Visible diode laser induced fluorescence detection of doxorubicin in plasma using pressurized capillary electrochromatography

A combination of single-drop microextraction and open tubular capillary electrochromatography with carbon nanotubes as stationary phase for the determination of low concentration of illicit drugs in horse urine

In this study we developed an interesting alternative to HPLC-mass spectrometry for the quantification of seven important drugs of abuse in racehorses. The procedure proposed in this work is a combination of single-drop microextraction (SDME) and an open tubular capillary electrochromatography (OT-CEC) using multi-wall carbon nanotubes (MWCTs) immobilized into a fused-silica capillary as a stationary phase. The SDME showed to be a powerful tool for extraction/preconcentration of the seven drugs analyzed in the study, showing an enrichment factor between 38- and 102-fold depending on the drug. We have investigated the electrophoretic features of MWCTs immobilized fused-silica capillary by covalent modification of the inner surface of the capillary. The results show a good run-to-run, day-to-day and capillary-to-capillary reproducibility of the method. Compared with the capillary zone electrophoresis (CZE), the coating of the capillary allowed the separation of the analytes with high resolution, with less band-broadening and without distortion of the baseline. The interactions between the analytes and the MWCTs resulted in an increased migration time and probably this was the reason of the front tailing effect. The results showed a good capillary efficiencies and an improved of the electrophoretic separation.

CEC of phytochemical bioactive compounds

Although there are many publications related to technological or methodological developments of CEC, few focus on the analysis of natural products, especially phytochemical bioactive compounds. This review summarized the application of CEC in the analysis of phytochemical bioactive components, including flavonoids, nucleosides, steroids, lignans, quinones and coumarins, as well as fingerprint analysis of herbs. The strategies for optimization of CEC conditions and detection were also discussed.

Pressure-assisted CEC versus CEC using methacrylate-based monolithic columns: influence of the polymerization-mixture composition

Pressure-assisted CEC (pCEC) can either be performed on a CE instrument by adding pressure at the column inlet, or by applying voltage on a capillary liquid chromatography system. This study investigates the pressure's added value in pCEC using an LC instrument as well as the influence of the polymerization-mixture composition on monolithic columns in such experimental circumstances. Two factors of the polymerization mixture, which is used to prepare the monolithic capillary columns, were varied according to an experimental design approach: the pore-forming solvent/total monomer ratio and the pore-forming solvents composition. Initially, the effect of the resulting stationary phase on the elution behavior of mainly pharmaceutical compounds was studied. Four responses were used to evaluate the effects on the chromatography: retention time, retention factor, peak asymmetry and number of theoretical plates. After processing the results, the stationary phase composition with the best chromatographic behavior was determined and tested. The advantageous properties of this stationary phase compared with the design center-point column were demonstrated. Secondly, the results of these pCEC experiments were compared with those generated in an identical experimental setup previously performed using CEC. Chromatographic conditions were chosen so that the center-point column showed similar retention in CEC and pCEC. The expected advantage (faster analysis) and drawback (decreased efficiency) of pCEC in the analysis of pharmaceuticals was evaluated. Analysis time and efficiency were both found to depend greatly on the porosity of the column. The conclusion of this comparison is that pCEC did not have a significant added value to CEC. However, this was mainly due to the instrument's limitation of the pressure-driven flow over the column. A clear benefit of the pCEC setup was apparatus-related, i.e. the presence of a loop injection system on the pCEC instrument, which avoids the injection problems that were occasionally observed in CEC.

Microfluidic immunoaffinity separations for bioanalysis

Microfluidic devices often rely on antibody-antigen interactions as a means of separating analytes of interest from sample matrices. Immunoassays and immunoaffinity separations performed in miniaturized formats offer selective target isolation with minimal reagent consumption and reduced analysis times. The introduction of biological fluids and other complicated matrices often requires sample pretreatment or system modifications for compatibility with small-scale devices. Miniaturization of external equipment facilitates the potential for portable use such as in patient point-of-care settings. Microfluidic immunoaffinity systems including capillary and chip platforms have been assembled from basic instrument components for fluid control, sample introduction, and detection. The current review focuses on the use of immunoaffinity separations in microfluidic devices with an emphasis on pump-based flow and biological sample analysis.

