Quality testing of human albumin by capillary electrophoresis using thermally cross‐linked poly(vinyl pyrrolidone)‐coated fused‐silica capillary

To detect the quality of medicinal human albumin by capillary electrophoresis, we produced a fused‐silica capillary coated with thermally cross‐linked poly(vinyl pyrrolidone) to prohibit protein adsorption. This type of capillary was easily obtained by injecting an aqueous poly(vinyl pyrrolidone) solution into a fused‐silica capillary and thermally annealing it at 200°C. Notably, stable and low electro‐osmotic flow was obtained in the poly(vinyl pyrrolidone)‐coated capillary at pH 2.20–9.00, and the separation of a mixture of four basic proteins indicated that the poly(vinyl pyrrolidone)‐coated capillary exhibits excellent repeatability and separation efficiency; moreover, the separation of these four basic proteins could even be achieved at pH 7.00. The protein recovery percentage of human serum albumin in a single‐protein solution and a mixed blood proteins solution was determined to be 97.03 and 95.40% in the poly(vinyl pyrrolidone)_50–3 (representing the concentration of the capillary‐injected poly(vinyl pyrrolidone) aqueous solution, 50 mg/mL, and thermal annealing time, 3 h) capillary, respectively. Based on these results, we used the poly(vinyl pyrrolidone)_50–3‐coated capillary to quantify the protein content of human albumin, and the results obtained from run to run, day to day and capillary to capillary demonstrated that the coated capillary could be used for quality testing commercially available human albumin.     

Surface initiated polymerization of a cationic monomer on inner surfaces of silica capillaries: Analyte separation by capillary electrophoresis versus polyelectrolyte behavior

[2‐(Methacryloyl)oxyethyl]trimethylammonium chloride was successfully polymerized by surface‐initiated atom transfer radical polymerization method on the inner surface of fused‐silica capillaries resulting in a covalently bound poly([2‐(methacryloyl)oxyethyl]trimethylammonium chloride) coating. The coated capillaries provided in capillary electrophoresis an excellent run‐to‐run repeatability, capillary‐to‐capillary and day‐to‐day reproducibility. The capillaries worked reliably over 1 month with EOF repeatability below 0.5%. The positively charged coated capillaries were successfully applied to the capillary electrophoretic separation of three standard proteins and five β‐blockers with the separation efficiencies ranging from 132 000 to 303 000 plates/m, and from 82 000 to 189 000 plates/m, respectively. In addition, challenging high‐ and low‐density lipoprotein particles could be separated. The hydrodynamic sizes of free polymer chains in buffers used in the capillary electrophoretic experiments were measured for the characterization of the coatings.     

Capillary electrophoresis using core‐based hyperbranched polyethyleneimine (CHPEI) static‐coated capillaries

With unique 3‐D architecture, the application of core‐based hyperbranched polyethyleneimine (CHPEI), as a capillary coating in capillary electrophoresis, is demonstrated by manipulation of the electroosmotic mobility (EOF). CHPEI coatings (CHPEI5, M_w ≈? 5000 and CHPEI25, M_w ≈? 25 000) were physically adsorbed onto the inner surface of bare fused‐silica capillary (BFS) via electrostatic interaction of the oppositely charged molecules by rinsing the capillaries with different CHPEI aqueous solutions. The EOF values of the coated capillaries were measured over the pH range of 4.0–9.0. At higher pH (pH >6) the coated capillary surface possesses excess negative charges, which causes the reversal of the EOF. The magnitudes of the EOF obtained from the coated capillaries were three‐fold lower than that of BFS capillary. Desirable reproducibility of the EOF with % RSD (n = 5) ? 2 was obtained. Effect of ionic strength, stability of the coating (% RSD = 0.3) and the dependence of the EOF on pH (% RSD = 0.5) were also investigated. The CHPEI‐coated capillaries were successfully utilized to separate phenolic compounds, B vitamins, as well as basic drugs and related compounds with reasonable analysis time (<20 min) and acceptable migration‐time repeatability (<0.7% RSD for intra‐capillary and <2% RSD for inter‐capillary).     

