Amadeus Sample Spectra 1. Dark spectrum Dark spectrum With no photons hitting the sensors a line is visible just above zero on the y-axis. You can correct for this “dark” spectrum by exporting the data to Excel and subtracting it from other spectra. The dark reading changes with integration time. Artificial colour can be applied beneath the spectrum line using the colour fill tool. 1. 2. 3. 4. 5. What are the shortest and longest wavelengths for the colour fill? What is the visible wavelength range of the human eye? What do we call light with λ >780nm What do we call light with λ < 380nm What is the operating range of this spectrometer 2. Blue LED Blue LED The y-axis unit of the spectrometer is photon counts (not calibrated). This means the number of photons hitting each sensor in the CCD array in one integration time. The zero line is always a little above the x-axis. This can be corrected by exporting the data and subtracting the dark spectrum signal in Excel. 1. 2. 3. 4. What is the peak wavelength emitted by the blue LED? What is the range of wavelengths emitted by the blue LED? What is the maximum intensity? What is the range of wavelengths emitted by the LED at half the maximum intensity? 3. Incandescent light bulb Incandescent light bulb 1. 2. 3. 4. What is the range of wavelengths emitted by the light bulb? Does the bulb emit any infrared light (above 780nm)? How much UV light (below 380nm) does the bulb emit? Which colours are emitted by the bulb? BE CAREFUL—This is not a black body curve. It is the response curve of the spectrometer. 4. Cloudy sky Cloudy sky 1. 2. 3. 4. What is the range of wavelengths coming from the sky? Compare the IR and UV radiation with the light bulb. Is the spectrum graph smooth like the light bulb? The sharp dips show that light at some wavelengths has been absorbed. Google Fraunhofer lines to find out what causes them. 5. Neon mains indicator Neon mains indicator lamp 1. 2. 3. How is this spectrum different from an LED? Which gas is used to fill the indicator bulb? There is no filament in the bulb because an electrical connection to the live terminal would be dangerous. The light comes from a tiny electrical discharge through the gas that makes it glow with a red colour. Why is the spectrum made from sharp peaks at many precise wavelengths? 6. Line spectrum library Line spectrum library Line spectra reference lines can be overlaid on the graph to identify the sources of line spectra. The library only shows the strongest lines 1. 2. 3. How many noble gases are in the library? How many alkali metals are in the library? Which two elements are shown on this graph? 7. Red LED Red LED 1. 2. 3. 4. 5. What is the peak wavelength emitted by the red LED? Is the peak wavelength shorter or longer than the blue LED? How many nanometres difference is there between the red LED and the blue LED? The red LED looks similar to the mains indicator neon lamp to the human eye. Compare the two spectra. Are they emitting in roughly the same range of wavelengths? Do they use the same method to make light? 8. Car rear light filter—using the snapshot tool Car rear light filter The red spectrum line is a snapshot of the white lamp spectrum. The colour filled spectrum shows the light after it has passed through the red plastic tail light cover. 1. 2. 3. 4. 5. Which wavelengths are absorbed by the red plastic? Which colours are absorbed by the red plastic? At about which wavelength is there a sharp “cut off” for the shorter wavelengths? Which wavelengths are allowed to pass through the red filter? Does any infrared light pass through? 9. Puzzle O A N E C Puzzle 1. Which spectrum is a red LED ? 2. Which spectrum is a green LED? 3. Which spectrum is a gas discharge emission? 4. Which spectrum shows Fraunhofer lines? 5. Which spectrum is an incandescent bulb? 10 Economy lamp Economy lamp The spectrum from a compact fluorescent lamp has sharp peaks caused by the atomic emission spectrum of a metal vapour in the tube. The red vertical lines are the library lines for mercury and the blue lines are the library lines for potassium. 1. 2. 3. 4. Which metal appears to be in the vapour? Humans see the bulb as a source of white light. Which three predominant colour peaks cause the light to look white? How much UV and IR is emitted by the lamp? Why are there strict laws about throwing away these lamps in household refuse? 11. CSV data export CSV data export Data from Amadeus can be saved to the clipboard by clicking the copy to clipboard icon. The data is saved in csv (comma separated variable) format and can be pasted into any Office application such as Excel. Saving in multiple columns allows spectra to be compared accurately and the dark spectrum to be subtracted. 1. 2. 3. 4. 5. What is this spectrum? Which Microsoft Office application is this? How could data be scaled? How else could the data be displayed? Would it be possible to falsify the data? 12. Absorbance and Transmission Absorbance and Transmission Quantum can display two graphs. These are the Absorbance and Transmission spectra of a food colouring solution in water. Before Absorbance and Transmission modes can be selected, both dark and reference spectra must be stored. 