Chemometric Optimization of the Methodology for Determination of Molybdenum in Soils and Plants by Square Wave Adsorptive Stripping Voltammetry

José Ricardo De Carvalho,Odilaine Damasceno,Antônio Augusto Neves,César Reis,Efraim Lázaro Reis,Alexsandro Antônio Matias

doi:10.21577/0103-5053.20190235

José Ricardo De Carvalho, Odilaine Damasceno + Show 4 more

Open Access

https://doi.org/10.21577/0103-5053.20190235

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Abstract

The method is based on the adsorptive accumulation of complex molybdenum(VI) with 8-hydroxyquinoline, using voltammetric square wave cathodic stripping voltammetry. The composition and concentration of the supporting electrolyte, frequency (Hz), amplitude (mV) and deposition time (s), were optimized by factorial design in relation to current reduction of molybdenum(VI). The optimum methodology provided the following values for the process variables: scan increase (0.5 mV), pulse amplitude (127 mV), frequency (96 Hz), adsorption time (80 s) and drop size (0.60 mm2), the concentration of KNO3 (2.0 mol L-1), acetate buffer (0.5 mol L-1) and 8-hydroxyquinoline (0.01 mol L-1). The results obtained after optimization showed a linear response in the range from 1.0 to 6.0 mg L-1 and limits of detection and quantification, respectively equal to 0.02 and 0.08 mg L-1. The molybdenum contained in the samples were determined using the optimized methodology, with values consistent with the values determined by atomic emission spectrometry with inductively coupled plasma (ICP-AES).

Highlights

Molybdenum is an essential trace element to living things and can be found practically in every biosphere
Using KNO3, acetate buffer, and 8-hydroxyquinoline complexing as mixing variables and levels chosen with Table 1, and according to the results presented in Table 4, the following optimized values were obtained for the variables: KNO3 (CK) 2.0 mol L-1, acetate buffer (ST) at 0.5 mol L-1 and 8-hydroxyquinoline (CO) 0.01 mol L-1
The comparison of the analytical results of the method described above with the results of the determination of molybdenum by atomic emission spectrometry with induced plasma source (ICP-AES) used as control method (Table 7), and the results reported in the literature,[24,25,26] shows good agreement and indicates that the proposed method may be adequate for the determination of traces of molybdenum in soil and plant samples

Summary

Introduction

Molybdenum is an essential trace element to living things and can be found practically in every biosphere. In the biological nitrogen fixation process, molybdenum is an essential micronutrient, whose functions in plants are related to the electron transfer system for nitrate reduction. The lack of this element in the soil, in which the adequate concentration should be between 0.01 and 0.70 mg kg-1, entails less synthesis of the nitrogenase enzyme in the plants, reducing the biological fixation of the nitrogen,[1] making the soil less productive. The concentration levels found in several matrices are very low, which makes monitoring and detection difficult. It is necessary to establish appropriate high sensitivity and selectivity methodologies for the determination of this element in complex matrices such as soils and plants.[2,3].

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