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DIY Spectrophotometer for Analytical Chemistry: SpecUP Educational Tool

Third-year chemistry students at the University of Pretoria, South Africa, build their own spectrophotometer using a kit, conducting experiments from fundamental to applied spectroscopy. The cost-effective SpecUP (~R600) offers hands-on learning compared to commercial models (~R30,000). Components include an aperture, slit, grating, detector, light source, lens, and colored LEDs. Calibration is done visually or with a moveable grating. Despite limitations, this DIY approach benefits analytical chemistry students and other disciplines needing spectrophotometry. Application areas include absorbance calibration, reaction kinetics, metal ion analysis, and environmental chemistry. The device also aids in studying resolution and sensitivity concepts.

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DIY Spectrophotometer for Analytical Chemistry: SpecUP Educational Tool

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  1. The SpecUP educational spectrophotometer Dr Patricia Forbes Department of Chemistry University of Pretoria, South Africa

  2. The motivation The analytical instrument

  3. The motivation The analytical instrument

  4. Results The motivation The analytical instrument

  5. Results The motivation The analytical instrument

  6. The motivation • And also: • High student numbers • Cost considerations

  7. 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.

  8. Cost of the SpecUP: • ~R600 as compared to ~R30 000 for a commercial spectrophotometer • Thor Labs educational spectrophotometer ~R12 000

  9. Possible components of a DIY spectrophotometer:

  10. Possible components of a DIY spectrophotometer Aperture Slit Grating Sample Detector linked to amplifier & voltmeter Light source Lens Detector = light dependent resistor. Resistance decreases when more light falls on it, thus current increases.

  11. Possible components of a DIY spectrophotometer Aperture Slit Grating Sample Detector linked to amplifier & voltmeter Light source Lens Yellow incident light

  12. Possible components of a DIY spectrophotometer- moveable slit Aperture Grating Slit Sample Detector linked to amplifier & voltmeter Light source Lens Green incident light

  13. Possible components of a DIY spectrophotometer- moveable slit Aperture Grating Slit Sample Detector linked to amplifier & voltmeter Light source Lens 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.

  14. ..or a moveable grating Aperture Grating Slit Sample Detector linked to amplifier & voltmeter Light source Lens

  15. …or coloured filters Aperture Slit Grating Colour filters Sample Detector linked to amplifier & voltmeter Light source Lens Disadvantages: Limited data points and low intensities

  16. 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.

  17. 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

  18. Electronics Spectrophotometer circuit diagram Yeh, T.-S., S.J. and Tseng S-S., 2006, Journal of Chinese Chemical Science, 53, 1067-1072.

  19. Electronics Spectrophotometer circuit diagram

  20. Final design…the SpecUP

  21. The SpecUP But what is inside?....

  22. Components of the SpecUP

  23. Components of the SpecUP

  24. Coloured LED with no diffraction grating Two modes of operation…. Table 1: LEDs to use for different colour solutions.

  25. 2. White LED with diffraction grating & manual adjustment Two modes of operation…. Table 2: Wavelengths of colours.

  26. Alternatively a colour chart can be used, for example: http://www.colour.org.uk/spectrum_chart%201.jpg

  27. Cost of the SpecUP: • Main cost components of the SpecUP are the: • Aluminium plate • Batteries • Multi-meter • Circuit board

  28. Applications

  29. 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)

  30. SpecUP results Green food colourant

  31. SpecUP results Red food colourant

  32. SpecUP results: Construction of a spectrum KMnO4 solution Vzero, Vwater & Vsample must be measured at each wavelength to calculate absorbance

  33. Or spectrum obtained using coloured LEDs

  34. 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

  35. Additional applications

  36. 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.

  37. 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

  38. Results of repeatability experiment:

  39. 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

  40. Conclusion Advantages of the SpecUP: • Low cost • Simple to construct • Open design • Moving components • Generates useable analytical results • Allows for inquiry-based learning

  41. Implementation of the SpecUP

  42. Workshop at UP, November 2013

  43. Workshops in Tunisia, March 2014 & 2015

  44. 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

  45. Questionnaires

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