Comparison of Alternating Variable Search and Simplex Methods of Optimisation for Inductively Coupled Plasma Optical Emission and Atomic Fluorescence Spectrometry

摘要

The performance of several cyclic alternating variable search (AVS) optimisation methods are compared withtwo simplex methods with respect to the number of changes of variable required to search a model two-factorresponse space. The roles of the initial step size and of the variable step size are discussed, and theinformation produced concerning the shape of the factor space is evaluated. An AVS method which startswith a fixed step size and then changes to a variable step size on second and subsequent cycles is comparedwith a variable step size simplex for the optimisation of an inductively coupled plasma optical emissionspectrometer and of the atomiser, source inductively coupled plasmas in atomic fluorescence spectrometry(the ASIA system). The order in which the variables are taken in the AVS method does not affect the value ofthe optimum eventually found. Both methods perform satisfactorily for the optical emission work, althoughthe AVS method provides information about the shape of the factor space which is easier to interpret than inthe simplex method. However, the simplex method was not always able to satisfy the conditions fortermination in the case of the atomic fluorescence studies and was much slower to implement than the AVSmethod as the latter used direct visual feedback from the output of the lock-in amplifier as a measure of thefigure of merit (total fluorescence signal).