Zborník príspevkov z vedeckej konferencie - Department of ...

The design consists of a factorial design with star points located at + and – values from the center of the experimental
domain [1, 4]. There is the main difference between used statistical software because NCSS uses spherical design (= ±1.73)
and Design Expert consists the rotatability CCD (= ±1.68). The distinction is due to the selection of star points (the axial
distance) [1]
Term
B
D
E
C
F
G
A
0
1
Pareto Chart of the Standardized Effects
(Alpha = 0,05)
2,306
2
3 4
Standardized Effect
Factor Name
A stirring rate
B extraction volume
C sodium chloride
D time
E dummy 1
F diameter
G dummy 2
Fig.1. Standardized main effect Pareto chart for the Plackett-Burman design. Vertical line in the chart defines 95 %
confidence level.
The overall number of runs was 20 (8-factorials, 6-central and 6-star experiments). The results were evaluated by
ANOVA test and a second-order polynomial regression model was used to calculate the response surface for each parameter
separately (Figs. 2-4). The coefficients of the polynomial fitting equation are presented in Tab.3
Table 2 The experimental variables, their levels and star points in the central composite design. (Design Expert)
Factor - (-1.68) -1 0 +1 + (+1.68)
Extraction time (min) 16 20 25 30 34
Extraction volume (heptane) (μl) 115 150 200 250 285
Weight of sodium chloride (g) 0.07 0.8 1.8 2.8 3.53
Zborník príspevkov
z 18. medzinárodnej vedeckej konferencie
"Analytické metódy a zdravie loveka", ISBN 978-80-969435-7-9
- 95 -
5
6
hotel Falkensteiner, Bratislava
11. - 14. 10. 2010
7