In the development of instrumental methods the ‘one
at a time’ procedure to study a single effect has been
shown to be of little use in practical applications. This
is basically because of a lack of representativeness for
test solutions and real samples’2-‘5. The simultaneous
study of all probable effects is the only way to identify
and monitor all interference problems in instrumental
determination of elements. For interference studies in this
method, the authors have used an experimental factorial
design which has been used for many years in industrial
research16-18. This design has also been used for
procedure optimization studies in the development of
analytical methods