Head-column field-amplified sample stacking in binary system capillary electrophoresis. Preparation of extracts for determination of opioids in microliter amounts of body fluids

Highly Sensitive SDS Capillary Gel Electrophoresis with Sample Stacking Requiring Only Nanograms of Adeno-Associated Virus Capsid Proteins

Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) has been the method of choice in the past decades for size-based protein analysis. However, in general it requires the protein concentration in mg/mL level and thus is not practical for trace level protein analysis, not to mention the lengthy labor-intensive procedures. The SDS capillary gel electrophoresis (SDS CGE) method reported herein requires only nanogram-sized proteins loaded onto the autosampler. A sample stacking technique (e.g., head-column field-amplified sample stacking (HC FASS)) was employed, providing three orders of magnitude sensitivity enhancement compared to conventional SDS CGE. This method has been used routinely in purity analysis and characterization of adeno-associated virus (AAV) intermediates and finished gene therapeutics of AAV vectors. The sensitivity achieved is comparable to the currently most sensitive size-based protein assay silver-stained SDS PAGE. The highly sensitive sample stacking SDS CGE can be used for other types of proteins as well.

Fundamental aspects of field-amplified electrokinetic injection of cations for enantioselective capillary electrophoresis with sulfated cyclodextrins as selectors

Head-column field-amplified sample stacking of cations from a low conductivity sample followed by enantiomeric separation using negatively charged chiral selectors was studied experimentally and with computer simulation. Aspects investigated include the direct electrokinetic injection of the analytes into the background electrolyte, the use of a selector free buffer plug, the contribution of complexation within the buffer plug and the application of an additional water plug between sample and buffer plug. Attention was paid for changes of ionic strength which is known to have a significant impact on complexation and thus effective mobility. Racemic methadone was selected as a model compound, randomly substituted sulfated β-cyclodextrin as chiral selector and phosphate buffers (pH 6.3) for the background electrolyte and the buffer plug. Results confirm that the buffer plug is providing a spacer between cationic analytes and the negatively charged selector during electrokinetic injection. Simulation predicts the required length and composition of the plug for a given injection time to avoid an interference with the selector. A short water plug added between the low conductivity sample and a high conductivity buffer plug is demonstrated to provide best conditions to achieve high sensitivity in enantioselective drug assays with sulfated cyclodextrins as selectors.

Electromigrative separation techniques in forensic science: combining selectivity, sensitivity, and robustness

In this review we introduce the advantages and limitations of electromigrative separation techniques in forensic toxicology. We thus present a summary of illustrative studies and our own experience in the field together with established methods from the German Federal Criminal Police Office rather than a complete survey. We focus on the analytical aspects of analytes' physicochemical characteristics (e.g. polarity, stereoisomers) and analytical challenges including matrix tolerance, separation from compounds present in large excess, sample volumes, and orthogonality. For these aspects we want to reveal the specific advantages over more traditional methods. Both detailed studies and profiling and screening studies are taken into account. Care was taken to nearly exclusively document well-validated methods outstanding for the analytical challenge discussed. Special attention was paid to aspects exclusive to electromigrative separation techniques, including the use of the mobility axis, the potential for on-site instrumentation, and the capillary format for immunoassays. The review concludes with an introductory guide to method development for different separation modes, presenting typical buffer systems as starting points for different analyte classes. The objective of this review is to provide an orientation for users in separation science considering using capillary electrophoresis in their laboratory in the future.

A highly sensitive CE-UV method with dynamic coating of silica-fused capillaries for monitoring of nucleotide pyrophosphatase/phosphodiesterase reactions

A new highly sensitive capillary electrophoresis (CE) method applying dynamic coating and on-line stacking for the monitoring of nucleotide pyrophosphatases/phosphodiesterases (NPPs) and the screening of inhibitors was developed. NPP1 and NPP3 are membrane glycoproteins that catalyze the hydrolysis nucleotides, e.g. convert adenosine 5'-triphosphate to adenosine 5'-monophosphate (AMP) and pyrophosphate. Enzymatic reactions were performed and directly subjected to CE analysis. Since the enzymatic activity was low, standard methods were insufficient. The detection of nanomolar AMP and other nucleotides could be achieved by field-enhanced sample injection and the addition of polybrene to the running buffer. The polycationic polymer caused a dynamic coating of the silica-fused capillary, resulting in a reversed electroosmotic flow. The nucleotides migrated in the direction of the electroosmotic flow, whereas the positively charged polybrene molecules moved in the opposite direction, resulting in a narrow sample zone over a long injection time. Using this on-line sensitivity enhancement technique, a more than 70-fold enrichment was achieved for AMP (limit of detection, 46 nM) along with a short migration time (5 min) without compromising separation efficiency and peak shape. The optimized CE conditions were as follows: fused-silica capillary (30 cm effective lengthx75 mum), electrokinetic injection for 60 s, 50 mM phosphate buffer pH 6.5, 0.002% polybrene, constant current of -60 microA, UV detection at 210 nm, uridine 5'-monophosphate as the internal standard. The new method was used to study enzyme kinetics and inhibitors. It opens an easy way to determine the activities of slowly metabolizing enzymes such as NPPs, which are of considerable interest as novel drug targets.

