Application of capillary electrophoresis with field-amplified sample injection for the detection of new adrenoreceptor antagonist enantiomers in plasma in the low ng/mL concentration range

Salt-assisted LLE combined with field-amplified sample stacking in CE for improved determination of beta blocker drugs in human urine

Background: A simple and sensitive CE method was developed and validated for the analysis of some beta blockers in human urine. Methods: In this study, salting-out assisted LLE combined with field-amplified sample stacking method was employed for biological sample clean-up and sensitivity enhancement in CE. Results: Under the optimal conditions good linearity (r2 ≥0.998) was obtained, within 0.025–1 µg/ml for propranolol and metoprolol, and within 0.05–1 µg/ml for carvedilol in urine samples. LODs and LLOQs ranged from 0.005 to 0.015 µg/ml, and from 0.025 to 0.05 µg/ml, respectively. The RSDs of intra- and inter-day analysis of examined compounds were less than 4.0%. The recoveries were in the range of 98–119%. Conclusion: The validated method is successfully applied to determine propranolol, metoprolol and carvedilol in human urine samples obtained from the patients who received these drugs.

Field-amplified sample stacking β-cyclodextrin modified capillary electrophoresis for quantitative determination of diastereomeric saponins

Successful simultaneous diastereomeric separation and sensitive determination of two pairs of triterpenoidal saponins have been achieved by capillary electrophoresis (CE) using β-cyclodextrin (β-CD) as a stereoselective agent to cooperate with borate complexation. A usual technique for isolation and group separation of saponins was developed as an appropriate purification step prior to the determination of individual saponins by CE. Soyasaponin I ( S1: ), azukisaponin V ( S2: ), bersimoside I ( S3: ) and bersimoside II ( S4: ) could be well separated within 14 min in a fused-silica capillary (60 cm long to the detector with an additional 10 cm to the cathode; 75 µm i.d.). The background electrolyte was borate buffer (80 mM, pH 10), containing 24 mM β-CD. The separation voltage was 14 kV with a detection wavelength of 195 nm. The sample was electrokinetically injected using a voltage of 16 kV for 12 s. Methanol (70%) was used as the diluent for field-amplified sample stacking after hydrodynamic injection of short water plug (5 cm, 4 s). The method was partially validated for linearity, repeatability, reproducibility, limits of detection and limits of quantification. The correlation coefficients of the calibration curves were all >0.998, and the recoveries were from 98.23 to 96.21%.

Electrophoretic analysis of cations using large-volume sample stacking with an electroosmotic flow pump using capillaries coated with neutral and cationic polymers

To realize the high-performance and simple-operation analysis of cationic compounds in capillary electrophoresis, we investigated large-volume sample stacking with an electroosmotic flow pump (LVSEP) using capillaries with hydrophilic and weakly cationic inner surface. Three capillary modification methods were employed: thermally passivated physical coating with polymer mixture of poly(vinyl alcohol) and poly(allylamine); covalent modification with random copolymer of acryl amide and 3-(methacryloylamino)propyltrimethylammonium chloride; easily preparable physical coating with dimethyldioctadecylammonium bromide and polyoxyethylene stearate. In these capillaries, the electroosmotic flow (EOF) was well suppressed in the high ionic strength (I) electrolyte under the acidic and basic pH, whereas the EOF was enhanced in the low I electrolyte, indicating a suitable EOF property for the rapid LVSEP and following separation. In the LVSEP-capillary zone electrophoresis (CZE) analyses of benzylamine and 1-naphthylethylamine, up to 550-fold sensitivity increases were successfully obtained in the three capillaries without significantly reducing the repeatability and resolution. LVSEP-cyclodextrin-modified CZE of chlorpheniramine and brompheniramine was also carried out, resulting in up to 380-fold sensitivity enhancement with keeping the baseline separation for the enantiomers. Finally, we performed the LVSEP-CZE analysis of basic proteins, where up to 100-fold sensitivity increases were achieved, but a peak broadening was observed due to the sample adsorption in the low I sample matrix.

