Determination of Phenolic Acids in Herba Epilobi by ITP–CE in the Column-Coupling Configuration

The combination of capillary isotachophoresis (ITP) and capillary zone electrophoresis (CZE) in the column-coupling configuration has been optimized in a mode in which the background electrolyte employed in the CZE step was different from the leading and terminating electrolytes of the ITP step. The optimum composition of the electrolyte system was 0.01 M HCl, 0.02 M IMI, 0.2% HEC, pH 7.2 (leading electrolyte), 0.01 M HEPES, pH 8.2 (terminating electrolyte), and 25 mM MES, 50 mM TRIS, 30 mM boric acid, 0.2% HEC, pH 8.3 (background electrolyte). All solutions contained 20% methanol. The timing of the transfer of isotachophoretically stacked analyte zones into the CZE column was also optimized. An ITP–CZE method with UV detection at 270 nm was developed for separation of nine phenolic acids (protocatechuic, syringic, vanillic, cinnamic, ferulic, caffeic, ρ-coumaric, chlorogenic, and gentisic acids) in a model mixture and used for assay of some of these acids in a methanolic extract of herba epilobi. Application of ITP–CZE resulted in 100-fold better sensitivity than conventional CZE; limits of detection ranged between 10 and 60 ng mL⁻¹. When MES–TRIS–borate-based buffer, pH 8.3, was used in the CZE separation step the linearity of the ITP–CZE response was satisfactory (correlation coefficients were from 0.9937 to 0.9777). Repeatability was also satisfactory (RSD values ranged between 0.77% and 1.28% for migration times and between 1.65% and 13.69% for peak area). Revised: 23 March and 27 April 2006     

In‐line preconcentration capillary zone electrophoresis for the analysis of haloacetic acids in water

Two in‐line enrichment procedures (large volume sample stacking (LVSS) and field amplified sample injection (FASI)) have been evaluated for the CZE analysis of haloacetic acids (HAAs) in drinking water. For LVSS, separation on normal polarity using 20 mM acetic acid–ammonium acetate (pH 5.5) containing 20% ACN as BGE was required. For FASI, the optimum conditions were 25 s hydrodynamic injection (3.5 kPa) of a water plug followed by 25 s electrokinetic injection (?10 kV) of the sample, and 200 mM formic acid–ammonium formate buffer at pH 3.0 as BGE. For both FASI and LVSS methods, linear calibration curves (r²>0.992), limit of detection on standards prepared in Milli‐Q water (49.1–200 μg/L for LVSS and 4.2–48 μg/L for FASI), and both run‐to‐run and day‐to‐day precisions (RSD values up to 15.8% for concentration) were established. Due to the higher sensitive enhancement (up to 310‐fold) achieved with FASI‐CZE, this method was selected for the analysis of HAAs in drinking water. However, for an optimal FASI application sample salinity was removed by SPE using Oasis WAX cartridges. With SPE‐FASI‐CZE, method detection limits in the range 0.05–0.8 μg/L were obtained, with recoveries, in general, higher than 90% (around 65% for monochloroacetic and monobromoacetic acids). The applicability of the SPE‐FASI‐CZE method was evaluated by analyzing drinking tap water from Barcelona where seven HAAs were found at concentration levels between 3 and 13 μg/L.     

Determination of muscimol and ibotenic acid in mushrooms of Amanitaceae by capillary electrophoresis

In this study, the CZE method for rapid quantitative and qualitative determination of ibotenic acid and muscimol in Amanita mushrooms naturally grown in Poland was developed. The investigations included the species of A. muscaria, A. pantherina, and A. citrina, collected in southern region of Poland. The studied hallucinogenic compounds were effectively extracted with a mixture of methanol and 1 mM sodium phosphate buffer at pH 3 (1:1 v/v) using ultrasound‐assisted procedure. The obtained extracts were separated and determined by CZE utilizing a 25 mM sodium phosphate running buffer adjusted to pH 3 with 5% content of acetonitrile v/v. The calibration curves for both analytes were linear in the range of 2.5–7000 μg/mL. The intraday and interday variations of quantitative data were 1.0 and 2.5% RSD, respectively. The recovery values of analyzed compounds were over 87%. The identities of ibotenic acid and muscimol were confirmed by UV spectra, migration time, and measurements after addition of external standard.     

