If you're concerned about the quality of the MSM (Organic Sulphur) you are purchasing, there are a number of factors to take into account. Firstly, there are grades to help you determine the intended use. Animal grade is for animal use only. Food grade is for human consumption, within limits, and is of low quality. Pharmaceutical grade is for human consumption and is of high quality.
In case you're wondering, MISMO MSM is pharmaceutical grade, which is the highest quality.
You also want to make sure there are no additives or fillers included in the product either. An easy way to determine this is the water will NOT be clear once the MSM is dissolved. Pure MSM will always be clear when it dissolves. MISMO MSM is absolutely pure with no fillers, additives or anti-caking agents.
Another point to consider is the water filtration of the MSM. Both MISMO MSM products use water that has been treated by a reverse osmosis process which ensures an extremely high water quality This is also a point of difference for MISMO MSM.
One final point to note, there are different types of MSM; Pure-Crystalline MSM and Distilled Ultra-Pure MSM. Universally, Distilled MSM is accepted as the purest form as it goes through a 4 stage distillation process. Alternatively, MSM Powder is manufactured using a crystallisation process. You can read more about the two different manufacturing processes here.
MISMO stocks Pure-Crystalline MSM and Distilled Ultra-Pure MSM, both of which are pharmaceutical grade.