Abstract: Accelerated mass spectrometry (AMS) is the exquisite method for the detection of long-lived isotopes at part-per-quadrillion sensitivities with good precision. AMS is traditionally used for studying the past by means of radiocarbon dating. In the last decade biomedical applications based on tracing 14C-labeled compounds through natural systems via AMS have been developing to elegantly solve complex problems including the metabolic fate of drugs up to several months, the formation of carcinogen-DNA adducts, the penetration of model aerosol particles inhaled at low dose by mice and cell renewal time. The most common approach for biological sample preparation is the conversion of organic samples to graphite as follows: solid or liquid tissue is dried, oxidized to carbon dioxide, CO2 gas is separated from impurities and reduced to graphite. Dried organic samples are typically combusted in sealed quartz tubes containing CuO at 900°C for an 1‒5 h. Carbon dioxide purified by means of passing through a series of cryogenic traps followed by the conversion to graphite commonly produced by the “overnight” reduction of CO2 by hydrogen or zinc over an iron catalyst. Multi-stage graphite production is time and resource consuming step of AMS analysis. To update the procedure mentioned above we suggest a simplified adsorption-catalytic method of sample preparation. The main features of novel approach are rapid and complete catalytic combustion of the sample and “inverted” carbon dioxide purification representing one-step CO2 separation from oxidation products by means of the selective absorbent based on CaO. The sample is burned in O2 flow at 600‒950°С followed by afterburning over the ICT-12-8 catalyst allowing carbon, CO and other pyrolysis products to be completely oxidized in 10 15 min even in the presence of chlorine and sulfur compounds. The products of complete combustion pass through the trap of water and heavy-boiling compounds representing a U shaped tube placed into snow/NaCl mixture having the temperature of 20°С. The further separation of combustion products is carried out by selective absorption of carbon dioxide on CaO at 550‒650°C followed by the system evacuation to remove the impurity gases mixture near the sorbent. Then the absorbent is moved to the high temperature zone (T > 900°C) to completely and irreversibly desorb CO2. Carbone dioxide is collected in the quartz graphitization reactor, loaded with Fe catalyst and equipped with a water trap, by means of liquid nitrogen cooling. The reactor is filled with H2 in a double excess, sealed and moved to the furnace preheated to 560°С for converting CO2 to graphite. The graphitization is a rate-limiting step of the sample preparation and requires about 5.5 h. However, the independence of the graphitization from the rest procedures allows several samples to be accumulated and simultaneous graphitized in the furnace. To sum up, the suggested method allows producing graphite targets from organic samples faster and cheaper making it perspective for biomedical applications.

Cite: Kalinkin P.N. , Lysikov A.I. , Kuleshov D.V. , Dralyuk R.I. , Vorobyeva E.E. , Sashkina K.A. , Parkhomchuk E.V. , Okunev A.G. , Petrozhitskii A.V. , Rastigeev S.A. , Parkhomchuk V.V.
Novel Simplified Absorption-Catalytic Method of Sample Preparation for AMS Analysis
In compilation IIS 2018 Prague. 13th International Symposium on the Synthesis and Application of Isotopically Labelled Compounds. Symposium Scientific Programme and Collection of Abstracts. – Czech Chemical Society., 2018. – Т.1. – C.69. – ISBN 9788086238890.

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