Question

Determining Conc. of DNA: A260 of 1.0 = 50µg/mL or 50ng/µL

Question: A DNA sample is at a concentration of 250ng/100µL. What would be the absorbance at 260nm of a 1/2.5 dilution of this DNA sample?

Answer is 0.02, please show all steps of how we got this answer

Answer 1

we know that

during dilution

mass of sample does not change

only volume of solution changes

so

mass of DNA sample = 250 ng

now

given that

1/2.5 dilution

that is

100 ul / 250 ul

so

the volume changes from 100 ul to 250 ul

so

the new concentration is given by

C = mass of DNA sample / final volume

C = 250 ng / 250 ul

C = 1 ng / ul

now

given that

abosorbance of 1 ----> 50 ng / ul

let abosorbance of y ----> 1 ng / ul

so

y = 1 x 1 / 50

y = 1 / 50

y = 0.02

so

the answer is 0.02