statistical treatment for storage stability data

[along]

Dear All,

Recently (last 1 year actually) I collected data for one of my experiment about the storage stability of pesticide residue in olive oil under our pre-selected storage condition.

This is the short description about the way I carried my experiment

2x20 vials of olive oil samples (5g each) were prepared from a stock of olive oil (500g) containing 0.25mg of pesticide of interest (Cypermethrin).
After this, all the samples were kept in freezer at -18 degree C (in dark).
At each sampling day (total 20 sampling days) , 2 vials were taken out from the freezer and the amount of cypermethrin was determined (with duplicate injections).

Now, I have two set of data namely set A and set B.

My questions are:
1. What should I do to determine whether the pesticide was degraded during the storage period? (In term of statistics or other ways)
2. How many replicates that normally needed for pesticide storage data?

Thanks

[sadsal123]

If over the 20 days, your pesticide levels dropped then surely it was because it was degrading. Plot a graph of Days vs Pesticide Level. I think it might be better to check your data in triplicates than duplicates. I am not an expert but these are just some suggestions.


Best Of Luck