Comparison of New Ultrasonic Digestion Approaches for Plant Matrices in the Analysis of Trace Metals by Inductively Coupled Plasma–Optical Emission Spectroscopy Analysis: Contrast with USEPA Method 3050B

ABSTRACT

An ultrasonic method using two approaches, A and B, along with a reference Environmental Protection Agency (EPA) Method 3050B [i.e., a mixture of 30 mL of nitric acid–hydrochloric acid–hydrogen peroxide–water (HNO₃-HCl-H₂O₂-H₂O)] were contrasted for leaching of a plant matrix. The trace metals were arsenic, cadmium, cobalt, chromium, copper, mercury, manganese, nickel, lead, selenium, and zinc (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Se and Zn) and quantified by ICP-OES followed by an investigation into residue formation and the impact of digestion time. Approach B was the most accurate and precise with percent recoveries ranging between 99 and 120%, whereas ultrasonic approach A and the USEPA method 3050B gave similar results with poor accuracies and precisions. In the optimization of the digestion time using approach B, the total metal recovery was fairly the same over a period of 120 min except for Cr and Cu, which showed slight variations.

KEYWORDS:

• Digestion
• inductively coupled plasma–optical emission spectroscopy
• multivariate statistics
• partial least squares
• ultrasonic

Acknowledgments

We acknowledge the Departments of Chemistry, Biology, and Geology for providing necessary chemicals, ultrasonic units and ICP-OES analysis facilities as well as other material and logistical support.

Funding

The authors thank the Office of Research and Development (ORD) at the University of Botswana for funding the postdoctoral fellowship for the first author.

Additional information

Funding

The authors thank the Office of Research and Development (ORD) at the University of Botswana for funding the postdoctoral fellowship for the first author.