HOMEBREW Digest #5202 Mon 02 July 2007

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  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 Return to table of contents
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