Efficient and reproducible analysis of peptides by capillary electrophoresis using noncovalently bilayer-coated capillaries

The usefulness of a noncovalent capillary coating consisting of two layers of oppositely charged polymers for the separation of peptides with capillary electrophoresis (CE) was studied. Capillaries were coated simply by subsequently flushing with solutions of 1% m/v Polybrene and 1% v/v poly(vinylsulfonate) (PVS) forming a bilayer, which showed to produce a strong and highly reproducible electroosmotic flow (EOF) at low pH. Using this coating in combination with a background electrolyte (BGE) containing sodium phosphate (pH 2.5) and 0.01% v/v PVS, initially broadened and overlapping peaks were obtained for some test peptides. By omitting the PVS from the BGE, the peak width and shape of the peptides improved resulting in baseline separation. A systematic study of the influence of the BGE composition showed that considerable further enhancement of the separation efficiency was achieved by increasing the ionic strength of the BGE. Using a BGE of 200 mM tris(hydroxymethyl)aminomethane (Tris)-phosphate (pH 2.5) plate numbers for the peptides were in the 300 000-600 000 range and the relative standard deviation of the peptide migration times was less then 0.3% (n = 5). The use of Tris-phosphate instead of sodium phosphate allowed the current to stay within acceptable limits when 30 kV was used as separation voltage. Overall, the bilayer coating showed a remarkable EOF repeatability, as well as long-term stability. Compared to bare fused-silica capillaries the intraday and interday repeatability of migration times was very favorable and coated capillaries could be used for over a month performing analyses with low and high ionic strength BGEs without any performance deterioration. The usefulness of the bilayer-coated capillaries for the analysis of positively charged peptides was demonstrated by the fast and efficient separation of various closely related enkephalins and the baseline separation of an isomeric peptide/peptoid couple exhibiting efficiencies of over 550 000 plates.     

Capillary Electrophoretic Separation of Tricyclic Antidepressants Using 1‐Alkyl‐3‐Methylimidazolium‐Based Ionic Liquids as Background Electrolyte

A capillary electrophoretic (CE) method coupled with the use of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (1E‐3MI‐TFB) ionic liquid as background electrolyte (BGE) has been developed for the simultaneous separation of nine tricyclic antidepressants, viz. amitriptyline (Ami), clomipramine (Clo), desipramine (Des), fluphenazine (Flu), imipramine (Imi), nortriptyline (Nor), promazine (Pro), thioridazine (Thi) and trimipramine (Tri). Resolution of TCAs with similar molecular structures and pK_a values was accomplished by minute manipulation of the electrophoretic velocities of TCAs via reversed electroosmotic flow (EOF) generated by adsorption of 1E‐3MI cations onto the capillary wall. The optimal separation was obtained with a 50 mM 1E‐3MI‐TFB as the sole BGE at pH 3. Symmetric peaks with efficiencies up to 2.4 × 10⁵ plates/m were achieved. RSD values on migration times and peak areas were in the ranges of 0.63–0.95% and 3.41–6.34% (n = 4), respectively. The role of different alkyl groups on the imidazolium cations was also investigated.     

Separation of somatropin charge variants by multiple‐injection CZE with Polybrene/chondroitin sulfate A double‐coated capillaries

The performance of dynamic double‐coated fused‐silica capillaries with Polybrene and chondroitin sulfate A has been compared with uncoated fused‐silica capillaries for the determination of recombinant human growth factor (somatropin) charge variants. The separations were carried out under the same electrophoretic conditions as described in the European Pharmacopoeia, i.e. at pH 6.0 and 30°C. The coating significantly reduced the interactions between the proteins and the surface of the fused‐silica capillary. The first five separations performed in a new bare fused‐silica capillary were discarded because of very poor separation performance as a result of protein–surface interactions. There was an approximate twofold increase in the interday migration time precision (%RSD ≤ 6.5%) in the double‐coated capillaries. The method was successfully transferred to a multiple CZE mode where two samples were analyzed in a single electrophoretic run. The average purity of somatropin certified reference standard was 98.0% (%RSD ≤ 0.3%) determined by using uncoated and coated capillaries.     

