EUTECH INSTRUMENTS NITRATE EPOXY Instruction Manual page 7

Instruction Manual
5. Using the semi-logarithmic graph paper, plot the mV reading (linear axis) against the
concentration (log axis). Extrapolate the calibration curve down to about 1.0X10
-1
NO ). A typical calibration curve can be found in Figure 1.
3
6. To a clean, dry 150 ml beaker, add 100 ml of the sample and 2 ml of ISA. Place the beaker
on the magnetic stirrer and begin stirring at a constant rate. Rinse the electrode tips with
distilled water, blot dry, and lower the electrode tips into the solution. When the reading has
stabilized, record the mV reading. Using the calibration curve, determine the sample
concentration.
7. The calibration should be checked every two hours. Assuming no change in ambient
temperature, place the electrode tips in the mid-range standard. After the reading has
stabilized, compare it to the original reading recorded in Step 3 above. A reading differing by
more than 0.5 mV or a change in the ambient temperature will necessitate the repetition of
Steps 2-5 above. A new calibration curve should be prepared daily.
A calibration curve is constructed on semi-logarithmic paper when using the
pH/mV meter in the millivolt mode. The measured electrode potential in mV
(linear axis) is plotted against the standard concentration (log axis). In the linear
region of the curve, only three standards are necessary to determine a calibration
curve. In the non-linear region, additional points must be measured. The direct
measurement procedures given are for the linear portion of the curve. The non-
linear portion of the curve requires the use of low level procedures.
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Nitrate Electrode
-5
M (1.0 ppm