On-line coupling of capillary isotachophoresis and zone electrophoresis for the assay of phenolic compounds in plant extracts

The combination of capillary isotachophoresis (ITP) and capillary zone electrophoresis (CZE) in the column coupling configuration was optimized in a mode where the electrolyte for the CZE step is different from the leading and terminating ITP electrolytes. Two colored markers, picric acid and 1-nitroso-2-naphthol, were used for exact timing of the transfer of isotachophoretically stacked analyte zones into the CZE column and for the control of the residual amount of the leading and terminating ITP electrolytes entering the CZE capillary together with the analytes, thus controlling the duration of transient ITP migration in the CZE capillary and ensuring good separation of the analytes and reproducibility of the migration times (relative standard deviations 1%). ITP-CZE was applied to the simultaneous assay of several cinnamic acid derivatives and flavonoids in methanolic extracts of Sambucus flowers and Crataegus leaves and flowers. The preconcentrating and cleansing effect of the ITP step allowed injection of relatively large sample volumes (30 microL). The limits of detection were approximately 20-50 ng x mL(-1) and 100 ng x mL(-1) for the acids and flavonoids, respectively ( thick similar 200-times lower compared to conventional CE) with spectrophotometric detection at 254 nm. The ITP-CZE exhibited satisfactory linearity and precision when using CZE buffer of pseudo "pH" 9.0; 1-nitroso-2-naphthol was employed as the internal standard. The separation took approximately 35 min. The ITP-CZE results for rutin, hyperoside, and vitexin-2-O"-rhamnoside were in good accordance with those obtained previously by high-performance liquid chromatography.     

Separation of Enantiomers by On‐Line Capillary Isotachophoresis‐Capillary Zone Electrophoresis

The ability of capillary zone electrophoresis (CZE) coupled on‐line with capillary isotachophoresis (ITP) sample pretreatment in the column‐coupling capillary electrophoresis equipment to separate trace enantiomers present in samples of complex ionic matrices and enantiomers present in their mixtures at significantly differing concentrations has been studied. Enantiomers of 2,4‐dinitrophenyl labeled norleucine (DNP‐Nleu) and tryptophan enantiomers were employed as model analytes in this work while urine and mixtures of tryptophan enantiomers of differing concentrations served as model samples. Experiments performed with urine samples spiked with the DNP‐Nleu racemate at sub‐μmol/L concentrations demonstrated excellent sample pretreatment capabilities of ITP (concentration of the analytes, in‐column and post‐column sample clean up) when coupled on‐line with chiral CZE separations. In the CZE separations of enantiomers present in the samples at trace concentrations the sample pretreatment could be performed in both achiral and chiral ITP electrolyte systems. The use of a chiral electrolyte system was found to be essential in the ITP pretreatment of the samples containing the enantiomers at very differing concentrations. For example, a 2×10^–7 mol/L concentration of L‐tryptophan could be detected in the CZE separation stage of the ITP‐CZE combination in samples containing about a 10⁴ excess of D‐tryptophan only when the ITP pretreatment was carried out in the electrolyte system providing the resolution of enantiomers (α‐cyclodextrin served for this purpose in the present work). A post‐column ITP sample clean up was found effective in enhancing the destacking rate of the trace enantiomer in the CZE stage when the migration configuration of the enantiomers was less favorable (the trace constituent migrating behind the major enantiomer).     

