which purged ammonia from the sample suspension in the thermostated
at 20 °C suspension reservoir, immersed in an ultrasonic bath
(UNISONICS,Australia),was directed through the donor chamber of
the GD cell to the ambient atmosphere. The nitrogen flow rate was
monitored using a flow-meter (AalborgInstruments&Controls,
USA).The acceptor solution was propelled through the acceptor
chamber of the GD cell using a peristaltic pump (VS4-10R-Midi,
Watson-Marlow),equipped with Tygons pump tubing. The acceptor
stream then passed through the flow-through cuvette (10mm
optical path length,Starna,UK) of the spectrophotometric detector
(NovaspecII,Amersham) setat 580 nm and connected to a PC