When you start to buy separate minerals you quickly find that understanding the purity, percentage, elemental composition and the trace element content of items like magnesium oxide can be very confusing. Many sellers describe their products as 99.9% pure but what exactly does this mean?
When you buy ready mixed supplements you have no idea of the quality of the minerals used. Where a mineral such as magnesium is supplemented in high amounts it is important that a high quality source is used to avoid heavy metal contamination.
This brief article has been written to help explain some of the numeric terminology you will come across.
Purity sometimes referred to as assay or potency is the easiest one to explain. Purity is always expressed as a percentage and simply indicates how much of the desired substance is present. For example imagine I had 100 grams of salt that was only 50% pure my 100g would actually contain only 50g of salt and 50g of other impurities mixed together. Similarly if I had 100 grams of salt that was 99% pure it would contain 99g of salt and 1g of impurities.
This one is a little more difficult and requires a basic understanding of chemistry.
If we take salt as an example again; the chemical formula of salt is NaCl and it consists of the elements sodium (Na) and chlorine (Cl). Atomic weight is an intrinsic property of an element and is embodied in the periodic table of elements. The atomic weight of sodium, Na = 23 and the atomic weight of chlorine, Cl = 35.5. Salt consists of one sodium atom and one chlorine atom and therefore the molecular weight of salt, NaCl = 23+35.5 = 58.5. The elemental composition of sodium in salt is therefore 23/58.5 = 0.393 multiplying by 100 gives this as a percentage i.e. 39.3% and similarly the elemental composition of chlorine in salt is 35.5/58.5 = 0.607 or 60.7%. Putting this another way 100g of pure salt will contain 39.3g of elemental sodium and 60.7g of elemental chlorine.
Let’s work through another example in this case magnesium oxide; the chemical formula of magnesium oxide is MgO and it contains one magnesium atom (Mg) and one oxygen atom (O). The atomic weight of Mg = 24.3 and the atomic weight of O = 16, therefore the molecular weight of magnesium oxide, MgO = 24.3+16 = 40.3 and the elemental composition of magnesium in MgO is therefore 24.3/40.3 = 0.603 or 60.3% and the elemental composition of oxygen in MgO is 16/40.3 = 0.397 or 39.7%. Therefore 100g of pure magnesium oxide will contain 60.3g of elemental magnesium and 39.7g of elemental oxygen.
Trace elements are tiny quantities of impurities present in minerals, you could call them the ‘hidden’ amounts of minerals you don’t want like iron. You find out the levels of trace mineral impurity in products by looking at the Certificate of Analysis. Because the levels are so low the quantities of trace elements present are often quoted in parts per million or ppm.
One part per million (1ppm) is literally 1 divided by a million that is 1/1000000. We can express this number as a percentage by multiplying by 100 so as a percentage 1ppm = 0.0001%. This may seem so small to be meaningless but in the mineral world this level of detail really matters. For example I may purchase some magnesium oxide that is described as having a purity of 99.9% containing 60.3% elemental magnesium, perfect you may say! But let’s look again and ask ourselves what is the remaining 0.1% of impurities in that magnesium? If it were iron for example 0.1% is equivalent to 1000ppm.
When you are buying any supplement for your horse whether it be a single mineral or a mix as a supplement or a premix added to a concentrate feed it is worth considering impurity content. You might just be feeding something which has a high level of impurity and particularly where iron is concerned adds to your horses burden.
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