I have two chambers, the inner contain a capillary tube and the outer chamber contains water to maintain the humidity. My problem is that when I fill the capillary tube (by capillary action) and I put a drop of parafin oil on the top of capillary tube (to avoid evaporation), there is still some evaporation happening.
Does anyone have any idea how to inhibit liquid loss inside the capillary?
I want to have a constant amount of liquid in the capillary tube.
However, I know there will be some evaporation at the end which i need to subtract it.
A few comments:
It depends on what the capillary tube is made of (e.g. flint glass, polycarbonate, polypropylene, Teflon...) as well as it's wall thickness. Plastic tubes made from porous materials will allow liquids and gases to diffuse through the walls. Glass will do a better job (but diffusion will still be present). Your "capillary tube" material choice has a large effect on this.
Temperature changes and vapor pressure can cause changes too. You did not tell us what liquid is being placed inside the capillary. This is an important fact needed to understand the overall process.
Paraffin wax is also porous and may not be providing the air tight seal or chemical compatibility you need. Some liquid and gas will still diffuse through it (both into and out of) the capillary over time. If the tube's porosity is not the main problem, then try an epoxy seal instead. This will do a better job of sealing the top. We use epoxy all of the time when we make electrodes and it works very well..
Thanks for all your answers. I have attached my setup with more detail.
The liquid inside capillary is sucrose 10%. I will try epoxy.
My capillary is a glass one.
Regarding the temperature, I put this apparatus in a 25C incubator.
I am actually trying to measure liquid consumption by Drosophila inside the inner chamber and its called CAFE assay.
Fascinating stuff. I worked with fruit flies many years ago and we did similar experiments.
Looks like you are measuring food intake so I think an epoxy coating might be overkill. You might want to try and stick the capillary tips directly into a wax pad (e.g. they seal glass caps used to draw blood from finger sticks in this manner. After drawing the blood up the capillary, the opposite and clean end of the cap is stuck down into a block of wax to "cap" while it stands up until needed in the short term). Another option might be to dip the other end in oil. It would act as a hydrophobic layer.
Temperature and humidity will need to be very stable or the fluid may move up or down the tube. I am sure you have identical control tubes set up (with sucrose) in tubes without flies to monitor any changes in these tiny "barometers". I suspect you want to measure only what the flies are drinking. *You can slow them down with some alcohol!
Forgot to ask, are you using siliconized capillaries or plain glass ones? The plain ones can be harder to read as the liquid creeps up the sides a bit. The siliconized ones create a textbook meniscus to more easily measure. Alternatively, cleaning the regular ones in an acid bath and drying them with filtered Nitrogen or Air, which removes particulate matter, can help too. Again, might be overkill for your application. ;)
Thanks alot Bill for very informative answers.
My challenge is actually stick the inner chamber with outer chamber and seal the outer chamber and not to allow alot of air exchange which will affect the water vapor speed. I am going to try a regular tape or epoxy to stick two tubes together as I found the parafilm was killing the flies compared to my previous experiments. I have put the capillaries inside the 200 ul tips so they are fine and they dont move.
I am using plain capillary glasses, so by using a blue dye which lets me see where the liquid is and also goes inside the flies abdomen and confirms they are drinking the liquid. Yes, I do have control with no flies.
They are some studies that they have shown when giving flies the choice of food with or without alcohol, they prefer the second one.
I see in the first picture, you are using a large centrifuge tube with another plastic tube inside it.
If you used two tubes which fit snugly together so they seal well, you could place a solid rubber stopper (which you have drilled two small holes through for the capillaries) on the inner tube as a 'cap'. Then simply slide in the two capillaries and seal the tops with a wax plug. No need for Parafilm. Upper tube would still have holes in the bottom. Depending on what sized tubes you have, the lower "tube" could also be a tall form glass beaker. ???
Yes, flies do not like alcohol. Perhaps it is the taste of it? No danger of alcoholic families of wild type fruit flies in nature.
oops sorry, I meant the first one. Actually they like food with alcohol.
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