In contrast to the NANOCOLOR Chlorine/Ozone tube test, the new standard test is selective for ozone. The determination of ozone can be performed even in the presence of chlorine (no disturbing effect of chlorine up to 3 mg/L Cl2).

The photometric determination of ozone is based on blue indigo trisulfonate. Ozone discolors the indigo compound. The discoloration of the blue dye is determined photometrically. Tis determination can be done in rectangular cells or in round tubes.