ISO 10523:1994

The method specified (using a pH-meter) is applicable to all types of water and waste water samples in the range from pH 3 to pH 10. The temperature, some gases and organic materials interfere with the pH-measurement. Suspended materials in the sample may cause significant errors. When measuring sewage and some surface waters, there is a particularly high risk of smearing the electrodes or contaminating the membranes and diaphragm with oil, grease or other contaminants.