Fluorescent Dye Experiment: pH of Pyranine - UVa

FOV: 4" wide.

 

This experiment demonstrates the shift in color from yellow-green to blue-green in aqueous solutions of pyranine when made acidic.

 

The fluid from a yellow hi-liter pen was removed and mixed with water (shown in the center test tube). The left test tube contains that solution with 1 drop of muriatic acid added. The test tube on the right contains the solution with 5 drops of a sodium hydroxide solution.

 

The pH of the left test tube was ~1 and the right test tube ~14. It was hard to measure the pH of the solutions since it dyed the pH indicator paper yellow.

 

Upon adding the drop of acid to the pyranine solution, it changed from yellow green to clear. This was because the pyranine had been protonated (provided a hydrogen ion) which reduced the absorption of light at 450nm.

 

Refer to this article: www.ugcfrp.ac.in/images/userfiles/30241-CPL_399_147.pdf

 

"At a pH less than 7, the absorption spectrum of pyranine

(HPTS) exhibits a peak at 405 nm which is ascribed to

the protonated form (ROH) while at a pH greater than 7 the

absorption spectrum exhibits an additional band at

450 nm arising from the deprotonated form (RO)."

 

 

See also:

nathan.instras.com/documentDB/paper-273.pdf

 

Contains:

Pyranine sol. pH less than 7 (FL Blue-green >UVabc)

Pyranine sol. pH greater than 7 (FL Yellow-green >BL/UVabc)

 

Shown under UVa light.

 

Key:

WL = White light (halogen + LED)

FL = Fluoresces

PHOS = Phosphorescent

Blue = 450nm,

UVa = 368nm (LW), UVb = 311nm (MW), UVc = 254nm (SW)

'>' = "stimulated by:", '!' = "bright", '~' = "dim"

 

pH of Pyranine

17Nov2015

 

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18 Watt Triple Output UV lamp from Polman Minerals - Way Too Cool UV lamps

Done