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- Joined: Fri Jul 08, 2016 8:03 pm
What are the best practices to make the most accurate dilutions in the ng/uL or pg/uL range? I was quite confident that it is more favorable to use serial dilutions, however this ISO9001 based procedure from Supelco (http://www.agilent.com/cs/library/certi ... C06999.pdf, page 2) has left me wondering.
Supelco standard preparation steps are summarized in quotes. I am assuming that they did not pre-measure the solvent but used a volumetric flask. Note that each solution is made from the STOCK solution
Std 1 0.010ug/ml: 0.10 ml of Stock Solution diluted with 499.9 ml solvent.
Std 2 0.025ug/ml: 0.25 ml of Stock Solution diluted with 499.75 ml solvent.
Std 3 0.100ug/ml: 1.0 ml of Stock Solution diluted with 499.5 ml solvent.
Std 4 0.500ug/ml: 1.0 ml of Stock Solution diluted with 99.0 ml solvent.
Std 5 1.000ug/ml: 2.0 ml of Stock Solution diluted with 98.0 ml solvent.
The concentrations are not the same, but if I were to start with a 5ng/uL (5000pg/uL) Stock solution I would use the serial dilution procedure below.
Std 1 10pg/ul: 10ul of Stock diluted to 5ml in volumetric flask.
Std 2 1pg/ul: 500ul of Std 1 diluted to 5ml in volumetric flask.
Std 3 0.10pg/ul: 500ul of Std 2 diluted to 5ml in volumetric flask.
Std 4 0.02pg/ul: 1000ul of Std 3 diluted to 5ml in volumetric flask
Std 5 0.01pg/ul: 2500ul of Std 4 diluted to 5ml in volumetric flask
Overall what is the more favorable procedure? Another thing that I noticed with the first set of procedures are that they use a large difference in diluent compared to the final volume, whereas I try to keep my diluent within 1-3 magnitudes of the final volume.
Thoughts?