This paper presented a novel method named wavelet packet transform-based partial
least squares method (WPTPLS) for simultaneous spectrophotometric determination of
α-naphthylamine, p-nitroaniline, and benzidine. Wavelet packet representations of
signals provided a local time-frequency description and separation ability between information
and noise. The quality of the noise removal can be improved by using best-basis algorithm and
thresholding operation. Partial least squares (PLS) method uses both the response and concentration
information to enhance its ability of prediction. In this case, by optimization, wavelet function and
decomposition level for WPTPLS method were selected as Db16 and 3, respectively. The relative
standard errors of prediction (RSEP) for all components with WPTPLS and PLS were 2.23%
and 2.71%, respectively. Experimental results showed WPTPLS method to be successful and
better than PLS