Determination of eight illegal drugs in human urine by combination of magnetic solid‐phase extraction with capillary zone electrophoresis

Using magnetite/silica/poly(methacrylic acid‐co‐ethylene glycol dimethacrylate) (Fe₃O₄/SiO₂/poly(MAA‐co‐EDMA)) magnetic microspheres, a rapid and high‐throughput magnetic solid‐phase extraction coupled with capillary zone electrophoresis (MSPE‐CZE) method was developed for the determination of illegal drugs (ketamine, amphetamines, opiates, and metabolites). The MSPE of target analytes could be completed within 2 min, and the eight target analytes could be baseline separated within 15 min by CZE with 30 mM phosphate buffer solution (PBS, pH 2.0) containing 15% v/v ACN as background electrolyte. Furthermore, hydrodynamic injection with field‐amplified sample stacking (FASS) was employed to enhance the sensitivity of this MSPE‐CZE method. Under such optimal conditions, the limits of detection for the eight target analytes ranged from 0.015 to 0.105 μg/mL. The application feasibility of MSPE‐CZE in illegal drugs monitoring was demonstrated by analyzing urine samples, and the recoveries of target drugs for the spiked sample ranging from 85.4 to 110.1%. The method reproducibility was tested by evaluating the intra‐ and interday precisions, and relative standard deviations of <10.3 and 12.4%, respectively, were obtained. To increase throughput of the analysis, a home‐made MSPE array that has potential application to the treatment of 96 samples simultaneously was used.     

Simultaneous determination of seven phenolic acids in three Salvia species by capillary zone electrophoresis with β‐cyclodextrin as modifier

A capillary zone electrophoresis method was developed for the simultaneous determination of seven phenolic acids, including protocatechuic aldehyde ( 1 ), salvianolic acid C ( 2 ), rosmarinic acid ( 3 ), salvianolic acid A ( 4 ), danshensu ( 5 ), salvianolic acid B ( 6 ), and protocatechuic acid ( 7 ), in Danshen and related medicinal plants. A running buffer composed of 20 mM sodium tetraborate adjusted to pH 9.0, and containing 12 mM β‐cyclodextrin as modifier. Baseline separation was achieved within 17 min running at the voltage of 20 kV, temperature of 25°C and detection wavelength of 280 nm. The relative standard deviations of migration time ranged from 0.2 to 0.7% and the peak area ranged from 1.5 to 3.7% for the seven analytes, indicating the good repeatability of the proposed method. The method was extensively validated by evaluating the linearity (R² ≥ 0.9992), limits of detection (0.14–0.36 μg/mL), limits of quantification (0.47–1.19 μg/mL), and recovery (96.0–102.6%). Under the optimum conditions, samples of Danshen and related medicinal plants were analyzed using the developed method with high separation efficiency.     

Determination of malachite green in fish water samples by cloud‐point extraction coupled to cation‐selective exhaustive injection and sweeping‐MEKC

We have employed a high‐sensitivity off‐line coupled with on‐line preconcentration method, cloud‐point extraction (CPE)/cation‐selective exhaustive injection (CSEI) and sweeping‐MEKC, for the analysis of malachite green. The variables that affect CPE were investigated. The optimal conditions were 250 g/L of Triton X‐100, 10% of Na₂SO₄ (w/v), heat‐assisted at 60°C for 20 min. We monitored the effects of several of the CSEI‐sweeping‐MEKC parameters – including the type of BGE, the concentrations of SDS, the injection length of the high‐conductivity buffer, and the injection time of the sample – to optimize the separation process. The optimal BGE was 50 mM citric acid (pH 2.2) containing 100 mM SDS. In addition, electrokinetic injection of the sample at 15 kV for 800 s provided both high separation efficiency and enhanced sweeping sensitivity. The sensitivity enhancement for malachite green was 1.9×10⁴ relative to CZE; the coefficients of determination exceeded 0.9928. The LOD, based on an S/N of 3:1, of CSEI‐sweeping‐MEKC was 0.87 ng/mL; in contrast, when using off‐line CPE/CSEI‐sweeping‐MEKC the sensitivity increased to 69.6 pg/mL. This proposed method was successfully applied to determine trace amounts of malachite green in fish water samples.     

