Thermal effects and band spreading in capillary electro-separation

Summary Four Capillary Electroseparation methods are distinguished. All have an ultimate efficiency limited only by axial diffusion and are in principle capable of achieving 10⁶ plates in <1 hour.The main limitation to performance arises from Ohmic heating of the electrolyte. While forced convection at 10ms^–1 is recommended to keep tubes cool, the parabolic temperature profile within the electrolyte limits the tube bore which can be used. A simple limiting expression is derived: (d_c/m)³ (E/kV m^–1)³ (c/mol dm^–3) <3.3×10⁹.Values of constants underlined     

Determination and Differentiation of Two Seemingly Identical Medicinal Herbs by Capillary Electrophoresis with Electrochemical Detection

A high-performance capillary electrophoresis with electrochemical detection (CE-ED) method has been employed for the determination of six bioactive ingredients in traditional Chinese herbs, Herba cepbalanoplosis segeti and Herba cirsii japonici. The effects of several factors such as the acidity and concentration of running buffer, the separation voltage, the applied potential and the injection time on CE-ED were investigated. Under the optimum conditions, the six analytes could be well separated within 21 min in a 75 cm length capillary at the separation voltage of 15 kV in a 50 mmol L^–1 borax running buffer (pH 8.4). A 300 m diameter carbon disk electrode was used as the working electrode positioned carefully opposite the outlet of the capillary in a wall-jet configuration at potential of +950 mV (vs. SCE). Good linear relationship was established between peak current and concentration of analytes over two orders of magnitude with detection limits (S/N=3) ranged from 1.5×10^–7 to 6.0×10^–7 g mL^–1 for all six analytes. This proposed method has been successfully applied for the analysis of traditional Chinese herbs after a relatively simple extraction procedure, further on, for the differentiation of these above two seemingly identical herbs based on their electropherograms or characteristic electrochemical profiles.     

Determination of levodopa methyl ester and its metabolites in rat serum by CZE with amperometric detection

A reliable and reproducible method, capillary zone electrophoresis with amperometric detection (CZE–AD), has been developed for separation and quantification of levodopa methyl ester (LDME) and its biotransformation products levodopa (L-DOPA) and dopamine (DA) in rat serum. A carbon-disk electrode was used as working electrode. The optimum conditions for CZE detection were 50 mmol L^–1 phosphate solution at pH 7.0 as running buffer, 17 kV as separation voltage, 1.0 V (vs Ag/AgCl, 3.0 mol L^–1) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 2.4×10^–2 to 2.2 g mL^–1 for LDME, 2.9×10^–1 to 49.5 g mL^–1 for L-DOPA, and 1.4×10^–2 to 1.5 g mL^–1 for DA with correlation coefficients of 0.9997, 0.9994, and 0.9999, respectively. The detection limits for LDME, L-DOPA, and DA were 14.6, 98.0, and 9.7 ng mL^–1, respectively. Recoveries were 80.3% for LDME, 93.5% for L-DOPA, and 86.5% for DA. This method was applied to serum samples after intravenous injection of LDME and L-DOPA to rats.     

Simultaneous determination of DTPA,EDTA, and NTA by capillary electrophoresis after complexation with copper

We present a method for simultaneous determination of the aminopolycarboxylic acids DTPA, EDTA and NTA in dishwashing detergents, paper mill waters, and natural waters by capillary electrophoresis (CE). The complexing agents were examined as their copper(II) complexes and separated by conventional CE with reversed polarity of the applied voltage. The optimum separation conditions were established by varying the pH and phosphate and tetradecyltrimethylammonium bromide (TTAB) concentrations in the run buffer. The separations were carried out in a fused-silica capillary (61 cm×75 m i.d.) filled with phosphate buffer (80 mmol L^–1, TTAB concentration 0.5 mmol L^–1, pH 7.1, voltage –20 kV) using direct UV detection at 191 and 254 nm. With this CE method all the peaks in the electropherograms were properly separated, the calibration plots gave good correlation coefficients and all three complexing agents could be detected in less than 4 min. Linear calibration plots were obtained for CuDTPA, CuEDTA and CuNTA; limits of detection were 0.03 mmol L^–1 for all complexing agents and recoveries for all tested samples were within the range 104±7%. Results obtained from dishwashing detergent samples were found to be reliable and comparable with those from HPLC (R²=0.989) and UV–Vis (R²=0.985) methods.     

