Week 1 Lab: Pipetting

Prelab

Dilution Practice 1

Scenario: The stock concentration of a mystery substance (MS) is 5 M. Dilute to 100 µM (0.1 mM) using serial dilutions.

5 M = 5,000,000 µM

Step 1: 500× dilution

5,000,000 µM / 10,000 µM = 500

This corresponds to a 1:499 dilution.

• 2 µL stock + 998 µL water = 10,000 µM

Step 2: 100× dilution

10,000 µM / 100 µM = 100

This corresponds to a 1:99 dilution.

• 10 µL of 10,000 µM + 990 µL water = 100 µM

Dilution Practice 2

Given:

• Stock concentration = 5 M
• Molar mass = 532 g/mol

Stock Concentration

5 mol/L × 532 g/mol = 2660 g/L
2660 g/L ÷ 1000 = 2.66 g/mL

Serial dilution plan (5 M to 100 µM)

Overall dilution:

5,000,000 µM / 100 µM = 50,000

Dilution plan:

• 1:100 to 50,000 µM
• 1:50 to 1,000 µM
• 1:10 to 100 µM

This would use 3 dilution steps and the P10, P200, and P1000 pipettes

Final Reaction

Total volume: 60 µL
Final MS concentration: 40 µM

Making 100 µM stock makes it easier to pipette and lets you make multiple final concentrations. Making 40 µM directly via serial dilution would require weird dilution ratios and introduce additional error.

Lab

In lab this week, we learned how to use pipettes and the basics of running a gel. It was my first time using a pipette and I quickly realized that my hands were not quite as steady as I wanted them to be. We didn’t follow the lab protocol exactly, it was more about trying all of the different pipettes and learning how they operate. I work with inkjets in my research but I didn’t realize that you could create beautiful tiny droplets by hand as well. Using the P20 I could create droplets only slightly larger than the ones my single-nozzle inkjets create.

My goal was to make a colorful picture in a petri dish similar to the dot paintings with the sequins. I began by using the P1000, but this was much too coarse and oftentimes my dots would bleed into each other, so I switched to a P200 and found I had much more control. I created a couple of abstract pieces whilst getting the hang of the pipettes.

Then we ran a gel and though we’re going more in detail in lab during week 2 it was cool to learn about how to set up a gel and the concept of ladders. I thought that ladders would be absolute, like physical markings on the side of the machine but it’s incredible that ladders are run beside your sample because it’s so context dependent. We also learned that you can recover a specific part of your sample from the gel, but that this is a lot of work compared to other methods. I’m looking forward to learning more about the process in lab next week.

Sources

AI Prompts -“Help me do math in mark down, make me a markdown math cheat sheet, I’m doing unit conversions and serial dilutions” -“Help me add images in markdown, how to add image in different upstream folder”