Zborník príspevkov z vedeckej konferencie - Department of ...

3.3. Optimization
The second order polynomial model was used to fit the optimal conditions. Applying (a) the desirability function,
Design Expert software located the optimal condition as follows: the extraction time was 16 min, the volume of heptane
115 μL and the addition of NaCl was 1.24 g. Applying (b) the Hooke and Jeeves method in NCSS the optimum was found at
extraction time 25 min, extraction solvent volume 200 μl and 1.26 g NaCl (Table 4).
Table 4 The optimal values of significant parameters found by two commercial software packages
Software Method
Optimal values of significant parameters
Extraction time
(min)
Extraction volume
(heptane) (μl)
Weight of sodium
chloride (g)
NCSS Hooke and Jeeves 25 200 1.26
Design
Expert
Desirability 16 115 1.24
To test the reliability of both the theoretical models the computer predicted optima were used for the real measurements
and the results were very good for both programs. Comparing the predicted results (dimensionless) with the real ones we can
see that: (a) NCSS program predicted the response value of 12.02 (sum of relative peak areas) and the experiment yielded
12.34 (102.7 % of the predicted value), and (b) Design Expert predicted 16.86 and the measurement gave 17.54 (104.0 %)
(Fig.5).
Response
20
18
16
14
12
10
8
6
4
2
0
NCSS Design Expert
Predicted Measured
Figure 5. Comparison between predicted and measured results for used statistical programs.
Zborník príspevkov
z 18. medzinárodnej vedeckej konferencie
"Analytické metódy a zdravie loveka", ISBN 978-80-969435-7-9
- 98 -
hotel Falkensteiner, Bratislava
11. - 14. 10. 2010