Chemiluminescence - The Glowing Spiral

Demonstration Experiment on Video

Chemiluminescence - The Glowing Spiral

Objective: Chemiluminescence

Peter Keusch

German version

Chemicals:
fluorescein (Sigma)
lucigenin (Sigma)
luminol (Fluka)
rhodamine (Aldrich)
ethanol 96 %
hydrogen peroxide 30 %
Na₂CO₃
NaHCO₃
(NH₄)₂CO₃ · H₂O
CuSO₄ · 5 H₂O

Apparatus and glass wares:
glass spiral assembly fitted with a glass funnel at the top and a stop cock at the outlet
2 separatory funnels
4 Erlenmeyer flasks 200 mL
volumetric flask 100 mL
4 beakers 200 mL
magnetic stirrer
2 magnetic stirring bars
stirring bar remover

Hazards and safety precautions:

Hydrogenperoxide 30 % is toxic, corrosive - can cause serious burns. Eye contact can cause serious injury, possibly blindness. Harmful by inhalation, ingestion and skin contact.

Rhodamine B is harmful oif swallowed, inhaled or absorbed through the skin.
Copper(II) sulfate is harmfull when swallowed.

Ethanol is highly flammable.

Safety goggles and protective gloves must be worn. Effective ventilation!

The following solutions are prepared:

Solution A: · 0.4 g of Na₂CO₃ are dissolved in 60 mL of dist. H₂O. 0.2 g of luminol are added. The mixture is stirred until homogenous. 2.4 g of NaHCO₃, 5 g of (NH₄)₂CO₃ · H₂O and 0.4 g of CuSO₄ · 5 H₂O are added and the mixture is stirred until dissolved. The solution is diluted to 100 mL.

Solution B: · 6 mL of 30% H₂O₂ are mixed with 95 mL of dist. H₂O.

Solution C: · 0.8 g of NaOH are dissolved in 65 mL of dist. H₂O. The solution is mixed with 30 mL of EtOH and 5 ml of 30 % H₂O₂.

Solution D: · 0.02 g of lucigenin dissolved in 100 mL of dist. H₂O.

Solution E: · 0.05 g of rhodamine B dissolved in 100 mL of dist. H₂O.

Solution F: · 0.1 g of fluorescein dissolved in 100 mL of dist. H₂O.

Experimental procedure:

The glass spiral is aligned vertically. Two separatory funnels are placed in such a way that their spouts can be positioned against the inner wall of the glass funnel at the top of the spiral. The separatory funnels are filled with the solutions: one funnel is filled with solution A and the other with solution B. The room is darkened. Simultaneously the stopcocks on the two separatory funnels are opened, allowing the solutions to pour into the glas funnel at the top of the glass-spiral apparatus. An erlenmeyer flask is placed under the spiral to collect the solution as it flows out of the exit tube.

In a further experiment the separatory funnels are filled with the solutions C and D, respectively. The experimental procedure occurs as above described. The color of the luminescence can be variied by addition of the solutions D und F.

Results:

Luminol generates a bright bluecolor.

The chemical reaction of lucigenin with hydrogen peroxide generates a pale-bluish glow. When the reacting solution is mixed with fluorescein a color change can be observed. The glow will be a yellow-green color. This process is called fluorescence. The rhodamine B dye will gradually change the color of the luminescence from blue to red. Adding a mixture of fluorescein and rhodamine B yields an orange luminescence.

Video clip (Download RealPlayer .rm Datei)

Video clip (Download RealPlayer .rm file)

Discussion:

Chemiluminescence is the emission of light during a chemical reaction. The light from such reactions is called "cool" light, because it is created without heat.

Luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) and lucigenin (N,N'-dimethyl-9,9'-diacridinium nitrate) produce excited molecules that emit light.

· · Luminol reacts with hydroxide to form a resonance stabilized diazaquinone dianion which is oxydized by hydrogen peroxide into an unstable peroxide. The oxydation is catalyzed by Cu²⁺. The decomposition of peroxide yields an excited carboxylate anion which emits a photon in returning to the ground state (1).

· · Lucigenin undergoes a reaction with hydrogen peroxide to form an unstable dioxetane whose decompostion leads to N-methylacridone in an electronically excited state (2). The excited acridone emits light as it relaxes to a stable state.

· · Sensitizers, such as rhodamine B and fluorescein are used as energy transfer reagents for enhancing the chemiluminescence.

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