Method for determining ammonium

1 . A method for determining of a plausibility of a measurement result of a determination of an ammonium content of an aqueous sample, the method comprising:

providing a blue indole dye mixture of the aqueous sample with an alkaline pH by,

providing the aqueous sample;

adding a base, a chlorinating agent, a phenol derivative, and nitroprusside, so as to obtain the blue indole dye mixture, whereas, the method further comprises:

determining a first extinction value of the blue indole dye mixture in a first absorption region from 650 to 670 nm, the first extinction value being the measurement result;

determining a second extinction value of the blue indole dye mixture in a second absorption region from 670 to 775 nm, wherein the second absorption region is distant from the first absorption region;

dividing the first extinction value by the second extinction value so as to obtain a quotient; and

determining the measurement result to not be plausible if the quotient ≥1.1.

2 . The method as recited in claim 1 , characterized in that the quotient is ≥1.5.

3 . The method as recited in claim 1 , characterized in that:

the first absorption region is substantially 660 nm; and

wherein, when the second absorption region is from 670 to <680 nm, the quotient is >1.1,

wherein, when the second absorption region is from 680 to <690 nm, the quotient is >1.2,

wherein, when the second absorption region is from 690 to <700 nm, the quotient is >1.3,

wherein, when the second absorption region is from 700 to <710 nm, the quotient is >1.4,

wherein, when the second absorption region is from 710 to <720 nm, the quotient is >1.5,

wherein, when the second absorption region is from 720 to <730 nm, the quotient is >1.7,

wherein, when the second absorption region is from 730 to <740 nm, the quotient is >1.9,

wherein, when the second absorption region is from 740 to <750 nm, the quotient is >2.1,

wherein, when the second absorption region is from 750 to <760 nm, the quotient is >2.3,

wherein, when the second absorption region is from 760 to <770 nm, the quotient is >2.8, and

wherein, when the second absorption region is from 770 to <780 nm, the quotient is >3.3.

4 . The method as recited in claim 1 , characterized in that the chlorinating agent is dichloroisocyanuric acid or sodium hypochlorite.

5 . The method as recited in claim 1 , characterized in that the phenol derivative is 2-chlorophenol or 2-hydroxy benzyl alcohol.

6 . The method as recited in claim 1 , characterized in that the alkaline pH of the aqueous sample with the alkaline pH is provided by adding a sodium hydroxide solution.

7 . The method as recited in claim 1 , characterized in that the alkaline pH is between pH 10 and 13.

8 . The method as recited in claim 1 , wherein the blue indole dye mixture of the aqueous sample is provided by:

providing the aqueous sample;

mixing a chlorinating agent and an alkaline buffer to obtain a first mixture;

mixing the aqueous sample and the fist mixture to obtain a second mixture;

adding a phenol derivative and a nitroprusside to the second mixture to obtain the blue indole dye mixture.

9 . The method as recited in claim 8 , characterized in that the phenol derivative is 2-hydroxy benzyl alcohol.

10 . The method as recited in claim 8 , characterized in that the chlorinating agent is sodium hypochlorite.

11 . The method as recited in claim 8 , characterized in that the alkaline buffer is an alkaline citrate buffer.