Separation of catechins and methylxanthines in tea samples by capillary electrochromatography

In this paper, the simultaneous separation of several polyphenols such as (+)-catechin, (-)-epicatechin, (-)-epigallocatechin, theophylline, caffeine in green and black teas by capillary electrochromatography (CEC) was developed. Several experimental parameters such as stationary phase type, mobile phase composition, buffer and pH, inner diameter of the columns, sample injection, were evaluated to obtain the complete separation of the analysed compounds. Baseline resolution of the studied polyphenols was achieved within 30 min by using a capillary column (id 100 microm) packed with bidentate C(18) particles for 24.5 cm and a mobile phase composed of 5 mM ammonium acetate buffer pH 4 with H(2)O/ACN (80:20, v/v). The applied voltage and the temperature were set at 30 kV and 20 degrees C. Precision, detection and quantification limits, linearity, and accuracy were investigated. A good linearity (R(2) > 0.9992) was achieved over a concentration working range of 2-100 microg/mL for all the analytes. LOD and LOQ were 1 and 2 microg/mL, respectively, for all studied compounds. The CEC method was applied to the analysis of those polyphenols in green and black tea samples after an extraction procedure. Good recovery data from accuracy studies ranged between 90% and 112% for all analytes.

Analysis of phenolic compounds in extra virgin olive oil by using reversed-phase capillary electrochromatography

In this work, the simultaneous separation of ten phenolic compounds (protocatechuic, p-coumaric, o-coumaric, vanillic, ferulic, caffeic, syringic acids, hydroxytyrosol, tyrosol and oleuropein) in extra virgin olive oils (EVOOs) by isocratic RP CEC is proposed. A CEC method was optimized in order to completely resolve all the analyzed compounds by studying several experimental parameters. The influence of the stationary phase type (C(18) and C(8) modified silica gel), buffer concentration and pH as well as the organic modifier content of the mobile phase on retention factors, selectivity and efficiency were evaluated in details. A capillary column packed with Cogent bidentate C(18) particles for 23 cm and a mobile phase composed by 100 mM ammonium formate buffer pH 3/H(2)O/ACN (5:65:30 v/v/v) allowed the baseline resolution of the compounds under study in less than 35 min setting the applied voltage and temperature at 22 kV and 20 degrees C, respectively. A study, evaluating the intra- and interday precision as well as LOD and LOQ and method linearity was developed in accordance with the analytical procedures for method validation. LODs were in the range of 0.015-2.5 microg/mL, while calibration curves showed a good linearity (r(2) >0.997). The CEC method was applied to the separation and determination of these compounds in EVOO samples after a suitable liquid-liquid extraction procedure. The mean recovery values of the studied compounds ranged between 87 and 99%.

Quantitation of chiral amino acids from microalgae by MEKC and LIF detection

In this work, chiral and nonchiral MEKC methods have been combined with LIF detection (MEKC-LIF) to identify and quantify a group of D- and L-amino acids (D/L-aa) in different microalgae samples. The combination of the nonchiral and chiral-MEKC-LIF methods made the identification of the microalgae amino acids easier, previously derivatized with FITC, providing a double proof on the correct detection of these analytes. Three microalgae species, Spirulina platensis, Dunaliella salina, and Tetraselmis suecica, were compared in terms of their content in D-Arg, L-Arg, D-Lys, L-Lys, D-Ala, L-Ala, D-Glu, L-Glu, D-Asp, and L-Asp. Also, a comparison between two Spirulina platensis samples dried under different conditions (i.e., hot air or lyophilized) was carried out in order to investigate the effect of the thermal processing on the amino acid content. Moreover, two procedures for the extraction of amino acids from microalgae (i.e., a classical procedure and pressurized liquid extraction (PLE)) together with different conditions for amino acid derivatization were studied in order to increase the sensitivity of the whole analytical method. By using the selected chiral-MEKC-LIF conditions (100 mM sodium tetraborate, 30 mM SDS, and 20 mM beta-CD at pH 9.7) the main microalgae D/L-aa are separated in less than 25 min with efficiencies up to 840 000 plates/m and good sensitivity (i.e., 330 ng of D-Arg per gram of microalga could be detected by this procedure for an S/N of 3). Several D-aa were detected in all the microalgae, observing interesting differences in their D/L-aa profiles, what corroborates the usefulness of the chiral-MEKC-LIF approach to characterize different microalgae species as well as different microalgae drying processes. Moreover, the use of PLE can selectively extract different free amino acids from microalgae.

