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While reading my book everywhere I found that 99.9% pure metal is obtained. Is it possible by any process that we get 100% pure metal on industrial level?

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    $\begingroup$ Nothing is 100% pure. $\endgroup$ – Zhe Dec 26 '16 at 18:37
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    $\begingroup$ 99.9% pure is 100% pure within certain tolerance. What tolerance do you want? $\endgroup$ – Ivan Neretin Dec 26 '16 at 18:39
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    $\begingroup$ Typical industrial silicon wafers for the fabrication of integrated circuits are 99.9999999 % pure. $\endgroup$ – Loong Dec 26 '16 at 18:41
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    $\begingroup$ related chemistry.stackexchange.com/questions/2870/… $\endgroup$ – Mithoron Dec 26 '16 at 19:47
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The only way to get a "100% pure" sample of an element is by mass spectroscopy, or something similar, which acts on each atom (or ion, actually) one at a time.

So you could get a sample of pure rubidium of a few dozen atoms. Caveat: "100 % pure" applies only to those atoms actually observed... there could be other elements in the vicinity that have not been observed.

Practically, though, there is no way to prevent a single atom of hydrogen, for example, from eventually contaminating your "100 %" pure sample.

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    $\begingroup$ True and false. There is no absolute vacuum, so any cluster would absorb some gas on their surface sooner or later even inside the ms chamber $\endgroup$ – Greg Dec 28 '16 at 11:11
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    $\begingroup$ Yes, that's what I wrote. $\endgroup$ – DrMoishe Pippik Dec 29 '16 at 3:45
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When we start talking about Fineness of metals we can deal with some misunderstanding. We generally have to make a distinction between absolute purity and the common metals basis purity. The first refers to all the impurities (all the elements of the periodic table) the second refers only to metals. On industrial level is not possible to reach 100% absolute purity, because this means that the whole process must be carried on in ultra-clean ultra-vacuum environment. We can however reach very high purity. Usually the purity is measured in Nines below you can find a table that summarize the purity grades:

\begin{array}{lllll} Nines & Purity \% & Total Parts & Matrix \space ppm & Impurity \space ppm \\ 1N & 90\% & 1,000,000 & 900,000 & 100,000 \\ 2N & 99\% & 1,000,000 & 990,000 & 10,000 \\ 3N & 99.9\% & 1,000,000 & 999,000 & 1,000 \\ 4N & 99.99\% & 1,000,000 & 999,900 & 100 \\ 5N & 99.999\% & 1,000,000 & 999,990 & 10 \\ 6N & 99.9999\% & 1,000,000 & 999,999 & 1 \\ 7N & 99.99999\% & 1,000,000 & 999,999.9 & 0.1 \\ - & 100\% & 1,000,000 & 1,000,000 & 0 \end{array}

In the past Royal Canadian Mint used to mint a 5 nines gold coin and that was something very unusual, the purest gold ever produced was 999.999—six nines gold that was claimed to be refined by the Perth Mint in 1957. At sigma aldrich you can buy 99.999% trace metals basis so is not the absolute purity. If you are interest in the topic this article could be helpful Schulze, K.K. JOM (1981) 33: 33. doi:10.1007/BF03354422 while a general discussion can be found here.

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