Jfcc. Lima et al., Flow-injection analysis of Kjeldahl nitrogen in milk and dairy products bypotentiometric detection, ANALYT CHIM, 385(1-3), 1999, pp. 437-441
A flow-injection analysis (FIA) system with a potentiometric tubular defect
or and a gas diffusion unit was developed for the determination of Kjeldahl
nitrogen in milk and dairy products. The samples were digested by the Kjel
dahl method and afterwards injected into the RA system without prior treatm
ent. NaOH solution was introduced into the system to promote the conversion
of ammonium ions to ammonia gas. The gas produced diffused through a gas-p
ermeable membrane towards an acceptor channel (Tris-HCl, pH=7.5). When in c
ontact with this solution, ammonia gas was reconverted to amonium cation an
d carried to a tubular electrode sensitive to this species. Therefore, a PV
C tubular ammonium ion-selective electrode was prepared without inner refer
ence solution and with the sensor system based on nonactine and monactine d
issoved in Tris-(2- ethylhexyl) phosphate.
The results obtained with the developed FIA system were in good agreement w
ith those of the reference method the relative deviations being less than 4
%. Reproducibility of the method was assessed by the relative standard devi
ation, which was always less than 0.5% for 12 consecutive injections of sam
ple digests. A sampling rate of 100 samples h(-1) was obtained. (C) 1999 El
sevier Science B.V. All rights reserved.