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Advisor(s)
Abstract(s)
In this work, an analytical system based on the coupling of gas diffusion separation and sequential
injection analysis for urea determination in milk is presented. A versatile manifold that could
simultaneously be used for either spectrophotometric or conductometric detection was constructed.
The sample and urease solution are sequentially aspirated into the holding coil and sent to a
thermoreactor, where urea is enzymatically hydrolyzed by urease and converted into ammonium.
This stream merges an alkaline solution at a confluence point where ammonia is formed. Ammonia
diffuses through a hydrophobic membrane and modifies the bromothymol blue indicator color, when
spectrophotometric detection is used, or changes the conductance of a boric acid solution acceptor
stream, when conductometric detection is used.This methodology was applied to the determination
of urea in 18 milk samples and the results were statistically comparable with those furnished by the
enzymatic recommended procedure. The detection limits were 2.6 10-4 and 2.8 10-5 mol L-1
for conductometric and spectrophotometric detection, respectively. Repeatability (relative standard
deviation, RSD) was better than 3.7% and 2.6% for conductometric and spectrophotometric detection,
respectively.
Description
Keywords
Sequential injection Milk urea determination Urease Gas-diffusion Spectrophotometry Conductimetry
Pedagogical Context
Citation
"Journal of Agricultural and Food Chemistry" . ISSN 0021-8561. 52: 23 (2004) 6887-6890
Publisher
American Chemical Society