Speciation analysis of chromium in water samples through sequential combination of dispersive magnetic solid phase extraction using mesoporous amino-functionalized Fe3O4/SiO2 nanoparticles and cloud point extraction

• New nonchromatographic approach for preconcentration/redox speciation of chromium with FAAS detection was developed.
• Mesoporous amino-functionalized Fe3O4/SiO2 nanoparticles retain selectively Cr(VI) specie.
• Cloud point extraction was used for Cr(III) preconcentration using 4-(2-thiazolylazo)resorcinol as chelating agent.
• Redox chromium speciation without changing sample pH or addition of oxidizing/reducing agents.

The present paper describes the sequential combination of dispersive magnetic solid phase extraction (DMSPE) with cloud point extraction (CPE) as a new nonchromatographic approach for preconcentration/redox speciation of chromium with FAAS detection. The method is based on sequential preconcentration of Cr(VI) at pH 5.0 onto mesoporous amino-functionalized Fe3O4/SiO2 nanoparticles followed by cloud point extraction of Cr(III) as metallic complex with 4-(2-thiazolylazo)resorcinol (TAR). The variables that play an important role on the performance of both preconcentration methods were thoroughly optimized by means of factorial design. Under optimized condition, an aliquot of 45.0 mL of sample was preconcentrated onto 25 mg of magnetic nanoparticles during 1 min following the elution with 0.5 mL of 2.5 mol L− 1 HCl. The supernatant containing Cr(III) was then subjected to CPE procedure, which was accomplished by using thermostatic bath at 90 °C during 45 min, 5.8 × 10− 4 mol L− 1 TAR and 0.3% (v/v) Triton X-114. The method provided preconcentration factors of 16 and 12 times yielding limits of detection (LOD) and quantification (LOQ) of 1.1 and 3.6 μg L− 1 for Cr(VI) and 3.2 and 10.5 μg L− 1 for Cr(III), respectively. A high tolerance toward potentially interfering ions (cations and anions) and humic acid was observed for the method. Precision (n = 10) of the procedure determined as relative standard deviation (RSD) were, 5.8 and 3.7% for Cr(III) using solutions at 15.0 and 165.0 μg L− 1 and 5.5 and 3.0% for Cr(VI) using solutions at 15.0 and 75.0 μg L− 1 concentrations, respectively. The applicability of method was attested by analysis of water samples yielding good recovery values (91.4–103.5%). The accuracy of method was also checked for biological samples using a certified reference material DORM-3 (Fish Protein Certified Reference Material for Trace Metals).