利用氟選擇性電極分析茶葉及茶湯中的氟含量   全文下載

Determination of Fluoride in Tea Leaves and Tea Infusions by Ion Selective Electrode

本研究係利用氟離子選擇性電極法分析茶葉及茶湯（1% 茶葉與沸水比）的氟化物含量。結果顯示本方法在0.02-2.00 mg/L 的氟含量範圍有良好的線性關係， 其R2 值可達0.999（p 值<0.05）； 利用梯牧草（timothy grass）及茶葉的標準參考物質進行植體中總氟含量的分析，並添加已知濃度的氟化鈉溶液至茶湯中進行回收率試驗，結果顯示標準參考物質的總氟含量測值接近其標準值，平均測值的變異係數（CV, %）<3%，而茶湯的回收率結果為94-107%，回收率平均值的變異係數≦ 1.2%，顯示利用氟離子選擇性電極分析植體及茶湯的氟含量有良好的準確度及再現性。不同沖泡次數及浸泡時間的茶湯分析顯示氟含量隨沖泡次數遞減，經連續5 次沖泡結果顯示茶葉的氟溶出率達63-78%；隨茶葉浸泡時間增加茶湯的氟含量呈現增加的趨勢直到浸泡時間達120 分鐘時茶湯的氟含量趨於穩定，經480 分鐘浸泡後，茶葉的氟溶出率可達82-83%。分析南投民間鄉12 種市售茶葉的總氟含量範圍為100-451 mg/kg d.w.，而茶湯氟含量範圍為0.39-1.21 mg/L，以每天飲用2 L 的茶湯估算，經由飲茶所攝取的氟含量低於成人氟攝取的每天最高容許量10 mg。"

A fluoride ion selective electrode method for the determination of fluoride contents in tea leaves and tea infusions was set up. Using commercial timothy grass powder and tea leaf powder as standard materials, this method demonstrated linearity between 0.02 and 2.00 mg/L of fluoride with R2 greater than 0.999. Both materials had coefficient of variations (CV, %) less than 3%, indicating good reproducibility in the determinations. The recovery tests of tea infusions spiked with different amounts of sodium fluoride demonstrated 94-107% of recovery with CV less than 1.2%, indicating that the method is very accurate. With 1% of tea leaves to boiling water ratio, up to 63-78% of fluoride in tea leaves could be released into tea infusion by repeated infusions and 82-83% by continuous infusion. By this method, total fluoride contents of 12 brands of tea leaves purchased from Nantou County were determined to be 100-451 mg/kg dry weight, and those of their infusions in boiling water for a 5-min period were determined to be 0.39- 1.21 mg/L. Assuming that daily tea infusions drinking for an adult is 2 L, fluoride intake from tea infusions of these tea leaves is far below the daily fluoride tolerable upper limit 10 mg.