M
Marvin
Bill said:
I said I would on request. He hasn't asked for it.
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building a spectrophotometer from off-the-shelf parts
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I said I would on request. He hasn't asked for it.
M
Marvin
Mark said:Betcha a nickel it's the biggest one in the solar system.
You owe me a nickel. Give it a charity in my name. The
light source was a 4W blacklight lamp.
I'll probably try that next. I've been putting distillate into a
graduated cylinder, weighing that, then using a density chart to get
ethanol fractions. Crude, but it (kinda) works.
The link is confusing. One pic shows a white LED; the title implies
use of a 100W light bulb.
I like Marvin's idea of using a small blacklight. Now, to get those
wavelengths one at a time...
Thanks,
Michael
I just realized google groups (if you're using it) might mangle my
email address. It's
m r d a r r e t t {at-symbol} g m a i l {dot} c o m
Thanks,
Michael
A
Allan Adler
One problem I've had with using ordinary light bulbs in optics is that
there is usually some writing on the bulb and it goes through the optics
along with the light.
F
Farooq W
My suggestion is that instead of finding ways to design a costly
spectrophotometer, which can scan wavelengths and is of course
delicate thing in terms of optics. You can design a colorimeter which
has a cheap source and optical filters. Both should be easily
available. BTW, does ethanol absorb in the UV? If it does, it would
lie towards quite short UV which is near 200 nm. First of all you need
to know the absorption spectrum of your analyte of interest and then
start looking for the source which emits near the wavelength of
maximum absorption and a optical filter. Tho, optical filters might be
available, a UV source might be more difficult to hand and obtain. The
rest of the work is for the electronics man!
Suggestions for IR or NIR, are perhaps impractical at home.
Read Dr. Marghoses reference on Ultraviolet Photometer, tho it is old
(~ 1950s) but the idea is still useful.
M. Farooq
D
default
Isn't the accepted way to measure the SG before and after fermentation
to determine how much sugar was converted to alcohol?
I make beer but never bother to measure the SG. Too much hassle, not
much you can do about it (beer happens) and there's risk of
contaminating the batch. There are some folks that claim it is
necessary to tell when fermentation is complete, but I find it easier
to control temperature and give it two weeks.
I did measure SG when I first started in 1990 - since a
hydrometer/thermometer came with the brewing kit I bought.
The only real reason to do it (that I can see) is to meet some
government requirement for labeling.
Single beam, single wavelength, crude, spectrophotometry is probably
not the answer for determining alcohol content. In the lab gas
chromatography was the first choice (another "easy" instrument to
build) then HPLC. Most HPLC can also be preformed with thin layer
chromatography (from what I understand) but TLC is better at finding
out what is in a compound than quantifying the amounts.
BTW we had an old Beckman spectro that used an auto light bulb for the
source and you adjusted the voltage (brightness) of the bulb to zero
the instrument then put the full cuvette in and measured the sample.
It was only useful for checking gross concentrations of substances
with relatively broad wavelength absorption. I'm pretty sure it would
be useless for alcohol.
Polarimetry may be a choice. Sugars twist light polarization -
optical rotation. It is a common instrument for checking sucrose
solutions. The instrument is a device with a light source, polarizing
filter, long 2-10" sample tube, with flat, optically clear, ends, and
a second - rotating polarizing filter before the detector. You
measure how much the second filter has to rotate to stop light from
reaching the detector between a blank (nothing in the cell or cuvette)
and the sugar solution.
Like SG it also has to be corrected for temperature - density.
Presumably you use maltose, I assume it would work with all sugars but
don't know for a fact.
Is this a hobby or business? Why do you care about alcohol and how
precise do you need to be? I have a few friends who are actual
chemists and do develop assays.
