Simple in‐house flow‐injection capillary electrophoresis with capacitively coupled contactless conductivity method for the determination of colistin

An in‐house flow‐injection capillary electrophoresis with capacitively coupled contactless conductivity detection method was developed for the direct measurement of colistin in pharmaceutical samples. The flow injection and capillary electrophoresis systems are connected by an acrylic interface. Capillary electrophoresis separation is achieved within 2 min using a background electrolyte solution of 5 mM 2‐morpholinoethanesulfonic acid and 5 mM histidine (pH 6). The flow‐injection section allows for convenient filling of the capillary and sample introduction without the use of a pressure/vacuum manifold. Capacitively coupled contactless conductivity detection is employed since colistin has no chromophore but is cationic at pH 6. Calibration curve is linear from 20 to 150 mg/L, with a correlation coefficient (r²) of 0.997. The limit of quantitation is 20 mg/L. The developed method provides precision, simplicity, and short analysis time.     

Simple and fast analysis of iohexol in human serums using micro‐hydrophilic interaction liquid chromatography with monolithic column

A simple and rapid method based on micro‐liquid chromatography using a synthetic monolithic capillary column was developed for determination of iohexol in human serums, a marker to evaluate the glomerular filtration rate. A hydrophilic methacrylic acid‐ethylene dimethacrylate monolith provided excellent selectivity and efficiency for iohexol with separation time of 3 min using a mobile phase of 40:60 v/v 50 mM phosphate buffer pH 5/methanol. Four serum protein removal, methods using perchloric acid, 50% acetonitrile, 0.1 M zinc sulfate, and centrifuge membrane filter were examined. The method of zinc sulfate was chosen due to its simplicity, compatibility with the mobile phase system, nontoxicity, and low cost. Interday calibration curves were conducted over iohexol concentrations range of 2–500 mg/L (R² = 0.9997 ± 0.0001) with detection limit of 0.44 mg/L. Intra‐ and interday precisions for peak area and retention time were less than 2.8 and 1.4%, respectively. The method was successfully applied to serum samples with percent recoveries from 102 to 104. The method was applied to monitor released iohexol from healthy subject. Compared with the commercially available reversed‐phase high‐performance liquid chromatography method, the presented method provided simpler chromatogram, faster separation with higher separation efficiency and much lower sample and solvent consumption.     

Simple preparation of a cadmium selenide-montmorillonite hybrid

The immobilization of organically modified cadmium selenide on montmorillonite was investigated by the reaction of modified cadmium selenide nanoparticles with montmorillonite. The intercalation of the nanoparticles was indicated by the expansion of the interlayer space and spectroscopic observations. The diffuse reflectance absorption spectrum of the product showed absorption onset at 567 nm. In comparison to the bulk cadmium selenide, the blue shift of the absorption onset of the hybrid was ascribed to the quantum size effect of the modified cadmium selenide nanoparticles. This study provides a new method for introducing nanoparticles into the interlayer space of layered inorganic materials.