Quantification of vanadium species in vanadium-fortified apples by liquid chromatography hyphenated with inductively coupled plasma atomic emission spectrometry

Vanadium is an essential trace element, but in contrast to many other essential transition elements, functional vanadium compounds have so far been detected only in the form of vanadium nitrogenases and vanadate-dependent haloperoxidases in a comparatively restricted number of organisms [1]. Vanadium may be beneficial in humans, since vanadium ions can play a role in biology as counterions for protein, DNA, RNA, and in various biological organelles [2]. Vanadium species ability to lower the blood sugar by inhibiting the phosphotyrosine phosphatase enzyme in fat cells of liver and muscle has been reported. Accordingly, V(IV) can contribute to reducing diabetic symptoms [3]. However, vanadium species can be toxic at high concentrations. Biological effects as well as toxicity are related to vanadium speciation. In particular, V(V) as vanadate has been known to be more toxic than V(IV) as vanadyl ion. Thus, the vanadium speciation is critical for the health risk assessment of the vanadium exposure. Anyhow, since the essentiality of vanadium species for humans has not been proven, WHO/FAO does not recommend the addition of vanadium substances to food [4].

A group of researchers from South Korea report about the appearance of vanadium-fortified apples in their fruit markets. These vanadium-rich apples are suggested to be beneficial to health particularly by helping insulin metabolism of human consumers. In order to analyse such apples for their vanadium content as well as vanadium speciation, they developed a method for speciation analysis. Vanadium was extracted from dried apple samples (1.0 h powder) with 10 ml of 3 mM EDTA solution assisted by ultrasonic irradiation (each 2 min, 10 times). The supernatant obtained after centrifugation was filtered through a 0.2-µm syringe filter, diluted with distilled water to a final volume of 20 ml. This final sample solution was then fed to the RP-HPLC column for species separation. Detection and quantification of separated species was obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES). Vanadium was found to be accumulated exclusively in the peel part, not the flesh, and its chemical form was identified to be V(IV). The average concentration was 0.61 +- 0.01 mg/kg.

The authors concluded, that the apple peel should be taken to get the postulated health benefit of the enriched vanadium. They also believe that the developed method can be applied to analyse other fruits or vegetables for vanadium species.

[1] Dieter Rehder, The role of vanadium in biology, Metallomics, 7 (2015) 730-742. DOI: 10.1039/c4mt00304g

[2] D. C. Crans, J. J. Smee, E. Gaidamauskas, L. Yang, The Chemistry and Biochemistry of Vanadium and the Biological Activities Exerted by Vanadium Compounds, Chem. Rev. 2004,104, 849-902. DOI: 10.1021/cr020607t

J. F. Jen, S. M. Yang, Simultaneous speciation determination of vanadium( IV) and vanadium(V) as EDTA complexes by liquid chromatography with UV detection, Anal. Chim. Acta, 289 (1994) 97-104. DOI: 10.1016/S0003-2670(96)00482-5