By Caroline Karbowski, Research Assistant: Department of Biological Chemistry and Pharmacology at Ohio State University
Caroline shares low and high technology options for measuring liquids in a science lab in this video demonstration.
Caroline has a 150 milliliter beaker and she put a bump square inside the beaker. At the water filter she fills up the beaker with water. She can feel when the water level hits her finger as it touches the bump square. Then she can stop it at just the right time.
This liquid level indicator is battery-operated. There’s two prongs that reach over the sides of the cup and when those two prongs are in contact with the liquid, they will beep. There’s a third prong above that and it will beep faster when it hits that one. Water is being put into the beaker.
[Beeping] Hit the first level.
[Beeping] Hit the second level.
I have a 50 mil volumetric flask with water inside. The Fill line is very hard to see. It’s gray or white, but if you take a permanent marker and draw on the line, it’s easier to see. You could also use a buret reading card, which is a white card with a black horizontal rectangle and you can use that to make the meniscus easier to see. And, when you’re done, you can just spray ethanol on a paper towel and wipe off any black marker that you used on glassware.
A serological pipette is connected to a pipette pump at the pipette cone. Above that is a side lever and above that is the thumb wheel. Caroline is filling up the serological pipette with water by putting the tip of the serological pipette in a beaker of water. She then uses her thumb to roll the thumb wheel. She rolls it more than what she would need, so water can be drawn into the serological pipette, much like using a straw. An internal piece of the pipette pump that has ridges on the side is connected to the thumb wheel, so when the thumb wheel is rolled, it starts to poke out the top of the pipette pump.
In order to have the correct volume of water inside the serological pipette, Caroline takes a small rectangle that has been cut to the correct size. She places it on top of the pipette pump and then pushes down the piece that is poking out of the pump. She pushes that down until the top of that piece hits the other side of the rectangle. Then she removes the rectangle and uses the side lever to dispense the liquid into a different beaker now that she has exactly 10 milliliters.
While this volume was for 10 milliliters, you can make rectangles for any volume. I also made a smaller rectangle for 5 mil. Both of these rectangles are engraved in print (10 mil or 5 mil) and have holes drilled into them corresponding to the number of milliliters. So 10 mil has 10 holes and 5 mil has 5 holes.
You could always use the density of water by measuring the temperature of the room if you need something more exact.
[Talking LabQuest voice]
“Us” really means USB. I put a weigh bowl on top of the scale. Caroline adds a beaker. I tear the balance. I fill up a pipette with water. I dispense a little bit of water. I’m putting the water into the beaker on the scale.
I’m listening for five grams. Getting close! I add a little bit more. I put the leftover water back in the storage beaker.
You can put tactile markings on a syringe plunger. Here I have a photo of a five milliliter syringe. I have bump dots cut in half placed on the plunger to mark different volumes. The syringe just naturally happens to have a notch at the five mil mark, so I can use that. You can also use a blade to cut into the plunger to feel that as well. When you want to use the syringe, fill it up all the way with your liquid. Then close the syringe until your tactile marking reaches the syringe barrel flange.
Here I’m showing four fixed volume micropipettes with volumes of 5, 10, 20, and 50 microliters. Every time you use these it will always be that exact volume and you don’t need to calibrate them, however you are limited to the volumes that you have with your pipettes and, if you want a volume that’s different, you have to combine volumes from different pipettes.
The way you use them is you attach a pipette tip to the end of the fixed volume micropipette then depress the plunger on the top of the fixed value micropipette to push out air. Place the tip into your liquid then release the plunger, so that way the liquid is drawn into the tip. Put your tip into your next beaker and then depress the plunger to push the liquid out. Compared to pipettes where you can change the volume, there is only one level to push down the plunger. You don’t have to push it down one level and continue to push to get out all of the liquid.
Caroline is filling the 50 microliter fixed volume micropipette with water. She then puts the water into a beaker which is on top of the scale.
[Talking LabQuest voice]
Wow, 0.05 grams is about 0.05 milliliters which is 50 microliters.
Of all the micropipettes I have used, these ones have the largest print for the numbers. It’s a black background with white numbers and then there are little hash marks for all the intermediate microliters. This is a p1000 so it does a thousand microliters or one milliliter. Right now the volume says 700, so that’s 700 microliters. Every time you hear a click that’s me turning the dial and it is going up one microliter, so if the pipette is handed to you at a certain volume, you can count with the ticks to figure out your other volumes that you need. So that was five ticks so now we’re at 705 microliters.
To get liquid into the pipette, it’s a similar system to the fixed-volume microbipette where you push all of the air out by depressing the plunger then releasing it. But then to release the liquid from your tip, you do need to push down the plunger once til you feel a small soft stop and then push again to push all the liquid out. It’s a two-stop plunger compared to just one stop.
There are also pipettes that have locks on the dial, so if you had multiple pipettes you could set them to the ones that you need, lock them, and you don’t have to worry about the dials moving around while you’re using the pipettes. There’s also electronic pipettes that can be controlled via other devices and there are opportunities for this to work with screen readers, although I have not used any of these myself.
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