Concepts and recent advances in microchip electrophoresis coupled to mass spectrometry: Technologies and applications.

The online coupling of microchip electrophoresis (ME) as a fast, highly efficient, and low-cost miniaturized separation technique to mass spectrometry (MS) as an information-rich and sensitive characterization technique results in ME-MS an attractive tool for various applications. In this paper, we review the basic concepts and latest advances in technology for ME coupled to MS during the period of 2016-2021, covering microchip materials, structures, fabrication techniques, and interfacing to electrospray ionization (ESI)-MS and matrix-assisted laser desorption/ionization-MS. Two critical issues in coupling ME and ESI-MS include the electrical connection used to define the electrophoretic field strength along the separation channel and the generation of the electrospray for MS detection, as well as, a miniaturized ESI-tip. The recent commercialization of ME-MS in zone electrophoresis and isoelectric focusing modes has led to the widespread application of these techniques in academia and industry. Here we summarize recent applications of ME-MS for the separation and detection of antibodies, proteins, peptides, carbohydrates, metabolites, and so on. Throughout the paper these applications are discussed in the context of benefits and limitations of ME-MS in comparison to alternative techniques.

Overloading behavior of fenoprofen and naproxen as two model compounds on a non-porous silicon pillar array column.

In this study, the adsorption behavior of naproxen and fenoprofen as two model compounds on a non-porous pillar array column (NPAC) was investigated under reverse phase liquid chromatography conditions. Band profiles of both analytes were recorded in overloaded concentrations using 30% methanol/water (v/v) as the mobile phase. Breakthrough experiments under the same chromatographic condition were carried out to measure the adsorption isotherms. Single-component adsorption isotherm data were acquired by frontal analysis for each analyte. The isotherms were found to be concave upward and downward for naproxen and fenoprofen, respectively. To find the best agreement between the experimental data points and the adsorption isotherm models, the obtained isotherms were modeled using several isotherm models. The Langmuir-Freundlich and anti-Langmuir models provided the best fitting for fenoprofen and naproxen, respectively. The solute and stationary phase properties determine the appropriate model. Adsorbate-adsorbate interaction is important in the case of naproxen, while the adsorbate- adsorbent (stationary phase) plays the main role in retention of fenoprofen on the NPAC. The validity of the selected isotherm models were checked by comparing calculated and experimental band profiles and plate heights. An excellent agreement was observed for the whole concentration range of both analytes, which confirmed the accuracy of the selected models.

Performance of laterally elongated pillar array columns in capillary electrochromatography mode.

In the present study, cylindrical and laterally elongated pillar array columns were investigated for use in capillary electrochromatography. Minimal theoretical plate heights of H = 1.90 and 1.46 µm (in absence of sidewall effect) were obtained for coumarin C440 under unretained conditions for cylindrical and rectangular (laterally elongated, aspect ratio 4) pillar array columns, respectively. By comparing dispersion at the entire channel width to that at the central zone only, it appears that sidewall related dispersion significantly contributes to overall dispersion. A 40% reduction of the plate height was observed by taking into account only the central channel zone. A kinetic plot analysis was performed to evaluate the potential of the studied geometries by considering a maximum operating voltage of 20 kV as limiting parameter. It was demonstrated that rectangular radially elongated pillars produce a higher efficiency than cylindrical pillars and other microfabricated column structures for microchip capillary electrochromatography previously studied.

Simultaneous enantioseparation of nonsteroidal anti-inflammatory drugs by a one-dimensional liquid chromatography technique using a dynamically coated chiral porous silicon pillar array column.

The preparation of a highly efficient chiral liquid chromatography (LC) column is explored by dynamically coating a reversed-phase porous silicon pillar array column with hydroxypropyl-ß-cyclodextrin (Hp-ß-CD) as the chiral selector. Analyte mixtures composed of non-steroidal anti-inflammatory drugs were tested to reveal the enantioseparation potential of the column. The mechanism of chiral discrimination was investigated. The adsorbed Hp-ß-CDs on the column surface experience different interaction with enantiomers. The chiral stationary phase showed satisfying stability and could be easily restored by recovering the selector with sufficient flushing and repeating the loading procedure. The peak capacity of the column was evaluated, and it was found high enough to separate three enantiomer couples using a one-dimensional LC technique.

Simultaneous chiral separation of tramadol and methadone in tablets, human urine, and plasma by capillary electrophoresis using maltodextrin as the chiral selector.

The stereoselective analysis and separation of racemic drugs play an important role in pharmaceutical industry to eliminate the unwanted isomer and find the right therapeutic control for the patient. Present study suggests a maltodextrin-modified capillary electrophoresis method for a single-run chiral separation of two closely similar opiate pain relief drugs: tramadol (TRA) and methadone (MET). The best separation method possible for the both enantiomers was achieved on an uncoated fused-silica capillary at 25°C using 100 mM phosphate buffer (pH 8.0) containing 20% (w v-1 ) maltodextrin with dextrose equivalent of 4-7 and an applied voltage of 16 kV. Under optimal conditions, the baseline resolution of TRA and MET enantiomers was obtained in less than 12 minutes. The relative standard deviations (n = 3) of 20 µg mL-1 TRA and MET were 2.28% and 3.77%, respectively. The detection limits were found to be 2 µg mL-1 for TRA and 1.5 µg mL-1 for MET. This method was successfully applied to the measurement of drugs concentration in their tablets, urine, and plasma samples.