<P> Common ion effect of H+ ions is thus, required for less concentration of sulphide ions . </P> <P> 3rd analytical group of cations includes ions that form hydroxides which are insoluble even at low concentrations . The reagents are similar to these of the 2nd group, but separation is conducted at pH of 8--9 . Occasionally, a buffer solution is used to ensure this pH . </P> <P> Cations in the 3rd group are, among others: Fe, Fe, Al, and Cr . </P> <P> The group is determined by making a solution of the salt in water and adding ammonium chloride and ammonium hydroxide . Ammonium chloride is added to ensure low concentration of hydroxide ions . </P>

What modern techniques are used as the basis for grouping