Micropipette Exercise

 

Objectives

·      Become familiar with micropipettes. 

·      Develop a visual “size” of certain volumes. 

·      Perform basic statistics on repeat measurements.

NOTE:  Some of you who took BIOS 311 or BIOS 312 may find this exercise tedious, boring, and/or insulting.  The purpose of this short refresher is two-fold:

Ø      The micropipettes in this lab are likely a different brand from those you have previously used and thus the “feel” of them is different.  You must be proficient in their use before you begin working with cells. 

Ø      Give you an opportunity to recall basic statistical calculations.

 

Materials

10 mL micropipette, 1000 mL micropipette

Deionized water

Clean, dry Coulter Counter vials

Analytical balance (Explorer model)

 

Safety

1.      Wear safety glasses at all times.

 

Procedure

EACH PERSON MUST DO THE ENTIRE PROCEDURE. 

1.      Tare Coulter Counter vial.

2.      Pipet 250 mL of water into vial using 1000 mL micropipette.  Record weight.

3.      Repeat step 2. four times (5 measurements total). 

NOTE:  Do not use a new vial for every measurement;  just add water to the existing vial.

 

Repeat Steps 1.-3. for the following:

·      Pipet 10 mL of water using the 10 mL micropipette.  Do 5 measurements total.

·      Pipet 1000 mL of water using the 1000 mL micropipette.  Do 10 measurements total.

 

Calculations/Questions

1.      Determine the mean and standard deviation of the mass for each of the three volumetric measurements of water.

NOTE:  Do the calculations for the mean and standard deviation by hand/calculator for one volume.  Show the work in your lab notebook.  You may use Excel or another computer program to do the rest of the calculations.

2.      Calculate the mean and standard deviation of the density of water for each of the three volumetric measurements of water.

3.      Prepare a graph with your data.  Use Excel or another computer program.  Include appropriate statistics such as standard deviation on the graph.

4.      Compare your calculated densities with the following values:

 

Temperature (°C)	Temperature (°F)	Density of Water (g/mL)
20	68	0.9982
25	77	0.997

 

How similar or different are your calculated values from one another and from the literature source?

5.      How repeatable is your pipeting?  What criteria did you use to evaluate this?

6.      Does the exercise with 10 measurements (1000 mL volume) have a higher or lower standard deviation as compared to the exercises with 5 measurements taken?  Explain.

 

Data and answers to questions should be recorded in your laboratory notebook.  The answer to each question is worth 5 pts. 

 

Handouts and other statistics reference books will be available for consultation.