The present invention relates to a method of extending the measurement range during the determination of the concentration of a dissolved substance (2), where the solution of the dissolved substance (2) is metered by means of a micrometering device (3, 4, 5) to a specified amount of precharged reagent (1) into a measuring cell (11) until the coloration which forms as a result of the reaction of the dissolved substance with the reagent, ascertained photometrically, achieves a predetermined extinction value X, whereupon the amount of consumed dissolved substance (2) is ascertained at the micrometering device (3, 4, 5) and the concentration is calculated on the basis of this, where the volume of (2) is much smaller than of (1).