[Dolphinsiu]

I have read my lab manual and need to answer the following questions

What are the useful wavelength ranges for tungsten-iodine and deuterium lamps?

What are the useful wavelength ranges for glass and plastic cuvettes?

Are all of these questions be solved by going to the library to search the reference books??

[Ψ×Ψ]

For the first question, you're looking for the wavelength ranges where the lamp emits appreciably. 
For the second, you need to know the range where the material does not absorb, because otherwise your spectrum will be missing a good chunk of information where the cuvette ate the incident light. 

[ARGOS++]

Dear Dolphinsiu,

Yes you are right with the answer you have already spent yourself!
Generally for this kind of information, the manufacturer of such products expose also
these important “product parameters”!

But the answer is on the other hand not all times so “simple”, as ?*? tries to introduce it.
As I know, quite a number of Universities call an hp 8452A their own, which has ONLY
a Deuterium Lamp build in, and measures anyway till 820nm (Why?).
Of course it is possible!, if …… .

A Lot of  such UV/Vis Spectrophotometer and cuvette information, most other
“Spectro info” too, you can find for example on
           the “Spectroscopy FAQ  ?  Beer-Lambert FAQ” page:

   http://www.p-forster.com/english/themes/Spectroscopy/Spectroscopy_FAQ.htm

Of the same course, there, on that Site, you will find a lot of other Spectroscopy Information, too.

Good Luck!
                    ARGOS⁺⁺


P.S.:    Sorry for my “abstinence” during several days, but I had nearly not one chance to be “on Air”!

[Dolphinsiu]

Thank you!

But I still get stuck in these two questions!

1. Comment on the wavelength accuracy of the instrument that you have studied.
(I find that there is little deviation from the instrument when calibration is done but I can't find out any reason. Why? Is it related to real/stray deviation or scattering or other reasons..?)

2. Why should we use the same cuvette and having the same side of the cuvette facing the measuring beam for all the absorbance measurement?
(My techician say it is due to the thickness of cuvette in all side is difference. And some book say temperature can change the absorbance. Are both of them true, or other reasons?)

Thank you!

[Ψ×Ψ]

I don't think it's so much the thickness of the cuvette.  Remember, the cuvette is intended to absorb as little light as possible in the wavelength range of interest.  The cuvette isn't perfect, though.  Some impurities may be present in the glass/quartz/plastic, or some gunk may be stuck on there and impossible to clean off (isn't supposed to happen but does, especially if lab members are lazy with cleaning).  Using the same cuvette, same side, etc. for the blank as well as for the measurements ensures that this bit of error is subtracted out. 
Back when I was doing CD spectroscopy, SOMETHING got on the cuvette that wouldn't come off and was optically active.  This might have caused issues with the data had we not taken a blank reading as the "baseline" and subtracted this from all the spectra taken.

By the way, Argos, it's "absence" rather than "abstinence."  Discussing the latter might be a bit inappropriate for this forum. 

[ARGOS++]

Dear Dolphinsiu,

(?*?,  - No, “abstinence” is the correct joke,  - compare the Forum with “a good red wine!”)

The answer is not so easy to give, if you don’t know, how much precision you prefer.
Generally: If you need high precision, then keep as much as possible of all
you don’t like to measure as constant as possible.

Wavelength Accuracy:
For mechanical spectrometers:  As light doesn’t know anything about nanometers manufacturer needs some kind of translation. Most of the time they use a special formed (coded) wheel, so its very easy possible, that on mechanical spectrometers you can find small or “not so small” deviations in “coding”.
For Diode Array Spectrometers (PDA’s):  The focused images of the entrance slit for all wavelengths are not located on a line, they lie on a circle. But the electronic chip is build linear and is of course “nanometer-spaced” and not “energy-spaced”, too.
Ergo, there is also a “translation” required, a mathematical one.
Big advantage of a PDA: it has no mechanical parts (for deviations) and maths is "not so" influenced for deviation.
Apropos: A “2.0 nm” PDA is easy comparable (better) with a “0.5 nm” mechanical spectrometer. (Why?)

Cuvettes:
Cuvettes are “made” by temperatures around 1000 °C (~ 1800 °F) and  mechanically, so you will not be able to find two cuvettes with exact the same size (The major problem).
As also the inner wall is not exact plan-parallel to the outer, the location of the cuvette has also an influence on the precision you prefer, as the result will be “some” dislocation of the measuring beam. (Little minor problem)  In this case dislocation will not be the same if you turn the cuvette, too.
Quintessence: Use for most reliable measurement the so called “Flow through cuvettes”, which you can easily hold in the same relative position for all measurements.
But of course, it depends on the reliable precision you prefer.