Design and evaluation of capillary coupled with optical fiber light‐emitting diode induced fluorescence detection for capillary electrophoresis

A new detector, capillary coupled with optical fiber LED‐induced fluorescence detector (CCOF‐LED‐IFD, using CCOF for short), is introduced for CE. The strategy of the present work was that the optical fiber and separation capillary were, in the parallel direction, fastened in a fixation capillary with larger inner diameter. By employing larger inner diameter, the fixation capillary allowed the large diameter of the optical fiber to be inserted into it. By transmitting an enhanced excitation light through the optical fiber, the detection sensitivity was improved. The advantages of the CCOF‐CE system were validated by the detection of riboflavin, and the results were compared to those obtained by the in‐capillary common optical fiber LED‐induced fluorescence detector (IC‐COF‐LED‐IFD, using COF for short). The LODs of CCOF‐CE and COF‐CE were 0.29 nM and 11.0 nM (S/N = 3), respectively. The intraday (n = 6) repeatability and interday (n = 6) reproducibility of migration time and corresponding peak area for both types of CE were all less than 1.10 and 3.30%, respectively. The accuracy of the proposed method was judged by employing standard addition method, and recoveries obtained were in the range of 98.0–102.4%. The results indicated that the sensitivity of the proposed system was largely improved, and that its reproducibility and accuracy were satisfactory. The proposed system was successfully applied to separate and determine riboflavin in real sample.     

An air‐assisted flow‐gating interface for capillary electrophoresis

A new kind of flow gating interface (FGI) has been designed for online connection of CE with flow‐through analytical techniques. The sample is injected into the separation capillary from a space from which the BGE was forced out by compressed air. A drop of sample solution with a volume of 75 nL is formed between the outlet of the delivery capillary supplying the solution from the flow‐through apparatus and the entrance to the CE capillary; the sample is hydrodynamically injected into the CE capillary from this drop. The sample is not mixed with the surrounding BGE solution during injection. The functioning of the proposed FGI is fully automated and the individual steps of the injection process are controlled by a computer. The injection sequence lasts several seconds and thus permits performance of rapid sequential analyses of the collected sample. FGI was tested for the separation of equimolar 50 μM mixture of the inorganic cations K⁺, Ba²⁺, Na⁺, Mg²⁺, and Li⁺ in 50 mM acetic acid/20 mM Tris (pH 4.5) as BGE. The obtained RSD values for the migration times varied in the range 0.7–1.0% and the values for the peak area were 0.7–1.4%; RSD were determined for ten repeated measurements.     

Graphene oxide coated capillary for chiral separation by CE

This article describes a new application of graphene oxide (GO) in CE based on the coating of fused silica capillary for chiral separation. The coated capillary was characterized by SEM, energy dispersive X‐ray spectroscopy, and Raman spectra. The results indicated that the capillary was coated with GO. Chiral separations were carried out in the GO‐coated capillary for the ephedrine–pseudoephedrine (E‐PE) isomers and β‐methylphenethylamine (β‐Me‐PEA) isomers at the optimal buffer conditions without any chiral selector by CE. The precision and reproducibility of GO‐coated capillary were investigated, and the RSDs of migration time (n = 6) for the E‐PE isomers were 1.35–1.41%, and 0.97–3.50% for β‐Me‐PEA isomers, respectively. The LOD for E‐PE isomers and β‐Me‐PEA isomers was 3 μM and 18 μM, respectively.     

Facile preparation of polysaccharide‐coated capillaries using a room temperature ionic liquid for chiral separations

In this study, the dissolution of polysaccharides into an ionic liquid was investigated and applied as a coating onto the capillary walls of a fused‐silica capillary in open‐tubular CEC. The coating was evaluated by examining the chiral separation of two analytes (thiopental, sotalol) with three cellulose derivatives (cellulose acetate, cellulose acetate phthalate, and cellulose acetate butyrate). Baseline separation of thiopental enantiomers was achieved by use of each polysaccharide coating (Rs: 7.0, 8.1, 7.1), while sotalol provided partial resolution (Rs: 0.7, 1.0, 0.9). In addition, reproducibility of the cellulose‐coated capillaries was evaluated by estimating the run‐to‐run and capillary‐to‐capillary RSD values of the EOF. Both stability and reproducibility were very good with RSD values of less than 7%.     

