Metrohm 746 VA Trace Analyzer User Manual

Page 475

6 Data processing and evaluation

746 VA Trace Analyzer / 747 VA Stand

6-12

•

Base points

Selection of the base points is decisive for the determination of all baselines.

In the automatic determination of the base points (

dU.front = auto

and

dU.rear = auto

), these are determined from the results

U.max

U.min

, and

U.peak

(see section 6.6) obtained in the recognition of peaks or waves. For

this, the two differences

Uw.front

and

Uw.rear

(which are identical only for

symmetrical peaks) are multiplied by the empirical factor f

defined using

ideal gaussian-shaped curves such that the height at the base point is 5% of

the maximum peak height. In the case of baselines with

Type = linear

Type = AC2...

, this factor is multiplied by 0.8, i.e. the base points are nearer

the peak maximum than baselines with

Type = polynom

Type = expon.

U.width

dU.front dU.rear

Uw.rear

Uw.front

U.min

U.max

U.peak

Uw.front =



U.peak - U.max



Uw.rear =



U.peak - U.min



U.width = Uw.front + Uw.rear

dU.front = Uw.front

dU.rear = Uw.rear

•

Slopes

Equally important as the selection of

base points is that of the associated

slopes. In the automatic determination

of the slopes (

S.front = auto

and

S.rear = auto

), these are calculated

from the smoothed curves at the loca-

tion of the base points. The slopes are

standardized so that the following al-

ways holds:

S = 0

horizontal slope

S = 1

diagonal slope

S =

∞

vertical slope

S = 0

S =

∞

S = -1

S = 1

•

Overlapping

Two peaks which overlap can mutually

influence each other to an extent which,

depending on the degree of overlap-

ping, can impair or even completely

prevent their evaluation. With the 746 VA

Trace Analyzer, the peaks are automati-

cally investigated for any overlapping

with neighboring peaks. The position of

the base points

Ur1

and

Uf2

is used

as a criterion for determination of the

overlapping:

∆

U.peak

U.width1

U.width2

Uf2

Ur1

Uf1

Ur2

Ur1 > Uf2

Overlapping at the rear of the 1

peak

Uf2 < Ur1

Overlapping at the front of the 2

peak