Temperature:
If you mean that temperature has an influence on spectra, the answer is: Of Course – Some times a BIG!
If you mean for Quartz or Glass, the answer is: Not in the temperature range of their use. 

You may see, it’s easy to make some mistakes, but it’s of the same ease to protect you from.


Good Luck!
                    ARGOS⁺⁺

[english]

Some impurities may be present in the glass/quartz/plastic, or some gunk may be stuck on there and impossible to clean off (isn't supposed to happen but does, especially if lab members are lazy with cleaning). 

Letting them soak in conc. nitric acid usually works.

[Ψ×Ψ]

Some impurities may be present in the glass/quartz/plastic, or some gunk may be stuck on there and impossible to clean off (isn't supposed to happen but does, especially if lab members are lazy with cleaning). 

Letting them soak in conc. nitric acid usually works.

Yeah, I'm pretty sure we tried that.

[ARGOS++]

Dear g_english,

It seems, that you couldn’t get the answer from the:
             Spectroscopy FAQ  ?  Beer-Lambert FAQ -Page,  but it’s still there, as I know.

Apropos:  “conc. nitric acid usually works”
             For “plastic-cuvettes” there is ONLY an “acid” adequate ENOUGH:
                                       The “Garbage Collector”!

Quintessence:  
             Not all that works,   ? works well,  ? AND very rarely - adequate!

Good Luck!
                    ARGOS⁺⁺

[english]

Dear g_english,

It seems, that you couldn’t get the answer from the:
             Spectroscopy FAQ  ?  Beer-Lambert FAQ -Page,  but it’s still there, as I know.

I don't quite understand your logic.  I only deal with quartz cuvettes.  Nitric acid is used for cleaning procedures, for my research at least.  We don't deal with very messy substances, and we definitely clean ours after every use. 

I don't usually use nitric acid, I actually use consecutive washings of acetone and methanol, as my solvent is relatively volatile.  Another student that uses the available cuvettes, however, uses tetrachloromethane, which is pretty difficult to remove and can get troublesome, especially if the cuvette must be used again with a different solvent directly after use. 

[Ψ×Ψ]

Acetone & methanol sounds more familiar.  We used to use repeated washings of water, ethanol & acetone.  It's also much easier and less time-consuming if you have a cuvette washer   I miss that thing.

[english]

Acetone & methanol sounds more familiar.  We used to use repeated washings of water, ethanol & acetone.  It's also much easier and less time-consuming if you have a cuvette washer   I miss that thing.

Eh we don't have one of those!   

 

[ARGOS++]

Dear g_english,   Dear ?*?, 

I can’t  see where your problem with CCl₄ or similar solvents are caused.
If you keep  the “Thumb-Rule” for the Eluotropic-Raw of Solvents in mind, it should never be a problem for you again:
      “NEVER do a  - SINGLE, TOO LARGE -  jump inside the Eluotropic-Raw! ”

Quintessence:     Use a intermediate eluotropic Solvent inbetween!
(We all have to do it this way, unexceptional, if we don’t use the chemical Hammer.)

Appropos:   
A cuvette-washer is only a very expensive “Formula 1-Ferrary-Tool” for people who don’t like to think once only for a second, but NEVER of practical use!!! 
 
The much cheaper AND much more useful way:
Buy only once one  “Flow-through-cuvette” instead (with a “Bar-sipper”).  Why?
  - The result: Much higher precision, AND higher reliability TOO.

Good Luck!
                    ARGOS⁺⁺

[FireflySci]

Apologies for booting an ancient thread here but we can definitely help out on one of the questions from this manual where I didn't see an answer thus far:

"What are the useful wavelength ranges for glass and plastic cuvettes?"

For glass, it's usually 340-2,500nm and for plastic cuvettes, it depends. Plastic can either be referring to acrylic/pmma, polystyrene or "UV Plastic". Here are their respective wavelength ranges: Acrylic/pmma (285-900nm), polystyrene (340-900nm), UV Plastic (220-900nm).

We have a ton of different articles on cuvette materials over at http://www.fireflysci.com. Give us a holler!

[Babcock_Hall]

http://www.brandtech.com/cuvettegraph.pdf

My own experience is that methyl acrylate cuvettes work to about 280 nm, but not much below that.