Quantification of Etoposide and Etoposide Phosphate in Human Plasma by Micellar Electrokinetic Chromatography and Near-Field Thermal Lens Detection

Rapid Detection of the Anti-Tumor Drug Etoposide in Biological Samples by Using a Nanoporous-Gold-Based Electrochemical Sensor

Monitoring etoposide is important due to its wide usage in anti-tumor therapy; however, the commonly used HPLC method is expensive and often requires complicated extraction and detection procedures. Electrochemical analysis has great application prospects because of its rapid response and high specificity, sensitivity, and efficiency with low cost and high convenience. In this study, we constructed a nanoporous gold (NPG)-modified GCE for the detection of etoposide. The electrochemical oxidation of etoposide by NPG caused a sensitive current peak at +0.27 V with good reproductivity in 50 mM of phosphate buffer (pH 7.4). The relationship between etoposide concentration and peak current was linear in the range between 0.1 and 20 μM and between 20 and 150 μM, with a detection sensitivity of 681.8 μA mM-1 cm-2 and 197.2 μA mM-1 cm-2, respectively, and a limit of detection (LOD) reaching 20 nM. The electrode had a good anti-interference ability to several common anions and cations. Spiked recovery tests in serum, urine, and fermentation broth verified the excellent performance of the sensor in terms of sensitivity, reproducibility, and specificity. This may provide a promising tool for the detection of etoposide in biological samples.

Selective Electrochemical Determination of Etoposide Using a Molecularly Imprinted Overoxidized Polypyrrole Coated Glassy Carbon Electrode

A simple and efficient new electrochemical sensor based on molecularly imprinted polymer has been developed for selective detection of an anticancer agent Etoposide (ETP). The sensor was prepared by electropolymerization via cyclic voltammetry (CV) of pyrrole onto a glassy carbon electrode (GCE) in the presence of ETP molecules. The extraction of ETP molecules embedded in the polymeric matrix was carried out by overoxidation in sodium hydroxide medium using CV. Various important parameters affecting the performance of the imprinted film (MIP) coated sensor were studied and optimized using differential pulse voltammetry (DPV). Under optimal conditions, the sensor response exhibited a linear dependence on ETP concentration (R2= 0.999) over the range 5.0×10−7M – 1.0×10−5M with a LOD (3σ/m) of 2.8×10−9M. The precision (% RSD, n=6) of the proposed sensor for intra- and interdays was found to be 0.84 and 2.46%, respectively. The selectivity of MIP/GCE sensor toward ETP was investigated in the presence of different interfering molecules including excipients and ETP metabolites. The developed sensor showed great recognition ability toward ETP and was successfully applied for its determination in injectable dosage forms and biological human fluids.

Transdermal Delivery of Etoposide Phosphate I: In Vitro and In Vivo Evaluation

Cancer chemotherapy frequently requires long periods of multiple intravenous infusions that often results in patients opting out of treatment. The main purpose of this study was to investigate the feasibility of delivering one of these anticancer agents: etoposide phosphate (ETP) transdermally using iontophoresis and a combination of iontophoresis/microporation. The iontophoresis conditions for ETP were first optimized in vitro then tested in vivo in a rabbit model. Both ETP and its active form etoposide (VP) were quantified in dermis (via microdialysis sampling) and in plasma, with a specially developed high-performance liquid chromatography method. In vitro, the amount of total etoposide permeated and the steady state flux increased (p < 0.05) with increase in iontophoretic current densities (100-400 μA/cm(2)). At 300 μA/cm(2), microporation/iontophoresis further improved both parameters by 2- and 2.8-fold, respectively. In vivo, exposure increased proportionally to current density in plasma, whereas dermal concentration dropped significantly at the highest current density. Microporation led to a 50% increase in Cmax and AUClast values in both skin and plasma. In conclusion, a mild current density (300 μA/cm(2)) and a small surface area (10.1 cm(2)) achieved and maintained the minimum effective concentration for the entire duration of electrical current delivery; microporation further increased the plasma concentrations at the same current density.

Electrochemical sensing of etoposide using carbon quantum dot modified glassy carbon electrode

In this study, carbon quantum dots were used for enhancement of the electrochemical signals of etoposide.

Analysis of anticancer drugs: a review

In the last decades, the number of patients receiving chemotherapy has considerably increased. Given the toxicity of cytotoxic agents to humans (not only for patients but also for healthcare professionals), the development of reliable analytical methods to analyse these compounds became necessary. From the discovery of new substances to patient administration, all pharmaceutical fields are concerned with the analysis of cytotoxic drugs. In this review, the use of methods to analyse cytotoxic agents in various matrices, such as pharmaceutical formulations and biological and environmental samples, is discussed. Thus, an overview of reported analytical methods for the determination of the most commonly used anticancer drugs is given.

