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

Description of the Measuring System

The sample enters the analyzer through the inlet valve. Then it flows through a constant head which is connected to the atmospheric drain.  A part of the sample flows with ca. 40 ml/min (20 ml/min in cation exchange monitoring) through the flow meter to the reagent mixing chamber.
The sample is mixed with reagent air, which contains the vaporous reagent that has been picked up in semi permeable diffusion tube of the reagent bottle.

The air-lift pump under the pH sensor forces the sample flow through the 3-way electro-magnetic inlet valve into the measuring cell. The pH sensor monitors the pH of the reagent treated sample. The reagent air flow is adjusted with the metering valve in the air flow meter to raise the pH of the sample above 10 to eliminate the pH interference of the sodium measurement.

The airflow in the air-lift pump is adjusted with the needle valve located behind the standard bottle head.
The sodium , reference , temperature electrode are mounted in the measuring cell together with a fluid ground for the 2 high-ohm input amplifiers to measure the sodium
and pH electrode potential. The outlet runs to the drain.

At the start of a calibration the 3-way electromagnetic inlet valve is switched to stop sample from entering the measuring cell. In this position of the inlet valve, the trapped calibration volume is circulating and becomes a homogeneous solution for calibration.

The electromagnetic calibration valves 1 and 2 are activated. The standard solution in the standard solution bottle, which is under a slight overpressure from the air pump, is pushed through the calibration loop to the drain.  After 5 seconds, the two valves are de-activated and the trapped standard solution in the calibration loop is injected into the measuring cell with the air from the air pump and then mixed in the calibration volume.

When the measured mV potential is stable its value will be stored as E2.

                    E2 = E0 + R*T/n*F*log {(CNa1 + Cb)/Ciso}  

Here CNa1 = The unknown Sodium concentration in the circulating calibration volume plus one
addition, Cb    =    Detection limit 0.001 ppb

For the 2nd calibration point, 2 additions are injected in the measuring cell with 10 seconds interval and the corresponding mV potential E6 is measured.

                   E6 = E0 + R*T/n*F*log [{(Vc*CNa1 + 2*Va*Ca + Vc*Cb)/{(Vc+3*Va)Ciso}]  

For the 3rd calibration point, 6 additions are injected in the measuring cell with 10 seconds interval and the corresponding mV potential E10 is measured.

E10 = E0 + R*T/n*F*log [{(Vc*CNa1 + 8*Va*Ca + Vc*Cb)/ {(Vc+9*Va) Ciso}]