Chemical Papers 62 (6) 541–546 (2008) DOI: 10.2478/s11696-008-0071-6 ORIGINAL PAPER Investigation of 3-amino-1,2,4-triazole azodye derivatives as reagents for determination of mercury(II) Abdalla M. Khedr* Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt Received 2 October 2007; Revised 21 March 2008; Accepted 21 March 2008 The reaction of mercury(II) with 3-(2,4-dihydroxyphen-1-ylazo)-1,2,4-triazole (HL 1 ), 3-(2- hydroxy-5-methylphen-1-ylazo)-1,2,4-triazole (HL 2 ), 3-(2-hydroxy-5-ethoxycarbonylphen-1-ylazo)- 1,2,4-triazole (HL 3 ), 3-(2-hydroxy-5-acetylphen-1-ylazo)-1,2,4-triazole (HL 4 ), 3-(2-hydroxy-5-formyl- phen-1-ylazo)-1,2,4-triazole (HL 5 ), and 3-(2-hydroxy-5-bromophen-1-ylazo)-1,2,4-triazole (HL 6 ) was studied. A new, direct, and simple procedure was suggested for the spectrophotometric determina- tion of mercury(II) based on its complexation reaction with HL 1 –HL 6 . The best reagent was found to be HL 3 due to its high sensitivity and selectivity. In aqueous media of pH 9.0 containing 40 vol. % of methanol, Hg(II) reacts with HL 3 to form a 1:2 (Hg(II) · HL 3 ) complex having a sensitive absorption peak at 490 nm with the molar extinction coefficient of 3.31 × 10 4 L mol -1 cm -1 using 4 × 10 -4 M of the reagent. Beer’s law is obeyed over the range from 0.00 μg mL -1 to 12.04 μg mL -1 of mercury(II). The proposed method was applied in the determination of mercury(II) in tap water, seawater and synthetic seawater samples, without the need of prior treatment, with satisfactory results. c  2008 Institute of Chemistry, Slovak Academy of Sciences Keywords: azo-triazole, spectrophotometric determination, mercury(II) Introduction Mercury is a toxic element easily absorbed by hu- mans and other organisms; thus, its occurrence in the environment is very harmful to all living organisms (O’Neil, 1995). Mercury content is to be monitored in all areas of modern life in order to prevent the en- vironment from mercury pollution, so the determina- tion of mercury is becoming increasingly important. Spectrophotometry is used for this purpose due to its simplicity and rapidity in analysis. The number of reagents available for the direct determination of mercury is relatively small and most of the known chromogenic reagents require extraction using organic solvents, pre-concentration (Kara & Tekin, 2005; Hos- seini & Hashemi-Moghaddam, 2004), and the use of surfactants (Khan et al., 2005) to increase the sen- sitivity and selectivity or reactants producing toxic cyanides (Feng et al., 1999). In this paper, six deriva- tives of 3-amino-1,2,4-triazole (Fig. 1) were prepared and their reaction with mercury(II) was studied in de- tail. Also, a new method for the direct spectrophoto- metric determination of mercury(II) using HL 1 –HL 6 ligands in a 40 vol. % methanol–water medium is pre- sented. The proposed method has been applied suc- cessfully to the determination of mercury(II) ions in different natural water samples with high precession and good accuracy without the need of extraction, pre- concentration or addition of any surfactants. Experimental Unless otherwise stated, all reagents and solvents used were of analytical reagent grade. Also, bi-distilled and de-ionized water or pure methanol was used for the solution preparation. UV-VIS 240 spectrophotometer (Shimadzu, Japan) was used for absorbance measurements and elec- *Corresponding author, e-mail: abkhedr2001@yahoo.com