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  1. #1
    Rudeofus's Avatar
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    Why does my pH 10 buffer smell like Ammonia?

    I have bought buffer solutions for calibrating my pH meter, and have been wondering ever since why my pH 10 buffer solution is not just some Carbonate/Bicarbonate mix but actually smells like Ammonia. The biggest cause of pH changes in alkaline buffer solutions is, AFAIK, aerial CO2 which lowers pH, and I expect an even stronger effect if this pH 10 standard solution leaks NH3. And sure enough, the expiration date on this bottle is less than 6 months ahead, whereas the pH 7 buffer lasts more than twice as long.

    Are there any advantages of using this buffer, or am I better off mixing my own Carbonate/Bicarbonate buffer?
    Trying to be the best of whatever I am, even if what I am is no good.

  2. #2

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    Do you know the composition of the buffer? Some amines have an odor similar to ammonia.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  3. #3
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    It's based on Ammonia, Ammonium Chloride and EDTA-Mg. From looking at the manufacturer's webpage (product number 98213.260, sorry, no direct link) and their emphasis on "buffer solution for determining water hardness", I assume they try to avoid anything that causes Ca2+/Mg2+ precipitates, which excludes the usual suspects for buffers in that range (Carbonate, Metaborate). But why would they add EDTA-Mg ??? And why would a chem supplier (I mean my local chem store) sell such a specialty product as standard buffer solution for pH meter calibration?

    I guess I will use the time until this bottle expires to find a suitable replacement based on either Carbonate/Bicarbonate or Borax/Metaborate ...
    Trying to be the best of whatever I am, even if what I am is no good.

  4. #4

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    Are you sure it's actually a pH buffer, intended for calibrating a pH meter?

    Perhaps it's some sort of reagent for use in water hardness analysis, and the "buffer" effect is for something other than pH? Just guessing, but you might want to check the exact wording in the description. (I see from your link that it's from VWR, but the item number doesn't show up in a search.)

  5. #5

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    At a pH of 10 any solution of ammonia and ammonium ion will release ammonia gas. It sounds like this is not intended for pH meter calibration purposes. A buffer solution should be stable over time. Recipes for buffer solutions can be found on the web. You do need a reasonably accurate scale though. But considering the accuracy of cheap pH meters they are not hard to make. I would never use an expensive electrode with photographic solutions. They are too easily damaged.
    Last edited by Gerald C Koch; 12-28-2013 at 06:51 PM. Click to view previous post history.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  6. #6
    Rudeofus's Avatar
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    Quote Originally Posted by Mr Bill View Post
    Are you sure it's actually a pH buffer, intended for calibrating a pH meter?
    It was sold to me as that, and is also described as buffer on its product page (I finally found a way to link to it, silly web 2.0).

    Conclusion: it seems to be a specialty product which was sold to me as standard buffer solution. If that local store doesn't have anything more generic (and with longer shelf life, and for less money), I'll mix my own buffer from Borax/Boric Acid and NaOH. I can still use the specialty soup for establishing a proper mixing ratio.
    Trying to be the best of whatever I am, even if what I am is no good.

  7. #7
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    Quote Originally Posted by Gerald C Koch View Post
    Recipes for buffer solutions can be found on the web.
    I do have one that resolves milligrams and should give me repeatable results within 0.01g. What concerns me more is the purity of the chemicals I mix my buffer from. Anhydrous Carbonate takes on water given enough time, and I have no idea how pure and stable my Bicarbonate is, NaOH seems to be another source of trouble. I wonder whether there are buffer recipes made from compounds that have very long shelf life, that don't have varying amounts of crystalline water and that won't take on Carbon Dioxide or find another lame excuse to change their composition.

    FWIW, it doesn't even have to have pH 10.0. My pH meter has one calibration knob for center (pH 7.0) and one for slope, so the non-pH-7 standard can have any pH, as long as it's stable and predictable.

    Quote Originally Posted by Gerald C Koch View Post
    But considering the accuracy of cheap pH meters they are not hard to make. I would never use an expensive electrode with photographic solutions. They are too easily damaged.
    My pH electrode was not exactly cheap (around 100 Euros), but it lasted for over a year and broke rather from my clumsiness and inexperience than from normal operation. I would even stir liquids with it when fine tuning pH of some photographic solution. The biggest issues I had were unreliable pH standards, and that's something I would like to resolve once and for all.
    Trying to be the best of whatever I am, even if what I am is no good.

  8. #8

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    I just use 5g/L borax pH 9.2.Would that do?

  9. #9
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    Quote Originally Posted by Alan Johnson View Post
    I just use 5g/L borax pH 9.2.Would that do?
    If that works reliably, I'm all for it, and since it's trivial to mix I don't care about shelf life of working solution. But how accurate is it, and how reproducible? Well, I have another 4 months to figure that out before my pH 10 Ammonia buffer runs past its expiration date. I shall report ...
    Trying to be the best of whatever I am, even if what I am is no good.

  10. #10

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    All the chemicals; borax, sodium bicarbonate, sodium hydroxide and sodium carbonate are stable if kept in well stoppered jars and not exposed to heat. Sodium hydroxide will absorb both water and carbon dioxide from the air. When this happens you will usually see the granules start to clump together.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

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