Please, if possible, check if my method of dilution is correct

Question

Problem: Given a very concentrated liquid PBS, dilute it to 1:15,000

My approach is to use serial dilution
First: dilute it 15x (50ul of PBS + 750ul of water)... this will give 1:15

Second: dilute 10xfold more (100ul PBS from step 1 + 900ul water)...this will give 1:150

Third: dilute anotehr 10x fold more (100ul PBS from step 2 + 900ul water)...this will give 1:1500

Fourth: dilute anotehr 10x fold more (100ul PBS from step 3 + 900ul water)...this will give 1:15000

Is my approach and calculation correct?

Answer 1

I saw this and didn't want to try and help because their is a lot of math involved for something so simple, and I believe that is why others have ignored it. The simple way to do this is to scale up because this, in my opinion, is a complicated process to achieve a 1:15,000 dilution. Take 10uL of sample and dilute it with 150,000uL of solvent, or 150mL of water. There are 1,000uL pipettes and just do that 15 times and vortex the thing for 30 seconds. That way you save reagent, and the systematic error that is associated with that many dilutions, in my opinion, is kind of high. Also, if you have a 1 to 5uL micropipette, take 1uL of sample and add 15mL of water; scale up as needed depending on how much of the concentration you need.