On the greenness of recent microwave-assisted digestion methods: An evaluation with AGREEprep

Microwave-assisted digestion (MAD) is a widely used technique for the preparation of samples for elemental analysis. Significant advances toward more efficient and less hazardous MAD methods have been described in recent years, even though no systematic evaluation has been carried out in terms of green sample preparation. The present work evaluates the effectiveness and environmental impact of recent MAD methods through the lens of AGREEprep, a recognized metric tool that identifies the greenness attributes of sample preparation methods. The metric tool was employed for the assessment of 38 decomposition methods for food analysis, including MAD methods involving decreasing amounts of oxidizing agents, considering supplemental reagents and assistances, such as oxygen pressure, hydrogen peroxide, ultraviolet irradiation, and microwave-induced combustion. In addition, conventional decomposition methods and alternative approaches involving infrared heating have been considered in the assessment. The 38 methods received overall scores in a wide range of 0.14 to 0.52, being MAD methods without acid consumption and those involving combustion the greenest methods (scores from 0.40 to 0.52). By systematically evaluating key criteria, such as reagent usage, energy consumption, process safety, and waste generation, AGREEprep provides a comprehensive view of MAD methods that can contribute to further improvements toward more sustainable analytical practices.