The SpecUP educational spectrophotometer
Dr Patricia Forbes
Department of Chemistry
University of Pretoria, South Africa
The motivation
The analytical instrument
The motivation
The analytical instrument
The motivation
Results
The analytical instrument
The motivation
Results
The analytical instrument
The motivation
And also:
• High student numbers
• Cost considerations
The concept
Third year analytical chemistry students build their own
spectrophotometer using components from a kit
provided.
They use their instrument to conduct experiments, ranging
from fundamental to applied.
The practical session should ideally follow on from or be
run in parallel to the presentation of a series of lectures
on spectroscopy.
Cost of the SpecUP:
• ~R600 as compared to ~R30 000 for a commercial
spectrophotometer
• Thor Labs educational spectrophotometer ~R12 000
Possible components of a DIY
spectrophotometer:
Possible components of a DIY spectrophotometer
Aperture
Grating
Slit
Sample
Light source
Lens
Detector
linked to
amplifier &
voltmeter
Detector = light dependent resistor.
Resistance decreases when more light falls on it, thus current increases.
Possible components of a DIY spectrophotometer
Aperture
Grating
Slit
Sample
Light source
Detector
linked to
amplifier &
voltmeter
Lens
Yellow incident light
Possible components of a DIY spectrophotometer
- moveable slit
Aperture
Grating
Slit
Sample
Light source
Detector
linked to
amplifier &
voltmeter
Lens
Green incident light
Possible components of a DIY spectrophotometer
- moveable slit
Aperture
Grating
Slit
Sample
Light source
Lens
Detector
linked to
amplifier &
voltmeter
The spectrum produced by the grating is projected onto graph paper to
produce a wavelength scale.
Calibration is preformed by eye, using a table of colour wavelength ranges.
..or a moveable grating
Aperture
Grating
Slit
Sample
Light source
Lens
Detector
linked to
amplifier &
voltmeter
…or coloured filters
Aperture
Grating
Slit
Sample
Colour filters
Light source
Lens
Disadvantages: Limited data points and low intensities
Detector
linked to
amplifier &
voltmeter
Main limitation of this design:
most components are fixed…
The spectrophotometer showing LED, LDR, amplifier and sample cuvette
…and the liquid sample is on the electric circuit board…

Tavener, S.J. and Thomas-Oates, J.E., 2007, Education in Chemistry, 44, 151-154.
Which spectrophotometer design?
Depends on the target audience:
• Primarily analytical chemistry students
• Other disciplines which use spectrophotometry
include:
• Physics
• Pharmacy
• Geography (e.g. sun photometer)
• Environmental science
• Food science
• Biochemistry
• Electrical engineering
• Computer science
Electronics
Spectrophotometer circuit diagram
Yeh, T.-S., S.J. and Tseng S-S., 2006, Journal of Chinese Chemical Science, 53, 1067-1072.
Electronics
Spectrophotometer circuit diagram
Final design…the SpecUP
The SpecUP
But what is inside?....
Top view
LED
Lens Grating
10-125 mm
400 mm
Cuvette LDR
70-200 mm
290 mm
100 mm
340 mm
30 mm 20 mm
Fully retracted: 800 mm
Fully contracted: 540 mm
Side view
LED
Lens Grating
50-160 mm
Components of the SpecUP
Cuvette LDR
110-240 mm
Components of the SpecUP
Two modes of operation….
1. Coloured LED with no diffraction grating
Solution colour
LED colour
Green
Red
Blue or purple
Yellow
Red
Green
Yellow or orange
Blue
Table 1: LEDs to use for different colour solutions.
Two modes of operation….
2. White LED with diffraction grating & manual
adjustment
Colour
observed
Wavelength Range
(nm)
Mean wavelength
(nm)
Violet
400-430
410
Blue
430-490
470
Green
490-570
520
Yellow
570-595
580
Orange
595-650
610
Red
650-700
650
Table 2: Wavelengths of colours.
