PubMed · 8781245
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S S Abdel-Meguid. 1996. Structure determination using isomorphous replacement.. https://doi.org/10.1385/0-89603-259-0%3A153
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Stable isotopically labeled tracers offer a reliable and safe alternative to the use of radioactive tracers for studies of metabolic kinetics. This overview examines some of the principles and technical issues regarding mass spectrometry instrumentation, and reviews some of the approaches used in the application of stable isotopically labeled tracers to studies of protein, lipid, and carbohydrate metabolic kinetics.
Concentrations of elements, especially of trace elements toxic as well as non-toxic in biological materials show a high degree of biological, seasonal and spatial variability. These factors should be taken care of while sampling. Samples, even though collected at a great distance of time and space, should be representative and quantitatively comparable which is important for biomonitoring. Reference Materials (RM's) from biological materials such as leaves acquire importance in Analytical Quality Assurance work. A knowledge of element concentrations in highly consumed leafy samples is of interest. A large number of medicinally important leafy samples (50) have been analysed for elemental concentrations such as Zn, Cu, Ni, Co, Pb, As, Se, K, Cr, Na, P, S, Fe, Ca Mg, Mn and Fe. The concentrations of macro nutrients such as Ca, P, Mg, K, Fe and S range from 9.62 to 4174, 1.00-8.630, 3.53-35.50, 12.04-56.28, 0.111-3.845 g/kg and 1.124-5.843 mg/kg, of micro nutrients such as Cr, Co, Cu, Mn, Na and Zn range from 0.360-8.630, 0.050-3.470, 17.60-57.30, 10.5-81.6, 1.47-27.10 and 10.06-145.6 mg/kg whereas those of trace metals such as Pb, Cd, Ni, As and Se range from 1.19-16.30, 0.0036-0.453, 1.23-19.60, 0.12-7.360 and 0.654-3.50 mg/kg respectively. Influence of sampling parameters such as season and spatial variations has been assessed and the results are interpreted. Spatial variation and seasonal variation are observed to be statistically significant for Cu, Zn and Mn. Preparation of Secondary Reference Materials (SRM's) from the samples analysed is explored. Nutritive values of the leaves and intercorrelation between the metals are also discussed.
Hard rock groundwater (145) samples collected from private drinking water wells in the environs of Oslo and Bergen were analysed for their radon and fluoride contents. A further 62 elements were determined by inductively coupled plasma mass spectrometry (ICP-MS). For 59 elements, more than 50% of all concentration values were above the detection limit. Characteristic differences between the Oslo- and Bergen-dataset can be shown to be related to host rock lithology. Variation in element contents generally spans 2-6 orders of magnitude. Concentrations of several elements (e.g. Ba, F, Fe, Mn, Na, Rn) exceed current drinking water action levels in a significant number of cases. High levels of other parameters such as Be, Mo, Th and U, which could have an impact on health, were observed. There are no Norwegian action levels currently defined for these elements. The economic and toxicological impacts of these findings require urgent assessment.