Preparation of sub-nanomole quantities of nitrogen gas for stable isotopic analysis

Abstract

Describes a technique for the extraction and purification of sub-nanomole quantities of nitrogen for stable isotopic analysis. The procedures described are intended for use with a high-sensitivity static vacuum mass spectrometer such as that describes by Wright et al. (1988). It is essential that low nitrogen blanks are obtained during the sample treatment; it can be demonstrated that contributions of nitrogen from the extraction and subsequent gas handling procedures can be limited to as little as 0.021 nmol. Experiments are described to verify that species such as CO₂, CO and CH₄, which would otherwise interfere with the nitrogen isotopic measurements, can all be removed during the purification operations. A study of the difficulties which might be encountered if some nitrogen were converted to nitrogen oxides has also been undertaken. It is concluded that N₂O would be totally decomposed to the elements during purification but nitrogen in the form of NO and NO₂ is only partially recovered. A method for investigating whether nitrogen oxide production is a real problem during the analysis of geological samples has been devised. Some examples using the technique are presented.