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GR: Guaranteed Reagent
AR: Analytical Reagent
CP: Chemical Reagent

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    $\begingroup$ I want to use mouse liver, brain and freeze the complete organs at -80℃. $\endgroup$
    – Ming
    Oct 26, 2022 at 3:41
  • $\begingroup$ You would like to prevent the formation of ice crystals? $\endgroup$ Oct 26, 2022 at 4:33
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    $\begingroup$ Depends on what you are doing with the frozen tissues. If you're flash freezing for histology, it probably doesn't matter. If you're doing some kind of metabolite extractions for analysis, you'll probably want to use a reagent suitable for HPLC or mass spec (probably AR in this case, but many manufacturers will sell products described as HPLC grade). $\endgroup$
    – MikeyC
    Oct 26, 2022 at 16:26

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Those reagent 'grade' labels are done by manufacturer and are not standardized; see some examples:

https://chemistry.stackexchange.com/questions/575/what-do-the-different-grades-of-chemicals-mean

https://www.emdmillipore.com/US/en/lab-technical-resources/grade-definitions/c9Ob.qB.r7MAAAFEgSYWq.DI,nav

https://www.avantorsciences.com/pages/en/grade-definitions

https://www.westlab.com/blog/2018/04/06/a-guide-to-chemicals-and-chemical-grades

Some companies break these down into very fine scales. Personally, I think about them in roughly 3 grades: 1) ultrapure reagents that are the best of the best, used for the most delicate protocols; these come with a huge price premium, 2) normal academic laboratory grades that are as pure as is efficient - the specific purity depends on the chemical and how separable it is from contaminants, and 3) junk grade for budget experiments in teaching labs. I'm sure other people will bicker with me over this, but it's the system I've always kept in my head when ordering. I'm not certain in all cases that the actual contents you will receive are any different among some of the grades, depending on manufacturing practices it's more about what has been tested.

I don't know if your three grades listed are going to fit into these three categories that I personally came up with, but I'd probably put your GR and AR together in that second/middle grade; CR might belong in the third.

That said, I don't think the purity is going to matter much between those grades for your use; don't spend 3-10X the cost to get something more pure, I'd select something from my "middle" grade. Your samples themselves aren't "pure", and you're not really using isopentane as a reagent in a reaction but instead as a liquid interface for transferring temperature. Higher grades are probably more free of water and other contaminants, but the stuff you pour out is going to get filled with (small amounts of) water from the atmosphere anyways while you chill it. I've never seen a freezing protocol that was explicit about needing to use a very high purity of isopentane.

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