Ultratrace determination of arsenic by hydride generation atomic absorption spectrometry with preconcentration on gold nanoparticles

Abstract

A fast and simple preconcentration step was developed for ultratrace arsenic determination after hydride generation. The quartz modular trap-and-atomizer device designed recently was employed for arsane enrichment as well as subsequent arsenic detection by atomic absorption spectrometry. The modular design of the device allows simple replacement of the preconcentration compartment. Three types of gold-based materials including gold wire, gold coated alumina and gold nanoparticles (60 nm) were tested as potential preconcentration surfaces. The best results were achieved for gold nanoparticles (5.5 μg Au), at a trapping temperature of 350 °C and volatilization at 900 °C. The whole preconcentration procedure is controlled by temperature only while the atmosphere composition is kept constant (75 ml min⁻¹ carrier H₂). The optical arm of the device is permanently heated to 900 °C and supplied with 20 ml min⁻¹ O₂ as outer gas for efficient atomization. A preconcentration efficiency of 90% was found under the optimized conditions while the limit of detection reached 6.5 pg ml⁻¹ As (117 pg) for 300 s preconcentration (sample volume 18 ml). The method proposed was successfully validated by As determination in four certified reference materials including drinking (AQUA-1), waste (ERM-CA713) and sea water (NASS-5). The modification of the quartz surface by gold nanoparticles was studied including the ageing processes by scanning electron microscopy and energy dispersive X-ray spectroscopy. Homogeneous distribution of gold nanoparticles over the quartz surface was found in freshly prepared traps followed by agglomeration of the nanoparticles after several preconcentration cycles but not affecting preconcentration efficiency.