Determination of doripenem and related substances in medicinal product using capillary electrophoresis

Doripenem, the latest carbapenem antibiotic licensed in the United States (15 October 2007) and the European Union (25 July 2008), has been implemented into therapeutic use along with imipenem, meropenem and ertapenem. The described method of zone electrophoresis in a low pH buffer for the separation of doripenem from its impurities has been successfully performed using field‐amplified sample stacking (FASS), followed by UV absorption detection at 214 nm. The best results were obtained with phosphate buffer (100 mM) pH 2.9 containing 10% (v/v) of methanol, as the background electrolyte. Uncoated fused‐silica capillary (60/52 cm; 75 μm id) with normal polarity, and voltage values of 25 kV, was used throughout the investigation. The optimised method of doripenem determination was validated in terms of linearity, accuracy and precision, and provides a detection limit of 3.0 μg/mL of doripenem. The repeatability, expressed by relative standard deviation (RSD) of the migration time, for doripenem and its degradation products varied from 1.37 to 2.51%, whereas the corrected peak areas were about 0.91–9.87%. Satisfactory separation was achieved within 20 min of electrophoresis; moreover, all carbapenems (imipenem, meropenem, ertapenem and doripenem) were well separated from each other during this time. The evaluated CZE method was applied in the analysis of a medicinal product containing doripenem Doribax^® powder for solution for infusion.     

Inverse colloidal crystal membranes for hydrophobic interaction membrane chromatography

A collaborative study on the robustness and portability of a capillary electrophoresis‐mass spectrometry method for peptide mapping was performed by an international team, consisting of 13 independent laboratories from academia and industry. All participants used the same batch of samples, reagents and coated capillaries to run their assays, whereas they utilized the capillary electrophoresis‐mass spectrometry equipment available in their laboratories. The equipment used varied in model, type and instrument manufacturer. Furthermore, different types of sheath‐flow capillary electrophoresis–mass spectrometry interfaces were used. Migration time, peak height and peak area of ten representative target peptides of trypsin‐digested bovine serum albumin were determined by every laboratory on two consecutive days. The data were critically evaluated to identify outliers and final values for means, repeatability (precision within a laboratory) and reproducibility (precision between laboratories) were established. For relative migration time the repeatability was between 0.05 and 0.18% RSD and the reproducibility between 0.14 and 1.3% RSD. For relative peak area repeatability and reproducibility values obtained were 3–12 and 9–29% RSD, respectively. These results demonstrate that capillary electrophoresis‐mass spectrometry is robust enough to allow a method transfer across multiple laboratories and should promote a more widespread use of peptide mapping and other capillary electrophoresis‐mass spectrometry applications in biopharmaceutical analysis and related fields.     

Comparison of three modifications of fused‐silica capillaries and untreated capillaries for protein profiling of maize extracts by capillary electrophoresis

In this work, capillary electrophoresis was applied to protein profiling of fractionated extracts of maize. A comparative study on the application of uncoated fused‐silica capillaries and capillaries modified with hydroxypropylmethylcellulose, ω‐iodoalkylammonium salt and a commercially available neutral capillary covalently coated with polyacrylamide is presented. The coating stability, background electrolyte composition, and separation efficiency were investigated. It was found that for zeins separation, the most stable and efficient was the capillary coated with polyacrylamide. Finally, the usefulness of these methods was studied for the differentiation of zein fraction in transgenic and nontransgenic maize. Zeins extracted from maize standards containing 0 and 5% m/m genetic modification were successfully separated, but slight differences were observed in terms of the zein content. Albumin and globulin fractions were analyzed with the use of unmodified fused‐silica capillary with borate buffer pH 9 and the capillary coated with polyacrylamide with phosphate buffer pH 3. In the albumin fraction, additional peaks were found in genetically modified samples.     

Bacterial surface layer proteins as a novel capillary coating material for capillary electrophoretic separations

A novel concept for stable coating in capillary electrophoresis, based on recrystallization of surface layer proteins on hydrophobized fused silica capillaries, was demonstrated. Surface layer protein A (SlpA) from Lactobacillus acidophilus bacteria was extracted, purified and used for coating pre-silanized glass substrates presenting different surface wettabilities (either hydrophobic or hydrophilic). Contact angle determination on SlpA-coated hydrophobic silica slides showed that the surfaces turned to hydrophilic after coating (53 ± 5°), due to a protein monolayer formation by protein-surface hydrophobic interactions. Visualization by atomic force microscopy demonstrated the presence of a SlpA layer on methylated silica slides displaying a surface roughness of 0.44 ± 0.02 nm. Additionally, a protein layer was visualized by fluorescence microscopy in methylated silica capillaries coated with SlpA and fluorescein isothiocyanate-labeled. The SlpA-coating showed an outstanding stability, even after treatment with 20 mM NaOH (pH 12.3). The electroosmotic flow in coated capillaries showed a partial suppression at pH 7.50 (3.8 ± 0.5 10⁻⁹ m² V⁻¹ s⁻¹) when compared with unmodified fused silica (5.9 ± 0.1 10⁻⁸ m² V⁻¹ s⁻¹). To demonstrate the potential of this novel coating, the SlpA-coated capillaries were applied for the first time for electrophoretic separation, and proved to be very suitable for the isotachophoretic separation of lipoproteins in human serum. The separations showed a high degree of repeatability (absolute migration times with 1.1–1.8% coefficient-of-variation (CV) within a day) and 2–3% CV inter-capillary reproducibility. The capillaries were stable for more than 100 runs at pH 9.40, and showed to be an exceptional alternative for challenging electrophoretic separations at long-term use.     

