It is not possible to bulk ionize some liquid substance to produce a plasma at ambient pressure. The temperatures required to produce the plasma are greater than the vaporization temperatures of anything we have on hand- so, the stuff vaporizes before it ionizes.
At the center of the sun, the density of the plasma is of order ~150 grams/cc which is 150 x the density of water, but since there is nothing you could possibly make a pipe or bucket out of that could withstand the temperature there, the "liquidness" of that substance can only be inferred by studying the transmission of pressure waves around the insides of the sun. This is called helioseismology and the results from that field indicate that the sun's core behaves much like a liquidan ideal gas under tremendous pressure.