Determination of total, volatile and acid detergent insoluble nitrogen in silage by sequential injection

This work proposes a sequential injection procedure to determine the total, volatile and acid detergent insoluble nitrogen content in silage. An ammon ium tubular selective electrode coupled to a sequential injection manifold was used as detector to accomplish the potentiometric determinations made a fter on-line ammonia diffusion in alkaline medium through a Teflon membrane and NH3/NH4+ conversion. Different sample treatments, taking into account the species to be analyzed, were adopted to apply the proposed procedure to silage samples. An analytical frequency of 30 samples h(-1) and a detectio n limit of 3.0 mg N l(-1) were observed when 300 mu l of 3.0 mol l(-1) NaOH solution and a sample volume of 150 mu l were employed. The use of the pro posed procedure allowed the automation of the determinations, low sample an d reagent consumption and small waste production, emphasizing the versatili ty and potentiality of the flow methods when applied to animal nutrition la boratories.