Biomedical Engineering Reference
In-Depth Information
1.5 Calculations in Quantitative Analysis
The evaluation methodology depends on demand of results: Are
only Yes/No answers needed or semiquantitive statements
(“strong” - “medium” - “weak”), or are reliable values necessary?
To get the first two types of results you have only to choose the
right assay protocol and measuring range. For quantitative evalu-
ations often more points of view have to be considered, e.g., rules
of statistics. (Some statistic parameters are given in Chap. 9.)
The choice of measuring range is essential for precise results.
Most of the quantitative methods have only a relative small lin-
ear correlation between measuring signal and amount. As far as
this range is covered by the used standards, interpolation between
standard and sample is possible. Attention should be paid if ex-
trapolations are used, because especially in the higher range the
standard curve becomes flat followed by unacceptable mistakes in
calculated values. Figure 1.1 illustrates typical standard curves for
protein estimations between 0 and 150
µ
g (standard: BSA).
Fig. 1.1.
Examples for standard curves resulting from multiple determi-
nations of different amounts of BSA.
Line with circles
: protocol according
to L
OWRY
et al.
Solid line
: nonlinear regression;
dotted line
: linear regres-
sions; wavelength 720 nm.
Line with squares
: BCA protein determination.
Solid line
: nonlinear regression;
dotted line
: linear regression; wavelength
562 nm).
Findings
means an example for graphical evaluation
