Determination of Arsenic by ICP‐OES after Cloud Point Extraction with Salt Induced Phase Separation: Application to Gadolinium Based MRI Contrast Agent**.

A new separation and preconcentration procedure based on cloud point extraction was developed for arsenic trace analysis using inductively coupled plasma optical emission spectrometry. Arsenic in +5 oxidation state was complexed with ammonium molybdate, Triton X‐100 was used as a surfactant. Optimal parameters such as pH value and Triton X‐100 concentration were determined. Phase separation was induced by adding a salting‐out agent to avoid an analyte loss because of temperature changes. The combination of Triton X‐100 with ammonium sulphate as a salting‐out agent was firstly suggested as an extraction system for arsenic quantification. Conditions for arsenic (III) into arsenic (V) oxidation were established. The proposed procedure was successfully applied for arsenic quantification in a gadolinium based magnetic resonance imaging (MRI) contrast agent gadobutrol at the level indicated in the guideline for elemental impurities approved by International council for harmonisation of technical requirements for pharmaceuticals for human use (ICH Q3D) as a limit concentration. [ABSTRACT FROM AUTHOR]