Flow splitting at the inlet electrode as a method for decreasing the electric current in electric field assisted liquid chromatography

The combination of pressurized flow and electric field offers, with the use of capillary columns, several options for retention control. However, it has been shown that the utility of this technique is strongly limited by the high electric current that is generated at the high electric field strengths that are needed. We have earlier shown that the high current is a result of locally increased mobile phase ion concentration in the electric field, particularly around the inlet electrode. In this paper, we report that by splitting the mobile phase flow around the inlet electrode a relatively constant ion concentration around the electrode can be obtained and the high currents are there by reduced.

Spectrophotometric Determination of Anthracycline Anticancer Agents with Aluminum(III) and Chromazurol S in a Nonionic Surfactant Micellar Medium

A simple and highly sensitive spectrophotometric method for the determination of anthracycline anticancer agents, such as Daunorubicin hydrochloride (DAU), was established by using aluminum(III) and Chromazurol S (CAS) in a nonionic surfactant micellar medium. In the case of determination of DAU, the apparent molar absorptivity was 1.3 x 10(5) dm3 mol(-1) cm(-1) at 615 nm. Beer's law was obeyed in the concentration range of 0.028 - 2.82 microg ml(-1) for DAU. Owing to no need for solvent extraction, this method could be applied to assays of DAU and related drugs in pharmaceutical preparations.

Controlling the retention in capillary LC with solvents, temperature, and electric fields

Once a suitable stationary phase and column dimensions have been selected, the retention in liquid chromatography (LC) is traditionally adjusted by controlling the mobile phase composition. Solvent gradients enable achievement of good separation selectivity while decreasing the separation time as compared to isocratic elution. Capillary columns allow use of other programming parameters, i.e. temperature and applied electric fields, in addition to solvent gradient elution. This paper presents a review of programmed separation techniques in miniaturized LC, including retention modeling and method transfer from the conventional to micro- and capillary scales. The impact of miniaturized instrumentation on retention and the limitations of capillary LC are discussed. Special attention is focused on the gradient dwell volume effects, which are more important in micro-LC techniques than in conventional analytical LC and may cause significant increase in the time of analysis, unless special instrumentation and (or) pre-column flow-splitting is used. The influence of temperature upon retention is also discussed, and applications where the temperature has been actively used for retention control in capillary LC are included together with the instrumentation utilized. Finally the possibilities of additional selectivity control by applying an electric field over a packed capillary LC column are discussed.

Deviation from Ohm’s law in electric field assisted capillary liquid chromatography

Earlier studies of electric field assisted LC (EF-LC) have shown that the effect on charged analytes of the application of an electric field over a capillary LC column is relatively small. Charged analytes can only be affected by the electric field while present in the mobile phase, which makes the effective time for influence of the electric field t(0) independent of retention time. Because the charged analytes only can be affected for a short time the electric field strength ought to be high in order to increase the impact of the electric field on the separation. We have, however, found that only a relatively low electric field strength can be used in EF-LC when pressure is used as main driving force. The useful field strength was limited by a dramatic increase in the current. This increase in current was found to origin from an increased concentration of buffer ions that have an electrophoretic mobility towards the pumped flow.

The separation of biomolecules using capillary electrochromatography

The unique properties of capillary electrochromatography such as high performance, high selectivity, minimum consumption of both reagents and samples, and good compatibility with mass spectrometry make this technique an attractive one for the analysis of biomolecules including peptides, proteins, carbohydrates, nucleosides and nucleotides. Irreversible adsorption between the biomolecules and the charged packing surface leads to a lack of reproducibility and serious peak tailing, so various approaches have been taken to overcome this and to improve the technique for future challenges.

Detection of doxorubicin and metabolites in cell extracts and in single cells by capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis with laser-induced fluorescence detection was used to separate and detect doxorubicin and at least five metabolites from NS-1 cells that were treated with 25 microM doxorubicin for 8 h. Using 10 mM borate, 10 mM sodium dodecyl sulfate (pH 9.3) as separation buffer, the 488-nm argon-ion laser line for fluorescence excitation, and a 635 +/- 27.5 nm bandpass filter for detection, the limit of detection (S/N=3) for doxorubicin is 61 +/- 13 zmol. This low limit of detection allows for the detection of a larger number of metabolites than previously reported. Two extraction procedures were performed: a bulk liquid-liquid extraction and an in-capillary single-cell lysis. While in the bulk liquid-liquid extraction procedure, recovery for doxorubicin range from 50 to 99%, in single cell analysis the recovery is expected to be complete. Furthermore performing lysis of a single cell inside the separation capillary prevents doxorubicin or metabolite loss or degradation during handling. Based on the bulk method the calculated metabolite abundance is in the sub-amol per cell range while it varies from 0.1 to 1.1 fmol per cell in single cell analysis confirming metabolite loss during handling. Each metabolite was found at a level less than 0.1% of the doxorubicin content in either method, suggesting a slow metabolism in the NS-1 cell system or effective removal of metabolites by the cell.

