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Re: EDTA and blue water..#592
Subject:
Craig Bingman wrote:
on edta packaging:
>Take it up with Hach, who seem to think it is stable enough to sell in
>natural polyethylene containers.
Hach products are designed for cheap, rapid analysis, requiring minimal
skill, where errors of 30% or so are irrelevant. They are excellent for
this purpose.
Not a product typically found in an accredited analytical lab.
on absorbance spectra and edta stability:
>Those C=O's aren't absorbing anywhere near the visible region, and the
>light that makes it through window glass and is generated by fluorescent
>fixtures just isn't much of a problem.
Experimental evidence is contrary to your position on this matter.
Despite this, reaction mechanisms are more significant than absorbance
in photochem. Reaction kinetics count!. Otherwise (assuming life were
possible), chemists would all simply use phase diagrams, we'd be called
physicists.
on redox chem:
>The relevance of the rest of your post was irrelevant as far as the
>stablity of Fe:EDTA in light.
EDTA drops the redox potential of Fe(2)->Fe(3). This has direct
consequences for the stability of Fe(2) with or without the presence of
light. It means that a stock solution of ferrous edetate is less stable
than one of say FeSO4. I apologise to all for not making this more
obvious.
>I'm not sure you have the chemistry quite right. Fe:EDTA participates
>in Fenton chemistry slowly in the presence of oxygen, like a shot in the
>presence of hydrogen peroxide.
Fentons chem. involves the production of hydroxyl radicals. Totally
irrelevant to the simple redox chem. I referred to.
on blue water:
>> As water has no obvious chromophores <g>, confirmed by its UV-Vis
>> spectra, It is plain that *pure* water *should* appear colourless.
>Wrong. You can see the effect in even short path lengths with a very good
>visible spectrometer. It should be very obvious at 10 cm. Zero it in
>air. Measure the cell, then the cell plus water. There should be
>obvious absorption in the red, becoming stronger in the near IR.
The absorbtivity clearly is too small to be observed by the human eye
over any reasonable path length. A good UV-Vis spectrophotometer uses
dual beams, one measurement only required, otherwise instrument drift
becomes too significant.
More simply just look it up in a spectro' reference.
>Check out a book on marine optics.
The absorbtion of red light by marine waters, or air (blue mountains in
the distance) is predominantly due to light refraction by minute
suspended particles, not by the water/air itself.
>Craig
Craig it would be inappropriate to discuss this further on the list. If
you wish to learn I can supply you with appropriate references.
Toado.
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