Trace determination of ammonia nitrogen in marine waters using a flow analysis method with flow manipulation

A very sensitive and simple gas-diffusion flow method for the determination of ammonia nitrogen in marine waters has been developed. This method is completely continuous, requiring no manual sample introduction. The reagents... [ view full abstract ]

A very sensitive and simple gas-diffusion flow method for the determination of ammonia nitrogen in marine waters has been developed. This method is completely continuous, requiring no manual sample introduction. The reagents used are non-toxic, show good stability over long periods of time, and their preparation is very simple. The method has a wide dynamic range and is one of the most sensitive colorimetric methods developed so far. The simplicity and automation of this method make it particularly suitable for long-term shipboard ammonia measurements.

The method developed is a modified stop-flow method, whereby the donor stream is continuously delivering a large sample volume to a gas-diffusion unit for a given period of time, during which the acceptor solution is oscillating 10μL backwards and forwards in the acceptor channel of the gas-diffusion unit. This flow manipulation has improved the efficiency of analyte accumulation in the gas-diffusion unit by enhancing mixing of the saturated surface layer of the 75 µL acceptor solution in contact with the Teflon membrane separating the two streams.

The system is characterised by an LOD of 0.11 µmol/L, linear range between 0.55 – 55 µmol/L, and repeatability of 0.49% (41.6 μmol/L, n = 10) and 4.25% (0.14 μmol/L, n = 10), and sample throughput of 15 per hour.