The extraction efficiency of an SPME method can be affected by the type and thickness of the extraction phase that is used, the extraction time and temperature, and the amount of sample [30]. These extraction variables can be optimized from an univariate approach in which each factor is modified separately or in a multivariate experimental design
[27,29], where in the simultaneous variation of all evaluated factors is done, making it possible to distinguish the interactions between factors which could not be detected using an univariate experiment. Besides that, generally, the multivariate optimization requires fewer experiments to obtain the complete information on the factors and their
interactions.