Question

A. 0.001 uL B. 0.01 uL C. 0.1 uL D. 1.0 uL

You have performed a 10-fold serial dilution of your phage sample from 100 to 10-4. You have been transferring 10 uL of sample from one tube to the next. How many microliters of the original 100 sample are in the 10-4 tube?

Answer 1

Disclaimer: Read the whole answer.

Look at the following table -

Sample Concentration	100	10	1	10^-1	10^-2	10^-3	10^-4
Number of dilution (fold)	0 (no dilution)	1	2	3	4	5	6

Thus we have done 6 ten fold dilutions to go from 100 to 10^-4

It is given that 10uL of sample is used for serial dilutions which means 10uL is taken from the sample and added to 90uL of solvent. Then 10uL is taken from this dilution and is added in another 90uL of solvent and so on. Total 6 such dilutions are done. Now look at the following table -

Number of dilution	1	2	3	4	5	6
Amount of original sample in that dilution	10uL	1uL	0.1uL	0.01uL	0.001uL	0.0001uL

Clearly there is no option of 0.0001uL. I think that the initail concentration is 10^0 and not 100. Hence if I consider initial population as 10^0 = 1 we get the following table -

Sample concentration	10^0 = 1	10^-1	10^-2	10^-3	10^-4
Number of dilution (folds)	0	1	2	3	4
Amount of original sample	NA	10uL	1uL	0.1uL	0.01uL

Hence the answer is B. 0.01uL

Hope this helped!