Organic Ion-associate Phase Extraction/Back-microextraction for the Preconcentration and Determination of Lithium Using 2,2,6,6-Tetramethyl-3,5-heptanedione by Liquid Electrode Plasma Atomic Emission Spectrometry and GF-AAS in Environmental Water

Abstract

We developed an ion-associate phase (IAP)-extraction / acid back-extraction system for the pre-concentration and atomic spectrometric determination of lithium trace amounts in water.The chelating reagent for lithium works also as a constituent of the extraction phase.The lithium in a 10 mL sample solution was converted through a chelate complex reaction with 2,2,6,6-tetramethyl-3,5-heptanedione (HDPM). Addition of a benzyldimethyltetradecylammonium ion caused the formation of an IAP suspension in the solution. Centrifugation of the solution led to the isolation of a liquid organic phase and the lithium complex was extracted as the upper phase from the centrifuge tube. After the aqueous phase was removed, lithium was back-extracted with a 400 µL nitric acid solution from the IAP.The acid phase was measured using liquid-electrode-plasma atomic-emission-spectrometry (LEP-AES) or graphite-furnace atomic-absorption spectroscopy (GF-AAS). The detection limits were 0.02 mg/L for LEP-AES and 0.02 g/L for GF-AAS. This system was applied to the determination of environmental waters.The HDPM in the organic phase was reusable.requires only 20 L of sample. Like many atomic spectroscopic methods, both LEP-AES and GF-AAS are affected by the matrix, so some pretreatment such as separation and concentration is required.Separation and pre-concentration methods that take advantage of the small sample volume required by both LEP-AES and GF-AAS include cloud point extraction, 7, 8 dispersive liquid−liquid extraction, 9, 10 thermoresponsive polymer-mediated extraction, 11 and homogeneous liquid-liquid extraction. 12,13 These techniques are based on the dependence between equilibration temperature and time, 7, 8 the use of chloroform or chlorobenzene as an extraction solvent, 9, 10 the application of heat, 11 or the use of a fluorine-based surfactant. 12,13 In this study, we develop an ion-associate phase extraction method 14 with improved sensitivity and discerning ability against the matrix, and apply it to atomic spectroscopy. 15 This technique converts the analyte in the environmental water into an appropriate form, if necessary, and adds an organic anion and an organic cation to form an ion-associate. The resulting ion-associate phase (IAP) is separated by centrifugation and the aqueous phase is discarded. The Analytical SciencesIAP is dissolved in an organic solvent, 15 and a mixed solution consisting of an organic solvent and acid, 6 back-extracted with acid, 16 and the analyte is then measured through atomic spectroscopic methods.The hydrophobic chelating agent, DPM, acts as the organic anion in the developed IAP.The combination of IAP extraction and back extraction is the best combination for lithium pre-concentration and LEP-AES measurement. Therefore, we used this method to measure lithium in seawater by LEP-AES and in river water and spring water by GF-AAS. River water and spring water were measured by GF-AAS because the concentration of lithium is more than an order of magnitude lower than seawater and cannot be measured...

Evaluation of an Ion-Associate Phase Formed In Situ from the Aqueous Phase by Adding Benzethonium Chloride and Sodium Ethylbenzenesulfonate for Microextraction

“…The organic anions considered were benzenesulfonate, TS − , 4-toluenesulfinic acid, EBS − , 2,4-dimethylbenzenesulfonate, and alkylsulfonate (CnH2n+1SO3 − , CnS − , n = 6-8). The IAP formed from some of the examined anions with Zephyramine floated [5,7], whereas those formed…”

“…The organic anions considered were benzenesulfonate, TS − , 4-toluenesulfinic acid, EBS − , 2,4-dimethylbenzenesulfonate, and alkylsulfonate (C n H 2n+1 SO 3 − , C n S − , n = 6-8). The IAP formed from some of the examined anions with Zephyramine floated [5,7], whereas those formed from Ben often formed at the bottom of the aqueous phase [5,[9][10][11]. In the latter case, the IAP can be separated from the aqueous phase by decanting after centrifugation.…”

“…The detection of chemicals in environmental water samples often requires pretreatments such as the separation and concentration of water [1][2][3][4]. Organic ion-associate phase (IAP) microextraction is one such pretreatment [5][6][7][8][9][10][11][12]. In ordinary solvent extraction, water and organic solvents are mutually soluble, allowing a maximum increase in concentration of approximately 40 times the initial concentration [13,14].…”

“…However, to the best of our knowledge, no study has yet elucidated the optimum concentration of the reagents used to form the solvent. In the IAP extraction system used in this study, at least one of the components of the IAP is a synthetic dye [5,6], chelating reagent [7,8], or pH buffer [9][10][11]; consequently, their concentrations are often already predetermined and only the counterion concentration need be altered. In these systems, the ratio of organic cations to organic anions (the constituents of the IAP) is not 1:1 [5,7,8], possibly because the ionization state of many of the components depends on the pH.…”

“…In the IAP extraction system used in this study, at least one of the components of the IAP is a synthetic dye [5,6], chelating reagent [7,8], or pH buffer [9][10][11]; consequently, their concentrations are often already predetermined and only the counterion concentration need be altered. In these systems, the ratio of organic cations to organic anions (the constituents of the IAP) is not 1:1 [5,7,8], possibly because the ionization state of many of the components depends on the pH. We assume that the IAP contains some form of neutral AppliedChem 2023, 3 33 molecular species; therefore, to investigate the formation of IAPs independent of pH in a simple system, we searched for an organic cation source among quaternary ammonium salts, which are not affected by pH.…”