Accurate analysis of urea in milk and milk powder by isotope dilution gas chromatography–mass spectrometry
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Isotope dilution
Dilution
Matrix (chemical analysis)
The paper reviews the applications that the gas chromatography and the derivatization gas chromatography in food analysis for the past many years.And it elaborated introduces the applications of gas chromatography-mass spectrometry(GC/MS) methods in analysis of fatty acids,saccharide and vitamin for the past few years.
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The oil of Idesia polycarpa var.vestita of the nature resources extracted from the fruit of tree used as controlled material for producing the Coated urea fertilizer was studied.The soil incubation experiment was carried out and the fertilizer treatment was seven.The coupling Coated urea and urea was studied.The method was adopted to measure the coated urea nutrient.the result showed the preliminary solubility rate of nitrogen coated urea was 12.2% and in comparison with applying urea,the preliminary solubility rate of nitrogen decreased 67.9%.The effect of Coated urea was to increase SPAD in the sugarcane.The Stalk weight in treatment 5 was more 0.31g than that of CK and was more 0.21 g than that of Coated urea of one way and was 0.25 g more than that of urea of one way.Plant height in treatment 5 was 50.5 cm more than that of CK and was 27.8 cm more than that of urea of one way.The treatment 5(Coated urea 70%+ urea 30%) was the best treatment.
Coated urea
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Electron capture detector
Electron capture
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1. The entry rates of urea into the urea pool of the body fluids have been measured in sheep given rations varying in crude protein percentage from 3.5 to 27.3. 2. Results obtained with a single injection and with continuous infusions of [ 14 C]urea were essentially the same. 3. The difference between the entry rate and the rate of excretion of urea in the urine was taken to indicate the quantity of urea degraded in the alimentary tract. 4. Plasma concentrations and urea entry rates were significantly and linearly related. 5. The relationship between excretion rate and plasma urea concentration was best described by a cubic equation. 6. Degradation of urea in sheep was found to be extensive in all the animals studied; as the protein intake increased, the quantity of urea degraded also increased but the percentage of urea entering the body pool that was degraded was decreased. Animals given a ration containing 3.5% crude protein degraded 76–92% of the urea entering the body pool. 7. A rectilinear relationship was found between pool size and plasma urea concentration. The urea space in animals given low-protein rations was significantly less than in animals on high-protein rations. 8. The effects of starvation for 2, 4 and 6 days on urea metabolism in sheep were investi-gated. In a11 the sheep starved for 2 days there was a significant increase in urea pool size, but the entry rate was markedly depressed indicating a retention of urea in the body pool on starvation. 9. A significant amount of nitrogen was found to go through the system: rumen ammonia → portal blood ammonia→blood urea→rumen ammonia. 10.Urea excretion rate, urea clearance by the kidney, urine flow rate and the ratio of the concentration of urea in urine to that in plasma (urea U:P ratio) were also examined. 11. There were significant correlations between urine flow rate and urea excretion and between plasma urea concentration and urine flow rate.
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SUMMARY Half‐saturation constants for urea uptake by 4 clones of neritic diatoms capable of utilizing urea were determined from short‐term uptake studies with 15 N‐labeled urea. K 8 values obtained were similar to those determined, earlier for ammonium, and since ammonium and urea concentrations are similar in the marine environment, it was concluded that these species are capable of utilizing ecologically significant concentrations of urea. Two of 3 species unable to grow on urea showed patterns of short‐term uptake not unlike those of species capable of utilizing urea, which implies that, their assimilatory rather than uptake processes are defective with, regard to urea utilization. The third species initially took 15 N (supplied as urea) into the cells but subsequently released it back into the medium.
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summary In a field experiment on a typic hapludoll in 1983 and 1984, deep placement of urea supergranules at 40 and 80 kg N/ha proved to be the best N source, of five tested, for grain production, but at 120 kg N/ha it was similar to neem-cake-coated urea. The results showed that deep placement of urea supergranules can save fertilizer use by 60% compared with prilled urea to obtain the same yield. Shellac-coated urea and dicyandiamide-coated urea was more effective than prilled urea in 1984. Differences in dry-matter production and grain yield were directly related to N uptake by the plants. On average, apparent recovery of applied N increased from 35% for prilled urea to 55, 52·5,46·5 and 37·5% for urea supergranules, neem-cake-coated urea, shellac-coated urea and dicyandiamide-coated urea, respectively.
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Following a single injection of 14 C-urea, the kinetics of urea metabolism have been studied in two female Arabian camels (Camelus dromedarius) fed roughage diets containing 6.1 (diet A), 9.6 (diet B), and 13.6% (diet C) crude protein. In general, plasma urea concentration, urea pool size, urea entry rate and urinary urea excretion rate increased as the dietary nitrogen intake increased. The mean extents of urea degradation were approximately 86, 74 and 47% for diets A, B, and C, respectively, as calculated from the ratio of urea degradation rate to urea entry rate, or from the fraction of 14 C-urea recovered in the urine. The following parameters were linearly related: urea entry rate and urea pool size, urea pool size and plasma urea concentration, percentage urea degraded and urea entry rate, and percentage urea degraded and crude protein intake.
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SUMMARY When behavioral avoidance cannot prevent an animal from being exposed to novel environmental toxins, physiological mechanisms must cope with the toxin and its effects. We are investigating the basis of urea tolerance in populations of Drosophila melanogaster that have been selected to survive and develop in food containing 300mmoll−1 urea. Previous research has demonstrated that the urea-selected larvae have lower levels of urea in their body than control larvae reared under the same conditions. The current series of experiments focuses on three possible ways of reducing urea levels in the body: urea metabolism, increased urea excretion and decreased urea uptake from the environment. We tested for urea metabolism directly, by assaying for activity of two urea-metabolizing enzymes, and indirectly, by looking for reduced urea content of their medium. To measure urea excretion rates in whole animals, we reared control and urea-selected larvae on urea-containing food (urea food), switched them to normal food and monitored the loss of urea from their hemolymph. We measured urea uptake by rearing control and selected larvae on normal food, switching them to urea food and monitoring the rate of urea appearance in the hemolymph. We found no evidence for urea metabolism by either direct or indirect methods. Control larvae excreted urea at a higher rate than selected, probably because they contained more urea than the selected larvae and thus had a greater gradient for urea loss. The rate of urea uptake in selected larvae was 2mmoll−1h−1 slower than the rate in control larvae, a difference that could account for the measured differences in body urea levels. Thus the selected larvae appear to have adapted to urea exposure primarily by decreasing the ability of urea to enter their body in the first place. The mechanism responsible for this reduction in uptake is uncertain.
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