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I'm having trouble digesting a paper sample for $\ce{Ti}$ analysis using our ICP-OES. I've been digesting my ash samples with 50% $\ce{H2SO4}$, but I'm still getting lower $\ce{TiO2}$ results than the target. What is the best way to digest paper sample with $\ce{TiO2}$?

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    $\begingroup$ When you say "trouble digesting" what is your trouble? You say the analyses come out other than expected, but do you mean "the solution is cloudy". Is this a fact? If the solution is clear it can still be a digestion problem for certain but if an analysis is off target it could be other issues. In short, why do you assume it is digestion? $\endgroup$ – Stian Yttervik Nov 10 '16 at 9:13
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    $\begingroup$ @StianYttervik I have converted your answer to a comment since it would have probably been deleted anyway. You are close to being allowed to comment anywhere, good luck! $\endgroup$ – Martin - マーチン Nov 10 '16 at 11:07
  • $\begingroup$ @StianYttervik: Hi Stian, trouble digesting because my sample doesn't get dissolved at all. I've added H2O2 and it works. My problem before about getting low results was actually because the process in our mill had a retention problem which we found out few weeks after I've done the test. All good now. Cheers mate $\endgroup$ – Mark Anthony Asemba Dec 5 '16 at 2:46
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If you want to stay with a sulfuric acid type of digestion, there is this(1) paper that describes a microwave digestion using copper(II) and hydrogen peroxide to facilitate the digestion.

From my personal experience, if your lab is properly equiped, my first choice would be an $\ce{HF}$ digestion or a nitric/perchloric acid digestion.

1)"A rapid and simple microwave-assisted digestion procedure for spectrophotometric determination of titanium dioxide photocatalyst on activated carbon", ScienceDirect, Talanta 71 (2007) 1867–1872

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    $\begingroup$ EMPHASIS ON "PROPERLY EQUIPPED"!! If you don't immediately know how nasty $\ce{HF}$ is, research it thoroughly before you even consider beginning work with it. Same thing with perchlorate: research first, then decide whether it's feasible to use. In both of these cases, specific safety equipment/apparatus is usually required. $\endgroup$ – hBy2Py Feb 18 '17 at 2:50

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