TN b calibration standard kit (35 mL each) for combustion based TOC analyzers, consisting of: preparation water, 1.0, 2.5, 5.0 and 10.0 mg/L N based on a 50 : 50 mixture of potassium nitrate p.a. (KNO 3 ) and ammonium sulfate p.a. ((NH 4 ) 2 SO 4 ) according to EN 12260, ISO 20236. Used for multi N/C 2100S, multi N/C 3100 and the duo systems according to installation protocol. TN b calibration standard kit (35 mL each) for combustion based TOC analyzers, consisting of: preparation water, 1.0, 2.5, 5.0 and 10.0 mg/L N based on a 50 : 50 mixture of potassium nitrate p.a. (KNO 3 ) and ammonium sulfate p.a. ((NH 4 ) 2 SO 4 ) according to EN 12260, ISO 20236. Used for multi N/C 2100S, multi N/C 3100 and the duo systems according to installation protocol.