Metrohm 746 VA Trace Analyzer - Manual (Page 473)

6 Data processing and evaluation
746 VA Trace Analyzer / 747 VA Stand
6-10
In the recognition of peaks or waves using these tests, the following three cases
must be distinguished:
• Defined substances with inputted verification voltage
For every peak found in the segment, the three recognition tests are per-
formed for the substances assigned to this segment:
1. aU.peak = U.verify ±± U.tol
2. U.width min < aU.width < U.width max
3. approx.peak > I.threshold or
approx.peak > t.threshold (for PSA)
If all three test conditions are met, this peak is assigned to the corresponding
substance and thus recognized as a substance peak.
• Defined substances without inputted verification voltage
For every peak found in the segment, the two recognition tests for the peak
width and the peak height or peak area are performed in turn for the sub-
stances assigned to this segment:
1.
U.width min < aU.width < U.width max
2. approx.peak > I.threshold or
approx.peak > t.threshold (for PSA)
If the two test conditions are met, this peak is assigned to the corresponding
substance and thus recognized as a substance peak.
• No defined substances
For every peak found in the segment the two recognition tests for the peak
width and the peak height or peak area are performed with the following
comparison parameters:
1.
25 mV < aU.width < 150 mV
2. approx.peak > 200 pA or
approx.peak > 4 ms (for PSA)
If the two test conditions are met, this peak is incorporated in the list of peaks
recognized in a segment but not assigned to a substance. In the representa-
tion of this segment on the dialog page "CURVES", the corresponding peak or
wave voltages can be shown in the system window by pressing the softkey
(see section 5.5.3).
Maximum 12 peaks or waves independent of any assignment to a substance can
be detected per segment. With recognized substance peaks, the exact position of
the minimum U.min and the maximum U.max as well as the peak voltage U.peak
(or half-wave potential U/2 ) are then determined exactly by interpolation. After the
recognition, the following results are thus available:
U.peak or U/2 Peak voltage or half-wave potential
U.width =

U.min - U.max
 Peak width or wave width
With detected peaks which differ drastically from the gaussian form,
the values
aU.peak
,
aU.width
and
approx.peak
estimated from the
differentiation can deviate greatly from the actual values U.peak ,
U.width and I.peak or t.peak not available until later. The ranges
selected for the substance parameters important for the recognition
test U.tol , U.width min , U.width max and I.threshold or
t.threshold should thus not be too narrow.