Trace analysis of acetylcholinesterase inhibitors with antipsychotic drugs for Alzheimer’s disease by capillary electrophoresis with on column field-amplified sample injection

A simple and sensitive capillary zone electrophoresis (CZE) with UV detection (214 nm) was developed and validated for the simultaneous determination of the acetylcholinesterase inhibitors (AChEI), donepezil, and rivastigmine, with antipsychotic drugs in plasma. A sample pretreatment by liquid–liquid extraction and subsequent quantification by CZE with field-amplified sample injection (FASI) was used. The optimum separation for these analytes was achieved in <20 min at 25 °C with a fused-silica capillary column of 60.2 cm?×?50 μm I.D. (effective length 50 cm) and a run buffer containing 120 mM phosphate (pH 4.0) with 0.1 % γ-cyclodextrin, 40 % methanol (MeOH), and 0.02 % polyvinyl alcohol as a dynamic coating to reduce analytes’ interaction with the capillary wall. Using phenformin as an internal standard (40.0 ng/mL), the linear ranges of the proposed method for the simultaneous determination of donepezil, rivastigmine, aripiprazole, quetiapine, risperidone, clozapine, ziprasidone, and trazodone were over the range 4.0–80.0 ng/mL, and olanzapine was over the range 1.0–20.0 ng/mL. The method was applied for concentrations monitoring of AChEIs and antipsychotic drugs in ten Alzheimer’s disease patients with behavioral and psychological symptoms of dementia after oral administration of the commercial products.

CZE separation of amitrol and triazine herbicides in environmental water samples with acid-assisted on-column preconcentration

A simple analytical scheme for the detection and quantification of amitrol and triazine herbicides (atrazine, ametryn and atraton) and degradation product (2‐hydroxyatrazine) in environmental water samples by CZE is reported. On‐column preconcentration of analytes from untreated water samples (mineral, spring, tap and river water) is accomplished by introducing an acid plug (200 mM citrate of pH 2.0) after the sample and then proceeding with the CZE separation, using 100 mM formiate buffer of pH 3.5 as running buffer and 25.0 KV as separation voltage. UV detection at 200 nm provides LODs from 50 to 300 nM in untreated samples and they were lowered tenfold by sample preconcentration by evaporation. Calculated recoveries were typically higher than 90%. Minimal detectable concentration of the electroactive amitrol could be decreased about 20‐fold when electrochemical detection was employed by monitoring the amperometric signal at +800 mV using a carbon paste electrode (LOD of 9.6 nM, 0.81 μg/L, versus 170 nM, 14.3 μg/L, using amperometric and UV detection, respectively) in untreated water samples.     

Enantioselective column coupled electrophoresis employing large bore capillaries hyphenated with tandem mass spectrometry for ultra‐trace determination of chiral compounds in complex real samples

A new multidimensional analytical approach for the ultra‐trace determination of target chiral compounds in unpretreated complex real samples was developed in this work. The proposed analytical system provided high orthogonality due to on‐line combination of three different methods (separation mechanisms), i.e. (1) isotachophoresis (ITP), (2) chiral capillary zone electrophoresis (chiral CZE), and (3) triple quadrupole mass spectrometry (QqQ MS). The ITP step, performed in a large bore capillary (800 μm), was utilized for the effective sample pretreatment (preconcentration and matrix clean‐up) in a large injection volume (1–10 μL) enabling to obtain as low as ca. 80 pg/mL limits of detection for the target enantiomers in urine matrices. In the chiral CZE step, the different chiral selectors (neutral, ionizable, and permanently charged cyclodextrins) and buffer systems were tested in terms of enantioselectivity and influence on the MS detection response. The performance parameters of the optimized ITP – chiral CZE‐QqQ MS method were evaluated according to the FDA guidance for bioanalytical method validation. Successful validation and application (enantioselective monitoring of renally eliminated pheniramine and its metabolite in human urine) highlighted great potential of this chiral approach in advanced enantioselective biomedical applications.     

