Determining Traces Metal Ions using Porphyrins as a Reagent

Abstract

Porphyrins moleculars is a macrocyclic compounds, suitable to be an excellent analytical reagent for spectrum analysis due to its highest molar absorption coefficient, for its complexes with wide range for several metal ions compared with the open chain reagent, so it can be used to determine traces of metal ions which coordinate with it.The multiplity of the bands for porphyrins reagent itself which reach to five bands cover all the spectrum (350-800)nm create inefficient direct molecular spectrum methods, because of overlap between reagent spectrum and formed complex spectrum, for thought, employment of (HPLC) can separate the excess reagent from the formed complex ,and separate the formed complexes from each other, at the same time, because the difference at retention time in the column,  and all the formed complexes with porphyrin have a common absorbance band called (Soret band) appear in the range (400-420)nm which allowed to fixing wavelength in the detector on (HPLC), thus enable to record the analytical signal for nano molar concentration for most metal ions which coordinate with porphyrins molecular formed a chelate complexes, these formed complexes are very stable, the dissuasion possibility is less for long storage period, comparing with other reagents, the overlap  on spectrum will be minimized.

This research can be a serious procedure to develop analytical high quality method to determine later transition metal ions, using HLPC technique and tetraphenylporphyrin (H₂TPP), we have acheived the following :

1- We studied the chromatographic behavior for the H₂TPP by using (UV-Vis) in several solvents: (DMF, CH₂Cl₂, CCl₄,C₆H₅-CH₃).

2- The possibility to form a chelating complex between H₂TPP and Zn ion has been studied, in addition to all effective factors which include the best formation, we have reach to the optimum conditions.   we have known to the chromatographic behavior of formed complex, and reach to the optimum separation condition between the formed complex and the excess concentration of the reagent .

3- we calculated the steichiometric composition for the formed complex by (Molar ratio and continuous method), calculated the molar absorption coefficient for formed complex, its constant formation, the linear relation between the analytical signal (peak surface) and the Zn concentration was achieved, which in contestable to Lambert-Beer law in the wide range.

4- The proposed method was applied on model samples of Zn indented with its actual contain.

5- we reached to the optimum chromatographic peaks  separation for formed  complexes(Zn-TPP, Ni-TPP, H₂TPP, VO-TPP), as the following retention time respectively : t_R=4.2 <   t_R=6  <   t_R=6.8 < t_R=12.4     (min)

6- We can confirmed according to the  results which we obtained: (RP-HPLC) to solve spectrums overlap between H₂TPP and formed metal complexes,  the possibility to insulate analytical chromatography peaks: sharp, symmetric, and related to the metal ions concentration  in a wide range and for nanomol ion concentration, consequently it well allow us to determine traces of metal ions.

Keywords: porphyrins  , chelate , complex , RP-HPLC ,  and traces ion.