MEKC as a powerful growing analytical technique

This review summarizes the principle and the developments in MEKC in terms of separation power, sensitivity, and detection approaches more than 25 years after its appearance. Newly used surfactants are mentioned. Classical and new sample concentration techniques in MEKC are described. The different detection approaches in MEKC with advantages, limitations, and future prospects are also discussed. This review highlights the wider application of MEKC in different analytical fields. Various recent selected applications of this technique in different analytical fields are reported.

Metabolite quantitation: detector technology and MIST implications

HPLC detector technology has advanced dramatically over the past 20 years, with a range of highly sensitive and specific detectors becoming available. What is still missing from the bioanalyst’s armoury, however, is a highly sensitive detector that gives an equimolar response independent of the compound. This would allow for quantification of compounds without the requirement for a synthetic standard or a radiolabeled analogue. In particular, such a detector applied to metabolism studies would establish the relative significance of the various metabolic routes. The recently issued US FDA guidelines on metabolites in safety testing (MIST) focus on the relative quantitation of human metabolites being obtained as soon as feasible in the drug-development process. In this article, current detector technology is reviewed with respect to its potential for quantitation without authentic standards or a radiolabel and put in the context of the MIST guidelines. The potential for future developments are explored.

Matrix effects in thermal lens spectrometry: influence of salts, surfactants, polymers and solvent mixtures

In this paper, we present an overall view of the matrix effects that can change or alter the signal in thermal lens spectrometry and we report the main works published in this field. The addition of salts, surfactants and polymers in aqueous solutions or the use of solvent mixtures is often needed in a variety of applications either to enhance the sensitivity of the thermal lens method or more generally because such media are required in the separation process prior to thermal lens detection. In most cases, matrix effects result in small changes in the thermo-optical properties of the solution and small signal variations. However, most important signal alterations can arise from the Soret effect. In binary mixtures as well as in solutions with macromolecular species which are initially homogeneous, the temperature gradient will induce the migration of molecules and the formation of a concentration gradient. This results in the formation of a concentration-dependent refractive index gradient which adds to the temperature-dependent refractive index gradient and contributes to the formation of a new signal. This effect can seriously alter the analytical signal and lead to erroneous interpretation of the experimental data. In contrast, time-resolved measurements can help in separating both signal components and have allowed to derive mass-diffusion times and mass-diffusion coefficients for a variety of micelles and polymers.

MEKC: An update focusing on practical aspects

This paper reviews recent methodological and instrumental advances in MEKC. Improvements in sensitivity arising from the use of on-line sample concentration (sweeping, stacking, and combination of both protocols) and derivatization (in-capillary reactions and coupling with flow-injection systems) and improvements in resolution obtained by changing the composition of the BGE (e.g., with organic modifiers, ionic liquids, nonionic and zwitterionic surfactants, mixed micelles, and vesicles) or using coated capillaries are discussed in detail. In addition, MS and LIF spectroscopy are examined in relation to their advantages and restrictions as applied to MEKC analysis. Some thoughts on potential future directions are also expressed.

Sensitivity improvement in capillary electrophoresis using organo-aqueous separation buffers and thermal lens detection

It is shown that organo-aqueous separation buffers show much promise when used in capillary electrophoresis separations with photothermal (thermal lens) detection systems. Acetonitrile-water and methanol-water mixtures were selected, as conventionally used in capillary electrophoresis. It is shown that, despite more sophisticated experimental conditions (significant heat outflow from the capillary body) and peak detection, the theoretical ratio of the thermal lens signal for a binary mixture to the thermal lens signal for an aqueous solution (or the corresponding ratio obtained experimentally under bulk batch conditions) can be used to predict the sensitivity of thermal lens detection in capillary electrophoresis. The limits of detection for 2-, 3-, and 4-nitrophenols selected as model compounds in 70% v/v acetonitrile separation buffers are 1 x 10(-6) M, 1 x 10(-6) M and 3 x 10(-7) M, respectively, and are therefore decreased by a factor of six compared to thermal lens detection in aqueous separation buffers. The overall increase in the thermal lens detection sensitivity in a 100% ACN buffer is a factor of 13.

