peptide concentration calculation - (Nov/27/2007 )

hi all,
can anyone please tell me how to check the concentration of peptide. I weighed my peptide (2 mg ) and dissolved in 500ul buffer. when i checked the concentration by Nanodrop I got the as 1.2 mg/ml instead of 4mg/ml. Can anyone please tell me why it is like this?? Is there any other way that i can confirm my concentration other that amino acid analysis???
thank u

hi,

let the peptide dissolve longer in the buffer
if the peptide does not form aggregate, make sure that your scales is well calibrated

your could lyophilize your prep and weigh once again...
have you any rapid biol/biochemical assay for measuring the peptide concentration?
if your peptide contains any aromatic residue, measure the solution OD at 280nm
depending on its length, you should test it by a Bradford-derivated assay, or run it in a gel, blot it on a nitrocellulose membrane and stain with Ponceau red vs a range of known concentrations of another peptide or protein

Sebastien

also, check the data sheet that came with your peptide and see if it is 2mg peptide or 2mg solids (with a lower peptide content).

its 2 mg petide only. ??

mdfenko means that 2 mg of solid certainly correspond to X mg of peptide +Y mg of salt (counter-ion) with X+Y=2 mg...

Sebastien