Abstract: Disclosed is a process photometer arrangement (10) with a photometric cuvette unit (20) comprising a cuvette body (24) defining a cuvette cavity (25) and a combined sample inlet/outlet opening (34), a photometer light inlet window (60) and a photometer light outlet window (62). The cuvette body (24) is movably supported by a cuvette body support element (88) and the cuvette unit (20) is provided with a cuvette vibration device (80) for vibrating the cuvette body (24) to thereby quickly and homogenously mix a liquid sample volume (31) within the cuvette cavity (25) without any separate mixing element within the cuvette cavity. This allows a short mixing action within a microfluidic cuvette.

Abstract: A method for the determination of a plausibility of a measurement result of a determination of an ammonium content of an aqueous sample. The method includes providing a blue indole dye mixture of the aqueous sample, determining a first extinction value of the blue indole dye mixture in a first absorption region, determining a second extinction value of the blue indole dye mixture in a second 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.

Abstract: A method for determining a phosphate concentration in a water sample includes providing the water sample, adding a first acid to the water sample to obtain a second water sample in which a concentration of the first acid is at least 0.5 wt.-%, performing a first photometric measurement of the second water sample, adding a coloring component to the second water sample to obtain a third water sample, performing a second photometric measurement of the third water sample, and calculating the phosphate concentration from a difference between the first photometric measurement and the second photometric measurement.

Abstract: A method for determining a phosphate concentration in a water sample includes providing the water sample, adding a first acid to the water sample to obtain a second water sample in which a concentration of the first acid is at least 0.5 wt.-%, performing a first photometric measurement of the second water sample, adding a coloring component to the second water sample to obtain a third water sample, performing a second photometric measurement of the third water sample, and calculating the phosphate concentration from a difference between the first photometric measurement and the second photometric measurement.