Analytical Sciences

Determination of Total, Volatile and Acid Detergent Insoluble Nitrogen in Silage by Sequential Injection

Fernando V. SILVA, Ana RITA A. NOGUEIRA, Ž€Û¨ilberto B. SOUZA, and Geraldo M. CRUZ

Embrapa Pecuaria Sudeste, P. O. Box 339, 13560-970, Sao Carlos SP, Brazil

This work proposes a sequential injection procedure to determine the total, volatile and acid detergent insoluble nitrogen content in silage. An ammonium tubular selective electrode coupled to a sequential injection manifold was used as detector to accomplish the potentiometric determinations made after on-line ammonia diffusion in alkaline mediumthrough 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 detection limit of 3.0 mg N l^-1 were observed when 300 ml of 3.0 mol l^-1 NaOH solution and a sample volume of 150 ml were employed. The use of the proposed procedure allowed the automation of the determinations, low sample andreagent consumption and small waste production, emphasizing the versatility and potentiality of the flow methods when applied to animal nutrition laboratories.

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