The beauty of having calibration cuvettes is that the light source no longer
matters. You can use sunshine, you don't need mercury vapor lamps. The
mercury vapor is for the frequency calibration, the cuvettes are for the
amplitude calibration, and more specifically for the DNA concentration
application. The absorption bands are pretty wide, so you would not get
great resolution using them in the frequency domain. But for that same reason,
going nuts about high resolution and resolving sub-nanometer lines is
overkill for the DNA application. If you're within a few nanometers, you are
just fine.
I'm not sure why you care about fiber coupling. It seems like an unnecessary
complication. But it is easy to take a glass rod and pull a fiber from it. This
gives you a nice gradual taper from the half-inch diameter rod to whatever
size fiber you want.
Your optics are probably good for a nanometer or so of resolution.
Paying for a special mercury vapor lamp that is good for ten thousand times
that much is probably a waste of money, when a cheap fluorescent bulb
will get results consistent with the resolution of the optics in your spectrometer.
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Get a free science project every week! "http://scitoys.com/newsletter.html"On Sun, Nov 27, 2011 at 9:21 AM, John Griessen <john@industromatic.com> wrote:
On 11/27/2011 04:54 AM, Cathal Garvey wrote:
However, I*do* like the idea of using an equivalent-absorbance sample
of non-DNA! That's pretty promising, you could pick something that
simply doesn't degrade much and it'd probably be cheap(er) to mass-produce.
I thought a little about that too. The instruction sheet to send with it could say,
"Consider this calibration reference as equivalent in absorption to ____ type of DNA
at these three wavelengths only: 253.7 nm, 435.833 nm, 546.074 nm, so be sure
to use only these spectral lines of mercury vapor for comparison to
actual DNA." The trick is you would want your equivalent absorbers to be at an absorption
maxima so any spectrometer system drift didn't impact them. A recipe
of just three overlapping absorbers would take a good bit of time using
a good calibrated spectrometer to do -- chicken/egg situation.
The price of calibrator reference material chunks could be really low if the recipe
for cooking them up was OSHW published. Looking up mercury spectral lines,
I came across a right angle adapter so you can shine calibrator light into a
1 cm cuvette holder space in a spectrometer priced at $300. That price is
bound to be a small market, low volume kind of price -- all it is, is a mirror
and some plastic and SMA 905 fiber connector.
Here's an available article about measuring accuracy of HG + Ar cal lamps:
http://pe2bz.philpem.me.uk/Lights/-%20UV-Lights/Uv-901-UV-ApplNotes/SpectralResearch/wavelengths.pdf
with conclusions: "With the
exception of the 434.7-nm line, the wavelengths are
consistent for the three lamps observed, and the values we
present should be useful as wavelength standards at the level
of 0.0001 nm for instruments with resolving powers of less
than 17 000."
So, I wonder how well small display back lights with Hg vapor and phosphors
would do? They're in glass tubes about 1/8 inch thick -- how would we aim
a long line of light down a fiber without refracting it much? A stair step
shape in acrylic might gather light and aim at a small spot so it goes in the
fiber, but refract some so far it misses...
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