Cloud Point Extraction Techniques for Metal Ion Analysis

Cloud point extraction (CPE) exploits the phase separation of non-ionic surfactants above a defined temperature, the cloud point, to concentrate and isolate metal ions from aqueous samples. In a typical procedure a surfactant is added to the sample and heated above its cloud point, inducing the formation of a micellar surfactant-rich phase and a dilute aqueous phase. Metal ions are complexed with chelating agents or chromogenic reagents to enhance their affinity for the micellar phase, enabling preconcentration factors of up to two orders of magnitude. Parameters such as surfactant type and concentration, temperature, ionic strength (salting-out), pH and ligand concentration are systematically optimised to maximise recovery and selectivity. The method offers an eco-friendly alternative to conventional organic-solvent extraction, reducing toxic waste while providing compatibility with spectrophotometric, atomic absorption and chromatographic detection techniques. Recent advances include micro-cloud point extraction at ambient temperature, mixed-micelle systems to tune selectivity, and integration with ultrasonic or microwave assistance for rapid phase separation. CPE has found broad application in monitoring trace levels of zinc, copper, nickel, cobalt and mercury in environmental and biological matrices, underlining its global significance for water quality and health assessment.

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Research from all publishers

In one study a micro cloud point extraction protocol was developed for the simultaneous preconcentration of zinc, copper and mercury from water samples without external heating. A non-ionic surfactant formed a micellar phase at room temperature, achieving limits of detection below 0.5 µg L−1 for each metal. The procedure simplified phase separation through rapid centrifugation and demonstrated recoveries in excess of 95% for environmental monitoring. Another approach employed mixed-micelle extraction to isolate trace nickel prior to graphite furnace atomic absorption spectrometry. By combining an anionic surfactant with Triton X-114 and optimising pH, surfactant ratios and incubation time, the method achieved a detection limit down to 0.03 ng mL−1 and a relative standard deviation of 2.1%. A foundational work introduced a cloud point method for cobalt determination in natural waters via complexation with a dithiocarbamate ligand. Under optimised conditions the technique delivered a detection limit of 0.5 µg L−1 and an enhancement factor of 67, illustrating CPE’s versatility across diverse metal ions and analytical platforms.

Cloud Point Extraction Techniques for Metal Ion Analysis publication trend

The graph below shows the total number of articles in cloud point extraction techniques for metal ion analysis across all publications each year (not limited to Nature Index journals).

Technical terms

Cloud point extraction (CPE): A separation technique in which non-ionic surfactant solutions become turbid and separate into surfactant-rich and aqueous phases when heated above a characteristic temperature.

Non-ionic surfactant: A surface-active agent lacking charged groups that forms micelles above a critical concentration and drives phase separation at the cloud point.

Micellar phase: The surfactant-rich layer that concentrates hydrophobic complexes or chelated metal ions after phase separation.

Preconcentration factor: The ratio of analyte concentration in the micellar phase to that in the initial sample, indicating the degree of enrichment.

Salting-out: The addition of electrolytes to decrease surfactant cloud point temperature and promote phase separation, enhancing extraction efficiency.

References

1. Determination of Zinc, Copper, and Mercury in Water Samples by Using Novel Micro Cloud Point Extraction and UV-Vis Spectrophotometry. Eurasian Journal of Analytical Chemistry (2016).
2. Determination of Trace Nickel in Water Samples by Graphite Furnace Atomic Absorption Spectrometry after Mixed Micelle-Mediated Cloud Point Extraction. Molecules (2018).
3. Development of a Cloud‐Point Extraction Method for Cobalt Determination in Natural Water Samples. Journal of Chemistry (2012).