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Non Life Sciences => Chemistry => Topic started by: scientizscht on 07/09/2020 19:42:16

Title: What is the water equivalent of blood glucose concentration?
Post by: scientizscht on 07/09/2020 19:42:16
Hello

I put 1 gram of glucose in 1 litre of water to produce a concentration of 100mg/dl.

I used a regular blood glucose meter to measure the concentration and it showed a "too low" indication which is less than 20mg/dl.

Why this happened? What am I missing? I was hoping that I can use a blood glucose meter to measure glucose in drinks or other solutions but it seems not possible.

Also, what is the glucose concentration in a water solution that is equivalent to the blood glucose concentration of 100mg/dl?

Any idea?

Thanks
Title: Re: What is the water equivalent of blood glucose concentration?
Post by: Bored chemist on 07/09/2020 19:51:19
I'd try adding 0.9% salt.
Title: Re: What is the water equivalent of blood glucose concentration?
Post by: scientizscht on 07/09/2020 21:26:37
I'd try adding 0.9% salt.

How that would change the glucose meter indication?
Title: Re: What is the water equivalent of blood glucose concentration?
Post by: Bored chemist on 07/09/2020 21:31:30
It makes the sample a lot more like blood.
Title: Re: What is the water equivalent of blood glucose concentration?
Post by: scientizscht on 08/09/2020 19:09:01
It makes the sample a lot more like blood.

But the salt won't change the glucose concentration significantly nor it will interfere with the glucose sensor.

So, how will this affect the reading?
Title: Re: What is the water equivalent of blood glucose concentration?
Post by: Bored chemist on 08/09/2020 19:18:01
You haven't provided much information.
So, as usual, you have left us guessing.
There are lots of glucose sensors on the market and we don't know which one you are using.
So, I know that it is meant to work with blood, and you are using it with water, and it's not working.
My suggestion is that you make the water more like blood.

I also  know that some chemical sensors are electrochemical.
A solution of glucose will barely conduct electricity.

Title: Re: What is the water equivalent of blood glucose concentration?
Post by: scientizscht on 08/09/2020 20:32:01
The electrochemical sensors detect the peroxide produced by the glucose and conductivity does not play any role.

Anyway I added the salt and now it displays ERROR, not even TOO LOW.
Title: Re: What is the water equivalent of blood glucose concentration?
Post by: Bored chemist on 08/09/2020 21:27:30
The electrochemical sensors detect the peroxide produced by the glucose and conductivity does not play any role.

Anyway I added the salt and now it displays ERROR, not even TOO LOW.
" conductivity does not play any role."
" it displays ERROR, not even TOO LOW."

Only one of those can be true.
Title: Re: What is the water equivalent of blood glucose concentration?
Post by: evan_au on 08/09/2020 22:38:07
Quote from: Bored chemist
I'd try adding 0.9% salt.
Thinking back to my distant chemistry lessons, I would need to know was this 0.9% by mass, or by molar concentration?
- Is there a convention chemists use when specifying % concentration?

Using the right kind of salt might be important. Have a look at the concentration levels of Sodium, Potassium and bicarbonate in mmol/litre in this graph (you will need to expand it greatly, and scroll down to the bottom left corner).
https://upload.wikimedia.org/wikipedia/commons/d/db/Blood_values_for_print.png
Title: Re: What is the water equivalent of blood glucose concentration?
Post by: Bored chemist on 09/09/2020 15:47:27
The convention, unless someone says otherwise is %m/v

Blood is about 0.9% m/v
Though 0.9% m/m is only about 0.5% rel different. The difference between two people's blood could easily be bigger than that
Not sure how moles would work.
0.9 moles of NaCl in 100 moles of water?
Title: Re: What is the water equivalent of blood glucose concentration?
Post by: evan_au on 09/09/2020 22:03:43
Pardon my ignorance, but could you expand on that a bit?
Quote
%m/v
Does this mean %mass per volume? ...like grams per liter?
Or %moles per volume? ...like moles per liter?

What is the % a fraction of?

Quote
%m/m
Does this mean %mass per mass?
...like grams per 100g total?

For completeness, I recall seeing %v/v: Is this % volume per volume,like ml per 100ml total?
...It's been a long time since I've studied any chemistry!
Title: Re: What is the water equivalent of blood glucose concentration?
Post by: scientizscht on 10/09/2020 19:39:36
It is mostly meant to be grams of solute per 100ml (or grams) of solvent, mostly water.
Title: Re: What is the water equivalent of blood glucose concentration?
Post by: Bored chemist on 10/09/2020 22:41:08
Pardon my ignorance, but could you expand on that a bit?
Quote
%m/v
Does this mean %mass per volume? ...like grams per liter?
Or %moles per volume? ...like moles per liter?

What is the % a fraction of?

Quote
%m/m
Does this mean %mass per mass?
...like grams per 100g total?

For completeness, I recall seeing %v/v: Is this % volume per volume,like ml per 100ml total?
...It's been a long time since I've studied any chemistry!
The m and v stand for mass and volume (you also see w for weight which is pretty much equivalent to mass unless your lab is somewhere odd.

So 0.9%m/v means 0.9 grams of salt in a total volume of 100 ml
(That's not quite the same as 0.9 grams in 100 ml of water. If you mix those the total volume will be slightly different from 100 ml.)
Similarly, 0.9% m/m means 0.9g of salt and 99.1 grams of water.