Introduction - Determination of Anions in Natural and Treated Waters - page 22

• Simple perfectly clear operation principle via guidance in the dialogue mode yet at the
same time high application flexibility thanks to the visual display and alphanumeric
keyboard
• Complete and convenient result recording with built-in thermal recorder/printer
The 675 VA sample changer is controlled by the 646 VA processor on which the user
enters the few control commands necessary. The 646 VA processor also controls the 677
drive unit and the 683 pumps. With these auxiliary units, the instrument combination
becomes a polarographic analysis station which can be used to carry out on-line
measurements.
The 646 VA processor is conceived as a central compact component for automated
polarographic and voltammetric systems. Thus, two independent 647 VA stands or a 675
VA sample changer can be added. Up to four multidosimats of the 665 type for automated
standard additions and/or addition of auxiliary solutions can be connected to each of these
wet-chemical workstations. Connection of an electronic balance for direct transfer of data
is also possible.
Program-controlled automatic switching and mixing of these three electrode
configurations during a single analysis via software commands occur. The complete
electrode is pneumatically controlled. A hermetically sealed mercury reservoir of only a
few millilitres suffices for approximately 200,000 drops. The mercury drops are small and
stable, consequently there is a good signal-to-noise ratio. Mercury comes into contact
only with the purest inert gas and plastic free of metal traces. Filling is seldom required
and very simple to carry out. The system uses glass capillaries which can be exchanged
simply and rapidly.
Up to 30 complete analytical methods (including all detailed information and
instructions) can be filled in a non-volatile memory and called up. Consequently, a large
extensive and correspondingly efficient library of analytical methods can be built up,
comprehensive enough to carry out all routine determinations conveniently via call-up of
a stored method.
The standard addition method (SAM) is the procedure generally employed to calculate
the analyte content from the signal of the sample solution. The SAM is coupled directly to
the determination of the sample solution so that all factors which influence the
measurement remain constant. There would be no doubt that the SAM provides results
that have proved to be accurate and precise in virtually every case.
The addition of standard solutions can be performed several times if need be (multiple
standard addition) to raise the level of quality of the results still further.
Normally, a real sample solution contains the substances to be analysed in widely
different concentrations. In a single multi-element analysis, however, all components
must be determined simultaneously. The superiority of the facilities offered by segmented
data acquisition in this respect is clear when a comparison is made with previous
solutions. The analytical conditions were inevitably a compromise; no matter what type of
analytical conditions were selected, such large differences could rarely be reconciled. In
the recording, either the peaks of some of the components were shown meaningfully—
each of the other two were either no longer recognisable—or led to gigantic signals with
cut-off peak tips. And all too often the differences were still too large even within the two
concentration ranges. Since the recorder sensitivity and also all other instrument and