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Investigating the loss of nitrogen, as urea, from the body

  1. Apr 4, 2008 #1
    I need to plan an investigation to find out how changes in the consumption of protein in the diet influence the excretion of urea in humans.

    it is possible to determine the urea concentration in urine using the enzyme urease which catalyses the following reaction:

    Urea+Water --> (with urease on top of arrow) --> Ammonium Carbonate

    Ammonium carbonate has an alkaline ph.

    Urease breaks down urea, the pH of the reaction mixture changes. Change can be shown by pH indicator. If reaction goes to completion the concentration of ammonium carbonate can be found by titrating against 0.1 mol dm-3 HCL. Volume of HCL used is an estimate of concentration of urea in original solution.

    How would i use determine the urea concentration when using urease

    This plan needs to be based on materials provided which are:

    10g per 100cm3 (10%) solution of urea
    urease tablets or 5g per 100cm3 (5%) solution of urease
    0.1 mol dm-3 HCL
    pH indicators
    School lab resources

    What apparatus would i use
    what is a possible method
  2. jcsd
  3. Apr 4, 2008 #2

    jim mcnamara

    User Avatar

    Staff: Mentor

    Quanticrom and other companies make urea assay kits for urine. Another kind of assay kit is available for BUN - essentially the level of urea in blood. Some of these are expensive but are very accurate. They require that your lab has a colorimeter.

    I'm not sure that pH paper or pH indicators is going to be very good at revealing concentrations of ammonium carbonate, but titration will work very well. Ask your lab teacher about titration, if you want to do that.

    You do realize that humans may "generate" more or less urine volume (meaning extra water which dilutes urea or less water which increases urea concentration) if they have been sweating profusely, exercising, sleeping, consuming alcohol or caffeine, etc. This means that concetration of urea fluctuates during the day/night.

    Simply measuring the concentration in one sample is NOT the same as figuring out how much urea is excreted in a day. Unless you collect and store a full day's production, keeping the reservoir in the fridge, then test one day's worth of urine all at once.

    As you stated your problem, I do not think you can get meaningful results. I may have misunderstood.
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