ocr A2 biology planning please help!!!

to determine the concentration of aspirin in urine in order to estimate the amount left in the human body
im really stuck with this and from looking through the posts i have realised u need to use a colorimeter but wat is it tat u are measuring in the colorimeter is it absorbance or light transmission.
also when u have done the colorimeter how does this help to find the amount of aspirin left in the body.

Reply 1

rahmed

you are measuring the light transmission through the urine, but i dont see how that will give you a definitive answer, there are other subtances in urine, not just aspirin.

Reply 2

iceman_jondoe

Well firstly you need to take in a known concentration of asprim into the body lets say 5mol dm^3 for example. Then you need to review the mechanisms which are involved in urine formation. Specifically you need to look out the kidneys and you need to figure out much is likely to be reabsorbed into the blood. THis may allow you to make an estimate of the concentration left. Perhpas you could possibly filter the urine or use a recrystallisation technique to determine its concentration....but i wouldnt be to sure. A colourimeter measures the ligh intensity through a olution. if you were to compare a sample of urine without asprin and one within you may obtain different readings which you could then use to again estimate the concentration of the asprin ?