Determination of Levodopa and Benserazide Hydrochloride in Pharmaceutical Formulations by CZE with Amperometric Detection

A novel method, capillary electrophoresis with amperometric detection, has been established for rapid and effective measurement of levodopa (L-dopa), and benserazide (BS) and its impurity (R,S)-2-amino-3-hydroxypropanohydrazide (Ro-04-1419) in co-beneldopa pharmaceutical formulations. Suitable separation and amperometric detection conditions were investigated and optimized. The optimum conditions of CZE detection were 40 mm phosphate solution at pH 5.3 as running buffer, 17 kV separation voltage, carbon-disk working electrode, 0.95 V (relative to Ag/AgCl) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 1.25 to 50 g mL^–1 for L-dopa, 1.2 × 10^–1 to 25.5 g mL^–1 for BS, and 1.0 × 10^–2 to 4.4 × 10^–1 g mL^–1 for Ro-04-1419, with correlation coefficients of 0.9994, 0.9951, and 0.9933, respectively. The detection limits for L-dopa, BS, and Ro-04-1419 were 0.38, 0.02, and 0.004 g mL^–1, respectively. Average recoveries were 100.2% for L-dopa, 102.4% for BS, and 90.8% for Ro-04-1419. This method was successfully applied to co-beneldopa granules and tablets.Revised: 30 November and 22 December 2004     

Capillary Electrophoretic Determination of Gatifloxacin from Pharmaceutical Preparation

Capillary zone electrophoresis has been used for the determination of gatifloxacin from its pharmaceutical preparation (tablets), using fused silica capillary. Separation was performed after hydrodynamic injection; the separation was achieved by applying 21 Kv voltage. Phosphate buffer solution (pH 9.5) was used as separation electrolyte. Detection was at 280 nm using a UV- detector. Under these experimental conditions the analysis takes 8 min. A linearity range for gatifloxacin was between 20.0 g mL^–1 to 60.0 g mL^–1. The method was validated and was found to be specific, precise, accurate, reproducible and robust and can be applied for the routine analysis of gatifloxacin from formulation and bulk drug.     

Separation of Structurally Related Anthocyanins by MEKC

Summary A method based on micellar electrokinetic chromatography has been developed for the simultaneous separation of six anthocyanins (malvidin-3,5-diglucoside, malvidin-3-glucoside, malvidin-3-galactoside, pelargonidin-3-glucoside, cyanidin-3,5-diglucoside, cyanidin-3-galactoside). Optimum selectivity was achieved in the buffer 30 mM phosphate + 400 mM borate-TRIS, pH=7.0 supported with 50 mM sodium dodecylsulphate. High content of borate was essential mainly for the separation of diastereomeric pair malvidin-3-glucoside-malvidin-3-galactoside. The calibration dependencies exhibit good linearity in the ranges of concentration 10–100 g mL^–1 for diglycosylated and 25–100 g mL^–1 for monoglycosylated derivatives (R² = 0.9711–0.9989). The optimized method was applied to a sample of wine grape skin extract. Malvidin-3-glucoside was identified as main anthocyanin colorant in this sample.     

Determination of rofecoxib,in the presence of its photodegradation product,in pharmaceutical preparations by micellar electrokinetic capillary chromatography

A simple and rapid micellar electrokinetic capillary chromatographic (MEKC) method for analysis of rofecoxib (ROF) and its photodegradation product (PDP) in pharmaceutical preparations has been developed and validated. Analyses were conducted in a fused silica capillary (72 cm effective length, 50 m i.d.) with a background electrolyte consisting of 25 mmol L^–1 borate buffer at pH 7.0 containing 15 mmol L^–1 sodium dodecyl sulfate (SDS) and 10% acetonitrile (ACN). The separation was performed by voltage-controlled system, applying 30 kV at 30 °C, detecting at 225 nm; injection was hydrodynamic at 50 mbar for 2 s. Nifedipine was used as internal standard (IS). Under the optimum conditions ROF, PDP, and IS were well separated with in 10 min. The method was validated with regard to linearity, limit of detection and quantitation, precision, accuracy, specificity, and robustness. The detection limit of the method was low, 0.8 g mL^–1, and the linearity range was wide, 2.5 to 125 g mL^–1. The method was highly efficient—5×10⁵ plates m^–1 for ROF. The method was applied to the tablet form of ROF-containing pharmaceutical preparations. The data were compared with those from the voltammetric method described in literature. No statistically significant difference was found.     

