Sample nonoxidizing acids

Ideally, the chosen reagent should cause the complete dissolution of the sample. As a general guide it is useful to classify the more common acid treatments according to whether they oxidize the sample or not. The nonoxidizing acids include dilute hydrochloric, hydrofluoric, sulfuric, and perchloric acids, whereas the oxidizing acids include hot, concentrated nitric, sulfuric, and perchloric acids. Dissolution of metals... 

Hydrofluoric acid is a weak, nonoxidizing acid that is particularly useful for dissolving silicate samples since it removes the silicon quantitatively as volatile SiF4. In many cases, hydrofluoric acid dissolution can be achieved by adding sodium fluoride to samples treated with hydrochloric acid. 

A nonoxidative alkaline sample digestion procedure using TMAH and a high-pressure, MW-assisted autoclave-digestion system was developed [16]. The Si concentrations of the solubilized samples were measured by ICP-AES. The method was developed and tested using Si-spiked ascorbic acid and applied to samples of animal tissue and organs. 

Attempts have also been made to improve the performance of the conventional Mo/ HZSM-5 catalyst [70]. The particle size of HZSM-5 affects the activity of Mo/HZSM-5 in the nonoxidative CH dehydroaromatization. Thus, ball-milling of the 5 wt.% Mo/HZSM-5 catalyst of an average particle size of 4 pm to produce the samples with the average particle sizes of 1.9, 1.0, 0.5, and 0.2 pm resulted in the lower Mo dispersion and lower acidity compared to the parent zeolite catalyst. The maximum benzene formation activities of the catalysts with the particle sizes of 1.9-0.5 pm were higher than that over the parent catalyst. All these data are indicative that the use of the zeolites with small particle sizes with less resistance toward the diffusion of formed benzene out of their short channels is effective in designing the Mo/HZSM-5 catalyst to ensure the high benzene formation activity. 

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