Sensitive determination of chromium (VI) in paint samples using a membrane optode coupled to a multisyringe flow injection system

In this work, the potential of a membrane optode coupled to a multisyringe flow injection system (MSFIA) was assessed for determining the Cr(VI) concentration in paint samples. The detection is based on the color obtained from the reaction of Cr(VI) with 1,5-diphenylcarbazide in the presence of sulfuric acid (H2SO4). The redox product was immobilized on a poly(styrene-divinylbenzene) (SDB-XC) membrane optode. The analyte in the sample was then directly quantified at the surface of the disk by measuring the intensity of reflected incident light using a bifurcated optical fiber at 540nm. Experimental parameters (concentration of reagents, sample volume, flow rate of sample solutions, eluent concentration, and effect of diverse ions) were studied in detail. The overall time required for the complete procedure was 4min and only required 0.2mL of the sample volume. The dynamic working response of Cr(VI) was found within the concentration range of 2.4–1000μgL−1 with a limit of detection (LOD) of 0.7μgL−1, while the relative standard deviation (RSD) for 400μgL−1 Cr(VI) was lower than 2% (n=6). This developed method was used to determine Cr(VI) concentrations in the paint samples, for which an alkaline extraction procedure was proposed. The extraction procedure was based on the use of a 7.5% Na2CO3/5% NaOH solution at 90°C for 30min. Under optimal conditions, the recoveries ranged from 99% to 101%. The complete method was validated using a certified reference material (ERA-QC540, soil sample) and by comparing the results with those obtained using atomic absorption spectrometry (AAS). ► A membrane optode coupled to a multisyringe flow injection system (MSFIA) enrichment procedure. ► Determination of Cr(VI) in paint samples. ► Alkaline extraction procedure>low sample/reagent consumption, and high selectivity sensitivity.