Gas diffusion techniques coupled sequential injection analysis for selective determination of ammonium

The design of an analytical system based on the coupling of gas-diffusion separation and sequential injection analysis is described and applied to ammonium determination. The sample and an alkaline solution are sequentially aspirated using an automatic burette and mixed by flow reversal while they are being propelled to a gas-diffusion unit. There, the ammonia formed diffuses through an hydrophobic membrane into an acid-base indicator solution. The change in the absorbance of the acid-base indicator solution used as acceptor stream is measured and referred to ammonium content in the sample. The system requiring simple and commonly available instrumentation is automated and has been applied to the determination of ammonium in environmental samples.