A New Microwave Acid Digestion Bomb Method for the Determination of Total Fluorine

Abstract

A new microwave acid digestion method for total fluorine analysis was compared to the reliable reverse-extraction technique. The commercially available Parr bombs which are compatible with microwave heating were modified for this purpose. The Mann-Whitney statistical test did not show any significant differences (p > 0.05) in the determinations of total fluorine in various samples between the two above-mentioned methods. The microwave method also gave high fluorine recoveries (> 97%) when fluoride was added to different samples. The great advantage of the microwave acid digestion bomb method is that the digestion under pressure is so aggressive that only a few minutes is needed for complete digestion (also of covalently bonded fluorine), which reduces the time for fluorine analysis dramatically, while no loss of fluorine or contamination from extraneous sources could take place during the ashing procedure. The digestion solution was made up of 300 μl of concentrated nitric acid plus 537 μl of water. After digestion 675 μl of ∼ 8.5 M sodium hydroxide plus 643 μl of citrate/TISAB buffer was added resulting in an alkaline solution (pH ∼ 12) which was finally adjusted to a pH of ∼ 5.3 for fluoride determination.