Electro-Chemical Devices (ECD) HYDRA Ammonium - Manual (Page 32)

Page 24 HYDRA NH
4
+ -N
4.2.2 Temperature Calibration
Place the HYDRA sensor in a beaker of water so that the bottom 3 inches (7.6 cm) of the body is
immersed. Allow the sensor to equilibrate for 10 minutes. Verify the displayed temperature agrees with
the thermometer. If not, then adjust the temperature in the Configure/Trim > °C/°F & temp cal > 1 Trim
°C menu to agree with the thermometer. This calibration was performed in the factory calibration but it
is advisable to perform a temperature check every 2-3 months.
4.2.3 Single point Calibration
Single Point Calibrations are used to standardize the sensor’s reading to a known value typically to
eliminate errors caused by drift or large changes in the makeup of the measured solution. A Single Point
Calibration adjusts the base potential of the sensor by shifting the response curve to a higher or lower
level but it does not affect the slope (mV/ppm) of the curve.
Single point calibration is available for each of the measured parameters in the appropriate Buffer
Menu, Channel 1 Buffer for the NH
4
+ -N, Channel 2 Buffer for the K + and Channel 3 Buffer for pH. (See the
Single Point Calibration Screen table below)
Immerse the front end of the sensor into a container of the calibration solution, enter the value of the
calibration solution or the value derived from a grab sample into the “1 (ion) xxx ppm” line of the
Buffer menu as described in Section 3.2.5 above. Accept the reading when stable by pressing either of
the MENU SELECT keys. The lower line in the menu, the Cal line will show the new mV value associated
with the entry.
***Important Note for Ammonium Calibrations*** When using the 1 ppm and 100 ppm NH
4
+ -N
calibration solutions to calibrate the HYDRA C22 analyzer the potassium ion compensation, the “K+
comp” line in the Channel 1 Setup menu should be turned on, it is on by default. These calibration
solutions contain no potassium ions but the ammonium ions interfere with the potassium ion electrode
and the potassium ion electrode registers a K + reading, this value must be accounted for in the NH
4
+ -N
calibration.
If the Single Point Calibration is the first point in a Two Point Calibration it is customary to use the
solution with the lowest value for the single point calibration. There are no restrictions on the value
entered in the “1 (ion) xxx ppm” line of the Buffer menu; it can be higher or lower than the value in line
2 of the menu. For the pH calibration the zero point is set with pH 7.0 calibration buffer and the slope is
set with the pH 4.01 calibration buffer.
Single Point Calibration Screens
Channel Screen Recommended Solution
Ch1 Buffer (NH4-N) 1NH4-N 1.000 ppm
Cal 320.0 mV 1.0 ppm NH4-N (Part# 2010445)
or Grab Sample value
Ch2 Buffer (K+) 1K+ 1.000 ppm
Cal 165 mV 1.0 ppm K (Part# 2010443)
or Grab Sample value
Ch3 Buffer (pH) 1 pH 7.00 pH
Cal 3.1 mV pH 7.0 Buffer (part# 2010101)
or Grab Sample value