Applications of CCD Array Spectrometers in Undergraduate

Education at EIU

Jonathan Blitz and Daniel Sheeran

Department of Chemistry

The traditional educational spectrophotometer

Single beam

Single channel

Multichannel Spectrometer

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

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.

Fluorescence

A typical luminescence spectrometer Our luminescence spectrometer

Handheld UV Source

Multichannel Spectrometer

Emission Monochromator Mulitchannel Detector

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

Fluorescence Emission Spectra

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Wavelength (nm)

Em

issi

on

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Co

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Quinine

Rhodamine BFluorescein

Eosin Yellow

The multichannel spectrometer has also been used as a detector for qualitative analysis in a traditional flame test …

Fiber Optic Collection of Na Flame Emission Spectrum

Flame Emission Spectra of the Alkalis

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Em

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Li

Na

K

Cs

Rb

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

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

ion

Inte

ns

ity

KNa

background Ca

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

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

Compressed Air

Spectrometer

Fiber optic

Na Calibration (Li Internal Standard)

R2 = 0.996

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ppm Na

Na

/Li

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oK Calibration (Li Internal Standard)

R2 = 0.995

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ppm K

K/L

i E

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n I

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Ra

tio

Cs Calibration (Li Internal Standard)

R2 = 0.999

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Rb Calibration (Li Internal Standard)

R2 = 0.995

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ppm Rb

Rb

/Li

Em

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Li Calibration (K Internal Standard)

R2 = 0.994

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Li/

K E

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Ra

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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

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