Unmodified Multi-Walled Carbon Nanotubes as Sorbent Material in Flow Injection on-Line Sorbent Extraction Preconcentration System for Cadmium Determination by Flame Atomic Absorption Spectrometry

Abstract

Unmodified multi-walled carbon nanotubes (MWCNTs) were demonstrated as hydrophobic sorbent material for flow injection on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry for cadmium determination in natural water samples. The method was based on on-line chelate complex formation between the analyte with sodium diethyldithiocarbamate and retention onto the surface of MWCNTs. Quantitative elution of the analyte was achieved with methanol which was whereupon delivered to the FAAS nebulizer for atomization and measurement. The microcolumn was packed with a mixture of MWCNTs and silica beads in order to minimize the generated back-pressure in the flow system which arises from the nano dimensions of MWCNTs. All factors affecting the performance of the proposed method were studied thoroughly. For a 180 s preconcentration time the enhancement factor was 54, the detection limit (3s) was 0.24 µg L⁻¹, and the precision as relative standard deviation at a 5.0 µg L⁻¹ Cd(II) concentration level was 3.2%. The method was applied to the analysis of environmental water samples and the accuracy evaluated via certified reference material and recovery experiments.

Keywords:

• Atomic absorption spectrometry
• Cadmium
• Flow injection
• Multi-walled carbon nanotubes
• Sorbent extraction

Notes

IV, injection valve; V, three-position valve; R1, R2, R3, positions of valve; P, peristaltic pump; SP, syringe pump; DDTC: Sodium diethyldithiocarbamate.

^a Mean value ±standard deviation based on three replicates.

^a Mean value ± standard deviation based on three replicates.

^b Recovery obtained from spiked samples.

^c DW: dry weight.

^d FW: fresh weight.

**present work.

PT, preconcentration (loading) time; SC: sample consumption; c _L, detection limit; s _r, relative standard deviation; EF, enhancement or enrichment factor; DDTP, ammonium diethyldithiophosphate; NAPdien, N,N-bis(naphthylideneimino)diethylenetriamine; SDS, sodium dodecyl sulfate; PCTFE, poly(chloro-trifluroethylene), MWCNTs, multiwall carbon nanotubes.