Ions in 5th analytical group of cations form carbonates that are insoluble in water. The reagent usually used is (NH)CO (at around 0.2 M), with a neutral or slightly basic pH. All the cations in the previous groups are separated beforehand, since many of them also form insoluble carbonates.
The most important ions in the 5th group are Ba, Ca, and Sr. After separation, the easiest way to distinguish between these ions is by testing flame colour: barium gives a yellow-green flame, calcium gives brick red, and strontium, crimson red.