Ion chromatographic and voltammetric determination of heavy metals in soils. Comparison with atomic emission spectroscopy

Abstract

It is widely known that the analysis of trace elements is tricky and that the results obtained often vary according to the analytical technique chosen.The aim of this paper is to compare different analytical techniques, a spectroscopic, an electrochemical and a chromatographic one to determine total heavy metals concentrations in soils and to establish a correlation between these three techniques even though soil solutions are complex matrices providing a lot of interference problems.Atomic emission spectroscopy is the method of reference for heavy metals concentrations analysis. This analytical technique is employed for multi-element analysis and is suitable for a routine measuring out [1]. Polarographic methods are commonly used because of their very low detection limits but still, they are time consuming. Ion chromatographic techniques are generally described in the literature for heavy metals analysis in simple matrix like water but no papers were found for complex matrices like soils or sediments.The first part of this paper presents the apparatus used and the analytical reagents. The second section describes the experimental results obtained with ion chromatography, anodic stripping voltammetry and atomic emission spectroscopy. The last section presents a discussion and a comparison of the results obtained with the different methods for each heavy metal studied. Materials and methods Ion ChromatographyThe measurements are carried out on a DIONEX DX 500 system which is composed of a peristaltic pump GP 40, a pre column CG5A, a CS5A column and a UV-Visible detector AD20. The CS5A column is compatible with pH 0 to 14, allowing the analysis of acid digested soil solutions. Two different Dionex eluents are used, the Met Pac PDCA and the Met Pac Oxalic Acid. The first one is a pyridine-2,6 dicarboxylic acid (PDCA) eluent which is a strong complexing agent that separates the metal ion complexes by anion exchange. The second one is an oxalic acid eluent which is a moderate strength complexing agent that separates the metals by a mixed mode mechanism, anion exchange for metals complexed with oxalic acid and cation exchange for free metals. The detection is accomplished by visible absorbance after post column complexation between heavy metals and a post column reagent. The post column reagent is prepared with 30 mg of 4- (2pyridylazo) Abstract. This work deals with the comparison between three analytical techniques for the total contents analysis of heavy metals in agricultural soils polluted by copper. The soils samples are digested to clear solutions using a mixture of perchloric and hydrofluoric acids. The metals studied are copper, lead, cadmium, nickel, cobalt, zinc and manganese. Soil solutions are complex matrices and the analytical techniques investigated are ion chromatography (IC), Anodic Stripping Voltammetry (ASV) or Adsorptive Stripping Voltammetry (AdSV) and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), or graphite furnace atomic absorption spectroscopy (AAS). The use of ion chroma...

Determination of trace elements in water and sediment samples from Ismaelia Canal using ion chromatography and atomic absorption spectroscopy

“…Therefore, the use of complementary eluant systems is necessary to obtain all the elements with different retention times (Fabre et al, 1999). In this case, two eluants were used to separate the peaks of the heavy elements as shown in Figure 2.…”

Fractionation and Speciation of Trace Elements in Soil Solution

“…An alternative to ASV for analysing positively charged metal ions is (cathodic) adsorptive stripping voltammetry (AdSV) [113][114][115]. In AdSV, a ligand is added to form a complex with the metal ion, which is preconcentrated by adsorption at the electrode surface, whereas the reduction peak of this adsorbed complex is measured in the second step.…”

“…In some studies, the test sample is deliberately perturbed by addition of a synthetic ligand forming well-known soluble voltammetrically labile or inert complexes with the test metal or complexes adsorbed on the electrodes, as in the AdSV technique, after which the free ion concentrations are computed from the known stability constants of the test metals with the synthetic ligands [111]. In another approach, trace metals are directly analysed in the unperturbed soil solution or a soil extract [120][121][122], or in an acid soil digest when the determination of (pseudo)total trace element contents in the soil solid fraction is targeted [114]. A simplified soil extraction procedure in combination with DPASV measurement which can yield semiquantitative data for rapid field-based screening of contaminated sites was recently developed [123].…”

Copper distribution in chemical soil fractions and relationships with maize crop yield

“…The residual fraction was extracted under the same conditions as the total metal content extraction (HF and HClO 4 instead of HNO 3 ). The exchangeable Cu was analysed for copper content by polarography (Gunkel et al 1999), whereas other soil fractions as well as the total soil acid digests were analysed by flame atomic absorption spectroscopy (Gunkel 2001).…”