It's a hobby for now; it will maybe eventually become a business if I
get enough time and funding. It's for fuel ethanol, not for drinkable
ethanol. I'm actually starting with starch solutions (analogous to
making vodka from potatoes, or making sake from rice followed by
distillation). The requirement of hydrolyzing starch complicates
things a bit. I have to calculate how much alpha-amylase I need to
add to the starch solution, and how long I get them to react, before I
reach a set glucose concentration for the yeast to much on (I'd like
to keep it at no more than 200 g dextrose/L). Accuracy to 10% would
be great. Research as to how it's done in industry revealed that some
factories use on-line spectrophotometers to measure the ethanol
concentration within the pipes. That's what inspired this whole post.
I'd imagine dextrose assays would be more accurate than using
hydrometers...?
Thanks,
Michael
D
default
Your original post did say "beer." You lied.
I dabbled a bit with distillation. The usual technique is fractional
distillation in fractionating packed columns - I did nothing so
sophisticated.
Anything that makes it past the fractionating column(s) or thumper box
is alcohol and water and not sugar or starch. Different ball game.
Think about the spectro for a bit. If you had sugar water, pure
alcohol and plain water in glass test tubes it is likely you may not
be able to distinguish which is which (save for things like refractive
index, viscosity, meniscus or wetting properties). So it stands to
reason that any resolution a spectro could offer wouldn't be in the
visible wavelengths.
Then it is a matter of wavelength, so you'd need a monochromator or
filter to let a narrow band of light through the cell - quartz so as
not to absorb UV (probably rules out 100 watt light bulbs and LEDs as
sources since incandescent bulbs are poor UV sources and LEDs are
already pretty narrow band).
see:
http://home.att.net/~ledmuseum/leduv.htm
for spectral plots of UV leds
If you are really lucky the led would either absorb or transmit the
exact color of the UV LED and the rest of the compound wouldn't. If
that's the case, invest in a state run lottery, its bound to be more
lucrative.
Reason why early spectros and lots of chemical assays are for 318 nano
meters and 354 - they have lamps that are narrow band for those
wavelengths.
Today they use quartz xenon lamps ($100-200) and power supply, for
wide band light and a monochromator to select a 1-2 nanometer wide
slice of that to pass through the cell, or a Deuterium lamp ($100-200
and constant current power supply) with monochromator.
My forte isn't chemistry but I did spend a lot of time in the
production facilities and an assay lab for the pharmaceuticals.
For a pharmaceutical assay you generally start out with a known
compound. You know what should have gone into it. The chemical
precursors to the compound are either made on site or purchased. In
any case, an assay is either performed on the precursors (and you know
what you started with) or accepted from the manufacturer (how a lot of
children died in South America when the company making cough syrup
bought ethylene glycol that was certified to be glycerine by the
Chinese company supplying it).
Anyhow, very few pharmaceutical assays are simple. Before it gets to
the spectrophotometer, the chemical compounds are separated out using
a packed column of silica gel particles, the usual procedure for most
stuff. Each compound will have a specific affinity for the silica gel
and larger molecules take longer - all the stuff is injected onto the
head of the column in a lump (after the tablet is dissolved and a
solution of liquid only is made). A high pressure low volume pump
pushes the material through along with a "mobile phase" (the packed
column is the "stationary phase" but just called a column). As the
compound percolates through the tightly packed micron sized particles
the molecules are slowed to varying degrees by their own affinity for
the stationary phase. When they get to the end of the line, 2-15
minutes later, (columns being about 1/4" diameter and 2-12" long for a
lot of HPLC) they go into a quartz flow cell which shines a narrow
wavelength UV light and measures the absorption. To know what it is
you measure the time it comes off the column and to know the quantity
you measure the absorption with the spectrophotometer (just called a
"detector" by the HPLC chemists)
With a lot of HPLC you only need one wavelength of light - but they
can use scanning or dual wavelength detectors as well (costs lots
more).
