Supporting Electrolyte Manipulation for Simple Improvement of the Sensitivity of Trace Vanadium(V) Determination at a Lead-Coated Glassy Carbon Electrode

Abstract

The paper presents a very simple way to extremely improve the sensitivity of trace V(V) determination. The application of a new supporting electrolyte composition (CH3COONH4, CH3COOH, and NH4Cl) instead of the commonly used acetate buffer (CH3COONa and CH3COOH) significantly enhanced the adsorptive stripping voltammetric signal of vanadium(V) at the lead-coated glassy carbon electrode (GCE/PbF). A higher enhancement was attained in the presence of cupferron as a complexing agent (approximately 10 times V(V) signal amplification) than in the case of chloranilic acid and bromate ions (approximately 0.5 times V(V) signal amplification). Therefore, the adsorptive stripping voltammetric system with the accumulation of V(V)–cupferron complexes at −1.1 V for 15 s in the buffer solution (CH3COONH4, CH3COOH, and NH4Cl) of pH = 5.6 ± 0.1 was selected for the development of a simple and extremely sensitive V(V) analysis procedure. Under optimized conditions, the sensitivity of the procedure was 6.30 µA/nmol L−1. The cathodic peak current of V(V) was directly proportional to its concentration in the ranges of 1.0 × 10−11 to 2.0 × 10−10 mol L−1 and 2.0 × 10−10 to 1.0 × 10−8 mol L−1. Among the electrochemical procedures, the lowest detection limit (2.8 × 10−12 mol L−1) of V(V) was obtained for the shortest accumulation time (15 s). The high accuracy of the procedure was confirmed on the basis of the analysis of certified reference material (estuarine water) and river water samples.

Adsorptive Stripping Voltammetry for Determination of Vanadium: A Review

“…The complexing agents used in the voltammetric analysis of vanadium are listed in Table 1 , together with the detection limits obtained. The most commonly chosen complexing agent in voltammetric procedures for the determination of vanadium is cupferron [ 45 , 46 , 47 , 48 , 49 , 50 ]. Other complexing agents are also used, such as chloranilic acid [ 51 , 52 , 53 , 54 ], catechol [ 55 ], chromoxane cyanine R [ 56 ], alizarin violet [ 57 ], pyrocatechol [ 58 ], 2,3–dihydroxybenzaldehyde [ 59 ], galic acid [ 60 ], pyrogallol [ 61 ], quertic–5–sulfonic [ 62 ] and 2,3–dihydroxynaphthalene [ 63 ].…”

“…In the case of cupferron concentration optimization, it has been observed that initial additions of cupferron to the sample solution result in a rapid increase in the vanadium signal, while higher cupferron concentrations result in a slower increase [ 45 , 48 ]. Higher concentrations of the complexing agent may also cause adsorption of the free ligand instead of the formed complex, which blocks the surfaces of the working electrode [ 51 ].…”

“…In the papers [ 45 , 46 ], the concentration of cupferron was optimized in the range from 5 × 10 −6 mol L −1 to 4 × 10 −5 mol L −1 , with a concentration of 2 × 10 −5 mol L −1 used for further research. It turned out that the concentration selected as the most optimal in the works [ 47 , 48 ] was 7 × 10 −5 mol L −1 . The lowest concentration of cupferron 8 × 10 −5 mol L −1 was used in the work [ 49 ], while the highest concentration of 1 × 10 −3 mol L −1 was selected in the vanadium determination procedure using BiµFE as the working electrode [ 47 ].…”

“…Much cheaper and simple methods are voltammetric techniques [ 39 , 40 , 41 , 42 , 43 , 44 ]. The method of choice is adsorptive stripping voltammetry (AdSV), which is also used to determine vanadium in natural samples [ 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 ]. The most important parameters and characteristics of these procedures are summarized and presented in Table 1 .…”

“…In the case of the use of stripping voltammetry in the determination of vanadium, AdSV is mainly used, whereby various complexing agents that form electrochemically active complexes with VO 2 (+) are used and undergo adsorption on various working electrodes. As can be seen in Table 1 , dozens of such procedures have been described in the literature, with vanadium detection limits ranging from 2.8 × 10 −12 to 1 × 10 −7 mol L −1 [ 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 ]. In the case of vanadium determination, anodic stripping voltammetry (ASV) is very rarely used, in which the determination is based on redox reactions associated with the change in the oxidation state of vanadium, and few papers on this are available in the literature [ 41 , 44 ].…”