Talk:Ultraviolet–visible spectroscopy

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Wiki Education Foundation-supported course assignment

This article was the subject of a Wiki Education Foundation-supported course assignment, between 26 August 2020 and 18 December 2020. Further details are available on the course page. Student editor(s): Imranwiki hunter.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 11:55, 17 January 2022 (UTC)[reply]

https://www.nature.com/articles/s41586-024-07094-9 78.3.186.246 (talk) 22:49, 17 March 2024 (UTC)[reply]

Maybe a new "Chemistry" section

Maybe a Chemistry section should be added to this article explaining electronic transitions, chromophores, lambda max, mentioning Woodward-Hoffman rules. H Padleckas 21:47, 14 May 2005 (UTC)[reply]

May not be necessary since all those terms are mentioned throughout the article. LostLucidity (talk) 20:18, 3 April 2008 (UTC)[reply]

Use in HPLC

Might be worth adding something about the use of UV/VIS spectrophotometers as detectors on High-Performance Liquid Chromatography (HPLC) instruments. Alan Pascoe 20:27, 22 July 2006 (UTC)[reply]

Done. Anything to add? --Rifleman 82 21:47, 22 July 2006 (UTC)[reply]

Types of instrument, tweak; See also: IR

I think the types of instruments listed is an artifact from how spectroscopy is traditionally taught. Single and double beam machines, choppers, etc. Stuff like diffraction gratings which are no longer used, now that we have FT.

I added the See also: IR because I feel that they are complementary techniques. One is quantitative, while the other is qualitative.

--Rifleman 82 18:50, 19 September 2006 (UTC)[reply]

Yeah, I'd just noticed that the content under "Types of Instrument" was all also under the section "Ultraviolet-visible spectrophotometer". It should certainly be there, since the majority of instruments are still dispersive, even with improvements in FT performance. UV/Vis and IR *are* complementary techniques, so we might as well 'see also' NMR, and Raman, and MS, since all of these also "complement" UV/Vis. (That's slightly ironic; I don't really suggest pointing to NMR since the two techniques aren't really very similar in either how they work or what they provide. Then again, I wouldn't have thought to point out IR as being particularly close to UV/Vis.) Anyway. I don't think any information's been lost, in either section; if you think I condensed too much feel free to change it back. :) Jaeger5432 19:22, 19 September 2006 (UTC)[reply]

Just sticking with spectrophotometers, I think it would be useful to explain more about the measurement limitations of these instruments. For instance, a user would be helped by understanding something about the useable dynamic range of the measurements that can be made with different instruments, why this might matter to them, and how they could go about determining it. A simple instrument such as the Spec 20 is challenged to measure to 0-2 AU (~1% transmission). A few, very elaborate, instruments can measure, without resort to a calibration curve, 0-6 AU directly (~0.0001% transmission). For monochromator-based instruments the key parameter is the stray light level.

--AJim (talk) 06:00, 17 December 2008 (UTC)[reply]

Molar (decadic) absorption coefficient

IUPAC recommends that ε be called the molar (decadic) absorption coefficient. See [1], [2], and especially [3].
— DIV (128.250.204.118 08:20, 7 September 2007 (UTC))[reply]

Capitalization consistency

Is there a standard way to capitalize UV/VIS? The page uses UV/VIS, UV/Vis, and UV/vis interchangeably, as far as I can tell. Perhaps a note should be added about this. Chessbot (talk) 16:46, 4 January 2008 (UTC)[reply]

I put in a vote for UV/Vis and have changed the article in the interim for the sake of consistency. This is the standard I have seen used in most UK and US hardcopy trade publications. If anyone disagrees, feel free to edit, but if you're going to do so please be consistent throughout... --SciHound (talk) 19:55, 3 June 2010 (UTC)[reply]

short path length measurements

I notice that information about instruments with built-in short path length capabilities has recently been deleted as non-notable advertising. I have experience in using short path length cells (0.1 mm or shorter) and I know just how difficult it is to work with them successfully; a lot of care and special technique is required. For instance, I never found a good way to clean dried protein deposits from cylindrical fixed length cells; when a sample was allowed to dry in one of these Suprasil cells, a very expensive cell became a total loss. The demountable cells, on the other hand, require great care in closing and sealing them. In the particular work I was involved in, short path cells, no longer than 1 mm path, were necessary in the UV below about 220 nm because of solvent absorption. Based on my experience, I think it is very difficult to create an instrument with a short path with a highly reproducible length and a good seal. A small sample volume has other obvious advantages as well. While many uses of spectrometers can be satisfied by a very simple instrument, I believe having a reliable method of using short paths and small volumes will make many new applications feasible and will also save considerable laboratory time and cost. So I think that describing this class of instruments is certainly notable and belongs in the article. --AJim (talk) 03:28, 7 March 2012 (UTC)[reply]

Absorption flattening

A relevant reference was added and a missing link deleted.

Definitions incoherent

Ultraviolet–visible spectroscopy or ultraviolet-visible spectrophotometry (UV-Vis or UV/Vis) refers to absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region. This means it uses light in the visible and adjacent (near-UV and near-infrared) ranges.

You've just redefined

"ultraviolet plus visible"

to mean

"near-UV plus visible plus near-infrared"

I'm sure these don't mean the same thing. So which range is it? 178.39.122.125 (talk) 07:28, 29 July 2016 (UTC)[reply]

The answer is that it depends on the instrument. The instrument spectral range supplied depends somewhat on design choices, mostly influenced by marketing considerations. There is at least a 30:1 range of price for commercial instruments in this general class, spectral range and dynamic range being major differentiating factors. So there are a lot of different designs that fall within this general category of UV/VIS, and some few instruments are actually called UV/VIS/NIR. FT techniques do not offer an advantage over the PMT. Therefore, most of these instruments use photomultipliers as the detector. These detectors are not inherently limited to the range of light that our eyes can see. Most photomultipliers are sensitive into what we call the near infrared, well beyond the nominal 700 nm limit for the eye. The dispersing mechanism is likewise not inherently limited to the visible. Instrument designers have to make trade-offs, but there is no reason why they have to stop at 700 nm, and some do not. PMT's are available that can be used out to about 1600 nm, and some special purpose instruments have been constructed to take advantage of that. There are some commercial UV/VIS/NIR instruments with a second IR detector added to explicitly extend the range to about 2000 nm. Again, there are other cost trade-offs. For instance, some commercial instruments incorporate an added-cost technique to extend the dynamic range of measurement, adding a chopper before the monochromator in order to deal with stray NIR light emitted inside the monochromator.

Some of the ultraviolet range comes almost for free. This is why even simple instruments can have a limited, but useful, UV range and can be called UV/VIS. For instance, a common tungsten-halogen light source works quite well out to about 300 nm, well beyond the visible, and most PMTs work well here. Extending the range below 300 nm generally requires another light source, a deuterium lamp being a common solution. The further you go into the UV the harder you must work though. Air absorbance becomes an obstacle below about 220 nm, for instance. High quality PMT's with "UV glass" windows are available that work quite well below that limit though. Mirror reflectance also needs to be enhanced for the low UV.

I just went and looked at the DU spectrophotometer article. Even this early instrument worked in the NIR, although it was called a "UV/VIS" instrument. There is a graph copied from the manual that shows performance out to 1000 nm. FWIW.

AJim (talk) 19:27, 24 April 2017 (UTC)[reply]

Ordering of sections

Much of the material in the section entitled Practical considerations would be more comprehensible if it were placed after the explicit description of the device in the section called Ultraviolet-visible spectrophotometer. 178.39.122.125 (talk) 12:35, 29 July 2016 (UTC)[reply]