FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups 
 ProfileProfile   PreferencesPreferences   Log in to check your private messagesLog in to check your private messages   Log inLog in 
Forum index » Science and Technology » Chem » Analytical
fluorescence of turbid samples
Post new topic   Reply to topic Page 1 of 1 [8 Posts] View previous topic :: View next topic
Author Message
Farooq W
science forum Guru Wannabe


Joined: 25 Mar 2005
Posts: 240

PostPosted: Thu Jul 06, 2006 4:28 am    Post subject: Re: fluorescence of turbid samples Reply with quote

Fabio Mancini wrote:
Quote:
dear all,
I know the lambda^-4 dependence of scattered light. What I am interested
now
is not this dependence (which however is experimentally seldom -4), but
to the
dependence of the shape of the Rayleigh peak.

Suppose you have the Rayleigh peak at 250 nm. When you scan the emission
monocromator from - let's say - 230 to 300, surely you will find a band
centered at 250 and not a line. OK: I am interested in the functional
dependence of this band from the emission WL (not the excitation WL).
Do you know something about it?
thank you


I will post this question in another forum and let you know here if a
reasonable solution is found.
Back to top
Fabio Mancini
science forum beginner


Joined: 22 Dec 2005
Posts: 17

PostPosted: Wed Jul 05, 2006 11:45 am    Post subject: Re: fluorescence of turbid samples Reply with quote

dear all,
I know the lambda^-4 dependence of scattered light. What I am interested
now
is not this dependence (which however is experimentally seldom -4), but
to the
dependence of the shape of the Rayleigh peak.

Suppose you have the Rayleigh peak at 250 nm. When you scan the emission
monocromator from - let's say - 230 to 300, surely you will find a band
centered at 250 and not a line. OK: I am interested in the functional
dependence of this band from the emission WL (not the excitation WL).
Do you know something about it?
thank you





--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
Back to top
Farooq W
science forum Guru Wannabe


Joined: 25 Mar 2005
Posts: 240

PostPosted: Wed Jul 05, 2006 2:23 am    Post subject: Re: fluorescence of turbid samples Reply with quote

Fabio Mancini wrote:
Quote:

what about a turbid sample without fluorescence? what is the WL
DISTRIbution
of scattered light?


The efficiency of Rayleigh scattering increases inversely with the fourth power of the
wavelength, so the spedtral distribution is skewed, though there are no new peaks.
Tyndell scattering is more complex, but again it won't make new peaks.

New peaks can come from fluorescence and Raman scattering. For both of these processes,
the new peaks at longer wavelength will be much stronger than at shorter wavelengths. And
there can be artifacts from the measuring instrument.


I came back to this original post to specify better my question.
You know that for turbidity measurement you can fit a turbidity curve
with a function of the type: abs = const1 * WL^(-const2), where const2
should be in principle 4 but very often is less than four.
if you have a turbid sample and excite it at - let's say 280 nm - and
collect
the emitted light from 280 to 350 (for example) you will have by sure
a turbidity peak (call it if you want Rayleigh peak of the I order).
My question was: what is the WL dependance of that peak? Can I fit it
with
some function?
thank you

If you have Galen W. Ewing "Instrumental Methods of Chemical Analysis"
5th Ed., see page 155. A relation is described for turbidity (tubidity
function) and wavelength. As Marvin said, it is inversely related with
wavelength to fourth power. I can email a scanned page for I can not
type it here.

I assume you are interested in emission spectrum of a turbid solution.
The easy identification point is that a peak will appear exactly at the
same position of the wavelength of excitation. e.g. you were scanning
from 280 to 350 nm using excitation at 250 nm. The Rayleigh peak will
appear at 250 nm.
Back to top
Fabio Mancini
science forum beginner


Joined: 22 Dec 2005
Posts: 17

PostPosted: Tue Jul 04, 2006 5:35 pm    Post subject: Re: fluorescence of turbid samples Reply with quote

Quote:

what about a turbid sample without fluorescence? what is the WL
DISTRIbution
of scattered light?


The efficiency of Rayleigh scattering increases inversely with the fourth power of the
wavelength, so the spedtral distribution is skewed, though there are no new peaks.
Tyndell scattering is more complex, but again it won't make new peaks.

New peaks can come from fluorescence and Raman scattering. For both of these processes,
the new peaks at longer wavelength will be much stronger than at shorter wavelengths. And
there can be artifacts from the measuring instrument.


