well, to explain it first, AR grade is Analytical Research Grade and LR is lab Research Grade. AR grade is purer than LR, but the % of impurities is not known. not to me atleast. however, considering the fact that LR grade is used in results which are considered standards for various things, the impurities cannot be too high. My question is, is using LR grade ok? cause the AR grade is much more expensive. For ex. the Potassium meta bisulphite AR grade is more than double the price of the LR grade and i dont wanna end up spending extra if i can help it.