Ali NİAZİ, Mahdi RAHMANİ, Marzieh HABİBİ

Simultaneous spectrophotometric determination of Zinc and Copper with 4-(2-thiazolylazo) resorcinol using parallel factor analysis (PARAFAC), partial least squares (PLS) and orthogonal signal correction- partial least squares (OSC-PLS).

Abstract. An Ultraviolet Spectrophotometry method utilizing 4-(2-thiazolylazo)resorcinol (TAR) was developed to simultaneous determination of Zn(II) and Cu(II) using parallel factor analysis (PARAFAC) and partial least squares (PLS) and orthogonal signal correction- partial least squares (OSC-PLS). TAR was chosen as the visible absorbing chelating ligand because of its ability to form stable complexes with a wide variety of metals. The work was carried out in pH range from 5.0 to 10.0 and wavelength range was from 200 to 500 nm. Multivariate calibration models using PLS, OSC-PLS and PARAFAC at different pH were elaborated for ultraviolet spectra deconvolution and metals quantitation. The calibration set was constructed with standard solutions in a concentration range of 2.0-20.0 ppm. The best model for the system were obtained with PARAFAC at pH=8 and. The capabilities of the method for the analysis of real samples were evaluated by determination of Zn(II) and Cu(II) in waste water. The accuracy of method, evaluated through the root mean square error of prediction (RMSEP), were 0.021 and 0.017 for Zn and Cu, respectively. This procedure allows the simultaneous determination of Cu(II) and Zn(II) with TAR in synthetic and real samples and good reliability of determination was proved.

Keywords:

TAR, PARAFAC PLS, OSC-PLS, simultaneous determination,

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Table 2c. Added and determined results of synthetic mixtures of cooper and zinc using OSC-PLS model (µg/ mL).
The optimum number of factors (NF) to be included in the calibration model was determined
by computing the prediction error sum of squares (PRESS) for cross-validated models using a
high number of factors. The optimum number of factors obtained by PLS, OSC-PLS and
PARAFAC models and PRESS values are summarized in Table 2.
Determination of uranium and thorium in real matrix samples
In order to test the applicability and matrix interferences of the proposed method to the
analysis of real samples, the method was applied in a variety of situations. For this purpose,
spiked samples were analyzed. The best model for the system were obtained with PARAFAC at pH=8.
Tanble 3. OSC-PLS and PARAFAC results applied on the real matrix samples (µg/ mL). 4. CONCLUSIONS
The cooper and zinc mixture is a complex system due to its high spectral overlapping
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overcome this problem. Finally it can be concluded that the model developed by the PARAFAC
method has more prediction ability especially for real samples with respect to PLS or OSC-PLS
methods, which clearly reveals that the tolerance limit of three-way calibration methods for
matrix effect is higher than of the two-way methods.
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