Current role of capillary electrophoretic/electrokinetic techniques in forensic toxicology

The current application of capillary electrophoresis in forensic toxicology has been critically reviewed with special focus on the areas where this technique has shown real advantages over chromatographic methods. For example, capillary electrophoresis has been most successfully applied to the chiral analysis of some drugs of forensic interest, including amphetamines and their congeners. Another typical application field of capillary electrophoresis is represented by protein analysis. Recently, special interest has been paid to carbohydrate deficient transferrin (CDT), the most important biological marker of chronic alcohol abuse. Other specific applications of capillary electrophoresis of potential forensic toxicological concern are also discussed. The review includes 62 references.

Direct and sensitive analysis of methamphetamine, ketamine, morphine and codeine in human urine by cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography

Cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-Sweep-MEKC) was directly used to test some abuse drugs in human urine, including morphine (M), codeine (C), ketamine (K) and methamphetamine (MA). First, phosphate buffer (50 mM, pH 2.5) containing 30% methanol was filled into uncoated fused silica capillary (40 cm, 50 microm I.D.), then high conductivity buffer (100 mM phosphate, 6.9 kPa for 99.9 s) was followed. Electrokinetic injection (10 kV, 500 s) was used to load samples and to enhance sensitivity. The stacking step and separation were performed at -20 kV and 200 nm using phosphate buffer (25 mM, pH 2.5) containing 20% methanol and 100 mM sodium dodecyl sulfate. Using CSEI-Sweep-MEKC, the analytes could be simultaneously analyzed and have a detection limit down to ppb level. It was unnecessary to have sample pretreatments. During method validation, calibration plots were linear (r>or=0.9982) over a range of 150-3,000 ng/mL for M and C, 250-5,000 n g/mL for MA, and 50-1,000 ng/mL for K. The limits of detection were 15 ng/mL for M and C, and 5 ng/mL for MA and K (S/N=3, sampling 500 s at 10 kV). Comparing with capillary zone electrophoresis, the results indicated that this stacking method could increase 6,000-fold sensitivity for analysis of MA. Our method was applied for analysis of 28 real urine samples. The results showed good coincidence with immunoassay and GC-MS. This method was feasible for application to detect trace levels of abused drugs in forensic analysis.

Analysis of amphetamine, methamphetamine and methylenedioxy-methamphetamine by micellar capillary electrophoresis using cation-selective exhaustive injection

Cation-selective exhaustive injection (CSEI) is used as an on-line concentration method for the high-sensitivity analysis of illicit amphetamines using CE. Optimum conditions for the determination of amphetamine, methamphetamine and methylenedioxy-methamphetamine were investigated. Sodium dodecyl sulfate (25 mM) in 100 mM phosphate buffer (pH 2.9) with 20% methanol as organic additive was used as the background electrolyte for CE separation. The LOD, based on an S/N of 3:1, was about 0.01 microg/mL using normal capillary micellar electrokinetic chromatography, while by using CSEI in combination with micellar sweeping the sensitivity increased up to 1000-fold with the LOD lower than 50 pg/mL. The reproducibility of CSEI combined with micellar sweeping for analyzing amphetamines was satisfactory (relative standard deviation around 10% by using area ratios against an internal standard). This method is highly sensitive and can be used to analyze trace amount amphetamines in human hair.

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).

Analysis of triazolopyrimidine herbicides in soils using field-enhanced sample injection-coelectroosmotic capillary electrophoresis combined with solid-phase extraction

In this work, a combined methodology using off-line solid-phase extraction (SPE), on-line field-enhanced sample injection (FESI) and coelectroosmotic capillary electrophoresis with UV detection (CE-UV) is developed for the trace analysis of five triazolopyrimidine sulfonanilide pesticides (i.e., flumetsulam, florasulam, cloransulam-methyl, diclosulam and metosulam). An adequate background electrolyte (BGE) was obtained for the separation of these pesticides using hexadimethrine bromide (HDB) as electroosmotic flow (EOF) modifier. This BGE consisted of 0.00042% HDB, 11 mM formic acid, 16 mM ammonium carbonate and 2.5 mM alpha-CD solution at pH 7.6. The use of this running buffer together with the FESI preconcentration method provided limits of detection (LODs) in the low microg/L range (i.e., between 13.0 and 31.5 microg/L). The optimized FESI-CE-UV method was combined with off-line SPE using C(18) cartridges and applied to the determination of the selected group of pesticides in soil samples. Recovery percentages ranged between 50 and 84% in these samples with LODs between 18 and 34 microg/kg. This work shows the great possibilities of the combined use of SPE-FESI-CE-UV to improve CE sensitivity allowing the achievement of LODs similar to other analytical techniques as GC or HPLC.

