LENGTH OF STAIN DETECTOR FOR HIGH ALKALINITY MEASUREMENT

4-dimethylaminoazobenzene is covalently bonded to a transparent triace tylcellulose film. Using a flow system, the dynamic range of pH, respo nse time and pk(a) of the immobilized indicator were studied. Since th e colour change of the membrane from its acidic to its basic form is v ery distinct, a length of stain detector in the shape of strips contai ning the modified membrane as the display part, was designed. The desi gn is simple and inexpensive and free from all accessories needed for operation of such detectors (such as pumps, densitometers, etc.....). Sodium hydroxide concentrations as low as 0.1 M can be measured with a relative standard deviation of about 5%. The membrane is stable for m onths.