Mineral salts and chelates: elemental content is the number you are buying

A quote for magnesium citrate at a given price per kilo tells you almost nothing until you know its elemental magnesium content. The compound is what ships; the element is what you formulate against.

The arithmetic that catches people out

Mineral compounds carry the mineral plus whatever it is bound to, and that binding partner is often the majority of the weight. Elemental content varies enormously between forms of the same mineral:

• Magnesium oxide — roughly 60% elemental magnesium.
• Magnesium citrate — roughly 16%.
• Magnesium bisglycinate — roughly 14%, and lower again for buffered grades.

To deliver 100 mg of elemental magnesium you need about 167 mg of the oxide or about 714 mg of the bisglycinate. The bisglycinate is not simply more expensive per kilo — it takes four times as much of it. Comparing the two on compound price alone is comparing nothing at all.

Buffered and blended grades

"Buffered" bisglycinate is the chelate blended with an oxide to raise elemental content and lower cost. That is a legitimate material, widely sold, and there is nothing wrong with buying it — as long as you know that is what it is. The elemental figure on the specification should always be accompanied by the form it comes from.

If a chelate quote looks unusually strong on elemental content for its price, ask directly whether it is buffered and in what proportion. A straight answer is a good sign about the rest of the relationship.

What belongs on the specification

• The compound, named precisely — magnesium bisglycinate, not "magnesium chelate".
• Elemental content as a percentage, with the assay method, typically ICP-OES or ICP-MS.
• Whether the grade is buffered, and with what.
• Heavy metals — lead, cadmium, arsenic and mercury limits. Mineral sources are the ingredient class where these matter most, because the contaminants and the active come from the same geology.
• Particle size and bulk density, which decide whether the material blends and fills at all.

Quote on the element

The cleanest way to compare mineral suppliers is to ask every one of them to quote a price per kilogram of elemental mineral delivered, alongside the compound price. It takes one line in the enquiry and removes the single most common source of confusion from the whole exercise.