(50% yeast, 25% water, 25% glycerin) is all you need to freeze Yeast.
The calcium buffer is not needed. If the ph is too high or low the dead yeast will even it out. All the yeast will not die. Chloride ions may affect the beer, but I am not sure, so it is best to leave them out as I know they are not needed.
And freeze in a NON-"frost-free" freezer. You do not want the thaw cycles. If your freezer is frost free keep your frozen yeast samples in a small styrofoam cooler packed with freezer packets so that the thaw cycles will not affect your yeast.