Head-column field-amplified sample stacking in a capillary electrophoresis-flow injection system

A simple, effective, and continuous online concentration method for the sensitive detection of alkaloids applying CE-flow injection analysis with head-column field-amplified sample stacking was developed. A series of samples was continuously introduced into the capillary by electrokinetic means without interrupting the high voltage. A short water plug was introduced by the EOF at the capillary inlet end prior to sample introduction. Under optimum conditions, 15-fold improvement in concentration sensitivity was achieved, giving an LOD of about 0.67 and 0.73 microg/mL for ephedrine (E) and pseudoephedrine (PE), respectively. The separation could be achieved within 4 min and sample throughput rate could reach up to 7/h. The repeatability (defined as RSD) was 3.62, 1.51% with peak area evaluation and 1.30, 2.58% with peak height evaluation for E and PE, respectively. This method has been successfully applied to the analysis of commercial pharmaceutical preparations containing E and PE, and the recoveries were 92.3-102.4%.

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.

Field-amplified sample stacking in capillary electrophoresis for the determination of clozapine, clozapine N-oxide, and desmethylclozapine in schizophrenics’ plasma

A method of field-amplified sample stacking in capillary electrophoresis is described for the simultaneous determination of clozapine (CZP) and its metabolites, clozapine N-oxide (CNO), and desmethylclozapine (DMC), in human plasma. Plasma (0.2 mL) was extracted with organic solvents (ethyl acetate/n-hexane/isopropyl alcohol, 8/1/1 by volume) and centrifuged. An aliquot of supernatant was evaporated and suitably reconstituted with water for CE analysis. An untreated fused-silica capillary was used (31.2 cm; effective length, 20 cm; 50 microm i.d.) for the analysis. The background buffer was phosphate buffer (400 mM, pH 3.0) containing 50% ethylene glycol. The separation voltage was 25 kV with a detection wavelength of 214 nm. In the method validation, the calibration curves were linear (r > or = 0.98) over a range of 50-800 ng/mL for CZP, 30-180 ng/mL for CNO, and 25-600 ng/mL for DMC. The relative standard deviation (R.S.D.) and relative error (R.E.) were all less than 11% for the intra- and inter-day assays. The limits of detection (S/N = 3, electric-driven injection, 99.9s) of CZP, DMC, and CNO were 5, 5, and 10 ng/mL, respectively. After continuing treatment with the CZP tablets, a blood sample from one male schizophrenic patient (41-year-old, 62 kg) who had been receiving ongoing treatment with the CZP tablets was prepared and analyzed. The levels of CZP, DMC, and CNO were determined and the feasibility of the method's application in clinical treatment was proven.

Is capillary electrophoresis a method of choice for systematic toxicological analysis?

This review presents an overview of current research on the use of capillary electrophoretic techniques for the analysis of drugs in biological matrices. The discussion focuses on the applicability of the methods for the identification of unknown toxic compounds, which is defined as systematic toxicological analysis (STA). The aim is to establish whether or not capillary electrophoresis (CE), in one or more of its separation modes, is a method of choice in systematic toxicological analysis. To answer this question, various aspects are discussed, including sample work-up, separation modes, detection techniques, electrophoretic concentration, and identification by database retrieval. Several ways to improve the poor reproducibility and sensitivity are discussed. This leads to the conclusion that CE can be comparable to HPLC in those respects, while it is more favorable in speed, efficiency, and cost. Thus, we conclude that CE is a method of choice for STA, keeping in mind that every method has its limitations and that a combination of several non-correlated methods is always required for the identification of unknown compounds.

