 Thus, by manipulating firstly the concentration of the weak acid, and secondly that of its conjugate base, the pH of the extracellular fluid (ECF) can be adjusted very accurately to the correct value.The bicarbonate buffer, consisting of a mixture of carbonic acid (H2CO3) and a bicarbonate () salt in solution, is the most abundant buffer in the extracellular fluid, and it is also the buffer whose acid to base ratio can be changed very easily and rapidly.An acid–base imbalance is known as acidaemia when the acidity is high, or alkalaemia when the acidity is low.