Optimization of a pressurized liquid junction nanoelectrospray interface between CE and MS for reliable proteomic analysis

A pressurized liquid junction nanoelectrospray interface was designed and optimized for reliable on-line CE-MS coupling. The system was constructed as an integrated device for highly sensitive and selective analyses of proteins and peptides with the separation and spray capillaries fixed in a pressurized spray liquid reservoir equipped with the electrode for connection of the electrospray potential. The electrode chamber on the injection side of the separation capillary and the spray liquid reservoir were pneumatically connected by a Teflon tube filled with pressurized nitrogen. This arrangement provided precisely counterbalanced pressures at the inlet and outlet of the separation capillary. The pressure control system was driven by an electrically operated valve and maintained the optimum flow rate for the electrospray stability. All parts of the interface being in contact with the CEBGE, spray liquid and/or sample were made of glass or Teflon. The use of these materials minimized the electrospray chemical noise often caused by plastic softeners or material degradation. During optimization, the transfer of the separated zones between the separation and electrospray capillaries was monitored by UV absorbance and contactless conductivity detectors placed at the outlet of the separation capillary and inlet of the electrospray tip, respectively. This arrangement allowed independent monitoring of the effects of pressure, CE voltage and geometry of the liquid junction on the spreading and dilution of the separated zones after passage through the interface.

Analysis of the second generation antidepressant venlafaxine and its main active metabolite O-desmethylvenlafaxine in human plasma by HPLC with spectrofluorimetric detection

A high-performance liquid chromatographic method has been developed for the determination of the recent serotonin and norepinephrine reuptake inhibitor (SNRI) venlafaxine and its main active metabolite, O-desmethylvenlafaxine, in human plasma. Separation was obtained by using a reversed-phase column (C8, 150 x 4.6 mm I.D., 5 microm) and a mobile phase composed of 75% aqueous phosphate buffer containing triethylamine at pH 6.8 and 25% acetonitrile. Fluorescence detection was used, exciting at lambda=238 nm and monitoring the emission at lambda=300 nm. Citalopram was used as the internal standard. A careful pre-treatment of plasma samples was developed, using solid-phase extraction with C1 cartridges (100 mg, 1 mL). The limit of quantification (LOQ) was 1.0 ng mL(-1) and the limit of detection (LOD) was 0.3 ng mL(-1) for both analytes. The method was applied with success to plasma samples taken from patients undergoing treatment with venlafaxine. Precision data, as well as accuracy results, were satisfactory and no interference from other drugs was found. Hence, the method is suitable for therapeutic drug monitoring of venlafaxine and its main metabolite in depressed patients' plasma.

Enantioselective separation of the novel antidepressant mirtazapine and its main metabolites by CEC

In this work, the simultaneous enantioseparation of the second-generation antidepressant drug mirtazapine and its main metabolites 8-hydroxymirtazapine and N-desmethylmirtazapine by chiral CEC is reported. The separation of all enantiomers under study was achieved employing a capillary column packed with a vancomycin-modified diol stationary phase. With the aim to optimize the separation of the three pairs of enantiomers in the same run, different experimental parameters were studied including the mobile phase composition (buffer concentration and pH, organic modifier type and ratio, and water content), stationary phase composition, and capillary temperature. A capillary column packed with vancomycin mixed with silica particles in the ratio (3:1) and a mobile phase composed of 100 mM ammonium acetate buffer (pH 6)/H(2)O/MeOH/ACN (5:15:30:50, by vol.) allowed the complete enantioresolution of each pair of enantiomers but not the simultaneous separation of all the studied compounds. For this purpose, a packing bed composed of vancomycin-CSP only was tested and the baseline resolution of the three couples of enantiomers was achieved in a single run in less than 30 min, setting the applied voltage and temperature at 25 kV and 20 degrees C, respectively. In order to show the potential applicability of the developed CEC method to biomedical analysis, a study concerning precision, sensitivity, and linearity was performed. The method was then applied to the separation of the enantiomers in a human urine sample spiked with the studied compounds after suitable SPE procedure with strong cation-exchange (SCX) cartridges.

