We have prepared plastic with As+3 compound. We applied 250 C temperature and pressure during the processing samples. After preparation of sample As state has been changed to +5. Please let me how it was changed. We have mixed other inorganic compounds also such Fe, Pb, Cr etc.
You can find that arsenite oxidation state change due to high temperature /pressure from the following papers:
Redistribution of arsenic in silicon during high pressure thermal oxidation
Applied Physics Letters;3/16/1987, Vol. 50 Issue 11, p688
Speciation and oxidation kinetics of arsenic in the thermal springs of Wiesbaden spa, Germany
Fresenius J Anal Chem. 2001 Dec;371(7):927-33.
In the experiment of arsenic species extraction, we applied microwave system at 80 W during 10 min( ＜ 90 C temperature and high pressure). The recoveries of standard additions of As(III) and As(V) were 90.2% and 93.8%, respectively. Therefore, I think that the high temperature (250 C) in your study may be the reason of As(III) oxidation.
See :
Ma J., Guo H.M.*, Lei M., Zhou X., Li F., Yu T., Chen T., Zhang H., Zhang X., Wu Y., Wei R. Arsenic Adsorption and its fractions on the Aquifer Sediment: Effect of pH, Arsenic Species and Fe/Mn Minerals. Water, Air and Soil Pollution, 2015, 226(8), DOI: 10.1007/s11270-015-2524-1
I agree with Ma Jie, In fact, even for As concentration in the plant samples, most of the time we use below than 80C for measuring DW of the biomass. Because above 80-90C, it increases As evaporation from the samples. So, i think high temperature is the main factor here.
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