2.4. data processing
A multivariate optimization strategy was carried out to determine the optimum conditions of the microextraction me thod. Statgraphics Statistical Computer Package Computer Package "Statgraphics Plus 5.1." (Warrenton, VA, USA) was used to build the experimental design matrices and evaluate the results. Cr(VI) was selected for the sample preparation optimization study bexause complexes formation with this specie is kine ti cally faster than Cr(III) complexes.