radiello® Diffusive Air Sampling Application - Hydrofluoric Acid (HF)

radiello Components Used:

Blue diffusive body Product No. RAD1201
Supporting plate Product No. RAD121
Vertical adapter Product No. RAD122 (optional)
Chemiadsorbing cartridge Product No. RAD166

Or: radiello-ready-to-use Product No. RAD1233

Principle

Cartridge RAD166 is made of microporous polyethylene coated with triethanolamine (TEA). Gaseous hydrofluoric acid is adsorbed by TEA and subsequently extracted with water to be quantified by ion chromatography or by ion selective electrode as fluoride ion.

Sampling is selective for the gaseous molecules: any airborne fluoride salt will not cross the diffusive membrane of radiello.

Sampling Rate

Sampling rate Q at 298 K (25 °C) and 1013 hPa is 187 ml·min-1.

Effect of Temperature, Humidity and  Wind Speed

Sampling rate is invariant with humidity in the range 10 - 90% for short exposure time (see Exposure) and with wind speed between 0.1 and 10 m·s-1.

The effect of temperature is under investigation.

Calculations

Let m be the mass of fluoride ion in μg found onto the cartridge and t the exposure time in minutes, the environmental concentration C of HF in μg·m-3 is obtained according to the equation:

where 1.053 is the ratio between molecular masses of HF and F-(see Analysis).

Exposure

Hydrofluoric acid is sampled linearly in the range from 10,000 to 50,000,000 μg·m-3·min.

Workplace Environment

In workplace environments we recommend exposure time from 15 minutes to 8 hours: the ceiling values can be measured.

Outdoor Environment

We recommend exposure time from 2 hours to 14 days. Protect radiello from rain by the mountable shelter Product No. RAD196.

Limit of Detection and Uncertainty

The limit of detection is 7 μg·m-3 for 24 hour exposure. The uncertainty at 2σ is 4.5% over the whole exposure range.

Storage

Kept in a dark place at 4 °C, the cartridges stay unaltered for at least 12 months before exposure and 4 months after sampling. Expiry date is printed on the plastic bag wrapping each cartridge.

If more than six months have passed since you received the cartridges, before environmental sampling campaigns, it is advisable to analyse some cartridges to measure any contamination from the background. Discard the cartridges if they contain more than 2 μg of fluoride ion.

Keep at least two unexposed cartridges for each lot and analyse them as blanks.

Analysis

Ion Chromatography

Add 5 ml of eluent solution to the radiello tube. Stir vigorously by a VORTEX stirrer for 1-2 minutes. Let the tube stand for 10 minutes, then stir manually and inject the solution in the ion chromatographic apparatus without further treatment.

Analyse 1-2 unexposed cartridges and subtract the average blank value to the samples.

Ion Selective Electrode

Prepare an ionic strength buffer as follows. Dissolve 57 ml of acetic acid in 500 ml water and add 50 g of sodium chloride and 0.3 g of sodium citrate. When complete solubilisation has been achieved, adjust the pH value to 5-5.5 (ideal value is 5.3) by adding drops of 10 M sodium hydroxide. Make up to 1 liter with water.

Add 5 ml water to radiello tube and stir vigorously by a vortexer for 1-2 minutes, then let stand for 10 minutes.
Introduce a magnetic stirring bar in a 20 ml beaker, add 10 ml of ionic strength buffer and 1 ml of the extraction solution of the cartridge. Start the magnetic stirrer and make the potentiometric measurement by an ion selective electrode for fluorides. In the described analytical conditions, the electrode response should be linear in the range from 1 to 1,000 mg·l-1 of F- with slope close to 59 ± 0.5 (if potential is expressed in mV).

Analyse 1-2 unexposed cartridges and subtract the average blank value to the samples.

IMPORTANT
Always use water with fluoride content lower than 0.5 mg·l-1.

Materials

     
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