17
6.
From
Table 3
, find the value, Q, that corresponds to the change
in potential,
∆
E. To determine the original sample concentration,
multiply Q by the concentration of the added standard:
C
sam
= QC
std
where:
C
std
= standard concentration
C
sam
= sample concentration
Q = reading from known addition table
The table of Q values is calculated for a 10% volume change for
electrodes with slopes between 57.2 to 60.1 mV/decade. The
equation for the calculation of Q for different slopes and volume
changes is given below:
p
Q =
(1+p)10
∆
E/S
-
1
where:
Q = reading from known addition table
∆
E = E
2
- E
1
S = slope of the electrode
volume of standard
p =
volume of sample
Electrode Storage
To store the electrode between samples, overnight or over a weekend,
immerse the electrode tip in a 0.1M NaCl storage solution. If the
electrode is not to be used for longer periods of time, completely
disassemble and rinse inner body, outer body, and cap with distilled
water. Dry and reassemble electrode without filling solution.
