Metrohm 746 VA Trace Analyzer - Manual (Page 10)

1.1 Instrument description
746 VA Trace Analyzer / 747 VA Stand
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1 Introduction
1.1 Instrument description
The 746 VA Trace Analyzer is a microprocessor-controlled measuring instrument for
universal use in polarographic and voltam(pero)metric analyses. The two concepts
polarography and voltammetry are defined as follows:
Polarography
Polarography is the measurement of current/voltage curves recorded at
electrodes whose material is liquid and whose surface is renewed periodi-
cally or continuously.
Example of such an electrode: DME
Voltammetry (actually voltamperometry, abbreviated to VA)
Voltammetry is the measurement of current/voltage curves recorded at
electrodes whose material is solid and/or whose surface is stationary.
Example of such electrodes: HMDE, RDE
The 746 VA Trace Analyzer is used as a master control unit for the devices at-
tached to it. Up to three 747 VA Stands can be connected as measuring stations
and up to four 685 Dosimats or 700 Dosinos used for dispensing operations. For
automatic determinations of relatively large sample series, the 695 Autosampler is
available as an option.
Operation of the 746 VA Trace Analyzer is based on the principle of interactive dia-
log via screen pages which can be called up directly by pressing the appropriate
yellow dialog keys. The instrument can be given instructions on the total of 17 dif-
ferent screen pages via the keyboard regarding the functions and their associated
parameters which should apply for a determination. A special position here is oc-
cupied by the two pages ”OP.SEQUENCE” and ”SEGMENTS” on which program
instructions can be used freely to define the course of a sample determination and
the recording of measured values. The current signals recorded at the measuring
stands are conditioned by the 746 VA Trace Analyzer and automatically evaluated.
Finally, the results are recorded in suitable form on the built-in or external printer.
The 746 VA Trace Analyzer contains a large, non-volatile data memory with space
for up to 256 fully developed, user-specific methods and up to 256 determinations.
In addition, both methods and determinations can be stored on and reloaded from
data cards. For the storage of data on a PC attached to the RS interface, a PC pro-
gram ”VA Back Up” is supplied.
The 747 VA Stand is the measuring stand accompanying the 746 VA Trace Ana-
lyzer. Its central element is the multi-mode electrode (MME), which combines the
dropping mercury electrode (DME/SMDE) and the stationary hanging mercury drop
electrode (HMDE) in a single construction. The rotating disk electrode (RDE) can
also be used in the stand.
Operation of the 747 VA Stand follows the potentiostatic 3-electrode principle in
which the voltage of the working electrode is controlled by means of a virtually cur-
rentless reference electrode to the preset desired value and the current flows
across a separate auxiliary electrode. The in part extremely small electrode signals
are recorded in the 747 VA Stand in analog form, amplified and digitized. In the
connecting cable to the 746 VA Trace Analyzer only the non-critical, digital signals
are interchanged.