Simple Procedure for Preparation of Permeation Tubes for Some Gases

Abstract

Using ordinary reagents in a laboratory, a simple procedure for preparation of permeation tubes for gases considered as an atmospheric pollutant was developed. It is based on a gas generation, concentration by a cryostatic trap and condensation of a liquidified gas into Teflon tube by a cryopumping effect. Nitrogen dioxide was generated by thermal decomposition of lead nitrate, sulfur dioxide by reduction of sodium sulfite with sulfuric acid and ammonia and amines by evolution from their aqueous solution by strong alkali. By gravimetric calibration in a thermostat, measuring a decrease in a tube weight in time, the permeation rate (ω) from the tube at 30°C was obtained as 16.5μg/min and 6.52μg/min for NO₂ and 0.52μg/min for SO₂. A temperature dependence of the permeation rate for NO₂ from PNO-2 tube was found to obey the following relation,
log₁₀ω=0.0342T-9.553
where T is a temperature of the thermostat in °K.
A gas permeating from the tube was diluted by a cleaned air. By comparing a concentration of NO₂ gas measured by Saltzman method with one calculated from the permeation rate and a flow rate of diluting gas, 0.72 as the equivalent factor was obtained.
The permeation tubes for offensive odor such as ammonia, trimethylamine and monomethylamine were also prepared as well as SO₂. The permeation tube th s prepared can be useful as the standard gas for a gaschromatography and/or cross-check samples for the analytical method.
The present technique is simple, cheap and safe because of no use of a high pressurized gas cylinder and furthermore it is convenient to be able to prepare the tube when necessary.