Half Life of radioactive insulin

[ming_li]

In my assay of 50uL of 125-I-insulin I have 20,000 cpm at the expiry date. The half life of 125-I-Insulin is 60 days. So how can I calculate how many counts a 50uL sample of 125-I-labelled insulin would contained at 4 months past the expiry date?

cheers

 

[Bystander]

Count half-lives.

 

[ravenprp]

To calculate the number of counts in a 50uL sample of 125-I-labelled insulin at 4 months past the expiry date, we can use the formula for radioactive decay: N = N0 * (1/2)^(t/t1/2), where N is the current number of counts, N0 is the initial number of counts, t is the time elapsed, and t1/2 is the half life.

In this case, N0 = 20,000 cpm, t = 4 months = 120 days, and t1/2 = 60 days. Plugging these values into the formula, we get:

N = 20,000 * (1/2)^(120/60) = 20,000 * (1/2)^2 = 20,000 * 1/4 = 5,000 cpm

Therefore, at 4 months past the expiry date, a 50uL sample of 125-I-labelled insulin would contain approximately 5,000 counts. It is important to note that this is just an estimate and the actual number of counts may vary slightly due to experimental error. It is always recommended to perform multiple measurements to increase accuracy.