Non-bleeding indicators and dyes therefor used in pH determination process
AssigneeE. Merck A. G.
InventorsKarlheinz Neisius, Wilhelm Baumer
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Abstract
In colorimetric indicators comprising a carrier such as cellulose saturated with one or more azo dyes having reactive groups capable of forming a chemical bond with the carrier material, the improvement wherein the indicator is made non-bleeding by using such dyes which, in addition to the reactive group, contain at least one additional sulfonic acid and/or carboxylic acid group, an example of such a dye being 4-anilino-3'-(2-hydroxysulfonyloxyethylsulfonyl)-azobenzene-6'-carboxylic acid.
Claims53
A process for determining the pH of a media, which comprises (a) contacting said media with a non-bleeding pH indicator comprising an insoluble polymer carrier having free hydroxyl or NH groups or mixtures thereof, and bound to said carrier an organic azo dyestuff capable of changing color in response to a change in pH, said dye being of the formula Ar -- N = N -- Ar wherein Ar is an aryl forming with the azo group said organic azo dyestuff, with the provision that at least one aryl group is substituted by at least one reactive group capable of forming a chemical bond with said polymeric carrier, and at least one aryl group is substituted by at least one other radical selected from the group consisting of --SO.sub.3 H and --COOH, said reactive group being 2-(hydroxysulfonyloxy)-ethylsulfonyl, N-methyl-N-[2-(hydroxysulfonyloxy)-ethyl]-sulfonamide, monochlorotriazinyl, dichlorotriazinyl, mono-, di- and trichloropyrimidyl, dichloropyridazinyl, dichloroquinoxalinyl, dichlorophthalazinyl or 2-(hydroxysulfonyloxy)-ethylamino-sulfonyl;
- and (b) determining the pH from the resultant color of said indicator.
Dependencies are inferred from the claim text.