Application of modern analytical techniques for quantification of selected radioactive metals in environmental samples

Abstract

In this study, the recent micro-extraction and pre-concentration techniques, namely vortex-assisted liquid-liquid micro-extraction (VA-LLME), dispersive liquid-liquid micro-extraction (DLLME) and membrane assisted solvent extraction (MASE) were used for the extraction of radioactive metals from the environmental samples. The VA-LLME and MASE were used for the extraction of cobalt, while DLLME was used for the extraction of palladium. The work is divided into five papers. The first paper of this work reviewed the modern developments for efficient applications of DLLME technique during analysis of radioactive metals in environmental samples (paper I). This study discussed various modifications of the DLLME technique used for improving the technique during the analysis of radioactive metals, as well as the challenges it present. The major advantage, among others, of DLLME is miniaturisation in which the volumes of the extraction and dispenser solvent are reduced tremendously. This was in attempt to solve challenging factors during the analysis of radioactive metals such as their existance in trace level that is normally lower than the limits of detection of most analytical instruments. Recent developments for efficient analytical separation techniques during analysis of radionuclides in environmental samples were reviewed (paper II). This part outlined the efficient analytical extraction and separation techniques during analysis of radionuclides with focus on the review of non-consecutive extraction of analytes, non-toxic solvents, less-hazardous waste generation, and high selective and green analytical separation methods. Furthermore, possible simultaneous selective extraction of metals of interest in a complex matrix such as water, soil and minerals were dicussed. This offers tremendous advantages for extraction and separation techniques of radionuclides. Cobalt concentration in environmental water samples was pre-concentrated using VA-LLME and detected using flame atomic absorption spectrometry (FAAS) (paper III). Based on the results, 2 min vortex time, 3 mL sample volume, 6.0 sample pH level, 600 mL volume of complexing angent give, and 300 μL extraction solvent give the highest enrichment factors. Trace amount of cobalt in real samples, were 102.5 ± 1.0 μg L-1 (n = 3, RSD) which is below the maximum acceptable limit for cobalt, according to Water Quality Guidelines for cobalt by British Columbia Report. The pre-concentration of palladium in the environmental samples by DLLME was studied (paper IV). The important parameters that have an impact on the effectiveness of DLLME technique were also optimized using the univariate approach. The methanol and chloroform was used as dispenser solvent and extraction solvent, respectively. The volumes of 500 μL for dispenser solvent and, 400 μL for extraction solvent showed the maximum enrichment factors. Dithozone was used as a chelating agent in this study, and acetone was used as a diluent to dissolve the sedimented phase in the DLLME method. The volume of 600 μL was an adequate amount of acetone used to ensure that sufficent palladium species in the samples are converted to form a complex. Cobalt extraction by MASE was also investigated (paper V). The key parameters that have an impact on the effectiveness of MASE technique were also optimized using the univariate approach. The maximum enrichment factors were obtained at the pH of 3.5; 60 min extaction time and 2.0 rpm stirring rate. Under the optimized conditions, the developed method was used for the analysis of real samples. The samples obtained from the area suspected to the exposure of cobalt were pre-concentrated using MASE prior to analysis with graphite furnace atomic absorption spectrometry (GFAAS). Hexane and dithizone were used as extraction solvent and chelating agent, respectively. The pH of the samples was adjusted using nitric acid or sodium hydroxide solution. The ammonium chloride buffer solution was used to precisely maintain constant sample pH at nearly optimal value during the MASE technique.