Advantages and limitations of coupling isotachophoresis and comprehensive isotachophoresis-capillary electrophoresis to time-of-flight mass spectrometry

Capillary isotachophoresis (ITP) and comprehensive isotachophoresis-capillary electrophoresis (ITP-CE) were successfully coupled to electrospray ionization (ESI) orthogonal acceleration time-of-flight mass spectrometry (TOF-MS) using angiotensin peptides as model analytes. The utility of ITP-TOF-MS and ITP-CE-TOF-MS for the analysis of samples containing analyte amounts sufficient to form flat-top ITP zones (30 microM) as well as for samples with trace analyte amounts (0.3 microM) was studied. Separations were performed in 150 microm internal diameter (I.D.) capillaries for the ITP experiments, and in 200 microm I.D. (ITP) and 50 microm I.D. (CE) capillaries for ITP-CE experiments. The fused-silica columns were coated with poly(vinyl alcohol) to suppress electroosmotic flow that can disrupt ITP zone profiles. The sample loading capacity in both ITP and comprehensive ITP-CE was greatly enhanced (up to 10 microl) compared with typical nanoliter-sized injection volumes in CE. It was concluded that ITP-TOF-MS alone was adequate for the separation and detection of high concentration samples. The outcome was different at lower analyte concentrations where mixed zones or very sharp peaks formed. With formation of mixed zones, ion suppression and discrimination could occur, complicating quantitative determination of the analytes. This problem was effectively overcome by inserting a CE capillary between the ITP and TOF-MS. In such an arrangement, samples were preconcentrated in the high load WTP capillary and then injected into a CE capillary where they were separated into non-overlapping peaks prior to their detection by TOF-MS. The advantage of this comprehensive arrangement, which we have described previously, is that there is no need to discard portions of the sample in order to avoid overloading of the CE capillary. The whole sample is analyzed by multiple injections from ITP to CE. Thus, this method can be used for the analysis of complex samples with wide ranges of component concentrations.

Electrophoretic analysis of amines using reversed-phase, reversed-polarity, head-column field-amplified sample stacking and laser-induced fluorescence detection

This paper describes the use of reversed-phase, reversed-polarity head-column field-amplified sample stacking (HCFASS) for on-line sample concentration in conventional capillary electrophoresis. The effective stacking efficiency was determined as a function of sodium hydroxide concentration in the sample matrix. Results concur with theoretical predictions where stacking efficiency depends on the conductivity (electric field strength) and electrophoretic mobility in the sample matrix solution. Fluorescein isothiocyanate-derivatized aniline and 2,4-dimethylaniline were dissolved in sodium hydroxide (800 microM), separated in a phosphate running buffer (0.05 M, pH 9.0) and detected utilising laser-induced fluorescence. The use of reversed-phase, reversed-polarity HCFASS with laser-induced fluorescence detection yielded sensitivity improvements with respect to normal injection schemes in excess of three orders of magnitude, and a limit of detection as low as 10(-13) M.

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

Throughout the separation of chiral basic drugs by capillary electrophoresis (CE) with neutral hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as chiral selector, the sensitivity of detection has been improved by using field-amplified sample injection (FASI). In the present work, this on-line stacking method has been used to detect low ng/mL levels of cationic enantiomers of a new adrenoreceptor antagonist in plasma. A systematic study of the parameters affecting on-line concentration of these enantiomers (nature of the preinjection plug, composition of sample solvent, injection times of water and sample plugs) has been performed enabling the detection sensitivity of antagonist enantiomers to be improved by 180 times compared with usual hydrodynamic injection. The quantification of each adrenoreceptor antagonist enantiomer in plasma samples was then performed in the 2-100 ng/mL (or 8-400 nM) concentration range after a solid-phase extraction step. Using this FASI-CE-UV procedure, the limit of quantification (LOQ) for each enantiomer was in the low ng/mL concentration range (3 ng/mL or 10 nM).

Capillary electrophoresis and capillary electrophoresis-ion trap multiple-stage mass spectrometry for the differentiation and identification of oxycodone and its major metabolites in human urine

Oxycodone (OCOD) and its metabolites, including oxymorphone (OMOR), noroxycodone (NOCOD) and noroxymorphone (NOMOR), are opioids that carry an OH group at position 14. Using capillary electrophoresis (CE) with a binary phosphate buffer containing 60% ethylene glycol (pH 7.9), the migration order of OCOD and OMOR with respect to their N-demethylated analogs was found to be reversed compared to that observed for codeine, dihydrocodeine, morphine and dihydromorphine, compounds that do not have an OH group at position 14. OCOD and structurally related compounds can also be distinguished from these opioids by their absorbance spectra at low wavelengths and via a characteristic neutral H2O loss at the MS2 level. Using the binary phosphate buffer, CE with UV detection is shown to be capable of monitoring OCOD, NOCOD, OMOR (after hydrolysis only) and NOMOR (after hydrolysis and in patient urine only) in alkaline liquid-liquid extracts of urines that were collected after ingestion of 10 mg OCOD hydrochloride and in a patient urine collected at steady state (80 mg OCOD hydrochloride daily). Using an aqueous pH 9 ammonium acetate buffer, these results were confirmed by CE-MS3. Based on CE-MS, MS2 and MS3 data, the absorbance spectra measured across the CE peaks and the relative position within the electropherogram, two peaks monitored in the UV absorbance electropherograms could be assigned to the two keto-reduced metabolites 6oxycodol (60COL) and nor6oxycodol, for which no standards were available. Comparison of data obtained with urines pretreated with two different enzyme products (beta-glucuronidase and beta-glucuronidase/arylsulfatase) suggest that OCOD, NOCOD and 6OCOL are mainly glucuronidated, whereas OMOR mainly forms other conjugates. Furthermore, in a first attempt to directly measure conjugates of the compounds of interest, solid-phase extracts were analyzed by CE-MS4, which revealed the presence of the acyl glucuronides of 6OCOL and OMOR and an unidentified OMOR conjugate. The quantitation of free OCOD and NOCOD by CE-MS using deuterated internal standards is also discussed briefly.

