Calculate Unlabeled Vitamin B12 - Radioactivity Help

In summary, the sample contained an unknown amount of unlabeled Vitamin B12. The final product contained 49ug of Vitamin B12 and 1.58x10^5 c.p.m of radioactivity. The amount of unlabeled Vitamin B12 in the sample is unknown, but was estimated to be 173 ug.
  • #1
darren t
6
0
Hi Guys,

Im just having a little trouble with this question, I was just wondering whether some one could point me in the right direction.

Fifty six micrograms of 60Co - labeled Vitamin B12 containing 7.36x10^5 c.p.m were added to a sample containing an unknown amount of unlabeled Vitamin B12. The sample was then extracted and the Vitamin B12 purified. The final product contained 49ug of Vitamin B12 and 1.58x10^5 c.p.m of radioactivity. Calculate the amount of unlabelled Vitamin B12 in the sample

I have no idea at all were to start! Could some one please help
Thank you in advance! All the best and happy new year. Darren
 
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  • #2
First you need to find out the half lives of the isotopes under consideration. Do you know the relation between activity and halv life?
 
  • #3
Hi thanks for getting back to me

Thats all the information i was given. I have tried to calculate it. What do you think??

Note first that the measured count rate for any sample can be converted to the weight of labelled B12 from the first line of information

count rate = 7.36 x 10^5 cpm/56 per microgram of labelled B12

Second, when the 56 ug is added to an unknown weight w of unlabelled B12, the ratio of unlabelled to labelled B12 is w/56.

The 49 ug of the mixture gives a count rate of 1.58 x 10^5 cpm and therefore contains [1.58 x 10^5/7.36 x 10^5] x 56 = 12.02 ug of labelled B12. The ratio of unlabelled to labelled B12 for this sample is (49 - 12.02)/12.02 and we must assume that this figure has not been altered by the processing of the materials. That is

w/56 = (49 - 12.02)/12.02 giving w = 173 ug
 
  • #4
This is a simple dilution problem, and 173 ug seems to be the correct answer.

In the real life you should check half life of 60Co, and compare it with the timescale of the expriment - if the difference is large enough you may safely assume that activity of the sample remains constant during experiment.
 

1. How do you calculate the unlabeled Vitamin B12 radioactivity?

To calculate the unlabeled Vitamin B12 radioactivity, you will need to know the specific activity of the labeled Vitamin B12, the amount of labeled Vitamin B12, and the amount of unlabeled Vitamin B12 present. Then, you can use the formula: unlabeled radioactivity = (specific activity x amount of labeled Vitamin B12) / amount of unlabeled Vitamin B12.

2. What is the specific activity of labeled Vitamin B12?

The specific activity of labeled Vitamin B12 refers to the amount of radioactivity per unit mass of labeled Vitamin B12. It is typically measured in units of becquerels per milligram (Bq/mg).

3. How do I measure the amount of labeled Vitamin B12?

The amount of labeled Vitamin B12 can be measured using techniques such as liquid scintillation counting or gamma spectroscopy. These methods involve detecting and measuring the radioactive emissions from the labeled Vitamin B12.

4. Can I use any unit of measurement for the amount of Vitamin B12?

It is important to use consistent units when calculating the unlabeled Vitamin B12 radioactivity. The amount of labeled and unlabeled Vitamin B12 should be measured in the same unit, such as milligrams (mg) or micrograms (μg).

5. How accurate is the calculated unlabeled Vitamin B12 radioactivity?

The accuracy of the calculated unlabeled Vitamin B12 radioactivity depends on the accuracy of the measurements used in the calculation. It is important to use precise and accurate measurements to ensure the accuracy of the final result.

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