Metrohm 757 VA Computrace - Manual (Page 39)

3.1 Electrodes
757 VA Computrace – Software
29
Notes:
• In the exploratory mode, the SMDE can be used for all meas-
urement modes except SqW, CV and PSA. In the determina-
tion mode, the SMDE can be used for all measurement
modes except DC, SqW, CV and PSA.
• An advantage of the SMDE compared with the DME is its
greater sensitivity as the electrode surface and hence the
baseline remains constant during the measurement. Further,
less mercury is needed. On the other hand, the MME capillary
is subjected 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 sub-
jected 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 per-
formed 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.
• The HMDE is primarily used for very sensitive stripping volt-
ammetry in which the analyte species is not measured until it
has first been electrochemically enriched.