• Solve for V1: C1 = 0.876ng/µl C2 = 0.15ng/µl V2 = 5µl
• You need to prepare a DNA dilution with a final concentration of 0.15ng/µl in a final volume of 5µl. If your sample has a starting concentration of 0.876ng/µl, what volume do you need of it to make the dilution?
• You need to prepare a DNA dilution with a final concentration of 0.15ng/µl in a final volume of 5µl. If your sample has a starting concentration of 0.876ng/µl, what volume of sample and water are needed?
• How do you prepare a dilution with a final concentration of 0.15ng/µl in a final volume of 5µl for a sample with a starting concentration of 0.876ng/µl?
• How do you prepare a dilution containing 0.75ng DNA in a final volume of 5µl for a sample with a starting concentration of 0.876ng/µl?
• How do you prepare a sample for amplification if its starting concentration is 0.876ng/µl and you need a final concentration of 0.15ng/µl in a final volume of 5µl?
• How do you prepare a sample for amplification if its starting concentration is 0.876ng/µl and you need 0.75ng in a final volume of 5µl?
• How do you prepare a sample for amplification if its concentration is 0.876ng/µl and you need 0.75ng in 5µl?
• STR amplification requires amplification of 0.75ng DNA in 5µl. How can you prepare a sample for amplification if its concentration is 0.876ng/µl?
• STR amplification requires amplification of 0.75-1ng DNA in 5µl. How can you prepare a sample for amplification if its concentration is 0.876ng/µl?
NOTE: “How do/can you prepare…” implies the volume of sample (e.g., DNA sample, stock reagent, etc.) and volume of diluent (e.g., water, TE, TE-4, etc.), as well as the preparation of any serial dilutions, if necessary. Keep in mind limitations imposed by pipets and tubes.
At some point, the starting and/or final volumes become obscured because, in practice, we take into account any or all of the following when preparing samples for STR amplification:
• Limitation of pipet, thereby potentially imposing a minimum volume (V1) to use of the sample (i.e., 2µl)
• “Ease” of dilution, accuracy of the pipette, and/or how much DNA extract you have to work with (e.g., 100-250µl), thereby imposing the use of an arbitrary volume (V1) of sample (e.g., 5µl, 10µl, etc.) or an arbitrary final volume (V2; e.g., 100-1000ml)
• Having plenty of dilution left over for future amplifications from the same dilution, thereby imposing a higher final volume (V2) than what is needed at the time (e.g., 20-100µl)

1. Solve for V2:
C1 = 2.251ng/µl V1 = 10µl
C2 = 0.10ng/µl

2. Solve for C2:
C1 = 3.159ng/µl V1 = 4.75µl
V2 = 150µl

3. Solve for C1:
V1 = 3.7µl
C2 = 10ng/µl V2 = 500µl

4. Solve for C1:
V1 = 9.8ml C2 = 100mM V2 = 1L

5. Solve for V1:
C1 = 10M C2 = 50mM V2 = 5L

Word problems:

1. You have a DNA sample with a concentration of 2.251ng/µl. What volume of water do you need to add to 10µl of your sample to make a dilution with a final concentration of 0.10ng/µl?
OR
You have a DNA sample with a concentration of 2.251ng/µl and use 10µl of it to make a dilution with a final concentration of 0.10ng/µl. What is volume of your dilution?

2. What is the final concentration of a 150µl dilution of DNA that was prepared using 4.75µl of a sample with a concentration of 3.159ng/µl?
OR
You prepared a dilution using 4.75µl of DNA (concentration of 3.159ng/µl) and 145.25µl of water. What is the concentration of the dilution?

3. To prepare 500µl of a 10ng/µl DNA dilution, you need 3.7µl of your undiluted DNA sample. What is the concentration of the sample prior to diluting?
OR
You must prepare a serial dilution of a highly concentrated DNA sample. For the final dilution, you will use 3.7µl of the previous dilution to obtain the desired concentration of 10ng/µl in 500µl. What is the concentration of the dilution used for the final dilution?

4. You need to make 1L of 100mM NaOH. If you use 9.8ml of your stock NaOH solution and 990.2ml of water, what is the concentration of the stock solution?
OR
What is the starting concentration of NaOH if you use 9.8ml of stock NaOH and 990.2ml of water to prepare 100mM NaOH?

5. How much 10M NaOH is needed to make 5L of 50mM NaOH?
OR
You need to prepare a 5L of 1:200 dilution of 10M NaOH. What volume should you use of the stock?

Additional questions:
1. How do you prepare a 1:100 dilution of 10M NaOH? What is the final concentration?
2. How do you prepare a 1:100 dilution of a DNA sample if you want a total of 700µl? If the undiluted sample has a concentration of 3.24µg/µl, what is the final concentration of the dilution?
3. Using serial dilutions, how can you prepare a DNA sample such that is diluted 2500x total?
4. How can you prepare 1L of 1mM NaOH from 10M stock solution?
5. How can you prepare a DNA sample (starting concentration of 4.16µg/µl) for amplification, if you need 1ng of DNA in 5µl for the PCR reaction?
6. You add 4.7µl of a DNA sample (starting concentration of 1.6µg/µl) that was serial diluted 1:100 two times to a 0.2ml PCR tube for STR amplification. What amount (not volume!) of DNA will be amplified?

• Solve for V1: C1 = 0.876ng/µl C2 = 0.15ng/µl V2 = 5µl • You nee...