Polyhexamethylene biguanide (PHMB) is a cationic disinfectant widely used for personal-care products and for sanitizers in swimming pools. This paper describes a promotion effect of PHMB on a glucose oxidase (GOx) enzymatic reaction with ferricyanide ion and its analytical application. The promotion effect arose from a polyion complex formation between polycationic PHMB and polyanionic GOx. The promoted GOx reaction was analyzed by Michaelis-Menten equation, and the Michalis constant and catalytic constant were estimated to be 240 μM and 31 s-1 , respectively. Utilizing the promotion effect, PHMB was successfully determined in the range of 0.05 to 0.40 ppm, and the detection limit was calculated to be 0.027 ppm. The visual detection and semi-determination of PHMB with the same concentration level were also possible. As an application, the method was applied to the determination of PHMB in a contact lens detergent and its model solution.
Grazing incidence X-ray reflectivity (GIXR), ellipsometry and X-ray photoelectron spectroscopy (XPS) have been used for measuring the thickness of ultrathin SiO2 films on Si(lOO). SiC>2 films were fabricated at a constant temperature to obtain a fixed interface structure for films with different thicknesses. The thicknesses obtained by GIXR and ellipsometry were in good agreement with each other, however, ellipsometry showed slightly larger values. The thickness of the adsorbed overlayer was also compared using GIXR and XPS. Uncertainties included in the XPS measurements of the carbonaceous layer thickness were estimated. The thicknesses of the carbonaceous layer obtained by XPS were slightly smaller, by about 0.16 nm, than those of the adsorbed overlayer obtained by GIXR. About 0.3-0.4 monolayer of adsorbed water molecules is believed to account for the differences in overlayer thicknesses between the GIXR and XPS measurments.
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