IAC SERIES 1100 SODIUM TECHNICAL INFORMATION

Why Measure Sodium? | Principle of Operation | Simple and Reliable Operation | Description of the Measuring System | Sodium Ion Selective Glass Electrodes

Principle of Operation

The sodium measurement is based on the proven accuracy of the glass sodium ion-sensitive electrode.  The logarithmic electrode response can be described as follows:

E = E0 + R*T/n*F*log {(CNa + Cb)/Ciso}  

E = [mV] measured potential of the electrode pair
E0 = [mV] measured potential when the sodium concentration in the sample equals Ciso
RT/nF = [mV/decade] temperature dependent slope of the electrode response
CNa = [ppb] sodium concentration in the sample
Cb = [ppb] the detection limit of the system.  This term is used to define the curvature of the electrode response near the detection limit.
Ciso = [ppb] the sodium concentration in the sample where the measured potential of the electrode pair is temperature-independent.

Sodium measurements below 1 ppb require a special glass formulation for the sensing electrode to ensure consistent electrode response.   A suitable reagent eliminates ammonium and hydrogen ion interferences from the unconditioned sample.  The measuring limit of 0.01 ppb sodium requires the conditioning of the sample pH to a minimum of pH 11.3.  This analyzer with the semi-permeable tubing can handle a sample stream with a pH down to 2.

The automatic double known addition calibration method through a calibration loop permits a calibration in the measuring range by using a single standard.  The volume of the calibration loop is about 300 times smaller than the total circulating volume so that with each addition sodium accurate concentration increase at ppb levels is achieved with a reliable ppm standard.

Continuous sodium monitoring during the various stages of water demineralisation ensures consistent water purity and efficient use of regeneration chemicals.

In the steam/water cycle of power plants sodium monitoring provides an early warning for condenser leaks; demineralizer train performance and carry over to the turbine.

IAC Series 1100 Sodium Analyzer tracks sodium levels accurately and reliably down to less than 0.01 ppb.

Reagent consumption rates are the lowest in the industry with 3 months between reagent changes.

Detection method
The sodium concentration is detected by a sodium ion selective glass electrode and double junction reference electrode. The sodium sensor develops a potential proportional to the log of the sodium ion concentration.

Chemistry
The pH of the sample is raised to 11.2 with a reagent to eliminate hydrogen ion and ammonium interference. The water soluble, volatile amine reagent is completely consumed with no residual product to dispose of.

Calibration

Sodium Series Model 1101: Calibration is fully automatic and follows the proven Double Known Addition technique. This method calibrates the instrument in the measuring range by adding accurate small volumes of concentrated standard in a large sample volume.
The electrode response to concentration changes is measured and used to determine the electrode pair performance characteristics.

Sodium Series Model 1102: Simple, easy two point manual calibration allows for total accuracy and precise measurements.

Sodium Series Model 1103:  When the monitoring of cation demineralizer effluent is required.