LAB REPORT

Lab Report

Abstract

A method for the simultaneous spectrophotometric determination of the divalent ions of iron, cobalt, nickel and copper based on the formation of their complexes with 1,5-bis(di-2-pyridylmethylene) thiocarbonohydrazide (DPTH) is proposed. The resolution of quaternary mixtures of these metallic ions was accomplished by several chemometric approaches. A comparative study of the results obtained for simultaneous determinations in mixture by using principal component regression (PCR) and partial least-squares regression (PLS-1 and PLS-2) for absorbance, first-derivative and second-derivative data is presented. In general, the best recovery values are obtained by the PLS-2 method for absorbance data. This procedure allows the simultaneous determination of the cited ions in alloys and biological materials Good reliability of the determination was proved.

Lab Report

Introduction

Iron, cobalt, nickel and copper are metals which appear together in many real samples. Several techniques such as X-ray fluorescence, atomic fluorescence spectrometry, polarography, chromatography, atomic absorption spectrometry, etc., have been used for the simultaneous determination of these ions in different samples. Among the most widely used analytical methods are those based on the UV-visible spectrophotometry techniques, due to both the resulting experimental rapidity and simplicity and the wide application. However, the simultaneous determination of these ions by the use of the traditional spectrophotometry techniques is difficult because, generally, the absorption spectra overlap in a bright region and the superimposed curves are not suitable for quantitative evaluation.

Quantitative spectrophotometry has been greatly improved by the use of a variety of multivariate statistical method, particularly principal component regression (PCR) and partial least squares regression (PLS). The widespread use of these methods is due to the proliferation of commercial software for laboratory computers and to the development of photodiode array detectors capable of recording full spectra very rapidly. (Reddy & Thriveni 2007 585-591)

The theory and application of PCR and PLS in spectrometry have been discussed by several workers. Also several multicomponent determinations of inorganic substances based on the application of these methods to spectrophotometric data have been reported. A particularly detailed study of multivariate calibration by PLS was carried out for the spectrophotometric determination of metals. The simultaneous determination of iron, cobalt, nickel and copper, among other metals, in aqueous solutions was carried out by Vitouchova et al., who developed a method based on the spectrophotometric response of the metallic complexes formed with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP) and using multivariate calibration with PLS evaluation of absorbance data. Ni later reported a method for the simultaneous determination of these metals in aqueous solutions using a two-component mixture of chromogenic reagents, Br-PADAP and 4-(2-pyridylazo)-resorcinol (PAR), and analysis of spectral data by conventional least squares, PCR and PLS regression methods. The best results were obtained by use of either the PCR and PLS approach. Also, Mac Laurin et al. investigated the practical application of some multivariate calibration routines to visible spectra for the simultaneous multicomponent determinations of the cited ions. (Wei & Xiao 2008 1-4)

This paper reports the simultaneous spectrophotometric determination of iron, cobalt, nickel and copper with 1,5-bis(di-2-pyridylmethylene) thiocarbonohydrazide (DPTH). This ligand is a good chromogenic ...