A generic technique for coating doped sol-gel films onto the inside of tubes for use as colorimetric sensors

Sol-gel thin films have been doped with bromophenol blue and eriochrome cya nine RC for measuring pH and Cu++ in solution respectively. The films were coated inside glass tubes by a novel method. Films doped with bromophenol b lue responded to pH changes from pH 3 to 8. They were stable to variations in temperature from 20 degrees C to 40 degrees C. The sensing films have be en subjected to leaching studies in different pH buffer solutions. Copper i ons in solution have been measured to a minimum concentration of 0.6 ppm by eriochrome immobilised in sol-gel films. The interferences of other metal ions were also studied. Doped sol-gel films coated onto the inside of test tubes offer a simple, none-invasive, reusable and fast optical chemical sen sing technique for the measurement of colour by spectroscopy or colorimetry .