Comparison of total ionic strength adjustment buffers III and IV in the measurement of fluoride concentration of teas
2018
Patel, Shilpa | Omid, Narges | Zohoori, Fatemeh V | Maguire, Anne | Waldron, Kevin J | Valentine, Ruth A
Tea is the second most consumed drink in the UK and a primary source of hydration; it is an important source of dietary fluoride (F) for consumers and also abundant in aluminium (Al). Varying ranges of F concentrations in teas have been reported worldwide which may be, in part, due to differences in analytical techniques used to measure this ion. The effect of using total ionic adjustment buffers (TISAB) III or IV when measuring F concentration of black teas available in the UK was investigated and compared. Based on this evaluation, the effects of three different infusion times, 1 min, 10 min and 1 h, caffeine content and tea form on the F contents of the tea samples were investigated. The F concentrations of 47 tea samples were measured directly using a fluoride ion-selective electrode (F-ISE), TISAB III and IV and infusion times of 1 min, 10 min and 1 h. Mean (SD) F concentration of tea samples for all infusion times was statistically significantly higher (p < 0.001) measured by TISAB IV (4.37 (2.16) mg/l) compared with TISAB III (3.54 (1.65) mg/l). A statistically significant positive correlation (p < 0.001) was found between Al concentration (mg/l) and differences in F concentration (mg/l) measured using the two TISABs; the difference in F concentration measured by the two TISABs increased with the magnitude of Al concentration. Due to higher concentrations of F and Al in teas and their complexing potential, use of TISAB IV facilitates more accurate measurement of F concentration when using an F-ISE and a direct method.
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