Glucose Analysis Titration

This video demonstrates the analysis of glucose through a pair of redox titrations. First, the glucose solution is reacted with a known excess of triiodide. After a short reaction period the remaining triiodide is quantified through a titration with thiosulfate. The amount of glucose in the solution can be determined from the difference in the number of moles of triiodide used and the number of moles that reacted with thiosulfate. The endpoint of this titration is made visible through the addition of starch, which turns blue when complexed with triiodide.

Category:

Education

Tags:

• Glucose
• Thiosulfate
• Triiodide
• Starch
• Redox
• Titration
• Chemistry
• Analytical

[rozibean]

Hi,

I want to do this reaction for my chemistry investigation in year 13 at school.

I was wondering if you think measuring the glucose levels in bananas, or another 'blendable' fruit, will work?

And what volumes of each solution should be used?

[crharrison]

@rozibean Though the reaction should work with any source of glucose there could be some significant problems with the starch that is naturally present in the bananas (and other fruits). Since there needs to be a five minute reaction period where the triiodide is mixed with the sample this could result in the triiodide binding irreversibly and making the colour change very difficult/impossible to see; though you would not need to add any starch to the solution. (continued below)

[crharrison]

@rozibean One option you may want to consider, though this may be a bit more costly and may not fit with the scope of what your project requires, is that you could use a blood glucose meter (test kit for diabetics) to measure the glucose concentration in the blended fruit (you may not even have to blend it). Good luck.

[k4yah91]

Hi,

has any one actually performed this?

Any chance if someone can tell me instructions/measurements/equi­pment etc...

Maybe the equation for this reaction.

Thanks!

[crharrison]

@k4yah91 The reaction ratio between the glucose and triiodide is 1:1. For the titration of the excess triiodide, two moles of thiosulfate are required for every mole of triiodide.

And yes, the reaction has actually been performed, this was a lab I had my undergraduate students do for a couple of years.

[rishmiester]

What ratios of Glucose react with the iodide?

[crharrison]

The glucose-triiodide reaction ratio is 1:1.

[jancrism]

Good day, Dr. Harrison

Can i I request for a copy of your glucose analysis stating the procedures on how to prepare the reagents (starch indicator and concentrations or amount of triiodide, NaOH, HCl used)..How did you prepare the titrant thiosulfate? last question sir, how can i calculate the amount of glucose present in the solution based on the titrant consumed?

Here is my email address sir, jancrism@gmail.comThank you very much.