Analysis of aromatic and terpenic constituents of pepper extracts by capillary electrochromatography

An original method based on CEC has been developed for the determination of aromatic and terpenic compounds in extracts of spices obtained from Piper nigrum. The method is based on the use of a fused silica capillary (effective length: 23.5 cm, internal diameter: 100 microm) packed with a C18 sorbent (packing length: 23 cm, particle size: 5 microm). The mobile phase is a 50 mM, pH 6.0 ammonium acetate/ACN (10:90 v/v) mixture. Applying a 30 kV voltage, the following 11 compounds were separated and analysed: terpinen-4-ol, caryophyllene oxide, limonene, alpha-pinene, 3-carene, beta-pinene, alpha-humulene, beta-caryophyllene, alpha-phellandrene, eugenol and piperine. Compound determination is carried out using a diode-array detector set at 265 and 338 nm for alpha-phellandrene and piperine, respectively, and at 210 nm (reference subtraction at 282 nm) for all the other analytes. The optimised method has been validated with good results in terms of linearity, limits of quantitation, detection and precision. The CEC method was successfully applied to the analysis of essential oils and methanolic extracts of 'black', 'white' and 'green' pepper.

Recent applications in nanoliquid chromatography

Since its first introduction by Karlsson and Novotny in 1988 nano-LC has emerged as a complementary and/or competitive separation method to conventional HPLC, offering several advantages such as higher efficiency, ability to work with minute sample sizes and lower consumption of mobile phases, and better compatibility with MS, etc. Although its use was not so extended initially, in the last years new and interesting applications have appeared which deserve to be carefully considered. The aim of this review is therefore to provide an updated and critical survey of different nano-LC applications in analytical chemistry.

CEC separation of insect oostatic peptides using a strong-cation-exchange stationary phase

The separation of several insect oostatic peptides (IOPs) was achieved by using CEC with a strong-cation-exchange (SCX) stationary phase in the fused-silica capillary column of 75 microm id. The effect of organic modifier, ionic strength, buffer pH, applied voltage, and temperature on peptides' resolution was evaluated. Baseline separation of the studied IOPs was achieved using a mobile phase containing 100 mM pH 2.3 sodium phosphate buffer/water/ACN (10:20:70 v/v/v). In order to reduce the analysis time, experiments were performed in the short side mode where the stationary phase was packed for 7 cm only. The selection of the experimental parameters strongly influenced the retention time, resolution, and retention factor. An acidic pH was selected in order to positively charge the analyzed peptides, the pI's of which are about 3 in water buffer solutions. A good selectivity and resolution was achieved at pH <2.8; at higher pH the three parameters decreased due to reduced or even zero charge of peptides. The increase in the ionic strength of the buffer present in the mobile phase caused a decrease in retention factor for all the studied compounds due to the decreased interaction between analytes and stationary phase. Raising the ACN concentration in the mobile phase in the range 40-80% v/v caused an increase in both retention factor, retention time, and resolution due to the hydrophilic interactions of IOPs with free silanols and sulfonic groups of the stationary phase.

Determination of sertraline andN-desmethylsertraline in human plasma by CE with LIF detection

A method has been developed for the analysis of the antidepressant drug sertraline together with its main metabolite N-desmethylsertraline (DMS) in human plasma. It is based on CE with LIF detection (lambda = 488 nm). A SPE procedure is employed for biological sample pretreatment, followed by a derivatization step with FITC; reboxetine was the internal standard. The effect of CD, acetone and N-methyl-D-glucamine (GLC) as constituents of the BGE for analyte separation was investigated. The final BGE consisted of 20 mM carbonate buffer, pH 9.0, with 2.5 mM heptakis(2,6-di-O-methyl)-beta-CD, 50 mM GLC and 20% v/v acetone. With 30 kV applied voltage, the electrophoretic run is completed in 7.5 min. Linearity was observed in the plasma concentration range from 3.0 to 500 ng/mL for sertraline and 4.0 to 500 ng/mL for DMS. Extraction yield was >97.1%, precision - expressed as RSD% - was <3.7, accuracy (recovery) was >95.6%. Due to its sensitivity and selectivity, the method was suited for the analysis of plasma samples from patients undergoing therapy with sertraline.

