Flotation-spectrofluorimetric determination of phosphate in natural water using Rhodamine B as an ion-pair reagent

Abstract

A sensitive and accurate spectrofluorimetric method is described for the determination of phosphate in natural water using Rhodamine B as an ion-pair reagent. A Rhodamine Bmolybdophosphate ion pair was floated as a membrane-like substance at the phase boundary between the aqueous phase and a diethyl ether phase. After the aqueous phase had been discarded, the excess of Rhodamine B extracted into the diethyl ether was removed by shaking with 25 ml of 1 .O M hydrochloric acid. The floated ion pair was dissolved by the addition of methanol to the diethyl ether phase. The determination of phosphate was performed by measuring the fluorescence intensity of the organic phase at 573 nm with excitation at 554 nm. The calibration graph was linear up to 0.25 pg of phosphorus with a correlation coefficient of 0.999. Although arsenic(\/) caused a positive error, no ions commonly existing in natural water, including silicate, interfere with the determination of phosphate. The proposed method was applied to the determination of phosphate phosphorus in some natural water samples.

Phosphate Determination in Aqueous Samples by Complex Formation with Rhodamine B

“…Initial experiments were performed to understand the light absorption, fluorescence and light scattering properties of the dissolved Rhodamine Bmolyb date complex. The fluorescence properties of Rhodamine B are well known, however relatively few papers have been published on the light scattering properties of the Rhodamine B complex with molybdo-phosphate (R-B-Mo P) [26][27][28][29][30][31]. A wavelength scan was performed to observe the spectral properties this complex.…”

“…Excitation of the extracted complex was achieved at 554 nm and fluorescence was measured at 573 nm. The formation of aggregate species in the aqueous phase between Rhodamine B and molybdo-phosphate results in the formation of an ion pair that scatters incident light [26,27]. The reaction for this complex has been described as follows [28]:  Therefore, quantification of phosphate in aqueous samples has been achieved by determining the intensity of scattered light using a fluorimeter and with a laser-scattering detector at 40°.…”

A membrane extraction method for trace level phosphate analysis

“…12 It is well known that PAMB and phosphomolybdate are anionic species that form ion pairs with organic cations such as a cationic dyes and quaternary ammonium ions. [13][14][15] In our previous work, ion pair formation was employed for the spot test for phosphate analysis, where PAMB was entrapped on the packing material in a mini column with a blue color band formed in the column. The packing materials were silica gel or polyvinyl chloride (PVC) particles coated with quaternary ammonium ions.…”

An online solid phase extraction method for the determination of ultratrace level phosphate in water with a high performance liquid chromatograph

“…Other methods for detecting trace phosphate are solvent extraction of PAMB; complex formation of PAMB with cationic dyes such as rhodamine (Frank et al, 2006;Nasu and Minami, 1989;Taniai et al, 2003), crystal violet (Fogg et al, 1977), or malachite green (Susanto et al, 1995a,;1995b); and flow-injection analysis (APHA, 1999;Dinz et al 2004;Estela and Cerdà, 2005;Mesquita et al, 2011;Ribeiro et al, 2013). Ultratrace levels of phosphate have also been detected by flow-injection analysis systems combined with PAMB-complex formation with a cationic dye (Li et al, 2005;Motomizu and Li, 2005;Susanto et al, 1995;Zhang and Chi, 2002;Yaqoob et al, 2004;).…”