Effect of polymer-precursor molecular mass on the formation and properties of covalently crosslinked chitosan cryogels

Features of cryotropic gelation in moderately frozen solutions of chitosan samples that have various molecular masses and that are covalently crosslinked with glutaraldehyde are studied. It is shown that the chain length of the macromolecular precursor, chitosan, affects the yield of the gel fraction; the swelling ability of the polymer phase of wide-pore cryogels; the dimensions of the gross capillary pores of cryogels; and, as a consequence, the hydrodynamic parameters of columns packed with a permeable continuous matrix based on the spongy gel material. The characteristics of the latter depend in a sophisticated manner on the molecular mass of the polymer used for formation of cryogels, a circumstance that is associated with competition of differently directed factors, specifically cryoconcentration effects, a strong increase in the viscosity of the reaction medium in the unfrozen liquid microphase, kinetic features of chain crosslinking at a high concentration of reagents, etc. Therefore, in each particular case, individual conditions for specific combination of the above-mentioned parameters of the process arise. As a result, a complex dependence corresponding is observed for the efficiency of cryostructuring of the chitosan-glutaraldehyde system and for the properties of the resulting cryogels.     

Determination of melatonin in biological samples by capillary electrophoresis

The determination of melatonin (MLT) in physiological samples was investigated using capillary electrophoresis (CE). Mouse blood was collected in tubes containing EDTA, centrifuged at 1500 g for 20 min at 4°C, and stored at −20°C. Plasma samples were extracted with dichloroethane, centrifuged and the aqueous phase was discarded. Then the organic phase was evaporated to dryness. The residue was dissolved in deionized water and filtered with a microfilter (0.22 μm). Separations were carried out using a CE system equipped with a fused silica capillary [80 cm (effective length 52 cm)×75 μm I.D.] and an ultraviolet–visible detector (200 nm), and programmed to provide 25 mM 2-(N-morpholino)ethanesulfonic acid (pH 5.7). Injection was performed hydrostatically by elevating the sample by 10 cm at the cathodic side of the capillary. The calibration curve, reproducibility, recovery and limit of detection were examined, and validation of the method was performed. The result showed that MLT in blood could be easily determined with the new method.