A different DNA ladder from NEB (Cat #N3200L) comes as 500 uL of a 1000 ug/mL solution and is not pre-mixed with the 6 X DNA loading buffer. If you want to load 150 ng of this ladder, how would you prepare the solution and what volume of the solution would you load on your agarose gel?

4 ul Loading Buffer + 19.70 ul dH2O + 0.30 ul DNA Ladder

Load 12 ul on the gel.

Explanation:

DNA Ladder concentration = 1000 ug/ml

1000 ug DNA in 1 ml DNA Ladder solution → 150 ng DNA = 0.15 ug DNA in ... 0.00015 ml = 0.15 ul DNA Ladder solution

6x DNA Loading Buffer → it has to be diluted by an equal volume 6 times (1 ul LB + 1 ul distilled H2O)

An appropriate volume to load on an average agarose gel is 12 ul, so:

2 ul Loading Buffer + 9.85 ul dH2O + 0.15 ul DNA Ladder = 12 ul

But since 0.15 ul is a very small volume and mistakes could be made while measuring it, let's make double:

4 ul Loading Buffer + 19.70 ul dH2O + 0.30 ul DNA Ladder = 24 ul

And load half of that solution (12 ul) on the gel.