Silica spheres coated with C18‐modified gold nanoparticles for capillary LC and pressurized CEC separations

Nonporous monodispersed silica spheres of 1.3 μm were coated with gold nanoparticles (AuNPs) and subsequently coated with n‐octadecanethiol. By transmission electron microscopy analysis, the average diameter of the AuNPs on the silica spheres was determined to be 12 nm. The chromatographic and electrochromatographic properties of self‐assembled n‐octadecanethiol AuNP‐coated silica microspheres (C18‐AuNPs‐SiO₂) were investigated using a group of nonpolar PAHs. The stationary phase appears to display a characteristic reversed‐phase behavior. Higher separation efficiency and shorter separation times were obtained using pressurized CEC (pCEC) compared with capillary LC (CLC). A maximum column efficiency of about 2.5×10⁵ plates per meter and less than 18 min separation time for benzene were obtained in pCEC while only 66 507 plates per meter and an analysis time of nearly 100 min were observed in CLC mode. A chemical stability test of the C18‐AuNPs‐SiO₂ stationary phase under extremely high and low pH conditions demonstrated that it is stable at pH 12 and 1 for at least 60 h. The results confirm that C18‐AuNPs‐SiO₂ possesses a high rigidity to withstand high packing pressures and can be used as a good stationary phase for CLC and pCEC.     

CE coupled to MALDI with novel covalently coated capillaries

CE offers the advantage of flexibility and method development options. It excels in the area of separation of ions, chiral, polar and biological compounds (especially proteins and peptides). Masking the active sites on the inner surface of a bare fused silica capillary wall is often necessary for CE separations of basic compounds, proteins and peptides. The use of capillary surface coating is one of the approaches to prevent the adsorption phenomena and improve the repeatability of migration times and peak areas of these analytes. In this study, new capillary coatings consisting of (i) derivatized polystyrene nanoparticles and (ii) derivatized fullerenes were investigated for the analysis of peptides and protein digest by CE. The coated capillaries showed excellent run‐to‐run and batch‐to‐batch reproducibility (RSD of migration time ≤0.5% for run‐to‐run and ≤9.5% for batch‐to‐batch experiments). Furthermore, the capillaries offer high stability from pH 2.0 to 10.0. The actual potential of the coated capillaries was tested by combining CE with MALDI‐MS for analysing complex samples, such as peptides, whereas the overall performance of the CE‐MALDI‐MS system was investigated by analysing a five‐protein digest mixture. Subsequently, the peak list (peptide mass fingerprint) generated from the mass spectra of each fraction was entered into the Swiss‐Prot database in order to search for matching tryptic fragments using the MASCOT software. The sequence coverage of analysed proteins was between 36 and 68%. The established technology benefits from the synergism of high separation efficiency and the structure selective identification via MS.     

Graphene oxide‐SiO2 hybrid nanostructure as coating material for capillary electrochromatography

Graphene oxide (GO) has been considered as a promising stationary phase for chromatographic separation. However, the very strong adsorption of the analytes on the GO surface lead to the severe peak tailing, which in turn resulting in decreased separation performance. In this work, GO and silica nanoparticles hybrid nanostructures (GO/SiO₂ NPs@column) were coated onto the capillary inner wall by passing the mixture of GO and silica sol through the capillary column. The successful of coating of GO/SiO₂ NPs onto the capillary wall was confirmed by SEM and electroosmotic flow mobilities test. By partially covering the GO surface with silica nanoparticles, the peak tailing was decreased greatly while the unique high shape selectivity arises from the surface of remained GO was kept. Consequently, compared with the column modified with GO (GO@column), the column modified with GO and silica nanoparticles through layer‐by‐layer method (GO‐SiO₂ NPs@column), or the column modified with silica nanoparticles (SiO₂ NPs@column), GO/SiO₂ NPs@column possessed highest resolutions. The GO/SiO₂ NPs@column was applied to separate egg white and both acidic and basic proteins as well as three glycoisoforms of ovalbumin were separated in a single run within 36 min. The intra‐day, inter‐day, and column‐to‐column reproducibilities were evaluated by calculating the RSDs of the retention of naphthalene and biphenyl in open‐tubular capillary electrochromatography. The RSD values were found to be less than 7.1%.     

