Test kits for water analysis
Test kits for water analysis

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Test kits for water analysis

4.2 Luminescence measurements

Luminescence refers to the production of light at low temperature; if emission is the result of a chemical reaction then the term chemiluminescence is used. An example is shown in Video 4 Chemiluminescence, a demonstration.

Download this video clip.Video player: Video 4
Skip transcript: Video 4  Chemiluminescence, a demonstration.

Transcript: Video 4  Chemiluminescence, a demonstration.

Here we mix a solution of 3-aminophalhydrazide - commonly known as luminol, with bleach. The blue glow is chemiluminescence. Bleach, an alkaline solution of sodium hypochlorite oxidises the luminol; the resulting aminophthalate ion contains electrons in an excited state. When these electrons drop down to the ground state, energy is lost in the form of light.
Let's see that again.
We generally associate the production of light with processes involving heat - an electric light bulb for example. But during chemiluminescence there's no change in temperature.
End transcript: Video 4  Chemiluminescence, a demonstration.
Video 4  Chemiluminescence, a demonstration.
Interactive feature not available in single page view (see it in standard view).

Question 8

Why is the production of light by chemiluminescence more efficient than that produced by a standard incandescent bulb?


No heat (or, strictly speaking, very little heat) is generated, in fact you'll sometimes see the phrase 'cold light emission' used to describe this process.

If chemiluminescence occurs naturally in a living organism, the term bioluminescence is used. One example of analytical importance is the glow of the firefly. This insect produces a pigment called luciferin, which reacts with oxygen to produce light. At dawn or dusk it will emit yellow, yellow-green and red luminescence with the aim of attracting a mate or prey.

The reaction may be summarised as:

Luciferin + ATP + O2 = oxyluciferin + AMP + PPi + CO2 + light
Equation label: (16)

This reaction is catalysed by the enzyme luciferase.

You'll note the abbreviations ATP, AMP and PPi.

ATP is adenosine triphosphate (Structure 3), a substance used to drive many biochemical reactions and cellular processes that require input of energy. In this reaction ATP forms a derivative, adenosine monophosphate (AMP), Structure 4, and the pyrophosphate anion, P2O74 (abbreviated to PPi), Structure 5.

Structure 3 Adenosine triphosphate.
Structure 4 Adenosine monophosphate.
Structure 5 The pyrophosphate anion.

But what use is this reaction to the analyst?

The answer lies with the ATP molecule.

ATP is an excellent indicator of biological activity, being found in all animal and vegetable matter, bacteria, yeasts and moulds. Its presence is a tell-tale sign of microbial activity, and so Equation 16 and in particular the associated bioluminescence, may be used as an indicator of microbial contamination. In other words, a measure of cleanliness.

Test kit manufacturers have produced portable apparatus incorporating inventive methods of mixing reagents, extracting ATP and portable (hand held) luminometers for measuring the emission.

One of the most common uses of these kits is monitoring hygiene in food preparation areas and hence reducing the likelihood of food poisoning. Harmful microbes can grow on food residues on surfaces and utensils which in turn can contaminate subsequent food preparation. Also, the cleanliness of workers' hands can be checked, which could lead to modifications to washing routines.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371