An inexpensive and easy to make µl re-pipette

Transcription

1 An inexpensive and easy to make µl re-pipette John Giannini Biology Department, St. Olaf College

2 Introduction To be able to do reliable science experiments, students and researchers need to be able to measure small quantities of solution accurately. Most modern labs use mechanical pipettes because of their accuracy and ease of use. One disadvantage of these devices is their relatively high cost. They can cost anywhere from $ per pipette. This is a large expenditure for a class of students limiting their use to well-funded schools and programs. In an effort to make science affordable and accessible to more students we describe how to build an inexpensive and easy to build mechanical pipette (10-75µl). We call it the OPN 10-75µl Re-pipette. 2

3 Materials - Assortment of 3D-printed parts (stl files available at: pages.stolaf.edu/opn-lab/ ) - 0.5cc BD syringe -.1ml, 1/1000 glass pipette - 5 minute epoxy glue - 2, 4-40, 1/2 inch wood screws - 1, 10-24,2 inch hex head bolt - 1, 1 1/8 inch, 5/16 inch diameter stiff spring - 1, 1 1/2 inch medium strength spring - Triangular file - Box cutter/ razor blade grit sandpaper (small piece) 3

4 Steps Step1. Lay out all of your materials (Fig.1) Figure 1. The parts used to make the re-pipette. 4

5 Step 2. Cut the bottom off of the 3ml syringe with a sharp razor blade (Fig.2). Figure 2. The 3 ml syringe after it has been cut with a box cutter or razor blade. 5

6 Step 3. With the triangular file make a small groove on the glass pipette about half way down the pipette. Then carefully break the pipette. Keep the piece that has the tip(fig.3).rough the tip of the pipette that is used for dispensing liquid with 200 grit sandpaper. This helps with water adhesion. Figure 3. The glass pipette after it has been scored and broken. 6

7 Step 4. Glue the 3D-printed connector to the pipette (fig.4). Do not glue the syringe into the connector. Figure 4. The 3D-printed connector glued to the pipette with epoxy. 7

8 Step 5. Glue the 3D-printed spacer on top of the syringe plunger. Then glue the bolt on top of the spacer. Keep everything centered (Fig.5). Figure 5. The bolt and 3D-printed spacer glued to the top of the syringe plunger. 8

9 Step 6. Place the spring on the plunger and insert the plunger into the syringe. Then place the syringe through the 3D-printed case. Glue the pipette with the 3D-printed connector onto the syringe (Fig.6). Figure 6. The syringe plunger inserted into the syringe with the spring. Next the syringe was glued onto the 3D-printed connector after it was inserted into the 3D-printed case. 9

10 Step 7. Screw the cap onto the case (Fig.7). Figure 7. The cap screwed onto the 3D-printed case. 10

11 Step 8. Place the stiff spring onto the screw. Then screw on the 3D-printed adjustment circle then screw on the 3D printed top (Fig. 8). The plastic pieces will self-cut threads when you screw them on. You can make this easier by tapping threads in the pieces. Figure 8. The 3D-printed adjustment ring screwed onto the bolt followed by the 3D printed cap. How to use the pipette To use the pipette, press the plunger down till you reach the stiff spring (Fig.9). Then place the pipette tip in liquid and slowly release the plunger. Next move the pipette to where you want to dispense the liquid and depress the plunger till you reach the stiff spring. Then push down on the plunger a bit more till you compress the stiff spring a small amount (Fig.10).To adjust the amount of liquid pipetted turn the adjustment ring and measure with the pipette how much is being taken up (Fig.11). Adjust the ring till you get the amount you want to pipette. 11

12 Figure 9. Pressing the plunger with your thumb. 12

13 Figure 10. When empting press the plunger till you slightly compress the stiff spring. 13

14 Figure 11. The adjustment ring where you can set the amount of liquid to be pipetted is located between the cap and the case. Testing results The pipette was set to measure 48µI of water. Ten consecutive measurements were made and weighed on an analytical balance. The average was mI (SD ). Conclusion The re-pipette we have presented is easy and inexpensive to make. It appears to have reasonable precision and is easy to use. This pipette design could be used as an alternative to more expensive models. 14

15 Helpful Hints A problem that we have had with the pipette is that bubbles form as you work with it. An easy solution is to place a 200µl plastic pipette tip on the end of the pipette once you have adjusted it for the volume you want to dispense. (Fig.12) Figure 12. A plastic pipette tip placed on the end of the glass pipette. The other problem we ran into was that occasionally the 3D printed connector between the syringe and the glass pipette leaked air. We solved the problem by coating the connector with epoxy. (Fig.13) 15

16 Figure 13. The 3D connector coated with epoxy. 16