3 years ago

Revival of ion selective appl covers.indd - Endress+Hauser

Revival of ion selective appl covers.indd - Endress+Hauser

C o n c e n t r a t i o

C o n c e n t r a t i o n ⎬ ΔC • Sample is measured mV1 • Known quantity is added ∆C • New measurement is taken mV2 • Sample concentration is calculated mV1 mV2 mV LIMITATIONS When applied to nutrients such as Ammonium and Nitrate in nitrification and denitrification sample preparation itself and the maintenance of the equipment could require too much maintenance. As a result there is a lack of reliability that impedes the use of the measurement for process control. LATEST DESIGNS Recent developments have improved the quality and the selectivity of the membranes opening their use directly in the nitrification and denitrification tanks eliminating the need for any sample preparation system. ELECTRODES The selectivity of the ISE is linked to the construction of the membrane that let the ion flow into the cell. For better selectivity, ionophores are used that facilitate the transfer of the ion to be measured. Distributed with permission of author(s) by ISA 2009 Presented at ISA 4 th WWAC Symposium 2009;

Membrane cap Ionophores in the membrane increase selectivity There are still some interferences that may need to be compensated for depending on the matrix of the individual wastewater. INTERFERENCES For the measurement of Ammonium the measurement always need to be compensated for pH as the relative concentration of ammonia and ammonium is pH dependent. The NH4 ISE electrode shows the most cross sensitivity to potassium. mg/l potassium / sodium NH4 needed to change Ammonium Vs reading by 1 mg/l Potassium NH4 Vs Sodium Manufacturer A 1:20 1:800 Manufacturer B 1:14 1:800 Manufacturer C 1:11 1:800 The addition of a Potassium ISE electrode will provide automatic compensation when required Distributed with permission of author(s) by ISA 2009 Presented at ISA 4 th WWAC Symposium 2009;

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