Metrohm 799 GPT Titrino - Manual (Page 26)

2.6 Parameters, key
799 GPT Titrino
22
Reagent feeding and EP evaluation of MET
In monotonic titrations, the volume increment is constant over the whole titration curve.
V step
Volume increment.
A prerequisite for good accuracy is the correct size of
the volume increments. A good value is given by V step
= 1/20 V
EP
(V
EP
= volume of the EP). In any case, the
increment size should always be between 1/10 V
EP
and
1/100 V
EP
; with steep jumps preferably in the region of
1/100 and with flat jumps preferably in the region of 1/10.
The accuracy of the evaluation can not be increased by
dispensing small increments as the changes in the
measured value can then be of the same order of
magnitude as the noise. This can produce "ghost EP's"!
EPC
The EP's are localized with an algorithm which is based
on Fortuin and has been adapted by METROHM for
numeric procedures. (METROHM Bulletin 2, No. 10,
1971). Here, the greatest change in the measured value
is sought (∆
n
). The exact equivalence point is determined
with an interpolation factor, which depends on the delta
values before and after ∆
n
:
V
EP
= V
0
+ ρ ∆V
V
EP
: EP volume
V
0
: Total dispensed volume before ∆
n
∆V: Volume increment
ρ : Interpolation factor (Fortuin)
Equivalence Point Criteria.
The preset EPC is compared to the found ERC
(Equivalence point Recognition Criteria) for each
evaluated equivalence point. The size of the ERC is
displayed in the titration curve, see page 83. ERC is the
sum of the measured value changes before and after the
break:
∆
n-2
+∆
n-1
+∆
n
+∆
n+1
+∆
n+2

(In certain cases there are only 3 or 1 summand).
EP's whose ERC is below the preset EPC will not be
recognized. For most titrations the standard value is
suitable.
The evaluation can be repeated at any time after the
titration in a "dry run" with changed evaluation criteria.
The old titration data are not deleted until a new titration
is started.