I came back to this original post to specify better my question.
You know that for turbidity measurement you can fit a turbidity curve
with a function of the type: abs = const1 * WL^(-const2), where const2
should be in principle 4 but very often is less than four.
if you have a turbid sample and excite it at - let's say 280 nm - and
collect
the emitted light from 280 to 350 (for example) you will have by sure
a turbidity peak (call it if you want Rayleigh peak of the I order).
My question was: what is the WL dependance of that peak? Can I fit it
with
some function?
thank you



--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
Back to top
Marvin
science forum Guru Wannabe


Joined: 24 Mar 2005
Posts: 224

PostPosted: Sat Dec 24, 2005 6:30 pm    Post subject: Re: fluorescence of turbid samples Reply with quote

Fabio Mancini wrote:
Quote:
my fluorofore is the green fluorescent protein (483/508) the shift is
quite
small. I know of the front-face accessory, but I would liketo know
whether someone knows something in general about the spurious peaks of
a turbid sample. In my instrument I observe several peak over a high
background
thank you

what about a turbid sample without fluorescence? what is the WL
DISTRIbution
of scattered light?


The efficiency of Rayleigh scattering increases inversely with the fourth power of the

wavelength, so the spedtral distribution is skewed, though there are no new peaks.
Tyndell scattering is more complex, but again it won't make new peaks.

New peaks can come from fluorescence and Raman scattering. For both of these processes,
the new peaks at longer wavelength will be much stronger than at shorter wavelengths. And
there can be artifacts from the measuring instrument.
Back to top
Fabio Mancini
science forum beginner


Joined: 22 Dec 2005
Posts: 17

PostPosted: Fri Dec 23, 2005 9:10 pm    Post subject: Re: fluorescence of turbid samples Reply with quote

my fluorofore is the green fluorescent protein (483/508) the shift is
quite
small. I know of the front-face accessory, but I would liketo know
whether someone knows something in general about the spurious peaks of
a turbid sample. In my instrument I observe several peak over a high
background
thank you

what about a turbid sample without fluorescence? what is the WL
DISTRIbution
of scattered light?


--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
Back to top
David C. Stone
science forum beginner


Joined: 05 May 2005
Posts: 48

PostPosted: Fri Dec 23, 2005 2:08 pm    Post subject: Re: fluorescence of turbid samples Reply with quote

In article
<5fe8db52f1d1135b91180f0fde0f8eb6.28560@mygate.mailgate.org>, Fabio
Mancini <p775184@yahoo.it> wrote:

Quote:
Hello friends
I was interested in doing some fluorescence of turbid samples. In all
fluorescence book I read this topic is treated at very low level and
with no systematic approach. Do you know a book or review that can be of
interest with respect of this subject?
thank you very much

True fluorescence or light scattering? I've done some work on solid
powder sample fluorscence using a front-surface sampling accessory,
and this works pretty much as you might expect - too much fluorescing
species per unit surface area, and you get non-linear calibration, plue
you have to worry about specular (and, to some extent, diffuse)
reflectance if the Stokes shift of your fluorophore isn't large enough.
Back to top
Fabio Mancini
science forum beginner


Joined: 22 Dec 2005
Posts: 17

PostPosted: Thu Dec 22, 2005 7:44 pm    Post subject: fluorescence of turbid samples Reply with quote

Hello friends
I was interested in doing some fluorescence of turbid samples. In all
fluorescence book I read this topic is treated at very low level and
with no systematic approach. Do you know a book or review that can be of
interest with respect of this subject?
thank you very much



--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
Back to top
Google

Back to top
Display posts from previous:   
Post new topic   Reply to topic Page 1 of 1 [8 Posts] View previous topic :: View next topic
The time now is Wed Jun 28, 2017 12:17 pm | All times are GMT
Forum index » Science and Technology » Chem » Analytical
Jump to:  

Similar Topics
Topic Author Forum Replies Last Post
No new posts Why fluorescence emission bands quite broad as compared t... Farooq W Analytical 1 Sat Apr 29, 2006 2:39 pm
No new posts Why are fluorescence emission bands comparatively broad? Farooq W Chem 0 Sat Apr 29, 2006 2:37 pm
No new posts Indentification of Raman and Rayleigh bands in Fluorescen... Farooq W Chem 16 Mon Apr 24, 2006 4:09 pm
No new posts Effect of Temperature on Emitted Wavelengths of Fluorescence Farooq W Chem 4 Thu Mar 09, 2006 6:35 pm
No new posts Statistical inference - likelihood with random samples Aleik Math 2 Tue Feb 14, 2006 1:47 pm

Copyright © 2004-2005 DeniX Solutions SRL
Other DeniX Solutions sites: Electronics forum |  Medicine forum |  Unix/Linux blog |  Unix/Linux documentation |  Unix/Linux forums  |  send newsletters
 


Powered by phpBB © 2001, 2005 phpBB Group
[ Time: 0.0222s ][ Queries: 20 (0.0035s) ][ GZIP on - Debug on ]