170135_inorganicventures_flipping

14.4 Ashing

Ashing Techniques: Low temperature ashing

§ Low-temperature Ashing involves treatment of the sample at ~ 120 ̍C using ac=vated (singlet state) oxygen. Life=me of excited osygen is ~ 1 second. (Oxygen is passed through a high- frequency electric field of 13.5 MHz) § Used for trace analysis of organic samples. Look for possible losses of halogens, S, and Hg. § OQen used on samples to avoid analyte losses of vola=le analytes (As, Cd, Sb) and virtually eliminates rxn between residue and ashing container reducing contamina=on. § Used for the trace analysis of coals. Sample size is greater than for acid diges=on. § Sample is spread out over ashing container to speed up process -is s=ll slow requiring 1-3 days depending upon sample size and organic structure.

14.5 Ashing

Ashing Techniques: Closed container Ashing

§ Closed System Ashing involves thermal decomposi6on in oxygen in a closed system such as a Schöniger flask or an oxygen Parr bomb. § Sample is wrapped in paper and held in a Pt basket. A solu6on at the bo@om of the flask is used to absorb the combu6on products. § This technique is most commonly used for halogens, P and S in combus6ble organic matrices. Convenient for analyzing compounds separated by paper chromatography. Useful in the analysis of radio- isotopes in biological materials( 3 H, 14 C, and 35 S). § Flasks are made of borosilicate glass or polypropylene for fluorine analysis. § A 1 litre Schöniger flask holds enough oxygen to combust up to 150 mg of sample.