Spectrophotometric Determination of Trace Amounts of Fluoride Using an Al-Xylenol Orange Complex as a Colored Reagent

Abstract

A new spectrophotometric reagent for the determination of trace amounts of fluoride has been introduced. This method is based on the decolorization of a complex of Al(III) with xylenol orange (XO) as an ultra-sensitive colored reagent. Since the Al-XO complex plays an important role in this method, the protonation and complexation of XO with Al(III) at an ionic strength of 0.1 mol L -1 at 25 C has been studied by a spectrophotometric global analysis method. The EQUISPEC program was used to evaluate the protonation constants of XO and the stability constants of the formed complexes with Al(III). The protonation and the stability constants of the major complex species such as ML, MLH and MLH2, were determined. Finally, a spectrophotometric method for the assay of fluoride based on a decrease of the color intensity of the Al-XO complex, in an aqueous solution has been designed. The effects of some important variables on the determination of fluoride based on the proposed method were investigated. The method was applied to the determination of fluoride under the optimum conditions (pH 5.2, ionic strength 0.1 mol L -1 , 25 C). The determination of fluoride in the range of 0.08 -1.4 μg mL -1 (SD = 1.2%) was successfully performed. Interferences of Fe(III) were easily eliminated by using ascorbic acid. The proposed method was applied to the determination of trace amounts of fluoride content of some real water samples.

Research on a new spectrophotometric method for determinating trace amounts of fluoride

“…Absorption spectroscopies of XO in the range of pH ≥ 5.5 have two peaks at 430 nm and 574 nm. The cause of this problem is probably due to the contributions of H3Q -, H2Q 2-, HQ 3-, Q 4-(They are the ions of XO reagent at different pH) [7].…”

“…The most common methods for fluoride assay are potentiometry using a fluoride selective electrode [5], ion chromatography method [6], and zirconium-alizarin method. Several other methods have been reported for the determination of fluoride in water, such as using resorcin blue complexes [1], using a complex of aluminum and xylenol orange (Al-XO) as a colored reagent [7], using capillary electrophoresis, using solvent extraction coupled to fluorometry [8,9]. Because of some advantages of spectrophotometric methods, such as accuracy, simplicity and reproducibility, we have been interested to design a new spectrophotometric method for the determination of trace amounts of fluoride in water.…”

“…Based on the research by Javad Zolgharnein [7], we noticed that his method using a complex of aluminum and xylenol orange as a colored reagent for the determination of trace amounts of fluoride is quite good, because the relative standard deviation of the method was 1.6%. The principle of his method is based on the reaction of fluoride with a complex of aluminum ion and xylenol orange reagent (Al-XO).…”

4 , 5-Dinitrochrysazin Complexes : Slovatochromism and Fluoride Determination in Jenin Groundwater Wells

“…Given their particular advantages (such as simplicity, facility, accuracy and reproducibility), spectrophotometric methods are widely used in the determination of fluoride (Zolgharnein et al, 2009). They are based on the reaction of fluoride with coloured metal chelate complexes, either producing a mixed-ligand ternary complex or replacing the ligand with fluoride to give a colourless metal-fluoride complex and a free ligand with a colour different from the metal-ligand complex (Einaga and Iwasaki, 1981).…”

Application of a new version of GA-RBF neural network for simultaneous spectrophotometric determination of Zn(II), Fe(II), Co(II) and Cu(II) in real samples: An exploratory study of their complexation abilities toward MTB

“…However, the fact that it undergoes a dissociation of six steps is almost confirmed. Xylenol orange is structurally very similar to MTB, but different mechanisms have been suggested for its deprotonated pathway[54,55].MTB possesses nine functional groups comprising of a sulfonic, a ketone, four carboxylic, a phenolic and two amine functional groups. Thus, the fully protonated form of MTB is displayed by LH9 .…”