Determination of total fluorine in vegetables and plants by open-flame ashing and microdiffusion

Improved recovery of fluoride in plant material using a low temperature sealed chamber digestion technique in conjunction with a fluoride ion‐specific electrode

“…Fumace lining material may emit F and thus contaminate samples, especially if the furnace has previously been used for ashing materials of high F content (6,14,21). However, using Method 1 we showed that when blanks were ashed at Digestion: Method 7 gave the lowest plant F' concentration and the lowest F recovery values.…”

“…Four fusion methods (6,22,23,24), one acid digestion Method (8), one oxygen-flask combustion Method (6) and the newly developed sealed chamber digestion method were compared. Only a brief description of each method is presented in Table 1 -all methods were performed exactly as described in the literature with the exception of method 2.…”

“…In open systems high temperatures are needed to digest plant material and at the same time increase the risk of loosing volatile F. At such temperatures even the use of fixatives under alkaline conditions do not eliminate the losses of volatile F (14). Closed chamber digestion also prevents any extraneous contamination such as the lining of muffle furnaces (6,14,31). Moreover, the proposed method is very simple and minimises the Table 4.…”

“…Fluoride is considered to be amongst the most phytotoxic of the more common pollutants (1,2,3). Certain types of industrial operations emit large amounts of F. Fluoride phytotoxicity and F toxicosis of animals has been reported in the vicinity of aluminium smelters, brick works and some fertilizer manufacturing plants (4,5,6,7,8). Continued use of phosphatic fertilizers is also likely to raise the F levels in soils as superphosphates contain up to 3% F as an impurity from the original phosphate rock (9).…”

“…The most widely used method for F analysis in vegetation has been alkali fusion followed by Willard and Winter distillation and determination of F by titration or spectrometric determination (15,16). However, more recently the development of the F ion-specific electrode has considerably simplified the determination of F as prior separation of interfering radicals by distillation became unnecessary (6,17,18,19). The major problem in the determination of F in plant material is now the sample preparation step.…”