Advanced CE for chiral analysis of drugs, metabolites, and biomarkers in biological samples

An analysis of recent trends indicates that CE can show real advantages over chromatographic methods in ultratrace enantioselective determination of biologically active compounds in complex biological matrices. It is due to high separation efficiency and many applicable in-capillary electromigration effects in CE (countercurrent migration, stacking effects) enhancing significantly (enantio)separability and enabling effective sample preparation (preconcentration, purification, analyte derivatization). Other possible on-line combinations of CE, such as column coupled CE-CE techniques and implementation of nonelectrophoretic techniques (extraction, membrane filtration, flow injection) into CE, offer additional approaches for highly effective sample preparation and separation. CE matured to a highly flexible and compatible technique enabling its hyphenation with powerful detection systems allowing extremely sensitive detection (e.g. LIF) and/or structural characterization of analytes (e.g. MS). Within the last decade, more as well as less conventional analytical on-line approaches have been effectively utilized in this field and their practical potentialities are demonstrated on many new application examples in this article. Here, three basic areas of (enantioselective) drug bioanalysis are highlighted and supported by a brief theoretical description of each individual approach in a compact review structure (to create integrated view on the topic), including (i) progressive enantioseparation approaches and new enantioselective agents, (ii) in-capillary sample preparation (preconcentration, purification, derivatization), and (iii) detection possibilities related to enhanced sensitivity and structural characterization.

Field-amplified on-line sample stacking for determination of carnosine-related peptides by capillary electrophoresis

An on-line sample stacking method, namely field-amplified sample injection, has been developed for the separation and determination of carnosine, anserine, and homocarnosine by capillary electrophoresis. Using electrokinetic injection, about 130- to 160-fold improvement of sensitivity was achieved without loss of separation efficiency when compared to conventional sample injection. For conventional injection, the samples were dissolved in running buffer and then hydrodynamically injected for 10 s (3.45 kPa). Various parameters affecting separation and sample stacking were optimized. Under optimum conditions, linear responses were obtained over two orders of magnitude and the detection limits (defined as S/N = 3) of carnosine, anserine, and homocarnosine were 1.5 x 10(-8) to 1.6 x 10(-8) mol/L.

Simultaneous enantioseparation and sensitivity enhancement of basic drugs using large-volume sample stacking

Simultaneous enantioseparation with sensitive detection of four basic drugs, namely methoxamine, metaproterenol, terbutaline and carvedilol, using a 20-mum ID capillary with native beta-CD as the chiral selector was demonstrated by the large-volume sample stacking method. The procedure included conventional sample loading either hydrodynamically or electrokinetically at longer injection times without polarity switching and EOF manipulation. In comparison to conventional injections, depending on the analyte, about several hundred- and a thousand-fold sensitivity enhancement was achieved with the hydrodynamic and the electrokinetic injections, respectively. The simple method developed was applied to the analysis of racemic analytes in serum samples and better recovery was achieved using hydrodynamic injection than electrokinetic injection.

Field-amplified on-line sample stacking for separation and determination of cimaterol, clenbuterol and salbutamol using capillary electrophoresis

A capillary electrophoresis method, using field-amplified sample injection (FASI), was developed for separation and determination of some beta 2-agonists, such as cimaterol, clenbuterol and salbutamol. The optimum conditions for this system had been investigated in detail. The precision of the migration time, peak height and accuracy were determined in both intra-day (n = 5) and inter-day (n = 15) assays. Under the optimum conditions, the detection limits (defined as S/N = 3) of this method were found to be lower than 2.0 ng/mL for all of these three beta 2-agonists, which were much lower than that of the conventional electro-migration injection method, the enhancement factors were greatly improved to be 30-40-fold. Such lower detection limit lets this method to be suitable for determination of above-mentioned beta 2-agonists in the urine sample. The mean recoveries in urine were higher than 96.2%, 95.6% and 95.3% for cimaterol, clenbuterol and salbutamol, respectively, with relative standard deviations lower than 3.5%.

Optimization of Field-Amplified Sample Injection for Analysis of Peptides by Capillary Electrophoresis−Mass Spectrometry

A versatile experimental approach is described to achieve very high sensitivity analysis of peptides by capillary electrophoresis-mass spectrometry with sheath flow configuration based on optimization of field-amplified sample injection. Compared to traditional hydrodynamic injection methods, signal enhancement in terms of detection sensitivity of the bioanalytes by more than 3000-fold can be achieved. The effects of injection conditions, composition of the acid and organic solvent in the sample solution, length of the water plug, sample injection time, and voltage on the efficiency of the sample stacking have been systematically investigated, with peptides in the low-nanomolar (10(-9) M) range readily detected under the optimized conditions. Linearity of the established stacking method was found to be excellent over 2 orders of magnitude of concentration. The method was further evaluated for the analysis of low concentration bioactive peptide mixtures and tryptic digests of proteins. A distinguishing feature of the described approach is that it can be employed directly for the analysis of low-abundance protein fragments generated by enzymatic digestion and a reversed-phase-based sample-desalting procedure. Thus, rapid identification of protein fragments as low-abundance analytes can be achieved with this new approach by comparison of the actual tandem mass spectra of selected peptides with the predicted fragmentation patterns using online database searching algorithms.

