Individual sample conditioning in flow analysis. Determination of N-total in plant materials

A flow-batch system allowing in-line individual sample matrix matching is p roposed for analysis of sample lots with high variability in acidity. The f easibility of the approach is demonstrated in the spectrophotometric determ ination of total nitrogen in Kjeldahl digests, using a column with a slight ly soluble reagent (AgCl). The solutions are sequentially injected by means of an 8-port selecting valve and processed in a mixing chamber that is als o used as a monitoring unit. The system yields reproducible results (r.s.d. usually < 2.5%) and the sampling rate is 14 samples/h. The analytical curv e is linear within 1.00 and 6.00% N (dry basis), and the regression coeffic ient is > 0.999 (n = 6). Results are in agreement with certified values of standard reference materials and with results obtained by conductometry.