There are lots of variations on this same theme using gas
chromatography and measuring the flame ionization potential, or
ionization from a nuclear isotope, capillary chromatography using long
coated capillary tubes and electrical conductivity or spectroscopy for
a detector, and thin layer chromatography (as seen on TV when showing
DNA analysis), better for substance ID but can be put into a box and
illuminated with light and reflection or fluorescence used to quantify
it.
PhD Chemists and especially professors, seem to think they know a lot
about chemical instrumentation and electronics. They generally have
no clue as to how incredibly sophisticated the instruments they use
have become from a technology viewpoint.
I'm not surprised to see the DIY "spectrophotometer" given the source
of the article - but I can say with a reasonable certainty that it
probably won't work for what you want. This guy found a substance
that absorbs in the near UV range with some source he had could
supply. He demonstrated the principles of how a spectrophotometer
works, not how to build a practical laboratory instrument. The fact
that the "peak" is so sloppy would seem to attest to the lack of a
good narrow wavelength source of light - and he does mention varying
the wavelength so he's using a diffraction grating as a monochromator
(or prism).
I couldn't find a representative spectrograph of KMnO4 on line, but
some references to detecting it in the IR range. That would have
been a good way to show how well his spectro works - comparing the
spectral plot of a real instrument to the DIY one.
If he had a better source, that sample would probably look like a
jagged series of sharp peaks. And You have no idea if one or more
compounds of what You want to resolve is at same wavelength - one peak
can cover and obscure another - one reason chromatography is used to
separate out the compounds before they are analyzed with a spectro.
In beer and traditional whiskey we take grains and let them sprout or
just germinate for a day or two, dry and crush them then let the
enzymes work on the mash while the solution/suspension of malt and
water is held at 150 F. The germination converts a lot of starch to
sugar and the enzymes develop and react on the remaining starch while
the drying stops the development of a plant and chlorophyll and other
yucky tasting things.
You're seeming to imply you have pure starch with no natural enzymes.
That doesn't sound like it will produce fuel economically - since to
arrive at pure (dead) starch, you inevitably start with some natural
substance and remove everything else that might convert it to sugar
naturally. Vodka was made long before you could just go out and buy
amylase enzyme . . .
Starch can always be used as food - so even if it were an unwanted
by-product there is a market for it.
An oversimplification, perhaps. Some experiments I did with alpha-
amylase and the kids' leftovers (closer to vodka, I guess); other
experiments I did with malted barley and the kids' leftovers (closer
to "beer" without hops), and some experiments I did with Aspergillus
oryzae (koji) and moldy bread (closer to sake). The A. oryzae's need
to be in a hot, aerobic environment made things... complicated.
It certainly doesn't make very good dinner conversation. "So, what
have you been up to?" "Oh, I've been collecting garbage and trying to
make fuel from it. Wanna hear about how my koji mold stank up my
garage?" <clattering of silverware>
I hadn't expected people to actually take an interest in my process,
so I oversimplified. Sorry to disappoint you.
Yep... the methods I learned in school involved trays and structured
packing. I remember stressing over q-lines while studying for the
Chemical PE exam several years back.
http://en.wikipedia.org/wiki/McCabe-Thiele_method
My feedstock is pretty much starchy food waste - kids' leftovers,
rice, bread, etc. I'll have to look up the history of vodka making...
Thanks,
Michael
R
Rich Grise
.
Have you tried getting methane from their poo? They have a virtually
unlimited supply of it, you know. ;-)
Cheers!
Rich
Have you tried getting methane from their poo? They have a virtually
unlimited supply of it, you know. ;-)
Cheers!
Rich
That reaction takes way too long - requiring really immense reactors
as a consequence. I estimate about three gallons of poo reactor to
get a single watt of electrical power. One single kWe would require
about 3000 gallons of poo reactor.
Reference: http://www.mnproject.org/pdf/Haubyrptupdated.pdf (page 23)
Then you have corrosion problems from the hydrogen sulfide...
Scale-up is impractical (at least on a home scale).
Michael
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