Column switching high-performance liquid chromatography with two channels electrochemical detection for high-sensitive determination of isoflavones

Gradient elution of hydroxyacetophenones by supercritical fluid chromatography with electrochemical detection

Linear gradient elution supercritical fluid chromatography with electrochemical detection was developed using hydroxyacetophenones as analytes. Separation was carried out with a diol column (4.6 mm id × 250 mm length, 5 μm) as a stationary phase and a mixture of supercritical carbon dioxide and methanol as a mobile phase, where the ratio of carbon dioxide and methanol was changed from 99:1 (v/v) to 60:40 (v/v). For the electrochemical detection, methanol containing 1.0 mol L^-1 ammonium acetate was used as a supporting electrolyte solution and + 1.2 V was applied to the electrochemical cell. We compared the performance of the present method to isocratic elution supercritical fluid chromatography, and the repeatability, linearity, and detection capability all showed better analytical parameters in the gradient elution. As such, we found that gradient elution supercritical fluid chromatography can achieve the faster separation and save resources compared to isocratic elution. Thus, the present method may contribute to the development of green analytical methods.

Quantitative comparison of caffeoylquinic acids and flavonoids in Chrysanthemum morifolium flowers and their sulfur-fumigated products by three-channel liquid chromatography with electrochemical detection

For the determination of seven caffeoylquinic acids [neochlorogenic acid (NcA), cryptochlorogenic acid (CcA), chlorogenic acid (CA), caffeic acid (CfA), isochlorogenic acid A (Ic A), isochlorogenic acid B (Ic B), isochlorogenic acid C (Ic C)] and two flavonoids [luteolin 7-O-glucoside (LtG) and luteolin (Lt)], a three-channel liquid chromatography with electrochemical detection (LC-3ECD) method was established. Chromatographic peak heights were proportional to each concentration, ranging from 2.5 to 100 ng/mL for NcA, CA, CcA, and CfA, and ranging from 2.5 to 250 ng/mL for LtG, Ic B, Ic A, Ic C, and Lt, respectively. The present LC-3ECD method was applied to the quantitative analysis of caffeoylquinic acids and flavonoids in four cultivars of Chrysanthemum morifolium flowers and their sulfur-fumigated products. It was found that 60% of LtG and more than 47% of caffeoylquinic acids were lost during the sulfur fumigation processing. Sulfur fumigation showed a destructive effect on the C. morifolium flowers. In addition, principle component analyses (PCA) were performed using the results of the quantitative analysis of caffeoylquinic acids and flavonoids to compare the "sameness" and "differences" of these analytes in C. morifolium flowers and the sulfur-fumigated products. PCA score plots showed that the four cultivars of C. morifolium flowers were clearly classified into four groups, and that significant differences were also found between the non-fumigated C. morifolium flowers and the sulfur-fumigated products. Therefore, it was demonstrated that the present LC-3ECD method coupled with PCA is applicable to the variation analysis of different C. morifolium flower samples.

Repeatability Assessment by ISO 11843-7 in Quantitative HPLC for Herbal Medicines

We have proposed an assessment methods to estimate the measurement relative standard deviation (RSD) of chromatographic peaks in quantitative HPLC for herbal medicines by the methodology of ISO 11843 Part 7 (ISO 11843-7:2012), which provides detection limits stochastically. In quantitative HPLC with UV detection (HPLC-UV) of Scutellaria Radix for the determination of baicalin, the measurement RSD of baicalin by ISO 11843-7:2012 stochastically was within a 95% confidence interval of the statistically obtained RSD by repetitive measurements (n = 6). Thus, our findings show that it is applicable for estimating of the repeatability of HPLC-UV for determining baicalin without repeated measurements. In addition, the allowable limit of the "System repeatability" in "Liquid Chromatography" regulated in a pharmacopoeia can be obtained by the present assessment method. Moreover, the present assessment method was also successfully applied to estimate the measurement RSDs of quantitative three-channel liquid chromatography with electrochemical detection (LC-3ECD) of Chrysanthemi Flos for determining caffeoylquinic acids and flavonoids. By the present repeatability assessment method, reliable measurement RSD was obtained stochastically, and the experimental time was remarkably reduced.

Novel on-line column extraction apparatus coupled with binary peak focusing for high-performance liquid chromatography determination of rifampicin in human plasma: a strategy for therapeutic drug monitoring

In order to develop a method that is completely suitable for the routine therapeutic drug monitoring, a sensitive and fully automated on-line column extraction apparatus in combination with high-performance liquid chromatography allowing binary peak focusing was developed and validated for the determination of rifampicin in human plasma. Rifapentine was used as an internal standard. The analytical cycle started with the injection of 100 μL of the sample pretreated by protein precipitation in a Venusil SCX extraction column. After the elution, the analytes were transferred and concentrated in an Xtimate C18 trap column. Finally, the trapped analytes were separated by an Xtimate C18 analytical column and were analyzed by an ultraviolet detector at 336 nm. With this new strategy, continuous on-line analysis of the compounds was successfully performed. The method showed excellent performance for the analysis of rifampicin in plasma samples, including calibration curve linearity (All r were larger than 0.9996), sensitivity (lowest limit of quantification was 0.12 μg/mL), method accuracy (within 6.6% in terms of relative error), and precision (relative standard deviations of intra- and interday precision were less than 7.8%). These results demonstrated that the simple, reliable, and automatic method based on on-line column extraction and binary peak focusing is a promising approach for therapeutic drug monitoring in complex biomatrix samples.

Microelectrode arrays with overlapped diffusion layers as electroanalytical detectors: theory and basic applications

This contribution contains a survey of basic literature dealing with arrays of microelectrodes with overlapping diffusion layers as prospective tools in contemporary electrochemistry. Photolithographic thin layer technology allows the fabrication of sensors of micrometric dimensions separated with a very small gap. This fact allows the diffusion layers of single microelectrodes to overlap as members of the array. Various basic types of microelectrode arrays with interacting diffusion layers are described and their analytical abilities are accented. Theoretical approaches to diffusion layer overlapping and the consequences of close constitution effects such as collection efficiency and redox cycling are discussed. Examples of basis applications in electroanalytical chemistry such as amperometric detectors in HPLC and substitutional stripping voltammetry are also given.

Rapid magnetic solid-phase extraction for the selective determination of isoflavones in soymilk using baicalin-functionalized magnetic nanoparticles

Most protocols of sample preparation for isoflavone determination in soymilk and other liquid soybean products involves tedious freeze-drying and time-consuming extraction procedures. We report a facile and rapid magnetic solid-phase extraction (MSPE) of isoflavones from soymilk for subsequent high-performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) analysis. The extraction was based on the selective binding of isoflavones to baicalin-functionalized core-shell magnetic nanoparticles (BMNPs). The proposed MSPE-HPLC-MS/MS analytical method had a linear calibration curve in the concentration range from 0.3 to 80 mg/L isoflavones. With the use of calycosin, an isomer of one of the isoflavones targeted as an internal standard, interday (5 days) precisions of the slope and intercept of the calibration curves were found to be in the range between 2.5% and 3.6% (RSD, n = 5). Six isoflavones, that is, daidzein, glycitein, genistein, daidzin, glycitin, and genistin were detected in commercial soymilk samples and quantified by the proposed analytical method. The results indicated that the method was useful for fast determination of isoflavones in soymilk and other liquid soybean products.