MicrobeHunter.com Microscopy Forum

In respect to microscopy, refractive index and permanent mounts are both glycerine vs glycerol equivalent?
Glycerine is available in pharmacies: PSP GO Glycerine - 100ml $4.49
https://www.londondrugs.com/psp-go-glyc ... 87729.html

glycerol is a bit more pricey
Glycerol Wet Mounting Medium 30 ML (1 oz) in Glass Dropper Bottles $12.99
https://www.amazon.com/Glycerol-Mountin ... hip&sr=1-5

Pharmaceutical Grade
Glycerin Vegetable - 1 Quart (43 oz.) - Non GMO - Sustainable Palm Based - USP - KOSHER - PURE - Pharmaceutical Grade $12.97
https://www.amazon.com/Glycerin-Vegetab ... 191&sr=8-3

Glycerol and glycerine are different names for exactly the same chemical.
The chemical purity of glycerine (=glycerol) might differ among makers and suppliers, according to projected use.
Glycerine is very hygroscopic, hence the likely "contaminant" in commercial glycerine is water. Moreover, when super-dry glycerine in hermetically sealed container is exposed to ambient air, it absorbs humidity. Yet I believe, that a few percent of water will not interfere with mounting - please check what Walter Dioni published about it.

About the three products in the links, reading the descriptions, the purities are:

The first - passes USP standards, that is the U.S. Pharmacopea, it is possible to check their standards (meaning the maximum allowed levels of contaminants in the glycerine).

The second - I could not find the claimed purity. As sold, it is marketed for mounting, and likely the price is derived from the package. A bottle with dropper is admittedly convenient for use.

The third - purity claimed to be 99.7%, also claimed to pass USP, certainly appropriate for mounting.
Please note, "Kosher" is a religion-related feature, it is given to products regardless of their quality or purity. It is somewhat equivalent to "Sacred".
This glycerine is described as palm-based, possibly manufactured from plant material. However, if a chemical is pure, its origin (synthetic, or extracted from plants, or other) is irrelevant.

Hi Doron,
do you know how to dry glycerine that has picked up moisture over time?

Bob

Hi Bob,
I have never dried glycerol. Usually, an organic solvent is dried by (1) fractional distillation, or (2) addition of a solid drying agent and letting it stand for a couple of hours/days depending on the hygroscopy of the solvent. Method (2) is more appropriate when the amount of water is low.
Glycerol avidly absorbs water, so for method (2), a powerful drying agent, that is NOT soluble in glycerol, is required. I guess that I would start with oven-dried 3A molecular sieves (tiny ceramic-like beads). Add them to the glycerol and seal the jar. Wait a day or two, and filter-off the glycerol (these beads often release some powder that will disturb mounting.

I think that buying fresh glycerol is a lot easier and much cheaper (at least for home use) than drying glycerol. But, if you still prefer method (1) or method (2) above, I can try to get hold of more specific and quantitative data.

BTW, the easiest way to estimate the amount of water in glycerol would be from its refraction index, if a reliable refractometer (or any other technique) is available. Its nD is 1.4722, water is 1.33, a significant difference. Other methods require specific analyzers.

MicroBob
>> do you know how to dry glycerine that has picked up moisture over time?

The "A Simple Express Technique to Process Nematodes" assumes that water evaporates.
Maybe store glycerine in a dry area for a few days -- like in a kitchen oven (turned off) or vegetable dehydrator?

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5411252/
"This “cocktail” lens will be kept overnight in open air at room temperature, covered from dust, allowing water evaporation. During this time, a gradual increase in glycerol concentration takes place, saturating the nematode tissues. Nematodes will slowly sink down into a more concentrated glycerol layer. After 12 hr, nematodes are in concentrated glycerol within the ring."

lperepol wrote:MicroBob
>> do you know how to dry glycerine that has picked up moisture over time?

The "A Simple Express Technique to Process Nematodes" assumes that water evaporates.
Maybe store glycerine in a dry area for a few days -- like in a kitchen oven (turned off) or vegetable dehydrator?

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5411252/
"This “cocktail” lens will be kept overnight in open air at room temperature, covered from dust, allowing water evaporation. During this time, a gradual increase in glycerol concentration takes place, saturating the nematode tissues. Nematodes will slowly sink down into a more concentrated glycerol layer. After 12 hr, nematodes are in concentrated glycerol within the ring."

The evaporation in this protocol is relevant to a high proportion of water to glycerol. MicroBob was asking about a small amount of water in glycerol. For the nematode process, much water (relatively) is layered on top of the glycerol to form the "lens". From this mixture, much (but not all) water can evaporate. The bottom layer of the lens does not become absolute glycerol (100% dry) IMO.
BTW, This article shows that, at least for nematode slide mounting, glycerol need not be 100% dry, but may contain some water.

Thanks for the very helpful notes

MichaelG.

.
Information for the benefit of UK readers:
I've recently purchased
https://www.ebay.co.uk/itm/500ML-GLYCER ... 0540218141
... which was well packed and very promptly delivered.

I plan to do experiments with glycerine soap embedding, like shown here: https://www.youtube.com/watch?v=EMYygHyUrzY
This was used in microscopy to some extent in the early years of microtome use, around 150 years ago but then got out of fashion.
Here I will have a mix of glycerin soap, glycerin, water and the objects and will probably have to dry them to some extent.

Bob

Not sure if this helps MicroBob.
A paper by Jonannes Hallman and Sergei A. Subbotin, Methods for Extraction, Processing and Detection of Plant and Soil Nematodes recommends that for permanent mounting of nematodes:

"For permanent mounts, a very small drop of anhydrous glycerol (heated for 4h at 40°C in an oven) is placed in the centre of a clean microscope slide ..."

The reasons for heating anhydrous glycerol are not given. Seems like a lot of hassle for a drop of glycerol. But maybe how some nematologists manage to show high clarity on some nematode images?

I know nothing about nematodes, yet the only logical reason to warm glycerol at 40C would be to decrease its viscosity and make it more fluid. I tried to locate the article by Hallman and failed, yet IMHO heating glycerol at 40 will not remove any water unless the glycerol contained huge amounts of water to begin with. Even then, it would be a very impractical drying method.
Probably, the whole flask of glycerol was kept warm for the mounting session, not just a drop.
Hope this helps.

Hobbyst46 wrote:I tried to locate the article by Hallman and failed

Located, but not yet read:
https://www.researchgate.net/publicatio ... _nematodes

MichaelG.

MichaelG. wrote:

Hobbyst46 wrote:I tried to locate the article by Hallman and failed

Located, but not yet read:
https://www.researchgate.net/publicatio ... _nematodes

MichaelG.

No wonder I missed it! the name is Hallmann
That article is a chapter in a book, which I cannot download; one lead from it, however, is an article by J. W. Bates, J Nematol. 1997 Dec; 29(4): 565–566, in which the author mentions that nematodes are being mounted in anhydrous glycerol. The cherry on the whipped cream is a sealing stuff called glyceel. It is made by mixing nitrocellulose with other chemicals (not glycerol). Nitrocellulose was available from ICI at that time.

Hobbyst46 wrote:No wonder I missed it! the name is Hallmann

I searched on the title, and hit lucky

MichaelG.

Oops, sorry about the spelling.