Optimizing analytical methods using sequential response surface methodology. Application to the pararosaniline determination of formaldehyde

Sequential response surface methodology is a general procedure to re-optimi ze common analytical methods on the basis of the application of the respons e surface methodology and of a ne rv approach to the steepest ascent method . This procedure, which is easy to apply, consists of estimating an analyti cal function relating the response with the experimental parameters by mean s of a second-degree polynomial. Thus, a 2nd order design covering the tota l experimental domain is used and when a maximum is obtained, the character istics of the response surface are confirmed using a new design, which is o btained contracting the first one. In the proposed methodology, Box-Behnken designs are used because they offer advantages in comparison with second o rder designs more frequently used in the steepest ascent method (central co mposite designs), i.e. fewer experiments are needed, they are more efficien t, they can be moved through the experimental domain and they can even be e asily contracted or expanded.