I have been making labeling medium for NMR work where I add the following:
K2HPO4 12 g/L
KH2PO4 9 g/L
15NH4Cl 3 g/L
NaCl 2.5 g/L
ISOGRO®-13C,15N, Powder 1 g/L
13C-Glucose 4 g/L
MgSO4 0.5 g/L
H2O 1 L (pH adjusted to ~7.4 with NaOH)
When I adjust the pH to 7.4 I observe a huge precipitation. What is precipitating?