Improving separation efficiency of capillary zone electrophoresis of tryptophan and phenylalanine with the transient moving chemical reaction boundary method

A simple and convenient mode--moving chemical reaction boundary method-capillary zone electrophoresis (MCRBM-CZE)--was designed for the enhancement of separating efficiency of CZE. In this mode, the transient MCRBM is used for the on-line pre-treatment of sample. By analyses of tryptophan (Trp) and phenylalanine (Phe) as an example, the experiments by MCRBM-CZE were carried out and further compared with those by normal CZE without the transient MCRBM. The results reveal that by carefully selected appropriate electrolytes, a strong condensation effect can be achieved by using MCRBM-CZE; this effect can greatly improve the separation efficiency, resolution and peak height of Trp and Phe in CZE as compared with those of normal CZE of Trp and Phe. Even if the sample comprises high concentrations of salt, such as 80 mM NaCl (concentration of sodium ion up to 145.6 mM), the same condensation effect can also been observed; this implies obvious significance for biological samples like urine and serum. However, if the electrolytes was chosen inappropriately only a poor compression effect of sample was observed in the MCRBM-CZE runs.

Highly sensitive chemiluminescence detection of copper(II) in capillary electrophoresis with field-amplified sample injection

Field-amplified sample injection of copper(II) was investigated using capillary electrophoresis with chemiluminescence detection. The sensitivity of copper(II) has been improved markedly by the field-amplified sample injection technique and the detection limit reaches 2 x 10(-11) M. By injection of a short plug of water before sample introduction, the sensitivity can be further improved 5-fold and the detection limit reaches 4 x 10(-12) M. The relative standard deviations (n = 6) of the migration time and the peak height are 0.61% and 4.7% at 1.0 x 10(-9) M Cu(II), respectively. Parameters affecting the field-amplified sample injection, such as separation voltage and concentration of electrophoretic buffer, have been investigated.

Advances ofcapillary electrophoresis in clinical and forensic analysis (1999-2000)

In this paper, capillary electrophoresis in clinical and forensic analysis is reviewed on the basis of the literature of 1999, 2000 and the first papers in 2001. An overview of progress relevant examples for each major field of application, namely (i) analysis of drug seizures, explosives residues, gunshot residues and inks, (ii) monitoring of drugs, endogenous small molecules and ions in biofluids and tissues, (iii) general screening for serum proteins and analysis of specific proteins (carbohydrate deficient transferrin, alpha1-antitrypsin, lipoproteins and hemoglobins) in biological fluids, and (iv) analysis of nucleic acids and oligonucleotides in biological samples, including oligonucleotide therapeutics, are presented.

Quantitation and on-line concentration of enantiomers in open-tubular capillary electrochromatography

The feasibility of open-tubular capillary electrochromatography (OTCEC) with UV detector for quantitation of enantiomers is explored, and a simple on-line sample concentration method to improve detection sensitivity of negatively charged enantiomers more than 1000-fold is described. With a capillary of 25 microm ID, the limits of detection (LODs) for absolute concentration and for enantiomeric ratio are 10(-6) M and 0.6-0.8% (signal-to-noise ratio S/N = 10). Good linearity and reproducibility are observed. The detection sensitivity is enhanced by combination with field-enhanced sample injection (FESI). A water plug is introduced hydrodynamically into the capillary inlet end and then the sample solution prepared with water is introduced with electrokinetic injection. With this concentration technique, the LOD for absolute concentration is reduced to a 10(-9) M level. On the other hand, due to the peak-sharpening effect of FESI, the LOD for enantiomeric ratio for the first-eluted enantiomer is significantly improved, being 0.3%. Effects of the injection conditions, such as length of water plug, buffer concentration, injection voltage, and injection time on the enrichment efficiency are investigated. Online concentration of a racemic compound with two chiral centers is demonstrated.

