applications of ccd array spectrometers in undergraduate education at eiu jonathan blitz and daniel...

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)

Em

iss

ion

Inte

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Ab

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rba

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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

Inte

nsi

ty (

Co

un

ts)

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

iss

ion

Inte

ns

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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

Em

iss

ion

In

ten

sit

y R

ati

oK Calibration (Li Internal Standard)

R2 = 0.995

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ppm K

K/L

i E

mis

sio

n I

nte

ns

ity

Ra

tio

Cs Calibration (Li Internal Standard)

R2 = 0.999

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Cs

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Rb Calibration (Li Internal Standard)

R2 = 0.995

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ppm Rb

Rb

/Li

Em

iss

ion

In

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y R

ati

o

Li Calibration (K Internal Standard)

R2 = 0.994

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ppm Li

Li/

K E

mis

sio

n I

nte

ns

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Ra

tio

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