SAMPLING THE ATMOSPHERES OF SMALL VESSELS

Gas-tight syringes and other gas sampling devices are not entirely satisfactory for use in many studies of soil processes requiring precise repeated sampling of the atmospheres of glass bottles and other incubation vessels. This report describes the construction and use of a gas-sampling apparatus that permits accurate, precise analyses of headspace gases contained in sealed vessels. The sampling apparatus consists of a 10-port gas-sampling valve fitted with a syringe used to fill a sampling loop with a representative sample of the atmosphere contained in the headspace of an incubation vessel. A supply of inert gas purges the apparatus between samples. Use of this technique is appropriate in experiments where repeated analyses of sample vessels are performed, because sampling removes a minimum of gas in excess of that used for analysis and does not appreciably alter the pressure within the vessel. Because the effects of previous sampling on headspace concentrations are calculated, small vessels can be repeatedly sampled with precision. The apparatus is easily assembled from readily available components.