AS 3580.13.2-1991

Sets out a method for the collection, separation and determination of acid-soluble particulate fluorides and gaseous fluorides in ambient air. Each form of fluoride is collected on a separate filter and determined by use of an ion-selective electrode.

This Standard sets out a method for the collection and separation of acidic gaseous and particulate fluorides from ambient air and their determination using a fluoride ion-selective electrode.This method is applicable to the measurement of acidic gaseous and acid-soluble particulate fluorides suspended in ambient air at concentrations of 0.1 mg/m3 and greater.For a one-day sampling period at a flow rate of 0.83 L/s (approximately 50 L/min), an atmospheric concentration of 0.1 mg/m3 of hydrogen fluoride in air can be measured with an accuracy of 10%. The detection level can be improved by sampling for longer periods, to a maximum of seven days, but the accumulated particulate matter may interfere with the collection of the gaseous fluorides especially if alumina is present in the particulate matter. The upper limits of determination are 55 mg/m3 for a one-day sampling period and 7.5 mg/m3 for a seven-day sampling period (at which point partial neutralization of the alkali-impregnated paper affects the results). The presence of acidic gases other than hydrogen fluoride affects the upper limit of determination.The resultant determination for a sampling period greater than two days may indicate elevated fluoride particulate levels with depleted fluoride gaseous levels but the total value will be valid (see Clause 6).NOTES:1 This method is subject to certain interferences. Particulate metallic salts such as those of aluminium, iron, magnesium, calcium and rare-earths collected on the initial filter may retain some or all of the gaseous fluorides. The presence of fluorophosphates or fluoroborates could contribute varying amounts of fluorides as they dissociate unpredictably. Acidic aerosols or gases may neutralize or acidify the alkali-impregnated final filter thus preventing the quantitative collection of acidic gaseous fluorides. Although a citric acid impregnated Whatman No. 52 initial filter paper has been shown to allow passage of gaseous hydrofluoric acid, it may permit passage of fluoride particles smaller than about 1 mm. Hence these may impinge on the alkali impregnated final filter paper. If initial filters of higher retentivity are required for removal of particles of size less than 1 mm, a citric acid impregnated filter of Whatman No. 42 filter paper or equivalent may be used.2 The addition of total ionic strength adjustment buffer (TISAB) eliminates a number of possible interferences. The effects of metallic ions are minimized by complexing agents. Variation in ionic strength is overcome by maintaining a high concentration of sodium chloride in the TISAB solution. The TISAB solution is buffered to pH 5 to 6 to avoid negative interference from the formation of complexes containing fluoride ions and positive interference from hydroxide ions being measured.

First published as AS 2618.2-1984.Revised and redesignated AS 3580.13.2-1991. First published as AS 2618.2-1984. Revised and redesignated AS 3580.13.2-1991.