Chemistry lesson - A guide to mmols

[Matt Cycle]

Today's lesson. Our daily blood glucose (in the UK at least) is measured in mmol/l and we all know what it is supposed to be but what is the measurement - mmol? The HbA1c is measured in mmol/mol - but what is that? After all, we all know what a gram and a litre are. Sad person I am I remember asking at the clinic many years ago and was told (quite obvious from the name I suppose) it is to do with molecules and atoms. Now it's over 30 years since I did any chemistry ( 😱 ) but the internet has come to the rescue again and I've found the following 'easy' guide to mmols written for nurses. Every day is a school day.

http://www.nursingtimes.net/student-nt/an-easy-guide-to-mmols/5041362.fullarticle

 

[Matt Cycle]

Oh bugger, it allowed me to read the article at first but now it says I must register. If any can see it can you copy the text and post it. 🙂

 

[Matt Cycle]

Had to register here it is:

Every nurse is familiar with seeing mol, mmol and occasionally µmol written on vials and infusion packs.

But it appears that many are unfamiliar with what they actually mean. Here is a small crash course in the mole!

Let’s take any medication; in this case let us look at something simple like a sodium chloride solution.

Sodium chloride (NaCl) is a salt made up of molecules which contain one sodium (Na) atom for every one chlorine (Cl) atom (a molecule is a collection of atoms to make a substance).

Because molecules are very small and atoms even smaller we cannot measure their weight in grams or even milligrams. To overcome this, the weights of atoms are measured in Atomic Mass Units (amu), molecular weights are a combination of the weight of all the atoms in that molecule. An amu is equivalent to 0.000000000000000000000000001g so using grams to express the weight of molecules would be a nightmare!


In the example here, NaCl, the molecular weight of one molecule is the sum of 23 (average weight of sodium atoms) and 35.45 (average weight of chlorine atoms) to give a weight of 58.45 amu. But we are never going to be dealing with only one molecule at a time.

This is where the concept of a mole comes from.

One mole is used to describe the number of atoms that are required so that the weight of the sample is equal to the atomic weight in grams, i.e.: one mole of NaCl weights 58.45g. This quantity of atoms is 602,214,150,000,000,000,000,000 (let’s call this number N). These figures are getting bigger and harder to handle so can you see why we refer to things in moles?

While mole describes the physically number of atoms we have to hand, mol is a unit to describe the concentration. If we have one mole of NaCl (58.45g) dissolved in one litre of water, this gives us a concentration of one mol. Similarly, if we only dissolve 5.845g of NaCl in one litre than this has a concentration of 0.1 mol (or 100 mmol, a mmol is a thousandth of a mol).

Finally, let’s put it all together at look at a saline solution. The bag will often say 0.9% w/v, this means that for every one litre of water there is 9 g of NaCl dissolved in. If one mole is 58.45g, then 9g is 0.154 moles (0.154 x N molecules). Now that we dissolve this into water, it becomes a concentration - 0.154 moles in 1 litre is a 154mmol solution.

This principle does not just apply to administered medication, but to anywhere you see a concentration written. Another example where this unit “mmol” is seen is blood sugar results. What exactly does that “3.9 mmol” reading mean? It means in each litre of blood there are 3.9 millimoles of glucose. If one mole of glucose is 180.16g, then the concentration of glucose in the blood is 0.7g/ litre.

Keep an eye out for any mol/mmol labels you see today and just think of the billons of trillion of atoms floating in that solution!

Dr. Julie Ann Lough has a Ph.D. in chemistry from the University of Warwick, specialising in potential anticancer agents (cisplatin derivatives). She has an interest in publicising the science of everyday life and has previously presented on BBC radio and television.

 

[Northerner]

Keep an eye out for any mol/mmol labels you see today and just think of the billons of trillion of atoms floating in that solution!

Of course, there is another explanation...



Once upon a time
In a little earthen hole,
Lived a tiny little creature
Whose name was Milly Mole.

She had a thousand cousins who,
If laid limb to limb,
Could fill a litre measuring jug
Right up to the brim!

Their life was one of tedium
Within the mole-filled lands,
Until one day they chanced upon
A scientist wringing his hands.

He said, ‘My goodness, look at you!
You’re just the perfect size
For me to measure sugar voles –
I can’t believe my eyes!’

‘What do you mean?’ said Milly Mole
And all her cousins too,
‘We’d never even heard of sugar voles
Till we met you!’

‘Let me explain’, the scientist said,
‘And all will soon be clear.
The sugar voles live in the blood
And are a source of fear.’

‘They like to live in people’s cells
But sometimes can’t get in
Because they need to wear a coat
Of shiny insulin.’

‘There are some people who produce
Some droplets of this stuff
But as their cells have sticky doors
It’s never quite enough’

‘For some, their poor old Pancreas
Has given up the ghost,
And they produce no insulin
For when they need it most.’

‘The sugar voles remain outside
And there their numbers grow,
But if they cannot count them all,
The people never know.’

‘There used to be a way if they
Could pee upon a stick –
But it wasn’t very sociable,
And it wasn’t very quick!’

‘And so I’ve made a meter which,
With just a drop of blood,
Can count up all the sugar voles,
Or, at least it could…’

‘I need something to live inside
And, when the blood comes in,
To count how many sugar voles
Can balance on a pin!’

‘And when you know, dear Milly Mole,
How many voles you’ve seen,
Why, then you’d type the number up
And show it on a screen!’

‘The people then would know the truth,
And they could make a start
To save their kidneys, eyes and limbs,
And hopefully, their heart!’

Well, Milly and her family
Said they could hardly wait
To help the humans count their voles –
They thought it would be great!

So, when you take that drop of blood
And place it on the meter,
Remember please, the Milly Moles –
A thousand to the litre!

 

[Matt Cycle]

Ha, that explanation is a bit easier to follow. Not sure what my chemistry or biology teacher would have thought of it though.

 

[trophywench]

Can't speak for science teachers, but as one of their O level students in the past - my eyes still glazed over about a third of the way through it ......