Trace Levels Of Contaminants Research Articles

Seasonal Trends and Tissue Distribution of Organochlorine Pollutants in Wild and Farmed Gilthead Sea Bream (Sparus aurata) from the Western Mediterranean Sea and Their Relationship with Environmental and Biological Factors

Seasonal trends and tissue distribution of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in gilthead sea bream (Sparus aurata) samples from the Western Mediterranean were investigated. Hexane extracts of white and red muscle, liver, and gills from wild and cultured specimens were purified by normal-phase high-performance liquid chromatography, and selected OCPs and PCBs were determined by gas chromatography coupled to mass spectrometry as indicators of contamination. The limits of detection for the analytical methodology allowed was 0.25 ng/g. Data obtained showed the presence of DDTs and PCBs in the different tissues, with the highest concentration of pollutants being in tissues of higher lipid content. Concentrations of organochlorine compounds in sea bream tissues strongly correlated with seasonal changes and the biological cycle of the species. In general, cultured fish had lower concentrations of contaminants and smaller season variability than wild fish. Trace levels of contaminants were found in fish muscle throughout the year, but always below the guidelines recommended for human consumption.

X-ray Absorption Spectroscopy on Copper Trace Impurities on Silicon Wafers

AbstractTrace metal contamination during wet cleaning processes on silicon wafer surfaces is a detrimental effect that impairs device performance and yield. Determining the chemical state of deposited impurities helps in understanding how silicon surfaces interact with chemical species in cleaning solutions. However, since impurity concentrations of interest to the semiconductor industry are so low, conventional techniques such as x-ray photoelectron spectroscopy cannot be applied. Nonetheless, chemical information on trace levels of contaminants can be determined with x-ray absorption near edge spectroscopy (XANES) in a grazing incidence geometry. In this study, silicon samples were dipped in ultra pure water (UPW) and 2% hydrofluoric (HF) solutions with copper concentrations of 5 and 1000 ppb, respectively. These samples were then analyzed using XANES in fluorescence yield mode to determine the oxidation state of deposited copper contaminants. It was found that copper impurities on the silicon surface from HF solution were metal in character while copper impurities deposited from the spiked UPW solution were deposited as an oxide. These results show that XANES can provide information on the chemical state of trace impurities even at surface concentrations below a few thousandths of a monolayer.

Factors to be considered in the preparation of single and multi-element standards for inductively coupled plasma optical emission spectrometry

The problems encountered with the production of single and multi-element inductively coupled plasma (ICP) optical emission spectrometry (OES) standards are reviewed. Purity, stability and characterization of starting materials, water and acids have profound effects on the quality of these standards. The trace level contaminants and the form of the starting materials can result in serious analytical errors. Long-term stability of the ICP-OES standard, dependent in part on the storage container composition, plays an important role in the accuracy of ICP-OES calibration. The relationship between inter-element correction factors and the quality of ICP-OES standards is discussed. Finally, some of the factors that must be considered during the manufacture of multi-element standards for instrument calibration, universal and customer-specific applications are delineated.

Determination of trace level contaminants in marine species using electron paramagnetic resonance

The concentrations of paramagnetic trace elements were determined from the electron paramagnetic resonance (e.p.r.) spectra of lyophilized bivalve mussels. The method is rapid and requires a minimum of specimen preparation. In many cases the trace elements present could be recognized by inspection of a single spectral run. E.p.r. is sensitive to metal speciation so that it can distinguish the toxic form from the metabolic form. We have shown that a number of bivalve species give consistent results. Levels below 1 part in 108 can be detected with a precision comparable to that of atomic absorption spectroscopy.