Electrochemical probe for total determination and speciation of selenium (IV& VI) species in water, drug formulations and foodstuffs using Thoron–I as selective chelating agent

The present study reports a highly sensitive, selective and cost effectiveness-sensing probe for total determination and speciation of selenium (IV & VI) species in complex matrices. The established probe was based upon controlled electrolysis of Se 4+ -Thoron – I chelate at hanging mercury-dropping electrode (HMDE) combining adsorptive differential pulse-adsorptive cathodic stripping voltammetry (Ads DP-CSV) and measuring the consequent cathodic peak currents (I p,c ) at −0.5 and − 1.1 V vs. Ag/AgCl electrode in aqueous solution of pH 2. At the optimal conditions of peak potentials at −0.5 and − 1.1 V, the plots of I p,c versus Se 4+ concentration were linear over the concentrations range 6.3 × 10 −9 –8.2 × 10 −8 and 5.0 × 10 −12 - 1.45 × 10 −10 M with limits of detection (LOD) and quantification (LOQ) of 1.6 × 10 −12 M and 5 × 10 −12 M of Se 4+ , respectively. The sensing probe was favorably used for detection of trace levels of Se 6+ after reduction to Se 4+ . The probe also displayed excellent sensitivity and selectivity towards detection of selenium species in water, foodstuffs and drug formulations. The probe was validated by analysis of selenium in certified reference material (CRM, IAEA- Soil-7) and in drug formulations. The average recoveries for the spiked water samples were ranged from 99.4 ± 0.60 to 110.0 ± 6.3. The probe was also validated by comparing the results with the inductively coupled plasma–optical emission spectrometry (ICP-OES) data using Student t and F tests at 95 % probability. Sequential and total determination of trace levels of inorganic Se 4+ and/or Se 6+ was also achieved by the proposed probe. Ads DP-CSVs and the corresponding calibration plots at peak potentials of −0.5 V (A) and − 1.1 V (B) at various concentrations (6.3 × 10 −9 –8.2 × 10 −8 and 5.0 × 10 −12 - 1.45 × 10 −10 M) of Se 4+ ions in B-R buffer solutions of pH 2 at HMDE versus Ag/AgCl electrode, respectively. Conditions; Deposition time = 120 s; deposition potential = −0.4 V; starting potential = −0.4 V; scan rate = 50 mV/s; pulse amplitude =60 mV and Thoron–I concentration = 4.3 × 10 −6 M. • A superficial electrochemical probe for total determination and speciation of Se 4+ & Se 6+ species has been established. • The probe displayed LOD and LOQ of 1.6 × 10 −12 M and 5 × 10 −12 M of Se 4+ , respectively. • Wide linear concentrations range (6.3 × 10 −10 –8.2 × 10 −8 and 5.0 × 10 −12 - 1.6 × 10 −10 M) of Se 4+ versus cathodic peak currents was achieved. • The sensing probe was applied for the analysis of selenium content in water, cow's milk and Mushroom samples.