Alternatively a colour chart can be used, for example:
http://www.colour.org.uk/spectrum_chart%201.jpg
Cost of the SpecUP:
• Main cost components of the SpecUP are the:
• Aluminium plate
• Batteries
• Multi-meter
• Circuit board
Applications
Absorbance calibration & Beer Lambert Law
• Molar absorption coefficient is
determined from the slope of line
of concentration vs A for standard
solutions
• Then determine concentration of
unknown samples
Calibration plot of absorbance
versus concentration for solutions
of KMnO4 (Tavener & Thomas-Oates, 2007)
SpecUP results
Green food colourant
SpecUP results
Red food colourant
SpecUP results: Construction of a spectrum
KMnO4 solution
Vzero, Vwater & Vsample must be measured at each wavelength to calculate
absorbance
Or spectrum obtained using coloured LEDs
KMnO4 (2.09x10-3 M)
Colour LED Wavelength (nm) Absorbance
Blue
470
0.21
Green
520
1.02
Yellow
580
0.45
Red
650
0.20
Reaction kinetics…the iodine clock reaction
• In the first step, iodine is generated from the iodide ion
by reaction with persulphate
2 I− + S2O82− → I2 + 2 SO42−
(1)
• In the second step, the iodine reacts with thiosulphate
I2 + 2 S2O32− → 2 I− + S4O62−
(2)
• Yellow colour of iodine is detected using blue LED

rate  k[S2O8 ][ I  ]
Additional applications
Determination of metal ion concentrations
• Environmental chemistry applications (waste water
testing)
• Based on absorption of coloured metal complexes
• Suitable wavelength LEDs are employed
• Interference effects can be studied
Hauser, P.C., and Rupasinghe, T.W.T., 1997, Fresenius J. Anal. Chem., 357, 1056-1060.
Concepts to be covered in all experiments:
• Resolution (eg: relationship between slit width and
spatial resolution)
• Sensitivity (eg: relationship between slit width and
spectral intensity)
• Selectivity (eg: differences between diffraction orders)
• Accuracy (comparison to commercial instruments)
• Precision and repeatability
• Limitations and sources of error
Results of repeatability experiment:
Educational outcomes include:
• Hands-on experience wrt workings of the instrument &
its components (including setup and adjustment)
• Experience with calibrating the instrument
• Understanding of relationship between absorption of
light & concentration
• Understanding of analytical concepts of resolution;
selectivity; sensitivity; accuracy & precision
• Specific outcomes for each application experiment
 Focus is on inquiry-based learning
Conclusion
Advantages of the SpecUP:
• Low cost
• Simple to construct
• Open design
• Moving components
• Generates useable analytical results
• Allows for inquiry-based learning
Implementation of the SpecUP
Workshop at UP, November 2013
Workshops in Tunisia, March 2014 & 2015
Implementation of the SpecUP in the
Analytical Chemistry III course at UP
•
•
•
•
Forty students
Work in groups of 3 students
Mix of commercial spectrophotometer & SpecUP
Some limitations identified and improvements made
Patricia B.C. Forbes and Johan A. Nöthling, Shedding light on spectrophotometry:
the SpecUP educational spectrophotometer, South African Journal of Science, 2014, 110 (1/2), 1-5,
http://dx.doi.org/10.1590/sajs.2014/20130096
Questionnaires
Before SpecUP use
Q5: Have you ever used a commercial spectrophotometer?
Q6: Have you ever used the SpecUP spectrophotometer?
Q7: Have you been taught the theoretical aspects of spectrophotometry in lectures?
Before SpecUP use
Q3: Spectrophotometers do not have moving components.
Q5: The only thing that is needed to be done to obtain a result from a spectrophotometer
is to place the sample cuvette inside the instrument.
Q9: I would recommend that all chemistry students get hands-on experience
with spectrophotometers.
After SpecUP use
Q2: The SpecUP helped me to understand spectrophotometry.
Q3: I enjoyed moving the components of the SpecUP to see the effect it had on the results.
Q5: The SpecUP made me think about how a spectrophotometer works.
Acknowledgements
• CSIR National Laser Centre & the African Laser Centre
• Dr Paul Motalane
• Prof. Andrew Forbes
• Thomas du Plooy
• Prof Mourad Zghal
• Leon Engelbrecht, Nico Van Vuuren (University of Pretoria)
• Phakama Botha
• Monné van der Linde
• Prof. Thomas-Oates (University of York)
ChromSAAMS 2012 Conference, South Africa
Thank you!