Determination of Cadmium in Water Samples by Automated Flow-Batch Cloud Point Extraction (CPE) Hyphenated to High-Resolution Continuum Source Flame Atomic Spectrometry (HR-CS FAAS)

Abstract

A computer-controlled multicommuted flow-batch system is reported that allows for the online cloud point extraction of metal ions followed by high-resolution continuum source flame atomic absorption spectrometric (HR-CS GFAAS) detection. This approach combines reduced sample and reagent consumption and a short analysis time with the increased precision and sensitivity characteristic of flow-batch analysis and modern extraction techniques. As proof of concept, cadmium in aqueous solutions was determined by the formation of a hydrophobic complex [Cd(PAN)₂]. Parameters related to complex formation (pH, pyridyl-azo-naphthol-PAN concentration, complexation time), cloud point extraction (Triton X-114 concentration, electrolyte composition, rich phase trapping), and the multicommuted flow-batch system (flow rates, timing control) were optimized. A small column packed with hydrophobic cotton was used as the interface between the extraction and detection stages to stack the cadmium-containing rich phase in a short plug. Optimized parameters led to a 5.0 to 75.0 µg L⁻¹ linear range, 1.3 µg L⁻¹ limit of detection, 4.3 µg L⁻¹ limit of quantification and 1.8% coefficient of variation (n = 12). Accuracy was evaluated by analyzing a certified reference material EP-H (drinking water) and by recovery tests employing tap water, groundwater, mineral water, and reuse water samples.

Keywords:

• Cadmium
• cloud point extraction
• flow-batch analysis
• high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS)
• metal pre-concentration

Conflict of interest statement

The authors declare no conflicts of interest.

Additional information

Funding

The authors are grateful to the FAPESP (São Paulo Foundation Research – 2011/19730-3, 2016/23878-0 and 2015/11.523-0) and CAPES (Coordination of Superior Level Staff Improvement – Finance Code 001) for financial support and Multiuser Central Facilities (UFABC) for experimental support. I. Gaubeur thanks CNPq (National Research Council) for a grant (308586/2018-2).