The Nernst equation is valid for very dilute solutions or solutions with constant ionic strength. Fluoride ion selective electrode responds to free ionized fluoride in solutions. This experiment aims to demonstrate the use of fluoride ion selective electrode (FISE) in the determination of fluoride concentration (TSU, 2013).
Tea (Carmelia sinensins) is naturally rich in fluoride. Plants absorb nutrients (inclusive of fluoride) from the soil). Most of these nutrients are stored in the leaves which for the case of tea are harvested for tea preparation due to easy harvesting, handling and brewing. New tea preparation techniques and consumption are deemed to have implications on the fluoride concentration. Josipa et al., (2012) determined fluoride concentration in various infusions of tea using fluoride ion selective electrodes which is a simple and fast method. In the study it was observed that the size of tea pieces greatly influences levels of fluoride in tea infusion. The finer the tea material, the grater the extraction of fluoride. Brewing time was found to also affect the concentration of fluoride in tea infusions. Brewing times of between 10 to 20 minutes gave optimal concentrations of fluoride especially for mint and pomegranate tea. It was advised that one should drink tea prepared more than 24 hours prior to preparation. Strong correlation were observed between concentration with change of time and also packaging effect especially for green tea.
Josipa Giljanović, Ante Prkić, Marija Bralić, Mia Brkljača (2012). Determination of Fluoride Content in Tea Infusion by Using Fluoride Ion-Selective Electrode. Int. J. Electrochem. Sci., 7 2918 –