Why might my Residual Solvent retest results show higher results after I purged them longer?

Concentrates (extract, essential oil, resin, BHO, CO2, waxes, shatters, budders, etc.) are almost always viscous liquids or even solids. Residual solvents get trapped or dissolved in the concentrate during the manufacturing process when the solvent is present in large amounts. Solids and viscous liquids with many components, such as cannabis extracts, are inherently heterogeneous because the different components can segregate differently at different temperatures and pressures and the rate of diffusion or mixing is very low. Even a process whereby the extract is heated to make it less viscous (flows faster) and stirring vigorously does not guarantee homogeneity. Among other reasons, when the extract is cooled back down, things may separate differently in different parts of the sample. That means sampling from different parts of the batch can give different results. To ensure that the test results are representative of a batch, it is important to submit samplings from many different regions of the batch - top, bottom, left, right, middle, etc. If only one test is desired, the client should mix those different samplings well in the container to be submitted and our techs will do their best to make sure the material submitted is stirred and sampled appropriately in the lab. However, even taking all of these measures into account, expect some variability from test to test. That means a test run after some extra purging might return a result even higher than the first test, before the additional purging (if the purging was inefficient).

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