Automated Analysis of Ammonia Using Membrane Diffusion and Conductivity Detection: How the Membrane Facilitates Automation

Wet Chemistry Automation - Session 2
Oral Presentation

Prepared by

Contact Information: john.stillian@timberlineinstruments.com; 303-440-8779


ABSTRACT

In 1978, Professor Robert Carlson at University of California Davis, Department of Pomology, introduced the analytical community to a new method for the determination of ammonia using a silicone membrane combined with conductivity detection. The combination is a chemically elegant way to remove the analyte, ammonia, from the sample matrix and move it into a deionized (DI) water stream for detection, thus leaving behind any interferences to detection caused by the sample matrix. Ammonia, as ammonium ion, is then detected using conductivity detection in a background of DI water providing excellent sensitivity and a broad dynamic range. In this way, the membrane allows for automation of ammonia analysis in complex matrices. Timberline Instruments has taken advantage of and improved upon Dr. Carlson’s technique for automated ammonia and nitrate (via in-line reduction to ammonia) analysis in difficult sample matrices. Not only is the analysis process automated through the use of a traditional autosampler and instrument software, so is the removal of the analyte from the sample matrix. Thus the analyte, ammonia, is automatically removed from difficult to analyse matrices such as KCl soil extract samples, Kjeldahl digest samples, compost samples, and municipal wastewater samples (for EPA ammonia discharge reporting) so that little or no sample intervention is required to analyze for ammonia and nitrate using this automated method. In this paper we will explore the application of this automated technique for ammonia and nitrate analysis in these and other complex sample matrices without the need for any significant sample preparation and show how automating sample preparation through the use of an in-line sample prep device, the membrane, automates sample preparation.