5.33. An article in Biotechnology Progress (2001, Vol. 17, pp. 366–368) described an experiment to investigate nisin extraction in aqueous two-phase solutions. A two-factor factorial experiment was conducted using factors A = concentration of PEG and B = concentration of Na2SO4. Data similar to that reported in the paper are shown below.

(a) Analyze the extraction response. Draw appropriate conclusions about the effects of the significant factors on the response.

(b) Prepare appropriate residual plots and comment on model adequacy.

(c) Construct contour plots to aid in practical interpretation of the density response.

A B Extraction (%) 13 11 62.9 13 11 65.4 15 11 76.1 15 11 72.3 13 13 87.5 13 13 84.2 15 13 102.3 15 13 105.6