Hi,

 

I am trying to run a superoxide dismutase assay for my RBC and serum samples. I need help with the calculations for the standard curve. I am using the sigma assay kit (http://www.sigmaaldrich.com/catalog/product/sigma/19160?lang=en&region=US) with this SOD (http://www.sigmaaldrich.com/catalog/product/sigma/S5395?lang=en&region=US).

 

SOD comes from Sigma as a powder at 3000 units of activity per mg; there are 5 mg in the vial. Thus, there is 15000 units total in the vial.

 

I want to make an initial dilution of the SOD powder with buffer to a concentration of 30000 units/mL and make several aliquots to freeze.

 

I'm stuck on a simple, but stupid question.

 

When calculating, do I simply add 0.500 mL to the 5 mg (=15000 units) of SOD, to bring it to a final Concentration of 30000 units/mL?

(Or do I need a final VOLUME of 0.500 mL?) Sorry, haven't looked at my gen chem in so long.

 

Thanks a bunch!

Normally the final volume is used.

How would you accurately measure that though? It seems difficult with such small volumes and weights.

Typically volume down to a ml are done with volumetric flasks (i.e. rinse the whole sample into it with appropriate buffer, then fill up to the mark). For smaller volumes often pipettors are used (which can be a bit tricky). That is why often stock solutions with somewhat higher volumes (i.e. at least an ml) are generally used and then diluted using pipettors.