Novel on-line sequential preconcentration system of Cr(III) and Cr(VI) hyphenated with flame atomic absorption spectrometry exploiting sorbents based on chemically modified silica

► SiO2/Al2O3/TiO2 and SiO2/AAPTMS was used for speciation of Cr(III) and Cr(VI). ► Different kinds of water and parenteral samples at the same pH were analyzed. ► Some shortcomings commonly observed in previous publication we avoided in method. ► Detection limits for Cr(III) (0.66 μg L−1) and Cr(VI) (0.27 μg L−1) were obtained.