Applications of14C-AMS in biomedical sciences (Bio-14C-AMS)

Mass spectrometry and isotopes: a century of research and discussion

In 1815, the British physician William Prout had advanced the theory that the molecular masses of elements were multiples of the mass of hydrogen. This "whole number rule" (and especially deviations from it) played an important role in the discussion whether elements could be mixtures of isotopes. F. Soddy's discovery (1910) that lead obtained by decay of uranium and of thorium differed in mass was considered a peculiarity of radioactive materials. The question of the existence of isotopes came up when the instruments developed by J.J. Thomson and by W. Wien to study cathode and canal rays by deflection in electric and magnetic fields were steadily improved. In 1913, Thomson mentioned a weak line at mass 22 accompanying the expected one at mass 20 when he analyzed the mass spectrum of neon. Subsequently Aston obtained the mass spectrum of chlorine with masses at 35 and 37. Still in 1921, Thomson objected heavily to the idea of isotopes. The isotope problem was finally settled, but more accurate mass measurements showed that even isotopic weights differed to some extent from the whole numbers. Based on earlier ideas of P. Langevin and J.-L. Costa, F.W. Aston and A.J. Dempster developed the idea of packing fractions and mass defects due to the transformation of a portion of the matter comprising the atomic nucleus into energy. While the determination of the exact isotopic masses had improved over the years, the accurate determination of isotopic abundances remained a problem as long as photographic recording was used. Here especially A.O. Nier pioneered using dual collectors and compensation measurements. This was the prerequisite for the discovery that isotopic ratios varied somewhat in nature. M. Dole discovered the fractionation of oxygen isotopes by photosynthesis and respiration. Today 13C/12C-ratios are employed to detect adulterations of food and in doping analysis, and 14C/13C-ratios obtained by accelerator mass spectrometry are used for dating historical objects, just to give some examples.

Formation of MTBE-DNA adducts in mice measured with accelerator mass spectrometry

Methyl tert-butyl ether (MTBE) is a gasoline oxygenate and antiknock additive substituting for lead alkyls currently in use worldwide. Previous studies have shown that MTBE at very high doses induces tumors in rodents. The aim of the present study was to examine directly the binding ability of MTBE onto DNA, demonstrating its potential genotoxicity. MTBE-DNA adducts and their decay kinetics in mice have been measured by using doubly 14C-labeled MTBE with an advanced, ultrasensitive technique: accelerator mass spectrometry (AMS). It was found that MTBE definitely formed adducts with DNA in mouse lung, liver, and kidney in a log/log linear dose-response relationship. The distribution sequence of DNA adducts in these tissues is: lung > liver > kidney. The level of MTBE-DNA adducts peaked at 12 h postadministration in the lung and peaked at 6 h postadministration in the liver. Then the adducts declined rapidly until 5 days postadministration and thereafter declined much more slowly. To our knowledge, this is the first report on DNA adduction with MTBE in vivo. The mechanism of the formation of MTBE-DNA adducts also is discussed.