Application of multi-walled carbon nanotubes as substrate for the on-line preconcentration, speciation and determination of vanadium by ETAAS

Abstract

This paper presents the development of a pre-concentration and speciation method for inorganic vanadium species by flow injection solid phase extraction-electrothermal atomic absorption spectrometry (FI-SPE-ETAAS). This was carried out by employing a conical mini-column filled with multi-walled carbon nanotubes mounted in the arm of the autosampler of the ETAAS. This system was applied to the on-line pre-concentration and speciation of vanadium in natural waters in conjunction with ETAAS determination. The time required for the pre-concentration of 1.0 ml of sample (1.0 ml min⁻¹), elution/injection (0.2 ml min⁻¹), reading/data acquiring and conditioning was about 2.9 min, resulting in a sample throughput of 20 samples per hour. A 20-fold total enrichment factor for a sample volume of 1.0 ml was obtained with respect to the vanadium determination by ETAAS without pre-concentration. The relative standard deviation for six replicates containing 200 ng l⁻¹ was 3.3%. A limit of detection (3s) of 19 ng l⁻¹ was achieved and the limit of quantification was estimated (10s), obtaining a characteristic concentration of 63 ng l⁻¹. The calibration curve was linear from the quantification limit up to 1500 ng l⁻¹, with a correlation coefficient of 0.9996. This method permitted us to determine the total inorganic vanadium in natural waters. For speciation purposes, V(IV) was masked with 1,2 cyclohexanediaminetetraacetic acid (CDTA) in order to determine the V(V) concentration selectively.