Aqueous solutions of 5 ppm HgCl2 were prepared at pH values of 3, 5, 9, and 11. The solution at pH =3 contained 1 mM HCl, the solution at pH = 5 contained 10 µm HCl, the solution at pH = 9 contained 10 µm NaOH, and the solution at pH = 11 contained 1 mM NaOH. A 5 ppm solution of HgCl2 was also used without adjusting the pH; this sample is referred to as the neutral sample (pH = 6.99). The mercury solutions were added to the silica gel coated with poly(S-r-limonene) and sampled and analyzed by CVAAS according to the general protocol described in 1.2.4.