Continuous automatic determination of ammonia by using an integrated separation/detection unit

An automatic continuous-flow photometric method for the determination of ammonia is proposed. It is based on the Berthelot reaction, the product of which is temporarily immobilized on a suitable support (Sephadex QAE) located in the flow-cell. The retained product is eluted after measurement by a cationic surfactant contained in the carrier solution. The method allows the determination of the analyte between 0.4 and 20.0 gmg/ml, with an RSD of 0.8%, at a sampling frequency of 13/hr. The determination limit can be reduced by a factor of ten by using a flow-cell with a two-fold longer path length, but the sampling frequency is also reduced as a result. The method was applied to the determination of this analyte in agricultural samples (plants and soils) and compared with standard methods for these types of samples.