Talanta 66 (2005) 813–817 Short communication Synthesis and analytical application of a novel tetradentate N 2 O 2 Schiff base as a chromogenic reagent for determination of nickel in some natural food samples Ali Reza Fakhari a,∗ , Afshin Rajabi Khorrami a , Hossein Naeimi b a Department of Chemistry, Shahid Beheshti University, Tehran, Iran b Department of Chemistry, Kashan University, Kashan, Iran Received 3 May 2004; received in revised form 25 November 2004; accepted 17 December 2004 Available online 25 January 2005 Abstract A novel sensitive chromogenic reagent, N,N ′ -bis(3-methylsalicylidene)-ortho-phenylene diamine (MSOPD), has been synthesized and used in the spectrophotometric determination of nickel. At pH 8, MSOPD can react with nickel ion at room temperature to form a 1:1 complex. The apparent molar absorptivity is 9.5 × 10 4 l mol -1 cm -1 at 430nm. Beer’s low is obeyed over the range 0–1.0 × 10 -5 M of nickel with a detection limit of 1.36 × 10 -8 M. The relative standard deviation for measurement of 3.41 × 10 -6 M nickel is 1.3% (n = 10). The method has successfully been applied to determination of trace amounts of nickel in some natural food samples. © 2004 Elsevier B.V. All rights reserved. Keywords: Nickel determination; Spectrophotometry; Schiff base; Chromogenic reagent; N,N ′ -bis(3-methylsalicylidene)-ortho-phenylene diamine 1. Introduction The importance of the determination of heavy metal ions, such as nickel, in environment samples can hardly be overem- phasized because they have undoubtedly a serious potential hazard to the human organism. US EPA has classified nickel as one of 13 priority metal pollutants for its widespread use [1]. Also, the knowledge of the nickel content in foods could be of a great interest for the dietary control of nickel-eczema patients. So, the demand for the determination of nickel in biological samples such as plants, foods and similar stuffs is increasing. Several techniques such as atomic absorption [2], atomic fluorescence [3], X-ray fluorescence [4], voltammetric [5,6], electrothermal atomic absorption or inductively coupled plasma mass spectrometry [7,8] have been used for the deter- mination of this ion in different samples. Spectrophotometric ∗ Corresponding author. Tel.: +98 21 2418679; fax: +98 21 2401765. E-mail address: a-zavareh@sbu.ac.ir (A.R. Fakhari). methods based on the UV-visible spectra are widely used due to their simplicity, rapidity, low costs and wide application. The main reagents available for spectrophotometric determination of nickel are dimethyl glyoxime [9], 5,17- bis(quinolyl-8-azo)-25,26,27,28-tetrahydroxy calix[4]arene [10], 5-(6-methoxy-2-benzothiazoleazo)-8-aminoquinoline [11], benzothiaxolyldiazaoaminoazobenzene [12], 2-[2-(5- methylbenzothiazolyl)azo]-5-dimethylaminobenzoic acid [13], p-acetylarsenazo [14], 1-(2-pyridylazo)-2-naphthol-6- sulfonic acid [15], 2-(2-imidazolylazo) phenol-4-sulfonic acid [16], 3-(4-methoxyphenyl)-2-mercaptopropenoic acid [17], 5-(6-methoxy-2-benzothiazoleazo)-8-aminoquinoline [18], 2-(2-benzothiazolylazo)-5-dimethylaminobenzoic acid [19], 7-(4,5-dimethyl-2-thiazolylazo)-8-hydroxyquinoline [20]. However, most of these methods lack sensitivity or selectivity, the procedures are sometimes rather complicated because of the need for extraction to separate interfering ions or expensive surfactants. The Schiff bases derived from salicylaldehyde (salens) as polydentate ligands are known to form very stable complexes 0039-9140/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2004.12.043