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Contents:
  Water Chemistry, please help.... (mabrooks)


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Date: Mon,  2 Jul 2007 12:37:46 -0400
From: mabrooks at vt.edu
Subject: Water Chemistry, please help....

I once did an experiment in the lab that compared three water samples.  All of
the samples started as ultra-purified, reagent grade, laboratory water with
absolutely nothing in it, except hydrogen and oxygen combined up to form water
molecules, I will call this "pure water".

The first sample was left alone and stored in a covered flask.

The second sample I added a known quantity of reagent grade standardized
phosphate solution of a known concentration,yet the sample remained as "clear as
the pure water".

The third sample I heated and added some CaHCO3, several types and
colors of crushed malted barley and let it steep for awhile at 152 degrees, I
then added several different types of hops and boiled it for awhile, and added
more hops during the boiling times according to my recipe. I cooled it and
pitched some yeast and let it sit for a week or so and transfered it to another
container and let it sit for a few more days.  The numerous different processes
that sample #3 was put through changed nature of the sample from its original
composition of "pure water". In fact, Sample #3 turned out to be deep golden
brown
in color with a nice hoppy nose and about 5.4% alcohol.

I ran a series of spectrophotometric analysis on all three samples after all had
been processed as above.  My results are as follows:

Sample #1 had absolutely no absorbance spectra whatsoever, i.e. 100%
transmittance. I diluted it 1:1 and found the same, no absorbance at any
wavelength.

Sample #2 initially had no absorbance spectra through the various wavelengths
either, however, after I added certain chemicals to it in a prescribed, approved
method, a resultant color appeared in the sample.  I ran this sample through the
spectrophotometer and found that it now had a "peak of maximum absorbance" at
880nm. The wavelength scan tapered off in the wavelengths before and after
880nm, so the peak was definitely there. I re-ran the scan using a measured
1:1 dilution of the original phosphate standard solution.  The results showed
that the re-run sample had the same "peak" at the exact same wavelength,
however, its absorbance was slightly less,after some calculations for the
dilution factor applied, and knowing "with certainty" the original concentration
I started with, I concluded that a specific species (phosphate)in Sample #2
was following the Beer-Lambert law.

Sample #3 had no definable color "peak" at any wavelength, it had it highest
absorbance values at 430nm, however, 430nm on a spectrophotometer is only
associated with the color Yellow, no other colors can be inferred to be in this
sample except Yellow, as no other peaks at other wavelengths were detected on
the scan. I diluted sample #3 1:1 and re-ran the spectrophotometer scan and
obtained
the same results, no real peaks of absorbance at any defined wavelength,
however, I did notice a corresponding decrease in absorbance value at 430nm in
relation
to the dilution. However, I did not have any known concentrations of standards
to begin with, and I did not know what the specific species was that was causing
this
"linear" Beer-Lambert type relationship.

>From this data I concluded the following :

Sample # 1 did not have any absorbance data, hence "pure water" does not have
any species in it that follow the Beer-Lambert law!

Sample # 2 started as "pure water" yet it did have absorbance values associated
with it, but how can this be true? Sample # 2 was the exact same as sample #1,
yet sample #1 does not follow the Beer-Lambert law? oh...wait a minute, sample
#2 had a phosphate solution added to it, and it was this specific analyte or
species in sample #2 that followed the Beer-Lambert law. The associated species
color at a specific wavelength folllowing an approved laboratory methodology
gave no doubt that concentrations of phosphate in water does follow beer-Lambert
law !

Sample # 3 was also "pure water" originally, however, I did subject it to
numerous brewing type processes and added quite a few ingredients to it.
Sample #3 did have an absorbance value at ~430nm.  Hence a species may have
been present that loosely followed the Beer-Lambert law with respect
to dilutions, how can this be? Oh yea I did add a bunch of stuff to it.
Hmmm, maybe it was something in all that stuff I added that was causing the
absorbance values at 430nm, but how can I be sure what it was, I
didn't have any known standards that had the same absorbance spectra to back up
my dilution results, or prove exactly what species/analyte I added that was
following the Beer-Lambert law.  How can I be sure what component of Sample # 3
was causing this relationship or if it is realted to the color of sample#3.  I
cant!

One can not state that a "solution" follows Beer-Lambert, as the "solution" does
not, it is the specific analyte in the solution that follows Beer-Lambert.  This
specific species may or may not be realted to or responsible for the apparent
color of the solution, depending on its: concentration in the solution,
intensity, hue,
etc...remember that Sample #3 only had absorbance in the 430nm "Yellow color
spectrum", hence, the actual "deep golden brown" color of a sample
(could have been red,or brown, or black depending on beer style) would not
have accounted for by absorbance at the 430 nm wavelength.  Only a specific
species in beer(that many are confusing with beer color)can associated with
following Beer-Lambert! and this species would be responsible for any absorbance
at 430nm and this species would not result in any of color other then yellow.
Further, a sample cannot follow Beer-Lambert with respect "other" colors if
they do not show up on the spectrophotometric scans, period!

One cannot make a blanket statement that "beer" follows Beer-Lambert (it shows a
level of ignorance to the water chemistry field), because, beer
no more follows Beer-Lambert then the Pure Water does.  A specific species
added to Pure Water or beer can follow Beer-Lambert, however, one needs
to prove what the species is and come up with a approved method to analyze
the sample specifically for it, perhaps it is more than one species, if so one
will need to have to have distinct and separate chemistry associated with the
species of interest in order to allow an analyst to determine each species
concentration without interferences from the other (btw: this is done all the
time in the water chemistry laboratory, as an analyst can measure absobances of
several species in a single sample using different methodologies, which result
in different absorbance wavelengths, each specific to the analyte of interest.)

Can someone please tell me how a glass of "beer" can follow Beer-Lambert, yet a
glass of Pure Water doesn't? Oh wait, maybe its not "beer" but rather a specific
"species" concentration in beer thats causing the perceived relationship.....OK
then, CAN SOMEONE PLEASE TELL ME WHAT THE SPECIES IS, AND WHY YOU THINK ITS
RESPONSIBLE FOR ANY COLOR OTHER THEN (430nm) YELLOW?  BTW: pour me up a Killians
RED!....no yellow color there...Guinness Stout...all black...where is the
(430nm)
Yellow color that is the sole basis for everyting associated with the misguided
"Beer color follows Beer-Lambert hence, you can use a spectrophotometer to
determine the
color of beer" thing going on with certain HBDers?

The apparent color a beer has, has little or nothing to do with Beer-Lambert.
Ahhh... but isnt ignorance Bliss!

Any respected (Masters or Ph.D)water chemistry professionals out there, please
help me to understand. Anyone?

TIA


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