Determination of monoamines in urine by capillary electrophoresis with field-amplified sample stacking and amperometric detection

A simple, rapid and low-cost method using capillary electrophoresis coupled with field-amplified sample stacking and electrochemical detection was developed for the separation and determination of monoamines. In this present work, a systematic study of the parameters (pH value and concentration of electrophoretic buffer, composition of sample solvent, injection voltage and time) affecting separation and on-line concentration of monoamines has been performed enabling the detection sensitivity of these monoamines to be improved by 5,000 times compared with the conventional electrokinetic injection. This developed method was applied to the direct analysis of these monoamines in human urine without off-line sample preconcentration. Due to the requirement for urine dilution to minimize the detrimental effects of high salt on analyte stacking, the real sensitivity improvement is about 50-fold when applying the optimized method to urine samples. In order to quantitate these monoamines accurately, internal standard calibration curves were constructed with standard monoamines in presence of salt with similar concentration as in human urine. In the method validation, the calibration curves were linear over a range of 1.0 x 10(-9) to 2.5 x 10(-8) mol/L for each monoamine and the limits of detection (signal to noise ratio of 3) for these monoamines were in the sub-nmol/L concentration range (6.0 x 10(-10) mol/L).

Determination of Pb(II), Cu(II) and Fe(III) with Capillary Electrophoresis Using Ethylenediaminetetraacetic Acid as a Complexing Agent and Vancomycin as a Complex Selector

The simultaneous determination of metal ions using ethylenediaminetetraacetic acid (EDTA) as a complexing agent and vancomycin as a complex selector was successfully studied by capillary electrophoresis with the U-shaped cell. The partial filling method (counter current mode) was used in order to gain selectivity of the separation, and also to increase the detection sensitivity. The effect of the vancomycin concentration on the separation behavior of free EDTA and metal products, and the effect of the EDTA concentration on the stability of metal-EDTA products were considered. Under the optimal condition, the reproducibilities (RSD) of the migration time and the peak area were less than 3.39% and 9.61%, respectively. With the high sensitivity of the method, Pb(II), Cu(II) and Fe(III) in tap water were successfully determined, and the recoveries were 99 - 105%. The concentrations of these metal ions found in tap water did not exceed the maximum allowed concentrations regulated by the U.S. Environmental Protection Agency.

Sensitive chiral analysis by capillary electrophoresis

In this review, an updated view of the different strategies used up to now to enhance the sensitivity of detection in chiral analysis by CE will be provided to the readers. With this aim, it will include a brief description of the fundamentals and most of the recent applications performed in sensitive chiral analysis by CE using offline and online sample treatment techniques (SPE, liquid-liquid extraction, microdialysis, etc.), on-column preconcentration techniques based on electrophoretic principles (ITP, stacking, and sweeping), and alternative detection systems (spectroscopic, spectrometric, and electrochemical) to the widely used UV-Vis absorption detection.

Dynamic pH junction-sweeping capillary electrophoresis for online preconcentration of toxic pyrrolizidine alkaloids in Chinese herbal medicine

There is a need to develop simple yet effective preconcentration methods to enhance concentration sensitivity for CE analysis of trace level analytes in real samples, particularly when commonly available but less sensitive detection methods, e.g., UV detection, are used. In this report, a hyphenated online preconcentration strategy combining dynamic pH junction with sweeping (i.e., dynamic pH junction-sweeping) was employed for the analysis of four toxic pyrrolizidine alkaloids (PAs) of senkirkine, senecionine, retrorsine, and seneciphylline in Chinese herbal medicine (Kuan donghua). Direct electrokinetically focusing of a large sample volume injection (up to 20% of capillary length) on the capillary was performed using the dynamic pH junction-sweeping method. A sample matrix consisting of 10 mM phosphate with 20% methanol at pH 4.0 and a BGE containing 20 mM borate, 30 mM SDS, and 20% methanol at pH 9.1 were utilized to realize dynamic pH junction-sweeping for PAs. This online preconcentration strategy resulted in sensitivity enhancement factors ranging from 23.8- to 90.0-fold for the four toxic PAs, giving an LOD as low as 30 ppb for the PAs. Critical factors such as sample matrix type, pH, and salt concentration were also examined to achieve higher sensitivity enhancement, shorter analysis time, and better resolution. The results indicate that the proposed dynamic pH junction-sweeping technique is a powerful alternative approach for identification and determination of trace levels of these toxic PAs and other hydrophobic, protonatable compounds in real samples.