UV Excitation Thermal Lens Microscope for Sensitive and Nonlabeled Detection of Nonfluorescent Molecules

An ultrasensitive and nonlabeled detection method of nonfluorescent molecules on a microchip was developed by realizing a thermal lens microscope (TLM) with a 266-nm UV pulsed laser as an excitation light source (UV-TLM). Pulsed laser sources have advantages over continuous-wave laser sources in more compact size and better wavelength tuning, which are important for microchip-based analytical systems. Their disadvantage is difficulty in applying a lock-in amplifier due to the high (>10(4)) duty ratio of pulse oscillation. To overcome this problem, we realized a quasi-continuous-wave excitation by modulating the pulse trains at approximately 1 kHz and detecting the synchronous signal with a lock-in amplifier. The optimum pulse repetition frequency was obtained at 80 kHz, which was reasonable considering thermal equilibrium time. Furthermore, a permissible flow velocity in the range of 6.6-19.8 mm/s was found to avoid sensitivity decrease due to photochemical reactions and thermal energy dissipation. Under these conditions, we detected adenine aqueous solutions on a fused-silica microchip without labeling and obtained a sensitivity that was 350 times higher than that in a spectrophotometric method. The sensitivity was enough for detection on a microchip with an optical path length that was 2-3 orders shorter than that in conventional cuvettes. Finally, the UV-TLM method was applied to liquid chromatography detection. Fluorene and pyrene were separated in a microcolumn and detected in a capillary (50-microm inner diameter) with 150 times higher sensitivity than a spectrophotometric method. Our method provides highly sensitive and widely applicable detections for various analytical procedures and chemical syntheses on microchips.

Limitations arising from two-photon absorption of solvent in pulsed-laser thermal lens detection: determination of the two-photon absorption coefficient of ethanol at 266 nm

Two-photon absorption of the solvent under pulsed-laser excitation at 266 nm produces a high background thermal lens signal interfering with the analyte signal. Discrimination of both solvent and analyte signals along with calibration of the photothermal response has allowed the determination of the two-photon absorption coefficient of ethanol. The obtained value, 3.0x10(-10) cm W-1, is close to the literature values obtained from transmittance measurements using picosecond or femtosecond laser pulses.

Optimization of instrumental parameters of a near-field thermal-lens detector for capillary electrophoresis

The optical scheme of a near-field dual-beam mode-mismatched thermal-lens detector for capillary electrophoresis with a crossed-beam configuration employing a multimode HeCd laser (325 nm) as an excitation source was optimized. It is shown that a multimode laser can be successfully used as an excitation source in thermal lensing with minimal deviations in thermal responses from Gaussian excitation sources. An equation for diffraction thermal-lens theory for near-field measurements is deduced, and the experimental results agree with the deduced equation. The temperature rise in the capillary was estimated, and the exponential decrease of the signal with time for static conditions and low flow velocities was explained. The optimum configuration of the detector from the viewpoint of the maximum sensitivity and beam sizes was found. The detector provides a significant improvement in the detection limits for model compounds absorbing at 325 nm (nitrophenols) compared to the results obtained with a commercial absorbance detector operating at the same wavelength.

Signal optimisation in cw-laser crossed-beam photothermal spectrometry: influence of the chopping frequency, sample size and flow rate

Optimisation of the optical design for cw-laser crossed-beam thermal lens spectrometry in infinite and finite samples has been investigated using different excitation beam waists and various lens combinations. The characteristics of the photothermal signal depending on the position of the sample with respect to the probe beam waist, the chopping frequency, the sample size and the flow rate have been considered. Depending on the irradiation duration, the size of the thermal element at the measurement time can be much greater than the waist of the excitation beam. As a result, the optimum sample position is closely related to the probe beam to thermal element size ratio and therefore depends on the chopping frequency and of the sample size. At low frequencies, the size of the thermal element is almost independent of the degree of focusing of the excitation beam because a smaller beam waist induces a faster thermal expansion. As a result, the amplitude of the optimum signal does not depend on the waist of the excitation beam. In contrast, at high frequency, the size of the thermal element remains closer to the size of the excitation beam and the signal is inversely proportional to the waist of the excitation beam as previously demonstrated under pulsed-laser excitation. Moreover, at moderate flow velocities, the signal is significantly enhanced because the negative effect produced by the displacement of the thermal element across the probe beam axis is more than compensated by a decrease of the effective thermal time constant due to radial mixing.

Recent advances in micellar electrokinetic chromatography

This review contains nearly 200 reference citations, and covers advances in electrokinetic capillary chromatography based on micelles, including stabilized micelle complexes, polymeric and mixed micelles from 2003-2004. Detection strategies, analyte determinations, and applications in micellar electrokinetic capillary chromatography (MEKC) are discussed. Information regarding methods of analyte concentration, analyte specific analyses, and nonstandard micelles has been summarized in tabular form to provide a means of rapid access to information pertinent to the reader.