F. M. McNabb and R. A. McNabb, “Proportions of Ammonia, Urea, Urate and Total Nitrogen in Avian Urine and Quantitative Methods for Their Analysis on a Single Urine Sample,” Poultry Science, Vol. 54, No. 5, 1975, pp. 1498-505.

has been cited by the following article:

• TITLE: Analysis of Urea in Petfood Matrices: Comparison of Spectro-Colorimetric, Enzymatic and Liquid Chromatography Electrospray Ionization High Resolution Mass Spectrometry Methods

  AUTHORS: Patrick Pibarot, Serge Pilard

  KEYWORDS: Pet Food; Food; Urea; Adulteration; Enzymatic Method; Spectro-Colorimetry; LC/UV-DAD; LC/ESI-HRMS

  JOURNAL NAME: American Journal of Analytical Chemistry, Vol.3 No.9, September 28, 2012

  ABSTRACT: Adulteration may consist in non authorized source of nitrogen addition to increase the protein content of some raw materials. Urea which is authorized for feed is a non nutritional source of nitrogen in food and pet food. Adulteration of food or pet food raw material by urea is thus monitored by manufacturer and governmental authorities with official methods which are either enzymatic (Association of Official Agricultural Chemists, AOAC) or spectro-colorimetric (European Community, EC). Each method gives results which are not comparable and spectro-colorimetric methods may result in false-positive urea detection. Liquid chromatographic (LC/UV-DAD) analysis of extracts from spectro-colorimetric method indicates that presence of free amino-acid may interfere with colorimetric detection of urea in the EC method with pet food samples. Liquid chromatography electrospray ionization high resolution mass spectrometry (LC/ESI-HRMS) has allowed to quantify low content (