What is a soluble carbonate?
All carbonates are insoluble except for those of the alkali metals...That's the general rule.
As a matter of fact, lithium carbonate is not terribly soluble in water, and is less soluble in water than
Ammonium salts are generally soluble. However, ammonium carbonate might be be better proposed as
Sometimes, tetraphenyl borate salts are used to precipitate ammonium ion, however, these salts are very expensive, and are not used in teaching laboratories.