Soil air sample storage and handling using polypropylene syringes and glass vials

Abstract

Accurate determination of gas concentration in soil air samples implies adequate sampling and storage procedures to preserve sample integrity. In this study, we tested polypropylene syringes and glass vials for handling and storage of N2O air samples. Losses of N2O were large and rapid when a gas standard was stored in polypropylene syringes (16% after 24 h). Moreover, gas adsorption on the inner walls (and rubber gasket) of the syringes reached a maximum of 5.8% of the initial N2O after 7 h of storage. These results indicated that polypropylene syringes are not reliable for storing air samples. Commercially available glass vials maintained a moderately high level of vacuum over time (89% after 136 d). However, their overall performance was decreased by contamination (approx. 3%) occurring at the end of the evacuation procedure when the hole left by the needle of the evacuation line took a few seconds to close up. The addition of a silicone septum was proposed to reduce this contamination. The modified vials maintained an average vacuum level of 98% after 136 d. The average contamination rate of N2O samples during the first 129 d of storage was 0.20 and 0.13% d-1 with one and two septa, respectively.