1. 2. 3. 4. 5. 6. 7. 8. What are the y-axis units on the Transmission graph? What would be in the reference cuvette? What are the y-axis units on the Absorbance graph? What is the wavelength of maximum absorbance ( λ max) of the solution? How much light is absorbed at 700nm? How much light is transmitted compared to the reference of pure water at 700nm. What is the absorbance of this sample solution at λ max? What colour is this solution; blue, green or red? 13. Beer Lambert Law, calibration line and concentration Beer Lambert Law, calibration line and concentration By measuring the absorbance of three known concentrations, Quantum can plot a calibration line for you. Then you can read off the concentration of an unknown sample directly from the absorbance. The unknown sample appears as a red dot on the calibration line. 1. 2. 3. 4. 5. What is λ max for this solution? Why has the calibration line been forced through the (0,0) point on the graph? (This is an option in the software) What is the absorbance at λ max for this sample? What is the concentration of this sample (no units)? What is the gradient of the calibration line called? 14. Kinetics Kinetics and reaction orders The Kinetics wizard sets up a graph of absorbance vs time. It can be used for any reaction that changes absorbance over time. The most common is the action of bleaches on coloured solutions. 1. 2. 3. What is the initial absorbance of the sample? What is the end point absorbance? How long did the reaction take? 15. Fluorescence Fluorescence –Stokes Shift The accessory 400 micron fibre picks up the faint fluorescence from the fluorescein solution at 520nm. In Absorbance mode the in-line fibre detects absorbance at 453nm. The difference in wavelength is called the Stokes shift. The fluorescence photons have less energy than the photons they absorbed. 1. Compare the integration times. Why are they so different? 2. Is the fluorescence wavelength longer or shorter than the absorbance wavelength? 3. What is the Stokes shift in this case? Answers 1. Dark spectrum 1. 380 to 780 nm 2. 380 to 780nm 3. Infrared 4. Ultraviolet 5. 350 to 850nm 2. Blue LED 1. About 465nm 2. About 80nm 3. About 35,000 4. About 30nm 3. Incandescent light bulb 1. From about 350 to ????? It is impossible to say because the spectrometer limit is 850nm 2. Yes– a lot. Be careful– the drop off in IR signal is the response of the spectrometer system. There is really a lot more IR. 3. Very little. Partly because it is the black body temperature curve at the UV end and partly because glass absorbs UV. Again be careful how you interpret this. 4. The whole visible spectrum 4. Cloudy sky 1. Greater than the range of the spectrometer 2. More UV than the bulb. Less IR. 3. No! 4. You should be able to identify many solar Fraunhofer lines and the oxygen absorption band from our own atmosphere. 5. Neon mains indicator 1. Not continuous. A line spectrum 2. Neon 3. These wavelengths correspond to energy level transitions in the Neon atom. It is a quantum effect. 6. Line spectrum library 1. 5 2. 2 3. Ne and Hg 7. Red LED 1. 654.5nm 2. Longer 3. About 189nm (If you know the minimum voltage to make the LEDs work, you can find Planck’s constant) 4. Yes - about the same 5. No. One uses gas discharge and the other is a semiconductor band gap emission. 8. Car rear light filter 1. Everything below about 580nm 2. Most yellow, green, blue, violet 3. At about 575nm 4. Yes— a lot 9. Puzzle Reading downwards, the answers spell O C E A N 10. Economy lamp 1. Mercury 2. Red, Green and Blue (RGB) 3. Very little IR, and a little UV 4. Mercury is a toxic heavy metal 11. CSV data export 1. The sky showing Fraunhofer lines 2. Excel 3. Multiply the whole column by a scale factor 4. As a bar graph, in 3D, whatever you like! 5. Yes, very easily. You could make your own Fraunhofer line, but that would not be scientific! 12. Absorbance and Transmission 1. Transmission as a percentage of transmission through the reference solution 2. In this case it is water, but it could be any solvent, depending on what you are investigating. 3. Absorbance number. This is a log scale from 0 to 3 4. About 506nm 5. None– the Absorbance number is zero at 700nm 6. 1.24 7. The absorbance in in the blue and green wavelengths so the solution is red. 13. Beer Lambert Law, calibration line and concentration 1. About 506nm 2. Zero concentration means zero absorbance 3. About 0.6 4. 1.7 5. Molar absorbance coefficient or molar extinction coefficient. Symbol ε (epsilon) 14. Kinetics 1. 2.5 2. 0.5 3. 800s NOTE: Concentrations of reactants need to be set to give reactions that reach there end points in a reasonable time. 15. Fluorescence 1. To measure absorbance the fibre is looking directly into the lamp, but the fluorescence signal coming from the side port is about 100 times weaker. 2. Longer 3. About 67nm NOTE: The absorbance is in the blue region. The longer wavelength light is not absorbed. If a blue filter is placed between the lamp and the cuvette there is almost no difference in the green fluorescence. A red filter cuts down the fluorescence to near zero.