The CLEAPSS
colorimeter
Flexible
Works
Biol.
.
Chem
Cheap
Physics
General principles The principle components of the CLEAPSS colorimeter are a pair of LEDs and a digital voltmeter, connected by electrical circuitry. The Emi er LED produces the incident light when a voltage is applied across it. The Detector LED produces a voltage when the transmi ed light shines on it. The digital voltmeter measures the voltage produced by the This s ll is from the CLEAPSS video“Seƫng up a
DIY colorimeter” and shows an LED detec ng the red light emi ed by another LED. The voltage is dis‐
played on the digital voltmeter. There are two versions of the CLEAPSS colorimeter, both using the same principles and components. The Open‐frame colorimeter: flexible in use but circuitry needs connec ng each me. The Closed‐unit colorimeter : permanent circuitry but is not flexible in use. The Open‐frame Colorimeter Emi er LED Detector LED Digital voltmeter The LEDs are placed in Lego blocks and connected by temporary electrical circuitry to a resistor and a ba ery. A cuve e containing the test solu on/suspension is placed between the LEDs. When in use, the detector LED is shielded from ambient light. The LEDs can be easily changed, so a range of incident lights and detectors can be used in an experiment. However, the circuitry is not fixed and so has to be re‐assembled for each use. The Closed‐unit Colorimeter Emi er and detector LEDs are enclosed The LEDs, LEGO supports and circuitry are enclosed in a box, which shields the detector LED from ambient light. A cuve e containing the test solu on/suspension is placed in a cavity in the box. This colorimeter is robust, so the colorimeter can be stored and re‐
used for repeat experiments. However, it is difficult to change the LED arrangement, so only one emi er and detector LED paring is possible in each experiment. To change the LED arrangement, the back of the colorimeter is removed and the LEDs replaced. The process of changing LEDs is shown in the CLEAPSS prac cal hub (LR2, Arts Building). Uses of the colorimeter 1 Measuring absorbance to find the concentra on of a dissolved pigment. The trend line equa on gives a value of 43% rela ve anthocy‐
anin concentra‐
on RC= RA ‐ 0.018 0.0099 RC = 0.45‐0.018 0.0099 RC = 43% Calibration beetroot anthocyanin using a blue emitter LED
Trend line equation RA = 0.0099RC + 0.018
1.2
1
0.8
Relative 0.6
absorbance
0.4
0.2
0
0
20
40
60
80
Relative anthocyanin concentration (%)
100
Some Biology examples  Beetroot anthocyanin to inves gate membrane permeability.  Benedict’s /DNSA reagents to find glucose concentra on.  Biuret reagent to find dissolved protein.  Bicarbonate indicator for rate of photosynthesis/respira on.  DCPIP reagent for photosynthe c or respiratory dehydrogenase.  Haemoglobin concentra on in plasma. Some Chemistry examples  Measuring copper concentra on in brass  Rate of reac on of the iodine /thiosulfate reac on In the CLEAPSS Prac cal hub room: (LR2, Arts Building)  Have a go at using the CLEAPSS colorimeter to find anthocyanin pigment’s concentra on, so inves ga ng membrane permeability.  See other examples in some new CLEAPSS publica ons Uses of the colorimeter 2 Measuring absorbance to find a suspended solid’s Concentra on (turbidity measurements). Protein concentra on can be determined using a colorimeter. Here a protein suspension is being broken down by enzymes. Some Biology examples  Breakdown of albumen and casein protein suspensions using a variety of protein diges ng enzymes.  Burs ng of red blood cells (haemolysis) by osmo c effects .  Growth of yeast popula ons in different condi ons.  Es ma on of algal popula ons in pond water.  Es ma on of bacterial popula ons. Some Chemistry examples  Water quality tes ng  Transi on metal catalysis on thiosulfate precipita on In the Prac cal hub (LR4 Arts Building) The AQA A level prac cal session (Catherine Wi er) 10:00‐12:00 Friday January 8th and Saturday January 9th. Have a go at the colorimetric and non‐colorimetric measurement of protein concentra on. Uses of the colorimeter 3 Absorp on spectra of dissolved pigments A wide range of emi er LEDs are used , and the light is shone through a cuve e containing the pigment (s). When the absorbance is plo ed against the emi er LED wavelength, the absorbance spec‐
trum is obtained. Some Biology examples  Absorp on spectra of plant chloroplast extracts, to compare with chromatograms made with the same extracts. Also comparison with photosynthe c ac vity of the plants to light of different wavelengths (the Ac on spectrum). Chemistry and Physics  Introduc on to spectroscopy In the CLEAPSS Prac cal hub ( LR2 Arts Building) Have a go at comparing the absorp on spectra of a variety of aqua c and land plants. For full details of the CLEAPSS colorimeter see the CLEAPSS website : 
Seƫng up a DIY Colorimeter video

A technical guide to seƫng up and using the CLEAPSS
colorimeter (GL192)

Make it Guide: Colorimeter (GL174) CLEAPSS prac cal hub room ( Arts Building LR2). For a range of Prac cal Procedures that use the colorimeter.