Highly Sensitive Spectrofluorometric Determination of Trace Amounts of Mercury with a New Fluorescent Reagent, 2-Hydroxy-1-naphthaldehydene-8-aminoquinoline

Abstract

The principalship of chemical analysis, especially in environmental sciences, is the determination and quantification of harmful substances. The determination of mercury in this type of sample is one of the problems, but, as already acknowledged, is a very important one. Firstly, there is the inherent toxicity of the element at low concentrations (water with a content of over 1 µg L -1 is considered to be contaminated). Secondly, there is the ease with which mercury is biologically transformed into alkyl-mercury compounds, which are longer lasting and more dangerous toxins, 1,2 which can result in death or severe damage to the brain. 3 In recent years, due to its involvement in poisoning incidents, its use in industry has somewhat declined. Despite this, it is still widely used, and is the most ubiquitous of all heavy metals, because it is the only metal that can exist as a liquid and as a volatile form at ambient temperature. It is thus necessary to monitor the mercury levels in products for human consumption and environmental samples.Molecular fluorescence is attracting a great deal of interest in environmental monitoring, since it is inherently more sensitive than spectrophotometry, 31 and thus it can be used for the analysis of very low trace concentrations. As far as mercury is concerned, only a few methods have been described so far for its fluorometric determination. [5][6][7][8][9][10][11][12][13][14] Moreover, the majority of these methods present problems of sensitivity, selectivity, reaction time or procedure complexity. In addition, mercury methods based on increasing fluorescence intensity measurements are scarce, of course, which is the more selective one. 2,4,6,7,10,12,15,16 Previously, several hydrazones, of which salicylaldehyde and 2-hydroxy-1-naphthaldehydene were parent substances, were synthesized in our laboratory. They were used as spectrofluorometric reagents for the determination of aluminum, 17,18 strontium, 19 copper, 20 molybdenum, 21 lead 22 and chromium. 23 In order to increase the degree of molecular conjugation and the coplanar effect of a particular complex, it is necessary to design the molecular structure. In the present work, a new fluorescent reagent, 2-hydroxy-1-naphthaldehydene-8-aminoquinoline (HNAAQ), was synthesized, and its complex with mercury was studied. The fluorescent intensity of the complex was obviously increased by a coplanar effect, and the degree of molecular conjugation, owing to the presence of a naphthalene ring and a quinoline ring at both ends of the reagent's structure. Moreover, according to the Lewis "Hard and Soft Acids and Bases Rules", Hg 2+ is a soft acid and -N=CH-and the pyridine ring are borderline bases. It is therefore very possible and easy that Hg 2+ and N of "-N=CH-" and N of the pyridine ring can be complexed with each other. They formed a steady structure, probably as follows:Based on this complexation, a new spectrofluorometric method with high sensitivity was developed for the determination of mercury. After a concentration step for th...

Spectrofluorimetric determination of aluminium using 2‐hydroxy‐1‐naphthylidene‐(8‐aminoquinoline)

“…The maximum fluorescence intensity was obtained at a mole fraction of Al 3+ of 0.5, confirming that the ratio of Al 3+ :NAQin the complex is 1 : 1. Similar complexation behaviour for HNAQ with other metals was previously reported by Jiang et al (29)(30)(31)(32)(33). Of course, additional exogenous ligands are expected in the coordination sphere to satisfy the required geometry at the metal center.…”

“…Similar complexation behaviour for HNAQ with other metals was previously reported by Jiang et al . (29–33). Of course, additional exogenous ligands are expected in the coordination sphere to satisfy the required geometry at the metal center.…”

“…It has been previously reported (29)(30)(31)(32)(33) that chelation reactions of HNAQ with molybdenum, chromium, lead and beryllium are time-dependent. Therefore, for comparison, the effect of time on the chelation reaction of HNAQ with aluminium was investigated.…”

“…The fluorescent reagent HNAQ has been used previously for the determinations of minute amounts of lead (29) in wheat and rice flour, molybdenum (30) and chromium (31) in porcine liver and muscles, beryllium (32) in mineral water and human hair as well as mercury (33) in waste water and prawns. We present in this paper the spectrofluorimetric determination of aluminium with the fluorigenic ligand 2‐hydroxy‐1‐naphthylidene‐(8‐aminoquinoline) as an extension of the previous studies mentioned above.…”

“…Recently, our research group has been interested in the development of fluorigenic methods for the sensitive and selective monitoring of metal ions in water (10,12,25,27,28). We have observed with keen interest that, over the past few years, the recognition of the fluorescent attribute of 2‐hydroxy‐1‐naphthylidene‐(8‐aminoquinoline), HNAQ, has turned the spotlight on this potentially tridentate hetero‐donor Schiff‐base ligand as a reagent for selective and sensitive spectrofluorimetric determinations of trace amounts of a diverse range of metals and metalloids (29–33). This ligand displays fascinating photophysical properties (34).…”