Chromium speciation in natural waters using serially connected supported liquid membranes

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Separation Science

Background:

• Chromium speciation is crucial for environmental risk assessment due to differing toxicities of Cr(III) and Cr(VI).
• Existing methods for chromium speciation can be complex and time-consuming.
• Supported liquid membranes (SLMs) offer a promising approach for selective ion extraction and preconcentration.

Purpose of the Study:

• To develop and optimize a novel supported liquid membrane (SLM) method for the selective speciation and determination of chromium species.
• To evaluate the efficiency of two different SLM systems for extracting anionic Cr(VI) and cationic Cr(III).
• To assess the stability of chromium species in water samples under various storage conditions.

Main Methods:

• Utilized two serially connected SLM units with specific carriers: di-(2-ethylhexyl) phosphoric acid (DEHPA) for Cr(III) and methyltricaprylammonium chloride (Aliquat) for Cr(VI).
• Optimized membrane parameters including sample pH, acceptor solution composition, and carrier concentration in organic solvents.
• Employed graphite furnace atomic absorption spectrometry (GFAAS) for the final quantitative determination of chromium species.

Main Results:

• Achieved high extraction efficiencies: 90% for Cr(III) using DEHPA and 40% for Cr(VI) using Aliquat.
• Demonstrated the method's applicability by analyzing chromium speciation in surface water from a contaminated tannery site.
• Identified optimal sample preservation conditions at neutral pH for maintaining chromium speciation stability over one month.

Conclusions:

• The developed SLM method provides a selective and efficient approach for chromium speciation analysis.
• The method exhibits a low detection limit of 0.01 µg/L, suitable for environmental monitoring.
• Understanding chromium speciation and stability is vital for accurate environmental assessment and remediation strategies.