Should I redo a calibration curve each time

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xochiatl
xochiatl's picture
Should I redo a calibration curve each time

Hello,

It is standard procedure in my lab that we do a calibration curve each time we do a colorimetric test such as measuring proteins or sugars in a sample.
On the other hand I learned in school that you only do your calibration curve once and you will verify with standards after that.
I have been searching on the internet but all I have been able to find is how to do one but not if I shouls do it every time (Which I personally think is not necessary)

Can anybody tell me if I should do one calibration curve every time I do a test and why?

Thanks very much,
David

Dr. Analytical
Dr. Analytical's picture
David:

David:
There are many opinions on this subject, and probably no universal agreement.

I could offer the following general ideas:
If the analysis and result are more important, you should put more effort into calibration.  This is typical in pharmaceutical analysis, where the system is calibrated each time there is an analysis (six injections of standard).  These labs have very tight tolerances and even a one percent change could be a problem.

At a minimum, you should verify calibration both before and after analysis (beginning and end).  If both experiments are within acceptable specifications, then everything between those two measurements is valid.

System, method, and compound stability all play a role in making your decision.

xochiatl
xochiatl's picture
 Thanks very much Dr.

 Thanks very much Dr. Analytical

Ruderus
Ruderus's picture
In my experience, calibration

In my experience, calibration is not required every time. 
It is very important however that you use standards in every assay, possibly always the same standards...let's say 2.5, 5, 7.5 and 10 micrograms of BSA for a protein assay... the standard curves should be very similar accross experiments and this will give you the confidence to say that the instrument is calibrated. As soon as you start seeing your standard curves behaving differently from the previous ones, then it is time to recalibrate!