Method for the determination of a concentration of a polyacrylic acid in an aqueous medium

A method for the determination of a concentration (C) of a polyacrylic acid (PAA) in an aqueous medium (AM), which comprises the polyacrylic acid (PAA), wherein the determination is performed photometrically in the presence of a dye of the general formula (I)

• wherein
• R1 is selected from the group consisting of H, C1-C10-alkyl, C6-C10-aryl and NR5R6,
• wherein
• R5 and R6 are independently of one another selected from the group consisting of H, C1-C10-alkyl and C6-C10-aryl,
• R2 is selected from the group consisting of H, C1-C10-alkyl, C6-C10-aryl and NR7R8,
• wherein
• R7 and R8 are independently of one another selected from the group consisting of H, C1-C10-alkyl and C6-C10-aryl;
• R3 is selected from the group consisting of H, C1-C10-alkyl, C6-C10-aryl and NR9R10,
• wherein
• R9 and R10 are independently of one another selected from the group consisting of H, C1-C10-alkyl and C6-C10-aryl;
• R4 is selected from the group consisting of H, C1-C10-alkyl, C6-C10-aryl and NR11R12,
• wherein
• R11 and R12 are independently of one another selected from the group consisting of H, C1-C10-alkyl and C6-C10-aryl;
• X+ is selected from the group consisting of NH+, O+ and S+;
• Y is N or CH;
• Z− is selected from the group consisting of OH−, F−, Cl−, Br−, I−, SO42−, PO43−, HCO3− and CO32−.
• comprising the steps:
• a) providing the aqueous medium (AM), which comprises the polyacrylic acid (PAA), comprising the steps:
• a1) providing an electrolyte-containing aqueous medium (EAM), which comprises the polyacrylic acid (PAA) and at least one electrolyte,
• a2) passing the electrolyte-containing aqueous medium (EAM) through a dialysis unit to give a dialyzed aqueous medium, which comprises the polyacrylic acid (PAA) and
• a3) adding deionized water to the dialyzed aqueous medium obtained in step a2) to obtain the aqueous medium (AM),
• b) addition of the dye (I) to the aqueous medium (AM) to obtain a dye-containing aqueous medium (DAM), which comprises the polyacrylic acid (PAA) and the dye (I),
• c) providing the dye-containing aqueous medium (DAM) obtained in step b) to a photometer,
• d) using at least two different wavelengths to measure at least two different transmittance values of the dye-containing aqueous medium (DAM) using the photometer and
• e) analysing the at least two different transmittance values obtained in step d) to determine the concentration (C) of the polyacrylic acid (PAA).