Nowadays biomass is widely used to produce electricity and heat. The growing demand for these stocks and their price results in the usage of low-quality biomass. In some cases, such biomass is mixed with herbaceous fuels and supplied to the heating plants. As such mix contains higher levels of volatile K, Na and Ca, there occurs ash-related problems such as slagging, fouling and agglomeration during combustion process. The aim of this work was to investigate the possibility to detect alkali-metals emission by chemiluminescence analysis during combustion in purpose to reduce the risk of ash-related problems. For experimental investigation, wood particle, wood pellet and wheat straw pellet were used. The chemiluminescence intensities of alkali species Na*, K* and Ca* and its variation during combustion of different biomass particle were evaluated. Results revealed that when fuel is changing during combustion, it is possible to predict the emissions of aforementioned radicals of different fuels and adjust appropriate regime of combustion.