Metrohm 797 VA Computrace - Manual (Page 50)

3 General settings for exploratory and determination mode
797 VA Computrace – Software
38
Notes:
•
In the exploratory mode, the SMDE can be used for the mea-
surement modes DC, NP, DP and AC. In the determination mo-
de, the SMDE can be used for the measurement modes DP and
AC
.
• An advantage of the SMDE compared with the DME is its grea-
ter sensitivity as the electrode surface and hence the baseline
remains constant during the measurement. Further, less mer-
cury is needed. On the other hand, the MME capillary is sub-
jected to greater mechanical stress than with the DME.
• A disadvantage of the SMDE compared with the HMDE is the
higher mercury consumption, in addition the MME is subjected
to greater mechanical stress.
HMDE
HMDE is an electrode mode of the Multi-Mode Electrode and
stands for Hanging Mercury Drop Electrode. Four mercury
drops of defined size are formed in succession at the MME. The last
drop remains suspended and the entire voltage sweep is performed
on this single stationary drop, in general with preceding deposition
(stripping voltammetry).
Drop size [ 1...9 ; 4 ]
Size of the mercury drop (surface 0.15 mm 2 ...0.60 mm 2 ).
t
Drop size
× 40 ms
Hg drop
surface
Notes:
•
The HMDE can be used for all measurement modes except
CPVS
.
• The HMDE is primarily used for very sensitive stripping voltam-
metry in which the analyte species is not measured until it has
first been electrochemically enriched.