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Abstract
4-dimethylaminoazobenzene is covalently bonded to a transparent triacetylcellulose film. Using a flow system, the dynamic range of pH, response time and pka of the immobilized indicator were studied. Since the colour change of the membrane from its acidic to its basic form is very distinct, a length of stain detector in the shape of strips containing the modified membrane as the display part, was designed. The design 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 months.