Determination of piribedil in pharmaceutical formulations by micellar electrokinetic capillary chromatography

A fast and simple micellar electrokinetic capillary chromatographic method was developed for the analysis of piribedil in pharmaceutical formulations. The effects of buffer concentration, buffer pH, sodium dodecyl sulphate (SDS) concentration, organic modifier, applied voltage and injection time were investigated. Optimum results were obtained with a 50 mM borate buffer at pH 8.0 containing 50 mM SDS by using a fused silica capillary (50 m internal diameter, 72 cm effective length). The sample was injected hydrodynamically for 4 s at 50 mbar pressure and the applied voltage was +30 kV. The detection wavelength was set at 205 nm. Diflunisal was used as an internal standard. The analysis was performed at 25 °C and the total run time was 14 min. The method was suitably validated with respect to linearity range, limit of detection and quantification, precision, accuracy, specificity and robustness. The linear calibration range was 5–100 g mL^–1 and the limit of detection was determined as 1 g mL^–1. The method developed was successfully applied to the determination of piribedil in pharmaceutical formulations. The results were compared with a spectrophotometric method reported in the literature and no significant difference was found statistically.     

Determination and Comparison of Phytoestrogens in Both Crude and Parched Flos Sophorae Immaturus by Capillary Electrophoresis with Electrochemical Detection

A method using high-performance capillary electrophoresis with electrochemical detection (CE-ED) has been developed for content comparison of phytoestrogens in both crude and parched Flos sophorae immaturus. Genistin, genistein, rutin, kaempferol and quercetin are important active constituents in this plant. The effects of several factors, such as acidity and concentration of running buffer, separation voltage, applied potential and injection time, were investigated to find the optimum conditions. Detection limits (S/N=3) ranged from 1.1 × 10^–7 to 2.8 × 10^–7gmL^–1 for all five analytes. This method was successfully used to analyse both crude and parched Flos sophorae immaturus after a relatively simple extraction procedure, and the assay results were satisfactory.     

Capillary zone electrophoresis for simultaneous determination of seven nonsteroidal anti-inflammatory drugs in pharmaceuticals

A simple capillary zone electrophoresis (CZE) method has been developed for analyzing seven nonsteroidal anti-inflammatory drugs (NSAIDs)—sulindac (SU), ketoprofen (KE), indomethacin (IN), piroxicam (PI), nimesulide (NI), ibuprofen (IB), and naproxen (NA). The separation was run using borate buffer (60 mmol L^–1, pH 8.5) containing 13% (v/v) methanol at 20 kV, and detected at 200 nm. Several conditions were studied, including concentration and pH of borate buffer, methanol percentage, and separation voltage. In method validation, the calibration plots were linear over the range 40.0–500.0 mol L^–1. In intra-day and inter-day analysis, relative standard deviations (RSD) and relative errors (RE) were all less than 5%. The limits of detection were 10 mol L^–1 for SU, IN, PI, and 20 mol L^–1 for KE, NI, IB, NA (S/N = 3, sampling 6 s by pressure). All recoveries were greater than 95%. This method was applied to the quality control of six NSAIDs in pharmaceuticals using NI as internal standard (IS). The assay results were within the labeled amount required by USP 25.     

Thermodynamic properties of binary mixtures: Hexamethylphosphoric triamide + a polar liquid at 25°C

Excess enthalpies H _m ^E excess isobaric heat capacities C _p,m ^E , densities, and speeds of sound of hexamethylphosphoric triamide (HMPA)+acetonitrile (AN), + N,N-dimethylformamide (DMF), and + dimethylsulfoxide (DMSO) were measured at 25degrC. H _m ^E =–1200 J-mol^–1 for HMPA + AN, –180 J-mol^–1 for HMPA + DMF, and 75 J-mol^–1 for HMPA + DMSO C _p,m ^E is positive and considerably larger than C _v,m ^E . V _m ^E for HMPA + DMSO was small and changed sign from negative to positive around HMPA mole fraction x=0.6. V _m ^E for the other two mixtures were negative. The excess compressibilities, K _m ^E for the other two mixtures were negative. The excess compressibilities, K _S ^E and K _T ^E were similar to V _m ^E Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30-June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

Sensitive biomonitoring of phthalate metabolites in human urine using packed capillary column switching liquid chromatography coupled to electrospray ionization ion-trap mass spectrometry

