Vitamin B12 [HSA-Biotin]

The objectives of this study are to probe the pH responsiveness of polydimethyl siloxane (PDMS)/polymethacrylic acid (PMAA) interpenetrating polymer networks (IPNs), and to relate pH-dependent changes in permeation to morphological changes. PDMS/PMAA IPNs of 70:30 mass ratio on a dry basis were prepared using a monomer immersion method [Macromolecules 33 (10) (2000) 3714]. IPNs made by this method have previously been shown to exhibit a bicontinuous morphology at pH 7 with PMAA structural features of 10-200 nm in dimension [Macromolecules 36 (6) (2003) 1962]. Equilibrium hydration, morphology and diffusion characteristics of the IPNs were investigated at different pH. Equilibrium hydration was gravimetrically determined to be in the range of 0.77-0.9 at pH 7 and 0.42-0.5 at pH 3. corresponding to average hydrations of 0.93 and 0.74 of the PMAA component, respectively. Morphology imaged using laser scanning confocal microscopy (LSCM) showed that the area fraction of fluorescein isothiocyanate labelled dextran (FITC-dextran) accessible regions decreased from pH 7 to 3. consistent with hydration data. Additionally at pH 3, the hydrogel domain appeared to be disconnected. Vitamin B-12 (VB12) permeability through the IPN was found to be 1.7 x 10(-7) cm(2)/s at pH 7, and below detection (<10(-13) cm(2)/s) at pH 3, consistent with the observed morphology. Dynamic responses in hydration and permeation to pH changes suggests a surface driven phenomenon with response times that are expected to be thickness-dependent. (C) 2004 Elsevier B.V. All rights reserved.

In the presence of polyacrylamide (PAM) and borax buffer solution, pyrogallol red (PGR) can emit the strong and stable phosphorescence on filter paper. And cobalt activated by polyacrylamide can catalyze the reaction of hydrogen peroxide oxidizing PGR, which causes its phosphorescence quenching. Based on the facts above, a new method for the determination of trace cobalt has been established. The phosphorescence intensity decrement (Delta I-p) is proportional to the content of Co2+ when the concentration of Co2+ is within the range of 4.8 similar to 960.0 ( x 10(-18) g/spot) (corresponding concentration is 0.012 similar to 2.40 ( x 10(-9) g/L), sample volume 0.4 mu L/spot). The regression equation of working curve is Delta I-p = 12.76 + 0.1248 m Co2+ ( x 10(-18) g/spot), with correlation coefficient r = 0.9993 (n = 7) and a detection limit of 1.2 x 10(-18) g/spot (corresponding concentration is 3.0 x 10(-12) g/L). RSDs are 3.6% and 4.7% for samples containing 4.8 and 960.0 x 10(-18) g/spot of Co2+, respectively (n = 11, sample volume: 0.4 mu L/spot). The Delta I-p for the system with polyacrylamide is 4.6 times higher than that without polyacrylamide. This sensitive, accurate, simple, rapid and repeatable method has been applied to analyze the content of cobalt in ligusticum wallichii, angelica, honeysuckle, dangshen and vitamin B-12(VB12) with satisfactory results.