# Talk:M9 salts

At first I thought that this discrepancy may have arisen due to a miscalculation somewhere down the line brought about by the difference in molecular mass between Na2HPO4$\cdot$7H2O and Na2HPO4, but I did a little digging and it seems that the real difference is who you trust more: Sambrook or Miller. The [Sambrook protocol] for 5x M9 salts uses 64g Na2HPO4$\cdot$7H2O while the [Miller protocol] for 5x calls for 30g Na2HPO4 (hence 60g Na2HPO4 in most 10x recipes).