It says; "To get your reading put 20 ul of your sample in 1 ml of water and place it in a quartz cuvette. The dilution factor in this case would be 1000/20 = 50 since you dissolved 20 ul in 1000 ul of water."

Should not the dilution factor be 51X instead of 50X, since the total volume is 1020ul and not 1000ul?

Actually, you should add 20 ul sample to 980 ul water so you will get exact 50x dilution. Be ware that some cuvettes doesn't need so much volume so read the instruction to find out the minimum volume needed by the cuvette and save your RNA or DNA sample.

1ml is a lot for a cuvette.

I think most will happily read 200ul

hi
basically, the dilution factor regarding 20µl in 1000µl is 51X. i agree but the concentration calculated with one or the other dilution fator would not change a lot. it's just simplification of calculs, but now excel is here for formulas so you can use 51.

as pointed out by PCR man, quartz cuvettes have generally small windows crossed by UVrays. The OD is measured in this window. In my lab, we have two dimensions for such windows. Cuvettes with small window only require 60µl of sample toi get a good measure and cuvettes with large windows requires 200µl of sample. Hence, i think you can save your prep by making a final sample in a smaller volume.

fred