Mercury Determination in Natural Zeolites by Thermal Decomposition Atomic Absorption Spectrometry: Method Validation in Compliance with Requirements for Use as Dietary Supplements.

Senila Senila,Miu Miu,Hoaghia Hoaghia,Cadar Cadar

doi:10.3390/molecules24224023

Abstract

Natural zeolites are hydrated aluminosilicate minerals that, due to their remarkable physical-chemical properties of being molecular sieves and cation exchangers, have applications in different areas such as environmental protection, catalysis, animal feed, and dietary supplements. Since natural zeolites may contain traces of undesirable compounds such as toxic metals, the accurate quantification of these elements is necessary. In this study, a direct method for Hg determination in zeolite samples based on the thermal desorption atomic absorption spectrometry (TD-AAS) technique is fully validated, taking into account the legislative requirements in the field. The chosen quantification limit was 0.9 µg kg−1, which is satisfactory for intended use. Trueness was evaluated by recovery rate using certified reference materials containing mercury, with satisfactory results. Other figures of merit, such as repeatability and measurement uncertainty, also fulfill the legislative requirements related to the analysis of dietary supplements. This paper presents, for the first time, a fully validated method for mercury determination in zeolite samples, and the obtained results reveal that the method can be applied successfully for the intended purpose.

Highlights

Zeolites are crystalline aluminosilicate minerals that belong to the class of tectosilicates that comprise about 75% of the Earth0 s crust
The validation of the analytical procedure for quantitative determination of mercury in zeolite samples was performed by evaluating selectivity, working and linear ranges, limit of detection (LoD)
A stock standard solution of Hg (1000 mg L−1 ) from Merck (Darmstadt, Germany) was used to prepare, by dilution, working standard solutions of 0.1 mg L−1 and 1.0 mg L−1, which were used for thermal desorption atomic absorption spectrometry (TD-atomic absorption spectrometry (AAS)) instrument calibration, and working standard solutions of 0.1, 0.2, 0.4, 0.6, 0.8, and 1.0 μg L−1, which were used for cold vapor (CV)-atomic fluorescence spectrometry (AFS) instrument calibration

Summary

Introduction

Zeolites are crystalline aluminosilicate minerals that belong to the class of tectosilicates that comprise about 75% of the Earth0 s crust. They have a three-dimensional cage-like structure of SiO4 and AlO4 tetrahedra, with well-defined channels and cavities [1,2]. Zeolites’ structure has a net negative charge that is balanced by exchangeable cations (sodium, potassium, and calcium) [3] Due to their structure, zeolites have remarkable properties: adsorption capacity, cation exchange, dehydration-rehydration, molecular sieve ability, and catalysis features, and, as a result, they have found extensive application in environmental protection, chemistry, biotechnology, water treatment, agronomy, and medical areas [4,5,6]. Natural zeolites are formed by the transformation of volcanic rocks (tuff) in contact with fresh water or seawater [7]

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