Metrohm 797 VA Computrace - Manual (Page 154)

5 Determination mode
797 VA Computrace – Software
142
Peak voltage
di/dU
U
Derivative
Peak height
U
i Peak area / Coulometric
Voltammogram
i
t
Peak area / Coulometric
Chronoamperogram
Comparing the evaluation quantities Area and Coulometric you
have to consider the differences between voltammograms and
chronoamperograms:
Voltammogram:
•
Area is Power (Voltage * Current): V*A = W
•
Coulometric is Charge (Voltage * Current / Sweep rate):
V*A/(V/s) = A*s = C
Chronoamperogram :
•
Area is Charge (Current * time): A*s = C
•
Coulometric is Charge (Current * time): A*s = C
Content calculation
With polarographic and voltammetric methods, the measured eva-
luation quantities
( Height , Area , Derivative or Coulometric ) for a
substance are proportional to its mass concentration. The relation
between evaluation quantity and mass concentration must be de-
termined by a calibration with reference solutions. The 797 VA
Computrace offers the following two techniques for this:
• Standard addition
Content determination using single or multiple addition of a
standard solution.
• Calibration curve
Content determination using a calibration curve previously de-
termined with reference solutions.
The goal of these calibration methods is to calculate the sample
concentration c(s) which is defined by the found substance
amount
Amount and the sample amount (mass or volume) in the
measuring vessel Sample amount :