Field-amplified sample injection and in-capillary derivatization for sensitivity improvement of the electrophoretic determination of histamine

The feasibility of the combination of field-amplified sample injection (FASI) and in-capillary derivatization was explored for improving sensitivity of histamine in capillary electrophoresis (CE). Naphthalene-2,3-dicarboxaldehyde (NDA) was used as derivatization reagent. The reagent and sample was introduced by tandem mode. The derivatization was accomplished by at-inlet mode with standing time of 1.5 min. The combination of FASI and in-capillary derivatization was successfully achieved with about 400-fold concentration sensitivity enhancement compared to pre-capillary derivatization at the same set-up. The detection limit of concentration for histamine reached 1.25 x 10(-11) M by CE and fluorescence detection with S/N = 3. Parameters affecting FASI and in-capillary derivatization process including sample matrix, buffer concentration and reagent injection amount, were investigated.

Trace analysis of zotepine and its active metabolite in plasma by capillary electrophoresis with solid phase extraction and head-column field-amplified sample stacking

A sensitive high-performance capillary zone electrophoresis (CZE) with head-column field-amplified sample stacking (FASS) in binary system has been developed for the simultaneous determination of zotepine and its active metabolite, norzotepine, in human plasma. The separation of zotepine and norzotepine was performed using a background electrolyte consisting of 50% ethylene glycol-borate buffer (20mM, pH 8.0) solution with 20% methanol as the running buffer and on-column detection at 200 nm. Under the optimal FASS-CZE condition, good separation with high efficiency and short analysis time is achieved. Several parameters affecting the separation and sensitivity of the drug were studied, including sample matrix, pH and concentrations of the borate buffer, ethylene glycol and methanol. Using clozapine as an internal standard, the linear ranges of the method for the determination of zotepine and norzotepine in human plasma were over 3-100 ng/mL; the detection limits of zotepine and norzotepine in plasma were 2 and 1 ng/mL, respectively. A sample pretreatment by means of solid-phase extraction (SPE) with subsequent quantitation by FASS-CZE was used. The application of the proposed method for determination of zotepine and norzotepine in plasma collected after oral administration of 125 mg zotepine in one schizophrenic patient was demonstrated.

Development and validation of a capillary electrophoresis method for the determination of phenothiazines in human urine in the low nanogramper milliliter concentration range using field-amplified sample injection

A capillary zone electrophoresis (CZE) method with ultraviolet-visible detection has been established and validated for the determination of five phenothiazines: thiazinamium methylsulfate, promazine hydrochloride, chlorpromazine hydrochloride, thioridazine hydrochloride, and promethazine hydrochloride in human urine. Optimum separation was obtained on a 64.5 cm x 75 microm bubble cell capillary using a buffer containing 150 mM tris(hydroxymethyl)aminomethane and 25% acetonitrile at pH 8.2, with temperature and voltage of 25 degrees C and 20 kV, respectively. Naphazoline hydrochloride was used as an internal standard. Field-amplified sample injection (FASI) has been applied to improve the sensitivity of the detection. Considering the influence of parameters affecting the on-line preconcentration (nature of preinjection plug, sample solvent composition, injection times, and injection voltage) and due to the significant interactions among them, in this paper we propose for the first time the application of a multivariate approach to carry out the study. The optimized conditions were as follows: preinjection plug of water for 7 s at 50 mbar, electrokinetic injection for 40 s at 6.2 kV, and 32 microm of H3PO4 in the sample solvent. Also, a solid-phase extraction (SPE) procedure is developed to obtain low detection limits and an adequate selectivity for urine samples. The combination of SPE and FASI-CZE-UV allows adequate linearities and recoveries, low detection limits (from 2 to 5 ng/mL), and satisfactory precisions (3.0-7.2% for an intermediate RSD %).

Enantioselective synthesis of 2- and 3-substituted 2,3-dihydro[1,4]dioxino[2,3-b]pyridine derivatives and enantiomeric purity control by capillary electrophoresis

A rapid and simple procedure for enantioselective preparation of 2- and 3-substituted 2,3-dihydro[1,4]dioxino[2,3-b]pyridine derivatives (A and B, respectively) is described. The enantiomeric purity of each isomer was determined by capillary electrophoresis using a dual-cyclodextrin system (S-beta-CD/beta-CD) dissolved in formic acid-ammonia buffer (pH 4, ionic strength 50 mM).