PARAMETERS INFLUENCING THE CALCINATION OF PLANT MATERIALS IN MUFFLE FURNACES AND THEIR IMPORTANCE FOR MICRONUTRIENT ANALYSIS

Calcination in muffle furnaces is a widely used method for the mineral ization of plant samples. During the combustion process, however, the atmosphere inside a muffle furnace tends to be reducing which has a ne gative impact on the recovery of micronutrients from plant materials. Higher loads of organic matter in a furnace decrease the recovery of C u < B < Zn. In the case of Cu and partly also of Zn the reason for the lower recovery is the absorption of Cu by organic particles remaining in the filter. In the case of B and Zn volatile losses of these eleme nts are the predominating reason for analytical faults related to the calcination process. The determination of B from samples combusted in muffle furnaces is disturbed by B released from fire-clay inlets, This error increases with the time the muffle furnace is in use. As B vapo rs are only absorbed by alkaline surfaces such as plant ashes, blank s amples will only detect this error if they contain an alkaline substan ce such as Ca(OH)(2).