Head-column field-amplified sample stacking in capillary electrophoresis for the determination of cimetidine, famotidine, nizatidine, and ranitidine-HCl in plasma

In this study, low concentrations of histamine2-receptor (H2-)antagonists were effected across a water plug, with separation taking place in a binary buffer comprising ethylene glycol and NaH2PO4 (pH 5.0), and detection at 214 nm. Liquid-liquid extraction with ethyl acetate- isopropanol is shown to provide extracts that are sufficiently clean. The calibration curves were linear over a concentration range of 0.1-2.00 microg/mL cimetidine, 0.2-5.0 microg/mL ranitidine-HCl, 0.3-5.0 microg/mL nizatidine, and 0.1-3.0 microg/mL famotidine. Mean recoveries were > 82%, while the intra- and interday relative standard deviations (RSDs) and relative errors (REs) were all < 13%. The method is sensitive with a detection limit of 3 ng/mL cimetidine, 30 ng/mL ranitidine HCl, 50 ng/mL nizatidine and 10 ng/mL famotidine (S/N = 3, electric-driven injection 90 s). This newly developed capillary electrophoresis (CE) method was applied for the determination of analytes extracted from plasma taken from a volunteer dosing a cimetidine, ranitidine, and nizatidine tablet simultaneously. These three H2-antagonists can be detected in real samples by this method, excluding the low dosing of famotidine tablet.

Head-column field-amplified sample stacking in presence of siphoning. Application to capillary electrophoresis-electrospray ionization mass spectrometry of opioids in urine

Capillary electrophoresis (CE) with head-column field-amplified sample stacking (FASS) in presence of a water plug inserted at the capillary tip is a robust approach providing a more than 1000-fold sensitivity enhancement when applied to low-conductivity samples that are analyzed in an integrated instrument. Employing modular systems comprising a small hydrodynamic buffer flow (siphoning) towards the capillary end and featuring UV absorption or electrospray ionization mass spectrometric (MS) detection, insertion of a water plug is demonstrated to deteriorate the performance of head-column FASS or making it unfunctional. Electroinjection in the absence of the water plug can be employed instead and is shown to provide a ng/ml sensitivity when applied to low conductivity samples. With some suction of sample into the capillary during electroinjection, contamination of the sample vial with buffer is thereby largely avoided. Electroinjection applied to the CE-ion trap MS-MS and MS-MS-MS analysis of twofold diluted urines, urinary solid-phase extracts and urinary liquid-liquid extracts is shown to provide much improved sensitivity compared to hydrodynamic injection of these samples. With electroinjection from diluted urine and urinary solid-phase extracts, the presence of free opioids and their glucuronic acid conjugates can be unambiguously confirmed in urines that were collected after single-dose administration of small amounts of opioids (tested with about 7 mg codeine and 25 mg dihydrocodeine, respectively). Thus, CE-multiple MS with direct electroinjection of opioids from untreated urines could prove to become a rapid and simple approach for unambiguous urinary testing of drug abuse. Procedures leading to the reduction of siphoning in modular CE setups are briefly discussed as well.

Capillary electrophoresis-electrospray ionization ion trap mass spectrometry for analysis and confirmation testing of morphine and related compounds in urine

Using an aqueous background electrolyte containing 25 mM ammonium acetate and NH3 (pH 9), CE-tandem MS and CE-triple MS with atmospheric pressure electrospray ionization in the positive ion mode are shown to represent attractive approaches for analysis and confirmation testing of morphine (MOR) and related opioids in human urine. Injection of plain or diluted urine permits monitoring of solutes at concentrations above 2-5 microg/ml. For the recognition of lower concentrations, solute extraction and concentration is required. Liquid-liquid extraction at alkaline pH is shown to be suitable for analysis of free opioids only whereas solid-phase extraction using a mixed-mode polymer phase is demonstrated to permit analysis of both free and glucuronidated opioids. The former sample preparation approach, however, requires about half of the time only. Commencing with 2 ml of urine, reconstitution to provide a sample volume of 0.2 ml and hydrodynamic sample injection, detection limits for free opioids are shown to be on the 100-200 ng/ml drug level. Much improved (ppb) sensitivity is obtained by infusing the extract directly into the source of the MS system. However, solutes that produce equal fragments (such as the two glucuronides of MOR) can thereby not be distinguished. CE-tandem MS and CE-triple MS are demonstrated to be suitable to confirm the presence of MOR, MOR-3-glucuronide, 6-monoacetylmorphine, codeine, codeine-6-glucuronide, dihydrocodeine, methadone and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in a toxicological quality control urine. The same is shown for selected metabolites of codeine and dihydrocodeine in urines collected after administration of pharmaceutical preparations.