Separation methods for anthraquinone related anti-cancer drugs

The quinoid anthracycline-related anti-cancer agents represent an important group of anti-tumour drugs with a wide spectrum of activity. We review here some of the separation techniques used for the analysis of anthracyclines and related compounds. In this review we have covered a range of compounds from the early anthracycline antibiotics such as doxorubicin to the more recent anthracenediones and anthrapyrazoles such as mitoxantrone and losoxantrone, respectively. We also include novel compounds such as AQ4N and C1311, both awaiting clinical trial. Separations of the anthraquinone related anti-cancer agents are predominantly by HPLC. These separation techniques have been used for a variety of applications including drug stability, protein binding and therapeutic drug monitoring as well as detailed pharmacokinetic and metabolic studies. Pharmacokinetics, and therefore drug analysis, plays a central role in both the development of new agents and also leads to a better understanding of clinically established agents in this class. Sample preparation and extraction methods including solid-phase and liquid-liquid extraction have also been highlighted. Many anthraquinone related compounds are highly coloured and fluoresce. They are suitable for a range of detection methods including UV-Vis, electrochemical and fluorescence. The methods described are used for sometimes complex separations that are needed for the evaluation of such compounds in biological samples.

Recent applications of capillary electrochromatography

A review is presented of the most important recent applications of capillary electrochromatography (CEC) for the analysis of acidic, basic, and neutral compounds, of biomolecules, environmental substances, natural products, pharmaceuticals, and chiral compounds. Packed-column CEC (packed-CEC), open-tubular (OT-CEC), as well as pressure-assisted CEC (pseudo-CEC) are hereby considered. Papers published between July 1999 and April 2001 were taken into account. Applications before July 1999 have been reviewed in Electrophoresis 1999, 20, 3027-3065.

Determination of anthracycline antibiotics doxorubicin and daunorubicin by capillary electrophoresis with UV absorption detection

Sweeping preconcentration and electrokinetic injection was used for the capillary electrophoretic analysis of trace amounts of biologically active anthracyclines with UV absorption detection. Phosphate buffer (100 mM), pH 2.5, with addition of 40% v/v methanol was used as background electrolyte (BGE). Sodium dodecyl sulfate (150 mM) was added to BGE in the inlet vial as the sweeping agent. The system enables effective separation of anthracyclines as well as cleanup from matrix impurities. Sweeping preconcentration of sample provides an excellent detection limit (1 x 10(-9) mol L(-1)). The method was applied for the determination of therapeutic levels of doxorubicin in real plasma samples.

Use of vancomycin silica stationary phase in packed capillary electrochromatography. II. Enantiomer separation of venlafaxine and O-desmethylvenlafaxine in human plasma

A capillary electrochromatography method, using vancomycin chiral stationary phase packed capillary, was optimized for the simultaneous chiral separation of the antidepressant drug venlafaxine and its main active metabolite O-desmethylvenlafaxine. Simultaneous baseline enantiomeric separation of the two compounds was obtained using a mobile phase composed of 100 mM ammonium acetate buffer pH 6/water/acetonitrile (5:5:90, v/v). The electrokinetic injection for sample introduction provided a limit of quantitation for both the compounds of 0.05 microg/ml racemate concentration suitable for the analysis of venlafaxine and metabolite in biological samples. The acetonitrile mobile phase concentration was found to modulate the analytes elution times, the enantiomeric resolution and the efficiency of the separation. The column was tested for repeatability and linearity showing RSD values (%) in the range of 0.13-0.24, 2.47-3.66 and 1.35-2.50 for migration time, sample/internal standard peak area ratio and enantiomeric resolution, respectively and correlation coefficients higher than 0.9990. The method was applied to the analysis of clinical samples of patients under depression therapy showing a stereoselective metabolism for venlafaxine.