Did I do this serial dilution wrong?

Math was never really my strong point.

Each solution has to be 10mL. I have to make a serial dilution from 4mg/mL to 2mg/mL, 1, .8, .6, .4, .2, and lastly .1

The first is 4mg/mL, so I took 40 mg of BSA (the protein I’m using) and mixed it with 10mL of PBS (the buffer I’m using)

For 2mg/mL, I took 5mL of the above and mixed it with 5mL of PBS.

For 1mg/mL, I took 2.5mL of the above and mixed it with 7.5mL of PBS.

For .8mg/mL, I took 2mL of the above, mix it with 8mL of PBS.

You can see where this is going, as each time I make it more dilute, I’m taking .5 less from the previous solution and mixing it with .5 more of PBS. (Except for the .1mg/mL, there it’s .25mL of .2mg/mL with 9.75mL of PBS)

I have to record the absorbances of these solutions. The 4mg/mL was fine, as was the 2mg/mL.

However, EVERYTHING below that is too dilute. By the time I observe .6mg/mL, I get 0 absorbance reading, like nothing is there.

Did I do this wrong? Did I have a brain fart and think something about this was logical and it’s really not? The thing is, this experiment has been done before, so I know something is wrong because the previous experiment had all these numbers for all these solutions. I got virtually nothing beneath 2mg/mL.