Sample stacking of cationic and anionic analytes in capillary electrophoresis

The behavior of charged species along concentration boundaries in capillary zone electrophoresis (CZE) that was first described in detail by Everaerts et al. in 1979 assured the possibility of concentrating charged solutes inside the capillary. The concentration effect is based on the sudden change in analyte electrophoretic velocity brought about by the difference in the magnitude of the electric field. Furthermore, this on-line method could be the needed solution to the problem of low concentration sensitivity in CZE. Sample stacking, which is now its well known name, has then found valuable use in applying CZE in many fields, especially after the in-depth studies performed in the early 90s by Chien and Burgi. This article reviews the theory and methodological developments of sample stacking developed for charged analytes in CZE and also in electrokinetic chromatography. A table conveying the reported applications especially in the biomedical and environmental fields is given. On top of this, other on-line concentration methods for charged species, namely, sample self-stacking, acetonitrile stacking, sweeping, cation selective exhaustive injection-sweeping, and use of a pH junction, are briefly discussed.

Stacking in capillary zone electrophoresis

Due to the short light path of the capillaries, the CE detection limit based on concentration, is far less than that of HPLC and not sufficient for many practical applications. Several methods, based on different electrophoretic maneuvers, can concentrate the sample (stack) easily on the capillary before the separation step of capillary zone electrophoresis (CZE). These methods incorporate different types of discontinuous buffers as the means for invoking different velocities to the same analyte molecules to produce a sharpening of the band (stacking). In CZE, these buffers can be often very simple such as sample dilution or adding to the sample a high concentration of a fast mobility ion. However, in other applications these buffers can be as complicated as those required for isotachophoresis. Stacking can often yield a concentration factor of 5-30-fold, which can improve greatly in CZE the detection limits bringing them very close to those of HPLC. Different methods of stacking, the importance of discontinuous buffers and the different mechanism for concentration on the capillary are reviewed here. As there is a need for more practical applications, there will be more methods devised for stacking in CZE.

Liquid-liquid extraction procedures for sample enrichment in capillary zone electrophoresis

This review article presents an overview of applications of liquid-liquid extraction (LLE) for analyte enrichment and clean-up of samples prior to capillary zone electrophoresis (CZE). The basic principles of LLE are discussed with special emphasis on analyte enrichment. In addition, attention is focused on the requirements for the final extract to be compatible with CZE. The paper discusses selected examples from the literature with special emphasis on detection limits in drug analysis and in environmental chemistry. Finally, the paper focus on alternative liquid-phase extraction concepts based on electroextraction, supported liquid membranes, and liquid-phase microextraction.

Analysis of codeine, dihydrocodeine and their glucuronides in human urine by electrokinetic capillary immunoassays and capillary electrophoresis-ion trap mass spectrometry

Screening for and confirmation of illicit, abused and banned drugs in human urine is a timely topic in which capillary separation techniques play a key role. Capillary electrophoresis (CE) represents the newest technology employed in this field of analysis. Two rapid competitive binding, electrokinetic capillary-based immunoassays are shown to be capable of recognizing the presence, but not the identity, of urinary opioids, namely codeine (COD), codeine-6-glucuronide, dihydrocodeine (DHC), dihydrocodeine-6-glucuronide, morphine (MOR), morphine-3-glucuronide and ethylmorphine (EMOR). In these approaches, aliquots of urine and immunoreagents of a commercial, broadly cross-reacting fluorescence polarization immunoassay for opiates were combined and analyzed by capillary zone electrophoresis or micellar electrokinetic capillary chromatography with laser induced fluorescence detection. With the fluorescent tracer solution employed, the former method is shown to provide simple electropherograms which are characterized by an opioid concentration dependent magnitude of the free tracer peak. In presence of dodecyl sulfate micelles, however, two tracer peaks with equal opioid concentration sensitivity are monitored. These data suggest the presence of two fluorescent tracers which react competitively with the urinary opioids for the binding sites of the antibody. Assay sensitivities for COD and MOR are comparable (10 ng/ml), whereas those for DHC and EMOR are about four-fold lower. Furthermore, glucuronides are shown to react like the corresponding free opioids. Analysis of urines that were collected after administration of 7 mg COD and 25 mg DHC tested positively in both assay formats. The presence of the free and conjugated codeinoids in these urines and their identification was accomplished by capillary electrophoresis-ion trap mass spectrometry (CE-MS). This confirmatory assay is based upon solid-phase extraction using a mixed-mode polymer cartridge followed by CE hyphenated to the LCQ mass spectrometer with electrospray ionization in the positive ion mode. With this technology, MS2 is employed for proper identification of COD (m/z 300.4) and DHC (m/z 302.4) whereas MS3 provides unambiguous identification of the glucuronides of COD (m/z 476.5) and DHC (m/z 478.5) via their fragmentation to COD and DHC, respectively. MSn (n > or = 2) is shown to be capable of properly identifying the urinary codeinoids on the 100-200 ng/ml concentration level.

