[RDX]

Having dabbled in chemistry, I find myself constantly trying to find ways to synthesize EVERYTHING. A lot of times, in my kitchen, I've needed pure corn starch and the bag of confectioners sugar makes me wonder. What should I study to learn how to separate these two substances? Can it even be done?

[P]

Is the corn starch soluble? You could dissolve the sugar out and dry the starch. I think starch dissolves in warm/hot water....  so dissolve the sugar in water at room temp and filter. It might take some time to dissolve all of the sugar at room temp.

I do not know what 'confectioners sugar' is. From what you wrote it sounds like a mixture of starch and sugar.

[RDX]

You were right. Confections sugar is sugar and corn starch. I've done what you've asked and mixed room temp water with it. It's all been dissolved, so to answer your question: YES corn starch is soluble.

 I've decided to put it in the freezer to cool it down and see if any of the starch will settle at the bottom, but I don't think it's going to work.

I understand you all have lives and this isn't very important to me, but it's just been on my mind lately. Can it be done? I'm curious... I've searched the internet, but couldn't find anything.

[billnotgatez]

...  Confections sugar is sugar and corn starch ... YES corn starch is soluble ...

Could it be a suspension of starch and a solution of sugar?

I wonder what the result would be if you used 100 proof grain vodka (other than a waste of good vodka)?

By the way ,as a side note, have you seen this article?
https://www.scientificamerican.com/article/bring-science-home-gooey-gels/

[Furanone]

Sugar is a general term but usually refers to sucrose (table sugar), the disaccharide of glucose and fructose bound together. Invert sugar is made when a dilute acid and heat is used to break the glycosidic bond with the liberated monosaccharides of glucose and fructose. Regardless, both will remain soluble in a solution of 80% methanol and 20% water.

Starch is also a general term and can refer to many forms of starch or starch products (especially when listed on the ingredient list). If it is uncooked "native" starch then it will be in a granule form totally insoluble, and will precipitate in 100% water without needing freezing, only sufficient time. Granular starch is visible under a microscope and this can usually help to determine the botanical type of starch it is (ie corn, potato, wheat, tapioca, rice, etc) based on its size and shape. If the starch has been heated above that botanical type of starch's gelatinization temperature, then it will no longer be in the granule form as the granules rupture and the polymer molecules of amylose and amylopectin (both very long chains of glucose) become solubilized in the aqueous solution and this is accompanied with a dramatic increase in solution viscosity. However, in a solution of 80% methanol and 20% water, these polymers will precipitate losing all viscosity, so this is an easy way to separate the sugars from any water-soluble polymers such as amylose and amylopectin. When these polymer molecules are precipitated and dried to a powder again, this is called pregelatinized starch (as used in instant puddings).

However, another form of starch still is called maltodextrin, which is either acid or enzyme (amylase) digested starch. Here the amylose and amylopectin polymers are degraded to much smaller molecular weight chains of glucose (on average about 10 glucose units) so maltodextrin is very soluble in water. With a 80% methanol and 20% water solution, much of the maltodextrin will remain soluble with any sugars, but some of the largest digested chains of glucose will precipitate. Separating the smaller, most soluble fragments of maltodextrin will be very difficult without using something like column chromatography or some other advanced method. If your starch solution in water is non-viscous when above 2% concentration, then it is likely maltodextrin as the form of starch in solution (if as you say it is fully soluble -- no granules).

A simple test for seeing if your separation was successful is using an iodine solution (tincture of iodine from medicine cabinet) and dripping into the sugar and starch solution. If there is any granule starch, pregelatinized starch or maltodextrin in your solution it will turn a purple-blue colour (if amylose and amylopectin are in solution) or a pinkish-red colour (if only amylopectin without amylose is in solution with this called waxy starch). If there is only a sugar solution, it will not turn bluish-purple or reddish-pink, only a very faded yellow-brown colour as the original colour of the iodine solution is.

Here is a short video showing the heat gelatinization of potato starch granules into solubilized amylose and amylopectin, if you are interested:

https://www.youtube.com/watch?v=Kl95yJ3tnA4

[billnotgatez]

@Furanone
can one use ethanol rather than methanol

[P]

Maybe you will find a temperature where the starch crashes out and the sugar stays in solution..  not sure though without knowing what the starch is exactly. Good luck though.

[Furanone]

@Furanone
can one use ethanol rather than methanol

Yes, of course ethanol or isopropanol can be used for this precipitation of the polymers, although since these are slightly more hydrophobic solvents than methanol the usage level may be slightly less than 80% in the water, and I have never optimized this.

The reason I only mentioned the 80% methanol in 20% water is because it is a very common, rapid extraction technique for metabolite profiling using GC-MS. You never want to gum up a GC injection liner or the GC column with polymers, and 80% methanol has been proven to work well in removing the unwanted larger molecules, while the remaining sugars, amino acids and organic acids can be quickly derivatized with MeOX then MSTFA (to make volatile) and then injected on the GC-MS for a wealth of information about your sample (Macro level-a metabolite fingerprint of your sample, and Micro level- many individual metabolites will give information about growing conditions including geographic region & climate, processing conditions, possible adulteration, etc.)

[billnotgatez]

I had suggested ethanol since it is less toxic and I think the OP is doing this as a home lab experiment.

[billnotgatez]

Maybe using Everclear Grain Alcohol 190 Proof and diluting it to the needed strength might be the less toxic method.