Fluorine (F) is one of several trace elements receiving much attention owing to its possible harmful effects on health and environment. Small amounts of fluoride have proven benefits for dental health, while continuous exposure to high intakes can result in severe adverse effects in humans (and animals), which include development of dental fluorosis in children or skeletal fluorosis in both, children and adults. Fluoride emissions represent a threat to vegetation and subsequently entire food chain in many parts of the world. Monitoring of human and environmental load with F is therefore of crucial importance in order to avoid negative impacts of fluoride emissions.

The content of F in samples is determined with fluoride ion selective electrode (F-ISE). Because this electrode measures concentrations of free fluoride ions (F–), samples containing bound F must be decomposed first in order to assure release of F from inorganic and organic compounds and formation of F–. The most important methods for decomposition of combustible material are alkali metal carbonate fusion and oxygen bomb combustion.

Alkali metal carbonate fusion has been proven to be effective for a variety types of samples, but has one big disadvantage - time of decomposition. For this reason, oxygen bomb combustion has been introduced in our laboratory. This method is widely used for sample decomposition, but there are only few articles from older studies where it has been used for decomposition of samples for subsequent determination of F and those studies do not include analysis of certified reference material (CRM) as a part of a quality assurance system.

The aim of this study was to compare the contents of F determined with F-ISE in CRM (NIST-2695) and some other vegetation samples (spruce needles, green tea and camomile) after total decomposition with oxygen bomb combustion and alkali metal carbonate fusion. The objectives were: (1) check the accuracy of both decomposition methods using CRM, (2) check if CRM’s matrix (timothy grass) is representative for other vegetation sample types.