A rapid and sensitive method for the determination of the phthalate monoesters monoethyl phthalate (MEP), monobutyl phthalate (MBP), monobenzyl phthalate (MBzP) and monoethylhexyl phthalate (MEHP), in human urine, using packed capillary column liquid chromatography coupled to electrospray quadrupole-ion trap mass spectrometry (ESI-QITMSⁿ) has been developed. Sample volumes of 200 L of deconjugated and diluted urine were loaded onto a precolumn of 30 mm×0.32 mm I.D. packed with Hypercarb 5 m particles, using a sample carrier consisting of acetonitrile/water (15/85, v/v, adjusted to pH 2 using HCl) with a flow rate of 20 L/min. Backflushed elution onto a 100 mm×0.32 mm I.D. analytical column packed with 5 m Hypercarb particles was conducted using a tetrahydrofuran/water gradient where both solvents contained 10 mM ammonium acetate, at a flow rate of 4 L/min. Determination of the monophthalates was achieved within 8 min. Ionization was performed in the negative mode and the analytes were observed as [M-H]^– at m/z=193.1, 221.1, 255.1 and 277.0 for MEP, MBP, MBzP and MEHP, respectively. Quantification was performed in the multiple reaction monitoring (MRM) mode monitoring the fragments at m/z=121.1, 177.0, 183.0 and 233.0 for MEP, MBP, MBzP and MEHP, respectively. The method was validated over the concentration range 2.5–125 ng/mL in pretreated urine samples, corresponding to 25–1250 ng/mL untreated urine, yielding correlation coefficients in the range 0.996–0.999. The within-assay (n=6) and between-assay (n=6) repeatabilities were in the range 4.0–18% and 4.8–15% RSD, respectively. The mass limits of detection were in the range 32–70 pg, corresponding to concentration limits of detection of 1.6–3.5 ng/mL of untreated urine.     

Determination of dextromethorphan and dextrorphan in urine by capillary zone electrophoresis: Application to the determination of debrisoquin-oxidation metabolic phenotype

Summary A capillary zone electrophoresis method has been developed for the determination of dextromethorphan and its metabolite, dextrorphan, in urine. A linear relationship was observed between the peak area and the concentration of both dextromethorphan and dextrorphan within the range of 490 ng mL^–1 to 500 g mL^–1 with a correlation coefficient of greater than 0.9999. The limit of detection was 80 ng mL^–1 for both compounds. The inter-day coefficients of variation for the concentrations of 2.5 g mL^–1 and 50 g mL^–1 were 6.2% and 4.1% for dextromethorphan, and 5.6% and 2.8% for dextrorphan (n=15). The method could be applied directly to the determination of dextromethorphan and dextrorphan in human urine without any sample pretreatment for the elimination of interfering compounds as is required in published highperformance liquid chromatography and gas chromatography methods. Using dextromethorphan as a probe of the debrisoquin-oxidation metabolic phenotype, the 44 healthy volunteers were phenotyped after oral administration of a 15 mg dose using both this capillary electrophoresis method and a high-performance liquid chromatography assay from the literature. Good agreement was found between the two methods.     

Experimental design-based development and single laboratory validation of a capillary zone electrophoresis method for the determination of the artificial sweetener sucralose in food matrices

A capillary zone electrophoresis (CZE) method, optimised chemometrically, underwent a complete in-house validation protocol for the qualification and quantification of sucralose in various foodstuffs. Separation from matrix components was obtained in a dinitrobenzoic acid (3 mM)/sodium hydroxide (20 mM) background electrolyte with a pH of 12.1, a potential of 0.11 kV cm^–1 and a temperature of 22 °C. Detection was achieved at 238 nm by indirect UV. Screening, optimisation and robustness testing were all carried out with the aid of experimental design. Using standard addition calibration, the CZE method has been applied to still, carbonated and alcoholic beverages, yoghurts and hard-boiled candy. The method allows the detection of sucralose at >30 mg kg^–1, with a linearity range of 50–500 mg kg^–1, making it suitable for implementation of the recently amended Sweeteners for use in foodstuffs Directive (European Parliament and Council (2003) Off J L237:3–12), which set maximum usable doses of sucralose for many foodstuffs, most ranging from 200 mg kg^–1 to 450 mg kg^–1.     