On-line preconcentration methods for capillary electrophoresis

The limits of detection (LOD) for capillary electrophoresis (CE) are constrained by the dimensions of the capillary. For example, the small volume of the capillary limits the total volume of sample that can be injected into the capillary. In addition, the reduced pathlength hinders common optical detection methods such as UV detection. Many different techniques have been developed to improve the LOD for CE. In general these techniques are designed to compress analyte bands within the capillary, thereby increasing the volume of sample that can be injected without loss of CE efficiency. This on-line sample preconcentration, generally referred to as stacking, is based on either the manipulation of differences in the electrophoretic mobility of analytes at the boundary of two buffers with differing resistivities or the partitioning of analytes into a stationary or pseudostationary phase. This article will discuss a number of different techniques, including field-amplified sample stacking, large-volume sample stacking, pH-mediated sample stacking, on-column isotachophoresis, chromatographic preconcentration, sample stacking for micellar electrokinetic chromatography, and sweeping.

Improvement of capillary zone electrophoresis sensitivity with artificial seawater as the background electrolyte utilizing transient isotachophoresis for the determination of nitrate and nitrate ions in seawater

We describe capillary zone electrophoresis (CZE) with transient isotachophoresis (ITP) for the determination of low concentrations of nitrite and nitrate ions in seawater. Bromide-free artificial seawater was adopted as background electrolyte (BGE) to eliminate the interference of high concentrations of salts in seawater. To reverse the electroosmotic flow (EOF), 3 mM cetyltrimethylammonium chloride (CTAC) was added to the BGE. High concentrations of chlorate were added to sample solutions as the terminating ion to generate the ITP process before the CZE separation. In general, the stacking effect increased with increasing amounts of chlorate injected into the capillary. The limits of detection (LODs) for nitrite and nitrate were 0.063 and 0.033 mg/L when the chlorate concentration was 600 and 200 mM, respectively; these were half of those obtained by CZE without the transient ITP. The LODs were obtained at a signal to noise ratio (S/N) of 3. The relative standard deviations (RSD, n = 10) of the peak areas for these ions were 3.2 and 2.9%. The RSDs of peak heights for these ions were 1.6 and 2.1%. The RSDs of migration times for these ions were 0.67 and 0.46%.

Sample self-stacking in capillary zone electrophoresis: behavior of samples containing multiple major coionic components

It is a frequent phenomenon in practice that a sample contains bulk levels of more than one coionic component that affect the stacking behavior of minor analytes and in this way also the sensitivity of the method. Here, attention is paid to stacking resulting from the presence of a macrocomponent of leading type that is deteriorated by the presence of another macrocomponent of like charge in the sample. Based on the isotachophoretic model of migration in the initial period of separation, a theoretical approach was elaborated both for strong and weak electrolytes which describes the separation process and finds the conditions that define whether transient isotachophoretic stacking of the analyte takes place or not. It is shown that the crucial parameter is the ratio of the concentrations of macrocomponents migrating in front and behind the analyte of interest. The destacking effect can also be expected when the coion of the background electrolyte is present in the sample. Rules how to cope with effects of destackers present in the sample are given. Theoretical considerations are illustrated by computer simulations and verified experimentally. Examples of antagonistic effects of macrocomponents are demonstrated for model serum samples.

Capillary electrophoresis in clinical and forensic analysis: recent advances and breakthrough to routine applications

This paper is a comprehensive review article on capillary electrophoresis (CE) in clinical and forensic analysis. It is based upon the literature of 1997 and 1998, presents CE examples in major fields of application, and provides an overview of the key achievements encountered, including those associated with the analysis of drugs, serum proteins, hemoglobin variants, and nucleic acids. For CE in clinical and forensic analysis, the past two years witnessed a breakthrough to routine applications. As most coauthors of this review are associated with diagnostic or forensic laboratories now using CE on a routine basis, this review also contains data from routine applications in drug, protein, and DNA analysis. With the first-hand experience of providing analytical service under stringent quality control conditions, aspects of quality assurance, assay specifications for clinical and forensic CE and the pros and cons of this maturing, cost-and pollution-controlled age technology are also discussed.