. A CD concentration as low as 5 mg/mL was effective to completely resolve napropamide and ethofumesate enantiomers. Buffer solutions containing 40 mg/mL of SBE-beta-CD were chosen to study the effect of buffer pH (7, 8, and 9) on chiral separation of the herbicides. No great differences in resolution and effective mobilities have been found in the pH 7-9 range. The addition of different organic modifiers to the background electrolyte at pH 9, containing 20 mg/mL of SBE-beta-CD, showed different effects. Methanol was the most effective in improving resolution but in some cases total loss in enantiomeric separation was observed. The qualitative analysis of an enantiomerically pure herbicide (flamprop isopropyl) commercial preparation is also shown.

Analysis of venlafaxine by capillary zone electrophoresis

Capillary electrophoresis has been used for the separation of venlafaxine and two of its impurities deriving from the synthesis process. The electrophoretic experiments were performed using background electrolytes at different pHs in the 2.5-9.2 range in order to study the effective mobilities and resolution of the three examined compounds. The optimum experimental conditions for the baseline resolution of the three analytes was found at pH 6.5. Very good repeatability for both migration time and corrected peak areas was achieved. The calibration curve was studied for venlafaxine (concentration range 26-224 micrograms/mL), and the plot of the peak area ratio (sample/internal standard [IS]) versus venlafaxine concentration was linear with a correlation coefficient of 0.9991. The effect of different cyclodextrins (CDs), namely, gamma-cyclodextrin (gamma-CD), hydroxypropyl-beta-CD (HP-beta-CD), and alpha-cyclodextrin (alpha-CD), on effective mobility and enantiomeric resolution (R) of venlafaxine (Wy45030) and its impurities (imp1 and imp2) was studied at different pHs, and the best results were obtained at pH 9.2. Venlafaxine was baseline resolved in its enantiomers using gamma-CD or HP-beta-CD, while imp1 (Wy45494) was baseline resolved using alpha-CD.

A practical procedure for the determination of association constants of the analyte-chiral selector equilibria by capillary zone electrophoresis

A practical procedure is proposed for the determination of association constants and mobility of the associate of a solute with a chiral selector in chiral separations by capillary zone electrophoresis. The procedure is based on the measurement of the effective mobility of a solute at zero and two different nonzero concentrations of the chiral selector. Simple explicit formulas have been derived in order to calculate the required data. The essence of the procedure is that all mobility data are adjusted to the background electrolyte (BGE) without chiral selector, serving as the viscosity reference. A simple procedure is described for measuring the viscosity of the operational electrolytes directly with the commercial capillary electrophoresis instrumentation, and Walden's rule has been utilized for adjusting the experimental mobility data to constant reference viscosity. The use of the procedure is exemplified by a separation of D,L-tryptophan in BGE containing alpha-cyclodextrin as chiral selector.

Identification of chiral drug isomers by capillary electrophoresis

Separation of optical isomers of compounds of pharmaceutical interest by capillary electrophoretic techniques is reviewed. The direct and indirect separation method, as well as the main resolution mechanisms and the parameters influencing the stereoselectivity are discussed considering capillary zone electrophoresis, micellar electrokinetic chromatography, isotachophoresis and electrochromatography. Several chiral selectors have been successfully used in CE for chiral separation, including cyclodextrins and their derivatives, modified crown-ethers, proteins, antibiotics, linear saccharides and chiral surfactants. Only applications in the pharmaceutical field with the most important experimental conditions are summarised in the Tables reported in this paper. The chiral analyses of drugs in real samples like biological fluids or pharmaceutical formulations are also reported.