Enantioselective analysis of amisulpride in pharmaceutical formulations by means of capillary electrophoresis

A capillary electrophoretic method has been developed for the enantioselective analysis of amisulpride in pharmaceutical formulations, using beta-cyclodextrin sulfate as the chiral selector. Several parameters, such as cyclodextrin type and concentration, buffer concentration and pH and capillary temperature were investigated for method optimisation. Baseline enantioseparation of the racemic compound was achieved in less than 10 min using a fused silica capillary (50 microm i.d. and 33.0, 8.5 cm, total and effective length, respectively), filled with a background electrolyte consisting of a 10mM citrate buffer at pH 3.5 supplemented with 0.22% (w/v) beta-cyclodextrin sulfate at 20 degrees C and applying a voltage of +15 kV. Formulation analysis was carried out after analyte extraction by methanol. The method was fully validated, with good results in terms of precision, selectivity, accuracy and amount of drug found with respect to the label claim. Thus, the method seems to be suitable for the enantiomeric analysis of amisulpride in pharmaceutical formulations.

Control of EOF in CE by different ways of application of radial electric field

Various ways of application of radial electric field for the control of electrokinetic potential and EOF in a home-made device for CE are presented. The device comprises three high-voltage power supplies, which are used to form a radial electric field across the fused-silica capillary wall. One power supply provides the internal electric field - a driving force for electrophoretic migration of charged analytes and for the EOF. Two power supplies are connected to the ends of the outer low-conductivity polymeric coating, which is formed by the dispersion of insoluble conductive copolymer of aniline and p-phenylendiamine in polystyrene matrix (dissolved in N-methylpyrrolidone) attached to the original outer polyimide coating of the capillary. They are able to constitute the external longitudinal electric field with variable values of electric potential at both ends of the outer coating. The potential gradient between the external and internal electric field is perpendicular to the capillary wall and forms a radial electric field across the capillary wall, which affects the electrokinetic potential at the solid-liquid interface and EOF inside the capillary. The developed device and methodology has been applied for the analysis of both chiral and achiral molecules such as terbutaline enantiomers and oligopeptides (diglycine and triglycine). The effect of magnitude, orientation, and different ways of application of the radial electric field on the flow rate of the EOF and on the speed, efficiency, and resolution of CZE separations of the above analytes in the internally noncoated fused-silica capillaries have been evaluated.

Separation of basic compounds of pharmaceutical interest by using nano-liquid chromatography coupled with mass spectrometry

Nano-liquid chromatography-mass spectrometry (nano-LC-MS) was evaluated for the separation of basic compounds of pharmaceutical interest. The separation of selected beta-blockers, namely nadolol, oxprenolol, alprenolol and propranolol in the presence of terbutaline was performed using two 75 microm I.D. capillaries packed with two different RP18 stationary phases (SP). The best results concerning resolution and efficiency were achieved using the SP where free silanol groups were not present. As expected, this latter SP proved to be very efficient and symmetry factors were observed mainly in the case of the more retained analytes. Baseline resolution of all studied basic compounds was achieved with the Cogent bidentate C18 silica phase (CBC18) eluting analytes at 800 nL/min with a mobile phase containing 500 mM ammonium acetate pH 4.5-water-methanol (1:8:91, v/v/v). The separated basic compounds were revealed using on-column UV detector at 205 nm and electrospray-ion-trap mass spectrometer (ESI-MS). The packed capillary was connected to the MS through a commercial sheath liquid interface or a sheathless nano-spray interface and in both cases the sensitivity was studied and the results compared. Limit of detection (LOD) as low as 0.1 ng/mL was measured for nadolol using the sheathless nano-spray interface and the capillary column packed with the CBC18 stationary phase.

Nano-liquid chromatography analysis of dansylated biogenic amines in wines

In this work, the simultaneous analysis of 10 biogenic amines (ethanolamine, methylamine, tryptamine, 2-phenylethylamine, putrescine, cadaverine, histamine, tyramine, spermidine and spermine) in wines by nano-liquid chromatography (nano-LC) using UV detection and a capillary bidentate C(18) column of 100 microm I.D. is proposed. The 10 selected amines, which are the most important to be determined in wine samples, were derivatized with dansyl-chloride (Dns-Cl) previous to their nano-LC determination. Excess of the derivatizing agent as well as other components of the samples were eliminated by the use of an on-line cleaning step employing a C(18) trapping column which also provided a pre-concentration effect. The mobile phase composed of acetonitrile, water, acetic acid and triethylamine (TEA) mixture was pumped at a low flow rate (634 nL/min). Limits of detection (LODs) achieved ranged between 18.3 and 48.3 ng/mL; while calibration curves showed good linearity (R(2)>0.9924). The method was applied to the analysis of this group of amines in white and red wine samples after suitable treatment with polyvinylpyrrolidone (PVP) and extraction with C(18) cartridges.