Sensitive Determination of Five Priority Haloacetic Acids by Electromembrane Extraction with Capillary Electrophoresis

A method for sensitive determination of five priority haloacetic acids in drinking water has been developed for the first time based on electromembrane extraction (EME) prior to CZE with capacitively coupled contactless conductivity detection (CZE‐C⁴D). The target analytes were extracted from 10 mL of the sample solution (donor phase), through the supported liquid membrane (using a polypropylene membrane supporting 1‐octanol), and into 10 µL of 50 mmol/L NaAc solution (acceptor phase). The extracted solution was directly analyzed by CZE‐C⁴D without derivatization. Several factors that affect separation, detection and extraction efficiency were investigated. Under the optimum conditions, five haloacetic acids (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid) could be well separated from other components coexisting in water samples within 23 min, exhibiting a linear calibration over two orders of magnitude (r?0.9943); the enrichment factors at 430–671 were obtained in a 30 min of extraction, and the limits of detection were in the range of 0.17–0.61 ng/mL. The intraday relative standard deviations for peak areas investigated at 10 ng/mL were between 1.2% and 9.7% for the combined EME‐CZE‐C⁴D procedure. This approach offers an attractive alternative to the officially proposed method for purified drinking water analysis, which requires derivatization procedure prior to gas chromatography analysis.     

Simultaneous determination of substrate and product in the process of preparation of valienamine by capillary zone electrophoresis

A simple and rapid CZE method was established for the simultaneous determination of valienamine, acarbose and validamycin A, using a 20‐kV CZE with the detection wavelength of 193 nm and 50 mM phosphoric acid–20 mM Tris (pH 5.3) as a running buffer. The calibration curves of valienamine, acarbose, and validamycin A showed a good linear relationship at a concentration range of 5–1000 μg/mL. The detection limits of valienamine, acarbose, and validamycin A were 0.3, 0.6, and 0.6 μg/mL, respectively, and the average recoveries of each of the above were 99.9, 99.5, and 100.3%. The method has been successfully applied for simultaneous determination of substrate and product in the process of preparation of valienamine.     

Matrix‐less laser desorption/ionisation mass spectrometry of polyphenols in red wine

Matrix‐assisted laser desorption/ionisation (MALDI) of small molecules is challenging and in most cases impossible due to interferences from matrix ions precluding analysis of molecules <300–500 Da. A common matrix such as ferulic acid belongs to an important class of compounds associated with antioxidant activity. If the shared phenolic structure is related to the propensity as an active MALDI matrix then it follows that direct laser desorption/ionisation should be possible for polyphenols. Indeed matrix‐less laser desorption/ionisation mass spectrometry is achieved whereby the analyte functions as a matrix and was used to monitor low molecular weight compounds in wine samples. Sensitivity ranging from 0.12–87 pmol/spot was achieved for eight phenolic acids (4‐coumaric, 4‐hydroxybenzoic, caffeic, ferulic, gallic, protocatechuic, syringic, vanillic) and 0.02 pmol/spot for trans‐resveratrol. Additionally, 4‐coumaric, 4‐hydroxybenzoic, caffeic, ferulic, gallic, syringic, vanillic acids and trans‐resveratrol were identified in wine samples using accurate mass measurements consistent with reported profiles based on liquid chromatography (LC)/MS. Minimal sample pre‐treatment make the technique potentially appropriate for fingerprinting, screening and quality control of wine samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Sequential preconcentration by coupling of field amplified sample injection with pseudo isotachophoresis–acid stacking for analysis of alkaloids in capillary electrophoresis

