Making sense of gas measurements: quantification of multicomponent gas mixtures in biological and chemical laboratory experiments

Abstract

Textbooks in physical chemistry start from the treatise of the ideal gas. Gaseous compounds are important reactants and products of (bio)chemical reactions, and thus their absolute amounts are needed to establish mass balances. However, in contrast to solid, for dissolved and liquid compounds, their qualitative and especially quantitative analysis is less widely established in biological and chemical laboratories. This can be mainly ascribed to the seemingly simple chemical nature of gaseous compounds that is in contrast to the effort needed for their precise quantification. In this article, we will guide the reader through the considerations and steps needed to perform a meaningful analysis of multicomponent gas mixtures, which are reactants for or products of (bio)chemical reactions in aqueous solutions in the laboratory environment and scale. After a brief introduction, special focus is set on the methods for quantification and calculations needed to derive absolute amounts of gases in a mixture. The overall concept will be exemplified by biogas production as well as by an electroorganic reaction (Kolbe electrolysis of n-hexanoic acid), and general pitfalls will be highlighted.