A new highly selective, sensitive, and rapid procedure to determine ng ml^–1 level of Hg(II) depended on the speed reaction of Hg²⁺ with 5-amino-2-(phenyldiazenyl)phenol (I) and/or 5-amino-2-(p-tolyldiazenyl)phenol (II) and the solid phase extraction (SPE) of the colored complex with a reversed phase polymer-based C18 cartridge have been developed. The I and/or II reacted with Hg²⁺to form a violet complex of a molar ratio 2: 1 [I and/or II to Hg²⁺] in the presence of 3.0 M of nitric acid solution and Triton X-100 medium. This complex was enriched by SPE with a polymer-based C18 cartridge. The enrichment factor of 200 was achieved. The molar absorptivity of the complex are 8.81 x 10⁸ and 9.57 x 10⁸ L mol^−1 cm^−1 at 626 and 649 nm, using I and/or II, respectively Beer’s law is  obeyed in the range of 2.5 – 200 ng ml^–1, whereas the optimum concentration ranges obtained from Ringbom plot was 10 – 175 ng ml^–1. The detection and quantification limit are given as 0.75 and 2.37 ng ml^−1 for I_, whereas their values for II are 0.80 and 2.48, indicating that a nanogram fraction of Hg²⁺can be determined. The relative standard deviation was 1.45 and 1.34 % using I and II, respectively, obtained from a series of 10 standards each containing 100 ng ml^−1 of Hg²⁺. This procedure was applied successfully to