A novel on-column sequential preconcentration method based on the combination of field-amplified sample injection induced by acetonitrile and pseudo isotachophoresis (ITP)–acid stacking is developed for simply but efficiently concentrating alkaloid cations in a high-salt sample matrix in capillary electrophoresis. Acetonitrile (70%) added to a sample solution with a high-salt sample matrix not only induces field-amplified sample stacking by decreasing conductivity but also acts as a termination reagent in the succeeding pseudo ITP. After sample injection had been completed, a plug of H⁺ was injected electrokinetically and a neutralization reaction between H⁺ and tartrate from the buffer solution produced a low conductivity zone, in which the injected analyte cations were further concentrated. With the sequential preconcentration method, a 3 orders of magnitude detection sensitivity (1,400-fold) increase could be observed compared with the conventional electrokinetic injection method, without compromising separation efficiency and peak shape, and detection limits of 0.1 ng/mL for myosmine and 0.3 ng/mL for anabasine with the conditions selected were achieved. The calibration curves demonstrated good linearity in the concentration ranges 1.3–600 ng/mL for myosmine and 4.9–900 ng/mL for anabasine, respectively. The proposed method has been used to analyze successfully trace alkaloids in cigarette samples. Figure Sequential preconcentration processes: a sample injection; b introduction of HCl; c capillary zone electrophoresis separation. A ⁻ tartrate, white circles acetonitrile, black circles Na⁺, sample zone, myosmine, anabasine     

Simultaneous determination of dihydroxybenzene and phenylenediamine positional isomers using capillary zone electrophoresis coupled with amperometric detection

In general capillary zone electrophoresis (CZE) separation models, o‐, m‐, and p‐phenylenediamine isomers can be separated in a weak acidic running buffer for their pK_a values being 4.52, 5.64, 6.04, respectively, while o‐, m‐, and p‐dihydroxybenzene isomers can be separated in a weak basic buffer for their pK_a values being 9.40, 9.40 and 10.04, respectively. So, it is hard to find a suitable running buffer at a fixed pH in normal CZE for simultaneous separation of these two groups of positional isomers. In this paper, a novel method based on alternately running two different pH buffers in CZE coupled with amperometric detection (CZE‐AD) was designed to simultaneously determine these two groups of positional isomers. It is found that when two different pH running buffers were employed alternately under appropriate order and time, the six analytes could be separated perfectly in less than 20 min and the detection limits were as low as 10^–7 mol/L. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE–AD were investigated. Experimental results demonstrated that the introduced method was practical to simultaneously determine two groups of positional isomers with different pK_a and had some advantages of high sensitivity, good repeatability and small sample requirement.     

On-line coupling of capillary isotachophoresis and capillary zone electrophoresis for the determination of flavonoids in methanolic extracts of Hypericum perforatum leaves or flowers

Five flavonoids (hyperoside, isoquercitrin, quercitrin, quercetin and rutin) were separated and determined in extracts of Hypericum perforatum leaves or flowers by capillary zone electrophoresis (CZE) with isotachophoretic (ITP) sample pre-treatment using on-line column coupling configuration. The background electrolyte (BGE) used in the CZE step was different from the leading and terminating ITP electrolytes but all the electrolytes contained 20% (v/v) of methanol. The optimal leading electrolyte was 10 mM HCl of pH* approximately 7.2 (adjusted with Tris) and the terminating electrolyte was 50 mM H3BO3 of pH* approximately 8.2 (adjusted with barium hydroxide). This operational system allowed to concentrate and pre-separate selectively the flavonoid fraction from other plant constituents before the introduction of the flavonoids into the CZE capillary. The BGE for the CZE step was 50 mM Tris buffer of pH* approximately 8.75 containing 25 mM N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid as co-ion and 55 mM H3BO3 as complex-forming agent. The ITP-CZE method with spectrophotometric detection at 254 nm was suitable for the quantitation of the flavonoids in real natural samples; kaempferol was used as internal standard. The limit of detection for quercetin-3-O-glycosides was 100 ng ml(-1) and calibration curves were rectilinear in the range 1-10 microg ml (-1) for most of the analytes. The RSD values ranged between 0.9 and 2.7% (n=3) when determining approximately 0.07-1.2% of the individual flavonoids in dried medicinal plants.     

