CHARACTERISTICS OF POTASSIUM ION-DOPED GLASS SLAB OPTICAL WAVE-GUIDE AS AN ABSORPTION CELL AND ITS APPLICATION TO THE SPECTROPHOTOMETRIC DETECTION OF METHYLENE-BLUE

The characteristics of a K+-doped glass slab optical waveguide (SOWG) as an absorption cell are discussed in terms of effective path length (L(eff)) and relative sensitivity (S/cm). The longest L(eff) value of 11 mum was observed with TM0 mode of the SOWG with a 30-min ion-exchange process in molten KNO3, which was in good agreement with the calculated value of 9.7 mum. The K+-doped SOWG provides higher sensitivity by one to two orders of magnitude than conventional absorption measurements of an analyte on a glass surface to which perpendicular irradiation of source light on the surface is applied. Octadecylsilane modification of the SOWG surface was effective for the sensitive detection of Methylene Blue by flow analysis where an ion pair of Methylene Blue and lauryl sulphate was formed.