I put 1.000g of glucose powder into a 1 L volumetric flask and filled the flask to the 1L line with room temperature distilled water.
I then inverted several times for 10 minutes to mix until there was no visible glucose crystals left and tested the solution using an oxidase glucose strip. Even though the glucose was all clearly dissolved, the reading I got after 10 minutes were only around 40 mg/dl. I waited an hour and the readings were now about 65 mg/dl. After 2 hours the readings were averaging about 125 mg/dl, a value that remained stable after 4 hours, and after 12 hours.
First off, the actual concentration was 100 mg/dl, but the test strip and glucometer estimate blood glucose, and real blood has other components that will effect that reading, so the reading of about 125 was not unexpected, but WHY might it take 2 full hours to achieve a peak and stable glucose reading from the solution?
The only ideas I had were that 1) the "dextrose" powder (lab grade) that I used MIGHT have been in polysaccharide form, maybe some monomers combining to make di- or tri-saccharides in the container which were able to hydrolyze in distilled water at room temp. I don't think this can happen without enzymes though. Perhaps some yeast enzymes in the air could have gotten in and done the job. 2) The glucose molecules had some degree of oxidation which made them un-affective to the test strip, but that the oxidation reversed in solution over time. This also doesn't make sense since I don't expect oxygen to spontaneously bond to a glucose molecule nor reverse without a catalyst. 3) maybe the glucose molecules bond loosely to something like carbon dioxide or nitrogen that comes off gradually in the solution.
I have repeated several times with the same results and time frame. The stable/peak glucose reading did seem to occur faster with warm water but reached the same peak value. I can't imagine that the powdered glucose is not completely dissolved short of 2 hours.