Dispersive liquid–liquid microextraction based on solidification of floating organic drop combined with field‐amplified sample injection in capillary electrophoresis for the determination of beta(2)‐agonists in bovine urine

Dispersive liquid–liquid microextraction based on solidification of floating organic drop (DLLME–SFO) was for the first time combined with field‐amplified sample injection (FASI) in CE to determine four β₂‐agonists (cimbuterol, clenbuterol, mabuterol, and mapenterol) in bovine urine. Optimum BGE consisted of 20 mM borate buffer and 0.1 mM SDS. Using salting‐out extraction, β₂‐agonists were extracted into ACN that was then used as the disperser solvent in DLLME–SFO. Optimum DLLME–SFO conditions were: 1.0 mL ACN, 50 μL 1‐undecanol (extraction solvent), total extraction time 1.5 min, no salt addition. Back extraction into an aqueous solution (pH 2.0) facilitated direct injection of β₂‐agonists into CE. Compared to conventional CZE, DLLME–SFO–FASI–CE achieved sensitivity enhancement factors of 41–1046 resulting in LODs in the range of 1.80–37.0 μg L^?1. Linear dynamic ranges of 0.15–10.0 mg L^?1 for cimbuterol and 15–1000 μg L^?1 for the other analytes were obtained with coefficients of determination (R²) ≥ 0.9901 and RSD% ≤5.5 (n = 5). Finally, the applicability of the proposed method was successfully confirmed by determination of the four β₂‐agonists in spiked bovine urine samples and accuracy higher than 96.0% was obtained.     

A new HPIC-UV method to quantify phenolic acids in food and environmental samples

A simple and rapid HPIC method has been developed for the separation and quantification of nine phenolic acids (PAs): gallic acid, syringic acid, vanillic acid, sinapic acid, ferulic acid, p-coumaric acid, protocatechuic acid, caffeic acid and ellagic acid. Separation was carried out on an Dionex Ion-Pac AS-11 (250 mm × 4 mm I.D.) column with a Dionex Ion-Pac AG-11 (50 mm × 4 mm I.D) guard column. Elution was performed using 1000 mM sodium hydroxide (NaOH) and 500 mM sodium acetate (NaOAc) in a multi step binary gradient at a flow rate of 1 mL min^?1. Detection was performed using diode array detector set at 230, 250, 280, and 330 nm. After optimisation of various parameters, the separation of the nine phenolic acids was achieved within 23 minutes with a good resolution. Peak areas for each compound showed good linearity (R2 > 0.999) in a relatively wide concentration range. Detection limits were in the range of 10–530 µg L^?1 at a signal-to-noise ratio 3 : 1 and the amount of phenolic acids determined were in the range 0.20–10.0 ng when 20 µl of sample was injected. The developed procedure was successfully applied for the determination of these compounds in food (green tea, tomato juice and wine samples) and environmental samples (soil, surface water, organic fertiliser, organic waste) with minimal sample preparation. Beside good performances (separation, resolution, sensitivity and linearity), the new method is very fast and not expensive which makes it interesting for both scientific research and routine analysis of food and environmental samples.     

DNA fragment separations by on‐line combination of capillary isotachophoresis–capillary zone electrophoresis with UV detection

A high‐speed DNA fragment separation system based on an on‐line combination of capillary ITP with CZE (CITP‐CZE) and using UV detection at 260 nm was developed. A novel CITP‐CZE buffer system of pH 6.1 was designed for the separation of ten DNA fragments with sizes ranging from 100 to 1000 bp. An effect of underivatized α‐, β‐ and γ‐cyclodextrins on the resolution of DNA fragments in the CZE step of the CITP‐CZE combination was systematically investigated. Methylhydroxyethylcellulose present in the BGE was used to eliminate the EOF. DNA ladder fragments were separated within 10 min with LODs in the range of 1–5 ng/μL (S/N = 3). The RSDs of the migration time and peak area of individual DNA fragments were in the range of 1–3 and 3–9%, respectively. The developed CITP‐CZE system was further applied to the analysis of digest plasmid DNA samples.