Why did I fail for residual solvents?

Vacuum seals can fail, valves in your vacuum system could be left open or closed, batches can get mixed up in processing and be under-purged, vacuum oven heating elements can fail. Different extraction solvents have different volatilities, so if you recently switched from iso-butane to n-butane you will need to lengthen your purge time.

There are several variables you can manipulate to improve the thoroughness of a purge program, the most important of  which is surface area per gram, or “specific surface area”. Like most physical and chemical processes, more surface area makes things go faster. Second to surface area is viscosity. Viscosity can work for you or against you. A more viscous product will tend to purge slower due to its slow flow rate. That said, a highly viscous product can be given a shape (through kneading or bubble addition) to increase its surface area and will hold that shape during purge. Viscosity depends both on the purge temperature and the product’s chemical make-up. A product with low viscocity and enough added heat will convect, which will expose new surface area and purge faster than if not heated. The following is a list of common names for concentrate consistencies ranked roughly in order of increasing surface area per gram (not comprehensive): shatter and pull-snap, sugar wax or “budder”, large-bubble honeycomb wax, small-bubble honeycomb wax or snap-wax.

If you’re trying a new purge process, a new product consistency, or you’ve changed your gas, or are in any way unsure if you’ve passed residual solvents, send in a sample for R&D residual solvent testing before you go for the I-502 test package. It is better to pay for one residual test than it is to go through the hassle of getting an LCB-authorized retest for the I-502 product.