Metrohm tiamo 1.1 Manual - Manual (Page 397)

Commands 369
Upper limit
-200.0 ... [ 200.0 ] µA (for Window = Measured value )
0.00000 ... [ 9999.99 ] mL (for Window = Volume )
0 ... [ 999999 ] s (for Window = Time)
Value for the upper limit of the window.
Additional measured values
Screenshot and parameters: see DET pH - Additional measured values
MET
Command for Monotonic Equivalence Point Titrations ( MET ).
Principle
With this command titrations with reagent addition at constant volume increments
are carried out. Measured value acceptance is drift-controlled (equilibrium titra-
tion) or after a waiting period.
Note
This command is suited for titrations with relatively high signal variations or sud-
denly occurring potential jump and for slow titrations or slowly responding elec-
trodes.
Evaluation
The equivalence points (EPs) are localized by a procedure based on the Fortuin
method which has been adapted by Metrohm for numerical methods. A search is
made for the largest measured value alteration (∆
n
). The exact EP is determined
by using an interpolation factor ρ; this depends on the ∆-values before and after
∆
n
:
V
EP
= V
0
+ ρ ∆V
V
EP
= EP volume, V
0
= total volume added before ∆
n
, ∆V = volume increment, ρ
= interpolation factor according to Fortuin
For the recognition of the EPs found the set EP criterion is compared with the ERC
( E quivalence point R ecognition C riterion) found. The ERC is the sum of the meas-
ured value alterations before and after the jump:
|∆
n–2
|+|∆
n–1
|+|∆
n
|+|∆
n+1
|+|∆
n+2
|
(In certain cases only three or only a single summand are taken into account.) EPs
whose ERC is smaller than the set EP criterion will not be recognized.