applications of ccd array spectrometers in undergraduate education at eiu jonathan blitz and daniel...
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Applications of CCD Array Spectrometers in Undergraduate
Education at EIU
Jonathan Blitz and Daniel Sheeran
Department of Chemistry
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The traditional educational spectrophotometer
Single beam
Single channel
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Multichannel Spectrometer
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Spectrophotometry – the mundaneMalachite Green Absorbance Spectrum from Multichannel Spectrometer
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Wavelength (nm)
Ab
sorb
ance Output from Spec-20:
Absorbance = 0.390
• Entire spectrum shows λmax and choice of analysis wavelength
• 2 spectrometers for lab of 24 students is sufficient
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The multichannel spectrometer is easily configured for emission spectrometry using a fiber optic probe for light input.
This has been used as a portable fluorescence emission spectrometer.
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Fluorescence
A typical luminescence spectrometer Our luminescence spectrometer
Handheld UV Source
Multichannel Spectrometer
Emission Monochromator Mulitchannel Detector
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Fluorescence Emission Spectrum
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Wavelength (nm)
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B. Fluorescence emission spectrum of quinine
C. Absorbance spectrum of quinine
A. Hand held UV source
Absorbance and Fluorescence Emission Spectra of Quinine in
Water
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Fluorescence Emission Spectra
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Wavelength (nm)
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Quinine
Rhodamine BFluorescein
Eosin Yellow
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The multichannel spectrometer has also been used as a detector for qualitative analysis in a traditional flame test …
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Fiber Optic Collection of Na Flame Emission Spectrum
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Flame Emission Spectra of the Alkalis
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Li
Na
K
Cs
Rb
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Qualitative Analysis
“Group IV” Cations: Na+, K+, Ca2+, Mg2+, NH4+
Visual Flame Test:
• Na: persistent yellow
• K: transient red or lavender
• Ca: unreliable, transient red
Na masks K when both are present (Co blue filter)
False + and false – for Ca common with visual flame test
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Qualitative Analysis
Spectrometer Flame Test:
•Na and K easily detected and distinguished
•Ca not detected, chemical test only
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Wavelength, nm
Em
iss
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Inte
ns
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KNa
background Ca
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Qualitative Analysis
Spectrometer Flame Test Student Results:
•Na > 95% correct on 1st try
•K > 95% correct on 1st try
•Ca > 98% correct on 1st try
Fewer false +, fewer false –
No blue filter for visual observation of K
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Quantitative Analysis
• Emission intensity is transient and variable
• Use another alkali as an internal standard
• Sample introduction with a nichrome wire does not provide adequate quantitative results
• Aspirate a sample using a continuous sprayer into the air intake of a Bunsen burner for improved sample introduction
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Compressed Air
Spectrometer
Fiber optic
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Na Calibration (Li Internal Standard)
R2 = 0.996
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Na
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Em
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oK Calibration (Li Internal Standard)
R2 = 0.995
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K/L
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Cs Calibration (Li Internal Standard)
R2 = 0.999
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Rb Calibration (Li Internal Standard)
R2 = 0.995
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Li Calibration (K Internal Standard)
R2 = 0.994
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K unknown = 200.0 ppm Measured = 202.5 ppm
Student results not that good, but calibrations are OK
Detection limits using spray: 30-40 ppm for all alkalis
Detection limits much lower using nichrome wire
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Conclusions
• A multichannel spectrometer is useful for teaching spectrophotometry
• Using a fiber optic probe the spectrometer was configured for the following tasks:
As a fluorescence emission spectrometer
For qualitative analysis of alkalis
For quantitative analysis of alkalis using an internal standard calibration