Comparison of adsorptive with extractive stripping voltammetry in electrochemical determination of retinol

Milan Sýs,Karel Vytřas,Libor Červenka,Simona Žabčí­Ková

doi:10.5219/713

Abstract

Adsorptive stripping voltammetry (AdSV) of retinol at solid glassy carbon electrode (GCE), carbon paste electrode (CPE) covered by thin layer of multi-wall carbon nanotubes (CPE/MWCNTs) and carbon paste electrode covered by thin layer of single layer graphene (CPE/Graphene) was compared with an extractive stripping voltammetry (ExSV) into silicone oil (SO) as lipophilic binder of glassy carbon paste electrode (GCPE). All types of selected working electrodes were characterized by a scanning electron microscopy to determine overall morphology of electrode surfaces together with spatial arrangement of used carbon particles. The retinol, also known as vitamin A1, was chosen as a model analyte because it is the most biologically active representative of retinoids which are classified as a significant group of lipophilic vitamins. Based on this comparison, it was observed that electrochemical method with high sensitivity (ExSV at GPCE) is generally characterized by shorter linear range of the calibration curve than in case of AdSV at CPE/MWCNTs or CPE/Graphene. Unlike AdSV at solid GCE, all other tested electrochemical methods could represent suitable analytical tools for monitoring of retinoids in different types of foodstuffs. Especially, content of retinol up to tenths milligrams can be easily determined using ExSV. Additionally, negative interference of chemical species present in real samples is minimal in comparison with direct voltammetric methods performed in supporting electrolytes based on organic solvents due to application of accumulation step in "ex-situ" mode.

Highlights

Adsorptive stripping voltammetry (AdSV) of retinol at solid glassy carbon electrode (GCE), carbon paste electrode (CPE) covered by thin layer of multi-wall carbon nanotubes (CPE/MWCNTs) and carbon paste electrode covered by thin layer of single layer graphene (CPE/Graphene) was compared with an extractive stripping voltammetry (ExSV) into silicone oil (SO) as lipophilic binder of glassy carbon paste electrode (GCPE)
According to different variants of deposition steps, analytical methods based on stripping voltammetry can be devided to several variants such as conventional stripping voltammetry with an electroplating step when the accumulation of an analyte on electrode surface is controlled by electrolysis (Hočevar et al, 2007) (i), adsorptive stripping voltammetry (AdSV) when the mentioned accumulation is realized by an adsorption of an analyte on electrode surface (Kalvoda and Kopanica, 1989) (ii), extractive stripping voltammetry (ExSV) where the analyte is extracted from a sample matrix into a paste liquid of a heterogeneous electrode (Wang and Freiha, 1984) (iii) stripping voltammetry based on specific reaction at chemically modified electrodes (Murray et al, 1987) (iv)
It is necessary to state that this kind of analysis includes a lot of time consuming steps such as hydrolysis of lipophilic sample matrix, extraction of vitamins into an organic solvent and own separation

Summary

INTRODUCTION

In food analysis, stripping voltammetry in combination with some pulse electrochemical techniques may offer up ultratrace electroanalytical method comparable to the inductively coupled plasma mass spectrometry (ICP-MS) (Abdel-Galeil et al, 2014), especially in determination of heavy metals (Švancara et al, 2010). As a further example of using the ExSV can be considered voltammetric determination of iodide where corresponding authors called the extraction of the iodide into a carbon paste electrode (CPE) based on tricresyl phosphate (TCP) as synergistic type of accumulation (Švancara et al, 1998). In this case, it is very difficult to determine where an electrochemical reaction of extracted analyte takes place, mostly at the interface between selected paste liquid and an aqueous supporting electrolyte. It should be noted that before the immobilization of CNs, these two dispersions of MWCNTs without any pretreatment and single layer graphene with high surface area had to be homogenised by ultrasound at laboratory temperature for 60 min (Sýs et al, 2015)

Procedure

RESULTS AND DISCUSSION

CONCLUSION