3. Experimental
3.1. Apparatus
Zero-order and first-derivative absorption spectra were recorded with a model 8453 Hewlett-Packard diode array UV–VIS spectrophotometer, using 1.00 cm quartz cells and 1-s integration time. The instrument operates from 190 to 1100 nm, with 1-nm resolution. From the full spectrum, a range pre-selection was made based on the maximum differences between the spectra of the individual complexes Metal- PAR. For recording, the individual spectrum of each analyte, the concentration of each metal was fixed in 0.5 mg, a value that falls within the linear concentration range of the five metallic cations of interest.