spec 20's

Carl Pike carl.pike at fandm.edu
Thu Apr 3 14:22:50 EST 2003



Following is a compilation from the CUR list a few years ago on spec
20s. Spec 20's
spec 20s - our meter-type spec 20s have also lasted forever.

About spec's... You need to think about the range of absorbancies you
will
need to work with.  That can dictate the spectrophotometer you use.  I
still
like the spec 20's, but haven't had experience with others.  I prefer
the
dial, rather than digital output, but I think everything is digital
today.

How often do you use them?  This is one place where we decided that for
the few
intro teaching labs where we use the Spec 20s the old gray analogs were
working
just fine, and we bought a few more of them used.  We spent the money we
saved
on microscopes, balances, pH meters and the like.  The upper-level
courses
(fewer students) use research instruments.

We have Spec 21's now that replaced most of the Spec 20's.  I 'm not
sure where you can get good used equipment-usually it's better to buy
new if
you can.

With respect to spectrophotometers, I would seriously considering
looking at fiber optic units from Ocean
Optics. We have one of them and are very satisfied with it.

Spec 20's as such don't exist anymore.  The Genesis replacement seems
pretty
good and we got a good deal from Fisher for 6 of them.  If you can scare
up
an additional $4K the Genesis 8 UV/vis spec is a nice little instrument
for
molecular biology.  Add $500 in software and scrounge up a computer and
it
is a general purpose scanning spec.

Pharmacia has a $2 K Vis spec that looks good but they don't seem too
excited about selling them.

I haven't heard anything more than mild enthusiasm, and some complaints
about Sequoia Turner.

spec 20's are really, really out of date.  I suspect that the
cheapest route is still to try to find a few used ones so that you
have a matched set.  However,If you have some money you might consider
updating to more modern and
robust equipment.  There is a company called ChemAT that makes a
spectrometer with very good specifications that should be student
proof because the sample chamber is isolated from the components (on
a Spec 20 a spill in the sample chamber will get in the optics or
electronics).  The big plus is they are relatively cheap compared to
the other options <$1000 for each unit.  They have good resolution
(much better than a spec 20), are stable and very sturdy having been
designed to operate in mines originally.

The reason I know about these is that we just replaced about 12
failed spec 20's and more modern NovaSpec II's with these instruments
from ChemAT.  The ChemATs were much cheaper than the much lower
performance NovaSpecs or similar replacements.

We have the same brand, in several flavors.  All of the newer analog
instruments have a 5mV DC output.  If you can afford it, you can convert

to digital with a couple of attachments from Qubit Systems Inc
(www.qubitsystems.com).  Call them and they will help you (and tell them
I
sent you).

As for the Spec 20's, these are fine for student labs.  There is a
company
   that refurbishes and repairs Spec 20's and the analog portion can be
   inexpensively converted to a digital output.  I don't know of other
less
   expensive student lab spectrophotometers.


I just bought new digital Spec 20's from Fisher for my general chem
lab.   I haven't used them yet, though.  They look nice!  I like the
fact that they hold cuvettes instead of test tubes.



For our biochemistry and general chemistry laboratories, we have
just switched from Spec 20's to Ocean Optics systems for visible (and
UV)
spectroscopy.  We got four of these computer-controlled visible systems
for
~$9K (this did NOT include the computers).  We have since purchased two
UV-visible systems (another ~$8K) which has worked well for our teaching

laboratory needs.

Once someone works through the software and puts together an
instruction sheet, these instruments are great!  In general chemistry,
students are able to collect much more data independently than in
previousyears.  In our upper level biochemistry labs, students collect
kinetic data
in a fraction of the time that it used to take, they can immediately
download their data to Excel for spreadsheet calculations, and they now
have time to anaylze their data during the laboratory session (and not
the
night before the lab is due!!).

I highly recommend you take a look at these systems and consider
upgrading.  The costs above include the trade-in discount we got for our

old spec20's.The ocean optics web site for these spectrometers is at:
http://www.oceanoptics.com/spectrometers.asp
Some of my students in instrumental analysis wrote a tutorial (in
microsoft powerpoint)... it is still undergoing modification but feel
free
to download it and take a look at that as well... although I will soon
be
making the site accessible only withing Colby so please take a look
soon....
http://www.colby.edu/chemistry/CH332/tutorial-list.htm

The Spec 20 is a 1950s spectrophotometer and I really don't recommend
buying more.  The band pass is 20 nm and this is so wide that it
introduces error into many determinations.  They are so old, that
they are almost never used in industry, so students are not being
trained on equipment like that they might see in a job.  The analog
output is not linear with absorbance, so they can't be used with a
chart recorder.  Finally, students cannot keep their hands off the
knobs and routinely twist them too fast or too far.

For about the same price you can buy a digital version of the Spec
20.  However, the company makes a series of more sophisticated
spectrophotometers under their 'Spectronic' logo.  These are much
better than the Spec 20 and don't have knobs.

If you buy a more expensive, but automated spectrophotometer, you
might find that more students can use it during the class period.  An
example would be the Shimadzu UV1201 which also does wavelength
scanning.

However, be aware that the more sophisticated spectrophotometers are
also more difficult to repair locally.  You might research which
company provides the best service locally.


I have dropped all use of spec 20's (the old ones are really unstable
and
the experience of calibrating them does nothing for the student
experience)
and replaced them with one plate reader. One microplate reader can do 96

samples at the same time, enough for a typical class - and a plate
reader
is self-calibrating and uses cheap (under $1 each 96-well microplates.)
There is nothing wrong, I think, in using the kind of equipment students

will see in the real world and (except perhaps for developing countries,

spec 20s are no longer used in hospitals and research labs.)


Re:  spec 20's.  These are useful for single wavelength analyses
but we have switched over to Diode Array spectrometers which offer
multiple wavelength capability, speed, and ease of use of computer
driven and modern equipment.  We happen to have Diode Array
spectrometers from Hewlett Packard.  Competing scanning UV-Vis fast
scanning spectrometers are also available from other manufacturers
such as Cary.

The only other specs we have purchased are Pharmacia-LKB UV-vis specs.
These are very easy to use with digital read out.  We have found them to
bevery student friendly and much more versatile than Spec 20s.

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