Polydopamine‐coated open tubular column for the separation of proteins by capillary electrochromatography

The separation and determination of proteins in food is an important aspect in food industry. Inspired by the self‐polymerization of dopamine under alkaline conditions and the natural adhesive properties of polydopamine, in this paper, a simple and economical method was developed for the preparation of polydopamine‐coated open tubular column, in which ammonium persulfate was used as the source of oxygen to induce and facilitate the polymerization of dopamine to form polydopamine. In comparison with a naked fused‐silica capillary, the direction and magnitude of the electro‐osmotic flow of the as‐prepared polydopamine‐coated open tubular column could be manipulated by varying the pH values of background solutions due to the existence of amine and phenolic hydroxyl groups on polydopamine coating. The surface morphology of the polydopamine‐coated open tubular column was studied by scanning electron microscopy, and the thickness of polydopamine coating was 106 nm. The performance of the polydopamine‐coated open tubular column was validated by analysis of proteins. The relative standard deviations of migration times of proteins representing run‐to‐run, day‐to‐day, and column‐to‐column were less than 3.5%. In addition, the feasibility of the polydopamine‐coated open tubular column for real samples was verified by the separation of proteins in chicken egg white and pure milk.     

A quantitative CE method to analyse tau protein isoforms using coated fused silica capillaries

We evaluated the potential of CE to analyse different isoforms of unphosphorylated recombinant tau protein and for separating one phosphorylated tau from the respective unphosphorylated protein. Different capillary coatings such as polyacrylamide, poly‐(ethylene oxide) and polybrene (PB) were evaluated to overcome the poor efficiencies obtained with fused‐silica capillary. Although peak asymmetry values were quite similar for the three investigated coatings, the peak efficiencies were 35‐fold and 5‐fold higher with PB coating than with polyacrylamide and poly(ethylene oxide) coatings, respectively. The recovery percentage (over 97%) was satisfactory and confirmed the efficacy of PB coating to limit the adsorption of tau protein to capillary walls. Moreover, PB coating produced higher repeatability for migration times (RSD values <1.2%) in comparison to the neutral coatings. The potential of PB‐modified capillary in producing high resolutive separations of one phosphorylated tau isoform from its unphosphorylated counterpart and of a mixture of phosphorylated and unphosphorylated tau peptides was demonstrated with 50 mM phosphate buffer pH 3.0. The separation of unphosphorylated tau isoform 352 (Tau‐352) from Tau‐352 phosphorylated in vitro by the mitogen‐activated protein kinase ERK2, was accomplished in less than 15 min.     

The determination of lansoprazole in pharmaceutical preparation by capillary electrophoresis

Summary A capillary electrophoretic method for the determination of lansoprazole in pharmaceutical preparations is described. The analysis was performed in a fused silica capillary using 20 mM borate buffer at pH 8.7 as a background electrolyte. The best resolution was obtained by applying a potential of 30 kV and vacuum injection of 1 s. Detection was made at 200 nm. Phenobarbital sodium was a good internal standard and the migration times were 4.1±0.2 min (lansoprazole) and 5.7±0.2 min (phenobarbital sodium). A well-correlated calibration equation was found in the range of 1.12×10⁻⁵ and 2.24×10⁻⁴ M. Limit of detection (LOD) and limit of quantitation (LOQ) were 1.4×10⁻⁶ M (RSD 1.44%) and 4.42×10⁻⁶ M (RSD 1.49%), respectively. The method was validated and applied to the capsules containing enteric coated pellets of lansoprazole. The results of the proposed method were compared those of UV spectrophotometry. Insignificant differences were found between the two methods at the 95% probability level. The described CE method is selective, rapid, sensitive and accurate for the analysis of lansoprazole in quality control laboratories.