2. Amperometric measuring principles ABL800 FLEX Reference Manual
Metabolite electrodes, Continued
Zero current
(continued)
• The baseline is extrapolated thoughout the whole electrode calibration or sample
measurement period, and represents the zero current time function.
• The I
0
baseline is used to determine the sensitivity of the metabolite electrode.
The extrapolated final zero current value at the metabolite electrodes at the last
updating (illustrated by the I
0
baseline) is determined as follows:
A
where:
A
1
= Empirical constant dependent on electrode and determined from
tests against the reference method
t
final
= Time of the last measurement updating on the calibration solution
or sample.
t
mean
=
The mean time of the N zero current measurements on the rinse
solution:
sec
N
t
t
N
1n
n
mean
∑
=
=
where t
n
is the time of the n
th
measurement on the rinse solution.
I
0
(mean) =
The zero current at the mean time (t
mean
):
pA
N
I
(mean)I
N
1n
n0,
0
∑
=
=
where I
0,n
is the zero current at the n
th
measurement on the rinse
solution.
I
slope
= The slope or gradient of the I
0
baseline
()
()
()
pA/second
tt
(mean)IItt
I
2
N
1=n
meann
0n0,
N
1=n
meann
slope
∑
∑
−
−×−
=
If I
slope
> 0.0, it is set to 0.0
The zero current of the metabolite electrodes should be less than 10000 pA.
Continued on next page
2-14
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