These test strips provide a convenient method for accurate colorimetric ph indication. The strips feature covalently bound indicator dyes so that they will not bleed even in strong alkaline solutions. Strips can be immersed in samples for extended periods, so that even weakly buffered solutions can be accurately tested without contaminating the sample. The universal strip tests the full 0-14ph range with a sensitivity of 1 ph unit. Intermediate range indicators provide a sensitivity of 0.3-0.5 ph units and narrow range strips provide a sensitivity of 0.2-0.3 ph units.