If 2.0 mu"L" of a sample must be diluted by a factor of 50, what volume of solvent should be added to accomplish this?

1 Answer

Mix 2.0 µ"L" of sample with a bit less than 98 µ"L" of solvent, then add solvent until you reach the 100 µ"L" mark.

Explanation:

You can use the dilution formula:

color(blue)(bar(ul(|color(white)(a/a)V_1c_1 = V_2c_2color(white)(a/a)|)))" "

We can rearrange this formula to get

V_1 = V_2 × c_2/c_1

V_1 = ?; color(white)(mmll)" "" "c_1 = c_1

V_2 = "100 µL"; " "" "c_2 = c_1/50

V_1 = "100 µL" × (stackrelcolor(blue)(1)color(red)(cancel(color(black)(c_1)))//50)/color(red)(cancel(color(black)(c_1))) = "100 µL" × 1/50 = "2 µL"

∴ Add a bit less than 98 µ"L" of solvent to 2 µ"L" of the sample, then fill up to the mark.

We don't quite add 98 µ"L" right away because we want to account for any solution volume changes (up/down) due to mixing.