Abstract
We describe a new on-line sensitive and selective procedure for the determination of trivalent and hexavalent chromium in liquid samples by a tailor-made contactor (TMC), specifically a liquid membrane annular TMC, coupled with inductively coupled plasma with optical detection. The TMC was designed and developed to integrate the extraction and stripping phases of the analyte in one module to minimize the membrane solvent’s consumption and maximize the speed of transport through the liquid membrane. Moreover, the particular geometry studied, which consists of two coaxial hollow fibers, allows the TMC to be used for both separating and preconcentrating purposes. Both (−)-N-dodecyl-N-methylephedrinium bromide (30 mM) in dichloroethane and HNO3 (0.75 M) were used as the liquid membrane and receiving solution, respectively. The proposed method’s performance was evaluated in terms of the hexavalent chromium extraction efficiency and the coefficient of variation percentages; these were higher than 85% and less than 5%, respectively. In addition, the proposed procedure was applied to two real samples: a tap water sample and an eluate from solid urban waste. In both cases, the analytical performances were good and comparable to those obtained using synthetic standard solutions.
Highlights
Chromium (Cr) has a wide range of applications, for example, in stainless steel industries; in several chemical industries for the production of pigments, explosives, ceramics, anticorrosive and antiseptic products; and in the galvanic and tanning industries [1,2,3].This intensive use of Cr has led to a considerable release of the element into the environment, often as waste [4,5]
The most common off-line methods consist of separation steps and preconcentration (by ion exchange columns, liquid–liquid, solid phase extraction (SPE), high-performance liquid chromatography (HPLC)), followed by flame atomic absorption spectrometry (F-AAS) [16,17,18,19], graphite furnace atomic absorption spectrometry (GF-AAS) [20,21,22], electrothermal atomic absorption spectrophotometry (ET-AAS) [23,24], voltammetry [25,26], inductively coupled plasma optical emission spectrometry (ICP-OES) [27,28,29,30] or mass spectrometry (ICP-MS) [31,32,33]
An on-line method such as a fiber-packed column coupled to F-AAS [34], a flow-injection system, which combines an F-AAS [35] or ET-AAS [36], and on-line preconcentration of Cr species by SPE–HPLC–ICP-MS [37] were proposed
Summary
Chromium (Cr) has a wide range of applications, for example, in stainless steel industries; in several chemical industries for the production of pigments, explosives, ceramics, anticorrosive and antiseptic products; and in the galvanic and tanning industries [1,2,3] This intensive use of Cr has led to a considerable release of the element into the environment, often as waste [4,5]. It is necessary to use sensitive and selective analytical techniques that can separate and measure the two species even at very low concentrations on the order of μg/L. Due to their different environmental behavior, the regulations require, in certain cases, different limits for the two chemical forms. This species is transported from a starting solution (feed) to an arrival solution (receiving) by two exchange processes at the interfaces with a liquid membrane
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