Microwave Single Vessel Acid-Vapor Extraction: Effect of Experimental Parameters on Co and Fe Determination in Biological Samples

Characteristic parameters of a single vessel procedure were investigated for Co and Fe determination in biological samples using nitric acid-vapor extraction under atmospheric pressure. A laboratory-made PTFE support vessel suitable for four cups containing the samples was adapted to fit on the microwave glass vessel. Biological samples (30mg) were weighed directly into these PTFE cups and exposed to nitric acid vapor stemming from 15mL concentrated HNO₃ placed in the bottom of the glass vessel. Sample cups were positioned at 50, 80, 110, and 140mm from the support base. We evaluated the temperature, acidity, and residual carbon content of each sample cup, i.e. parameters that could influence the efficiency of vapor-phase acid digestion. The influence of sample particle size on digestion efficiency was also considered. It was demonstrated that temperature was the main parameter for efficient recovery of both Co and Fe in biological samples, and higher temperatures allowed lower residual carbon contents.