MONG, Ash and Moisture: The Impurity Numbers That Decide Glycerin Grade

When a glycerin specification sheet lands on a buyer's desk, the headline figures are usually purity and colour. The numbers that actually decide whether a shipment behaves well in production sit further down the page: MONG, moisture, ash and chloride. These four move together, and together they say more about the refining route behind the drum than any single purity figure.

MONG is the honest measure of what refining removed

MONG stands for matter organic non-glycerol. It captures everything in the sample that is organic but is not glycerol: residual fatty acids, mono and diglycerides, fatty esters, and the smaller fragments left behind when a feedstock is poorly stripped. Because it is measured by difference after subtracting water, ash and glycerol, it is the least flattering number on the sheet. Refined material typically sits below 0.5 percent; crude material can run several percent. When MONG creeps up, the usual cause is a heavier feedstock or a distillation step run too fast, and the effect shows up downstream as odour, haze or a shorter shelf life.

Moisture moves first and moves furthest

Glycerol is hygroscopic. A drum opened in a humid warehouse will pick up water across the headspace within days, and an IBC left with a loose lid will do the same on a slower curve. For USP and EP grades the ceiling is usually around 5 percent; food grade is often tighter. Moisture above spec does not only dilute the glycerol. It shifts viscosity, changes the refractive index that incoming QC may rely on, and gives any residual ester the water it needs to hydrolyse. Storage discipline is therefore part of the specification, not separate from it: keep tanks blanketed, keep drums sealed, and re-test after any transfer that exposes the product to air.

Ash and sulphated ash point at the refining route

Ash measures the inorganic residue left after ignition. In glycerin it is mostly sodium or potassium salts carried over from neutralisation, plus traces of catalyst. Sulphated ash gives a slightly different picture because the treatment converts some salts into sulphates. Values are small, commonly under 0.01 percent for refined grades, but the trend matters more than the absolute figure. A supplier whose ash drifts upward between lots is usually telling you something about wash efficiency rather than about raw material.

Chloride and colour as supporting evidence

Chloride deserves attention in material intended for pharmaceutical or food use, and in any glycerin that will contact stainless steel at elevated temperature. Colour, expressed as APHA or a Gardner equivalent, is the quickest field indicator: fresh refined glycerin reads close to water-white, and a shift toward yellow after storage usually means heat exposure, air ingress or trace metal contamination rather than a new feedstock. Reading colour alongside MONG catches most of the problems a purity figure alone would hide.

Turning the numbers into a purchasing decision

The practical approach is to ask for a certificate of analysis per lot, then compare the same four numbers across three or four consecutive deliveries instead of judging a single sheet. Consistency inside a narrow band is worth more than a spectacular one-off result. Ask also how the sample was drawn: a top-of-drum grab and a bottom-of-tank sample describe two different products once moisture and MONG are in play.

SINOFO Group supplies refined and crude glycerin, propylene glycol, fatty acids, fatty alcohols and food ingredients from established producers, with lot-level documentation and technical support on specification questions. If you are qualifying a new glycerin source or reviewing an existing specification, send us your target parameters and we will confirm what our current stock can meet.