[gilly]

HI All,
Well I have searched past posts for what I am looking for but cannot find anything. If you can help, please answer the question I am asking and not go off on a tangent about how internal standards work etc. I am aware of why and how we do it and regularly use internal standard for sample analysis. I usually prepare std and sample to the same volume and use the same amount of internal standard in both - this calc is easy as the internal standard is the same conc in both so no need for different data in calculations. Here I am a bit confused - this time I do not have much sample. My internal standard is added at 0.1ml of a 0.5mg/ml soln and made to 1.2mls total.(1ml sample (or spiked placebo with std), 0.1ml int std, 0.1ml ppt reagent) Most samples are the same however I do not have 1ml of a couple of samples. Here I have 0.8mls or 0.9ml of sample and still add 0.1ml int std and 0.1ml ppt reag. Therefore the final volume for my sample is different. If I put 0.1ml of 0.5mg/ml int std in, do I need to adjust this amount for a total volume of 1.0 or 1.1mls?? In other words, is the internal standard as mg/ml final dilution or mg added per dilution when calculating? In a calc without int std you would multiply up by dilution to get the result so I am not sure if the internal std is multiplied up already or not if that makes sense.

 

[Pradeep]

It doesn't appear as a clear question. Anyway if you know the function of the internal standard that is the answer.

[Train]

I think that you have to adjust for the different concentration of internal standard.