Normal ultratrace element

The content of molybdenum in the ambient air is normally low compared with other trace and ultratrace elements. Concentrations of Mo in the air of urban areas are higher (0.01-0.03 pg Mom ) compared with the levels in rural areas (0.001 -0.0032 pg Mom Y The mobilization of molybdenum from fossil fuels produced a substantial elevation of molybdenum in the immediate vicinity of the site of combustion. Molybdenum concentrations in fly ashes range from 7 to 160 mg Mokg (Bar-celoux 1999). 

GF-AAS methods combine a very high atomization efficiency with a 100-1000 fold increase in sensitivity compared to the conventional flame technique. For this reason and also because of the capability of handling solid samples as well as samples which normally requires sample pretreatment, GF-AAS is one of the most popular methods in trace and ultratrace element determinations in clinical chemistry. 

Essential Trace and Ultratrace elements exercise normal functions... 

Since the concentrations of the various compounds or oxidation states in which trace elements can occur are always lower than the total content of the analyte, speciation analysis is normally an ultratrace determination in the ng L-1 range for solutions and the ng g 1 range for... 

Contamination. Contamination of samples by external sources can be a serious source of error and may be extremely variable. An excellent example of how serious this can be has been documented in the analysis of samples for polychlorinated biphenyls (PCBs). PCBs are synthetic mixtures of organochlorine compounds that were first manufactured in 1929 and have become of concern as significant environmental pollutants. It has been demonstrated that samples archived since 1914, before PCBs were manufactured, picked up measurable amounts of PCBs in a few hours just sitting in a modem laboratory (Erickson). Aluminum levels in the dust in a normal laboratory are so high that dust prohibits the determination of low ppb levels of aluminum in samples. A special dust-free clean lab or clean bench with a filter to remove small dust particles may be required, similar to the clean rooms needed in the semiconductor industry, for determination of traces of aluminum, silicon, and other common elements such as iron. When trace (inorganic analysis is required, the laboratory environment can be a significant source of contamination. 

In vitro analyses are not limited by a maximum irradiation dose, and the high sensitivity for many elements and the absence of blank values makes NAA the preferred method for analysis of many types of biological samples at the ultratrace level of concentration. The insensitivity to contamination has proven particularly valuable for establishing normal concentrations of a number of elements in human blood, including As, Cr, Mn, Mo, V, etc. [21], and results by NAA serve as a reference for testing or verifying the reliability of other methods. 

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