# Talk:M9 salts

(Difference between revisions)
 Revision as of 12:48, 9 June 2007 (view source) (→$Na_2HPO_4 \cdot 7H_2O$ Versus $Na_2HPO_4$)← Previous diff Current revision (22:39, 9 June 2007) (view source) (→Miller Vs. Sambrook) (3 intermediate revisions not shown.) Line 2: Line 2: (MDolinar) (MDolinar) - == $Na_2HPO_4 \cdot 7H_2O$  Versus  $Na_2HPO_4$ == + == Miller Vs. Sambrook == - I think that this may be explained by the additional mass of 7 waters associated with each Na_2HPO_4.  The molecular weight of Na_2HPO_4 is about 142g/mol, while that of $Na_2HPO_4 \cdot 7H_2O$ is about 268g/mol.  So 5x M9 salts could be made with either 64g/L $Na_2HPO_4 \cdot 7H_2O$ (according to Sambrook) or 33.9g/L Na_2HPO_4--the concentration will be the same.  Then if you double this for 10x salts, you would end up needing 67.8g/L, which is close to the 60g/L given in the standard 10x recipes.  I can only wave my hands at the 7.8g discrepancy and say that someone goofed or altered the recipe slightly. (dcekiert) + 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$7H2O and Na2HPO4, but I did a little digging and it seems that the real difference is who you trust more: Sambrook or Miller.  The [http://openwetware.org/wiki/M9_salts[Sambrook protocol]] for 5x M9 salts uses 64g Na2HPO4$\cdot$7H2O while the [http://www.changbioscience.com/protocols/recipe/M9salts10X.htm[Miller protocol]] for 5x calls for 30g Na2HPO4 (hence 60g Na2HPO4 in most 10x recipes). + + In the end, the two recipes are only slightly different when you take the difference in hydration into account.  When you make 1x medium from 10x Miller M9, you end up with ~42mM Na2HPO4, while 1x medium made from 5x Sambrook M9 leaves you with ~48mM Na2HPO4.  Presumably, this is close enough. + (dcekiert) + + ==References== + + J. Sambrook, D.W. Russell, ''Molecular Cloning: A Laboratory Manual'' (Cold Spring Harbor Laboratory Press, New York, ed. 3, 2001) pg. A2.2 +
J. Miller, ''Experiments in Molecular Genetics'' (Cold Spring Harbor Laboratory Press, New York, 1974) pg. 431

## Current revision

The 5x M9 salts recipe here seems to be almost identical to the 10x M9 salts protocol we use in our lab and which I also found elsewhere (see e.g. http://www.changbioscience.com/protocols/recipe/M9salts10X.htm and http://www.atcc.org/mediapdfs/2057.pdf). It could be that bacteria don't mind if they get the double of salts, but it might nevertheless be interesting to know what conc. of salts would be best to use... (MDolinar)

## Miller Vs. Sambrook

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).

In the end, the two recipes are only slightly different when you take the difference in hydration into account. When you make 1x medium from 10x Miller M9, you end up with ~42mM Na2HPO4, while 1x medium made from 5x Sambrook M9 leaves you with ~48mM Na2HPO4. Presumably, this is close enough. (dcekiert)

## References

J. Sambrook, D.W. Russell, Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Laboratory Press, New York, ed. 3, 2001) pg. A2.2
J. Miller, Experiments in Molecular Genetics (Cold Spring Harbor Laboratory Press, New York, 1974) pg. 431