A diffusion chamber for determining different parameters of an aqueous substance includes a vertical central cylinder having a sample chamber for receiving a substance sample and a needle-shaped pH-measuring sensor having a measuring tip which is brought into contact with the substance sample. A spectrophotometer having glass-fiber optics is configured to penetrate the substance sample. A gas supply into the sample chamber is configured to provide a variable gas exposure of the substance sample when determining parameters. A needle of the pH-measuring sensor is inserted into an obliquely extending groove of a slid-in sample slide. A sealing ring on the sample slide is pressed against the central cylinder by means of an inserted spacer ring, the sample chamber is tightly sealed with respect to gases from the surroundings of the diffusion chamber, and a minimum distance is maintained between the lower collimating lens and the substance sample.