9[2]DANIEL M J, MICHAEL J D. Manometric biosensor for on-line measurement of milk urea[J] . Biosensors and Bioelectronics. 2002, 17:557 -563.
10[3]MARSH W H, FINGERHUT B, KIRSCH E. Determination of urea nitrogen with the diacetyl method and an automatic aialyzing apparatus[J].American Journal of Clinical Pathology. 1957, 28:681 - 688.