Metrohm 746 VA Trace Analyzer User Manual
Page 103
4 Introduction to the operation
746 VA Trace Analyzer / 747 VA Stand
4-18
Further, you can also select all dialog pages with the exception of "STAND" and
"CURVES" and make changes to them. But be careful when making such changes as
they immediately become effective and could lead to uncontrollable conditions for the
active program.
2
Measurement of the sample solution
•
The first part of the lead determination involves the measurement of the
sample solution. It runs as follows (see also the description of the pages
"OP. SEQUENCE" and "SEGMENTS" in section 4.2.3):
−
Purging and stirring for 330 s
−
Wait time 5 s to stabilize the analysis solution
−
Call-up of the segment
SegPb
three times for measured value
acquisition. The lead in the solution is reduced at the dropping
mercury electrode (DME). The selected measurement mode DP
leads to a current peak with a maximum at ca. –380 mV.
•
During the voltage sweep the measurement window shows a continuous
display of the current measured values for voltage (
U
) and current (
I
):
•
In addition, the name of the segment (
SegPb
) and the current VR number,
which is composed of the number of the variation (
V
) and replication (
R
),
are specified. In the present example, in this first phase (variation 0)
three measurements are performed and are numbered as follows:
00
1
st
measurement of the sample solution
01
2
nd
measurement of the sample solution (1
st
repetition)
02
3
rd
measurement of the sample solution (2
nd
repetition)
Each single measurement recorded in a segment is consecutively numbered using
variation and replication, each from 0...8. The resulting VR number is used to identify the
individual results and curves on the dialog pages "RESULTS" and "CURVES" and for the
selective call-up of reports and curves on the "DOCUMENTATION" page.
•
During an ongoing determination, you have the possibility to display the
live curve by pressing the softkey
.
•
Instead of the "MONITORING" page, the graphical representation of the
measured current values (y axis) appears as a function of the voltage
values (x axis) with the current axis being automatically adjusted to the
measured values. The measurement window with the current experi-
mental data continues to be shown below the live curve.
If you do not desire automatic switching of the current axis in the display of the live
curve, you can fix this by changing the plot parameters for the segment to preset values
(see dialog page "SEGMENTS", section 5.6.2).
•
To return to the "MONITORING" page from the display of the live curve,
you must press either the
•
On completion of the 3
rd
measurement of the sample solution, the pro-
gram is interrupted. The screen shows the prompt to add 100
µ
L of the
standard addition solution
PbStd
to the measuring vessel:
Segment: SegPb 3 SWEEP 29 s
VR: 00
U = -0.2548 V
I = -1.961e-08 A