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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: jay on September 07, 2004, 10:23:36 PM

Title: Fluorescence
Post by: jay on September 07, 2004, 10:23:36 PM

hey, ive been given the below problem in an assignment and have no idea how to solve it. Please help.  :'(

Prblem: A solution of iodide ions gave a fluorescence reading of 62%T. A 10 ml aliquot of a 0.2 mg/L iodide standard was added to 5ml of the solution. What is the concentration of iodide in the solution if the fluorescence intensity of the spiked solution was 84%T?

i know i must use the formula

F= 2.303.K.0.P.E.b.c

where F= fluorescence
         K= Fraction of emitted radiation being  
              collected, usually 90 degrees
         O= fraction of species in sample which
              deactivates to yield the measured emission.
         b= light path
         c= concentration
         E= molar extinction coefficient
         p=incident radiation

any help would be great.

thanks

Title: Re:Fluorescence
Post by: Mitch on September 08, 2004, 01:25:46 AM

Maybe just Beer's law will do it for you?

Title: Re:Fluorescence
Post by: Demotivator on September 08, 2004, 10:39:44 AM

It's a standard addition problem
The ratio of intensities is proportional to the ratio of concentrations so
Funk/F unk+std = conc _unk/conc _unk+std
where
conc _unk+std
= (Vi/Vf)(conc unk) +(Vi/Vf)(conc std)
solve for conc unk

Only, I don't know why you have %T implying transmittance instead of F.