Spectrophotometric determination of mercury with 5,10,15,20-tetrakis(3-chloro-4-sulfophenyl)porphine by flow injection analysis

5,10,15,20-tetrakis(3-chloro-4-sulfophenyl)porphine (m-Cl-TPPS₄) was synthesized and used for the Spectrophotometric determination of mercury by flow injection analysis. A pseudo-first-order reaction kinetic mechanism was proposed with a rate constant of 0.8 min^–1 for Hg(II) withm-Cl-TPPS₄ in the presence of 8-hydroxyquinoline in a medium of 1.0M acetic acid and sodium acetate buffer solution (pH 6.22). In the optimum conditions of reaction temperature (85 ° C), stopped-flow time (60 s) and sampling volume (100 l), the method's relative standard deviation was 0.82% (n = 12) at 5.0 g ml^–1 mercury, with a linear range of 0–12.0 g ml^–1 and an analytical frequency of 60h^–1. The detection limit (3) was 0.025 g ml^–1. Interference studies showed that most metal ions co-existing with Hg²⁺ could be tolerated at 100-fold excess levels, but Zn²⁺, Cu²⁺ and Mn²⁺ needed to be masked. The method has been applied to the analysis of water samples with satisfactory results.     

Surface treatment,deactivation and coating in (GC)2 (glass capillary gas chromatography)

Summary The surface treatment, deactivation and coating of glass capillaries is discussed. Several techniques described in the literature are compared and for some critical points, new improved methods are advanced. Full details are given of optimised procedures yielding good results with every possible stationary phase. As an example, Table II mentions efficiencies of 3800 plates m^–1 for OV-17 and of 1850 plates m^–1 for OF-1, which hitherto was an impossible phase in (GC)² (proposed abbreviation for glass capillary gas chromatography).     

The lipid composition of the Western Mediterranean aerosol

Summary Marine remote aerosol samples collected in a fixed station situated at 1100 m above sea level in Mallorca Island (Western Mediterranean) have been analyzed for lipids, both neutral and acidic, by capillary gas chromatography (GC) and GC coupled to mass spectrometry. Higher plant and algal compounds are predominant. The former encompass distributions of even numbered C22–C32 n-alkan-1-ols (8–21 ng/m³) and n-aldehydes, C25–C32 odd numbered n-alkanes (3–6 ng/m³), and n-nonacosan-10-ol, -sitosterol (0–0.09 ng/m³), dehydroabietic acid and triterpenols. The latter are constituted by even numbered C14–C18 fatty acids (0.6–30 ng/m³) and cholest-5-en-3-ol (0–0.86 ng/m³). Pyrolytic polycyclic aromatic hydrocarbons are also found (86–410 pg/m³) whereas direct petrogenic inputs are not significant.     

Indirect determination of chloride and sulfate ions in alcohol fuel by capillary electrophoresis

A capillary zone electrophoresis method using indirect UV detection for the analysis of chloride and sulfate in alcohol fuel samples was developed. The anions were analyzed in less than 3 min using an electrolyte containing 10 mmol l^–1 chromate and 0.75 mmol l^–1 hexamethonium bromide (HMB) as electroosmotic flow modifier. Coefficients of variation were better than 0.6% for migration time (n=10) and between 2.05 and 2.82% for peak area repeatabilities. Analytical curves of peak area versus concentration in the range of 0.065–0.65 mg kg^–1 for chloride and 0.25–4.0 mg kg^–1 for sulfate were linear with coefficients of correlation higher than 0.9996. The limits of detection for sulfate and chloride were 0.033 and 0.041 mg kg^–1, respectively. Recovery values ranged from 85 to 103%. The method was successfully applied for the quantification of sulfate and chloride in five alcohol fuel samples. The concentration of sulfate varied from 0.45 to 3.12 mg kg^–1. Chloride concentrations were below the methods LOD.     

Sorption kinetics of tributyltin on Elbe river biofilms

For the first time detailed sorption kinetics of tributyltin on native Elbe river biofilms are presented. For this purpose a modified annular rotating continuous flow reactor has been used to develop a reproducible biofilm. Important parameters, such as flow rates, sheer forces, and nutrient concentrations could be varied independently and adjusted to natural conditions. Time-resolved sorption kinetics have been carried out with tributyltin, the most toxic compound in many antifouling paints. The highest sorption rates of tributyltin were observed during the first 0–10 min (0.60±0.05 g Sn m^–2min^–1) than they decreased to a value of 0.10±0.10 g Sn m^–2min^–1 (10–90 min) and increased to a value of 0.20±0.05 g Sn m^–2min^–1 (90–120 min).