Thanks for confirming the units that you want to use.
Going back to the last posts, we agreed that the standard that you have available is 45 nM/mL or 45,000 picomoles/mL or 45 picomoles per liter.and you want to your highest concentration to be 25 pmoles per milliliter? (Please confirm because 25 pmol could be interpreted as 25 pmolar, or 25 pmol per liter).
To dilute from 45,000 picomoles/mL to 25 picomoles/mL, you need to dilute your sample 1:1800. This dilution is too high to do in one step, so I recommend doing it in two steps:
This dilution will require a variable 10 uL pipette. Let me know if you don't have a pipette that will work for 6 uL.
1. First transfer 6 uL of the sample into a tube containing 995 uL of suitable diluent.. This is a 1:166 dilution and the concentration of the standard is now 271 picmoles/mL. Mix this dilution very well.
2. Next, transfer 10 uL into 100 uL of suitable diluent. This is a 1:10.8 dilution and will bring the concentration down to 25.1 pmol/mL. You can call it 25 pmol/mL.
There are other possible ways to do the dilution, so let me know what pipettes you have available if you need an alternative method.
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However, I do have some other suggestions if you need more help. From your description of the project so far, it sounds like you are working with cytokines, or a similar class of molecule. Cytokines are very unstable proteins, and it is important to work quickly, keep the samples cold, and dilute into buffers that contain protective proteins when working with them. Here is a link to an instruction manual for a cytokine assay that includes lots of details for handling the samples.
Please note the dilutions of the standard recommended on page 11 of this instruction manual; it is a series of 1:4 dilutions/ http://www.bio-rad.com/webroot/web/pdf/ ... 10004F.pdf
If you are working with a kit like this, I recommend looking up the toll-free number for the technical support department of the kit manufacturer and calling to talk to someone who knows about the kit. You should be able to talk to someone who can review the dilutions that you want to make and answer all of your other questions so that you will be ready to start your experiment. I am suggesting this because I think I have explained how to do the dilution you have requested, but it seems to be a very high dilution for this type of protein.
Also, please make sure you run one standard curve as directed in the instructions of the kit you are using so you can compare your results to the expected standard curve.
Please post again if you have more questions.