spectrophotometer 2010 ag revision

8/18/2019 Spectrophotometer 2010 Ag Revision

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Spectrophotometer (Spec)An instrument that measures the

amount of light that passes through(is transmitted through) a sample.


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Uses a type of light to detectmolecules in a solution

Light is a type of energy, and

the energy is reported aswavelengths, in nanometers(nm).


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Ultraviolet (UV) Spectrophotometers.Uses ultraviolet light of wave lengthsfrom 2 nm to !" nm.

Visi#le (V$S) Light SpectrumSpectrophotometers.Uses visi#le light (white light) of wavelengths from !" nm to % nm.


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R O Y G B I V


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Shines a #eam of light on a sample. &he molecules in the sample interact

with the light waves in of ! ways'

Absorb the energyReflect the energyTransmit the energy #etween andthrough the atoms and molecules ofthe sample.


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onsider #lue molecules, all thewavelengths of light are a#sor#ed,ecept for the #lue ones.

&he #lue wavelengths aretransmitted or reflected off themolecules. $f these #lue

wavelengths hit a detector (such asin the spectrophotometer or thenerve cells in your eye), they appear#lue.


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*olecules are whatever color oflight that they do not a#sor#.

+reen molecules appear green#ecause they a#sor# mostwavelengths of visi#le light,ecept the green wavelengths.


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&he spectrophotometer measuresthe amount of light transmittedthrough the sample

(&ransmittance). y using an e-uation (eers law),

it converts the transmittancedata to an a#sor#ance value.

hat /ind of data is this0


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&he concentration of an un/nownsample can #e determined #ycomparing the a#sor#ance data tostandards of /nown concentration.

&he data generated with the set of

/nown standards is called astandard curve.


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$nner partsLamp

1rism or grating that directlight of a specific wavelength.


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uter parts'

Sample Holder

Display

Knobs or buttons used to calibrate thespec to measure the designated

molecule.

WavelengthSelection


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Visi#le spectrophotometerontains a tungsten lamp that

produces wwhhiittee lliightght. Ultraviolet

spectrophotometer

ontains a deuterium lamp that produces light in the UVlight part of the spectrum.


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Visi#le Spectrophotometerhite light hits the prism or

grating, it is split into thecolors of the rain#ow (Visi#leSpectrum).

&he wavelength /no# rotatesthe prism3grating, directingdifferent color of light towardthe sample.


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&he wavelength of lightproduced #y the tungsten lamprange from a#out !" nm (Violet

light) to % nm (red light).

&he molecules in the sample

either absorb or Transmit thelight energy of one wavelengthor another.


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&he detector measures theamount of light #eing

transmitted #y the sample andreports that value directly (4transmittance) or converts it to

the amount of light a#sor#ed ina#sor#ance units (au) usingeers Law.


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After collecting data for yourconcentration an a#sorptionspectrum graph is created.

&hese can #e used when

attempting to identify un/nownsu#stances (e.g. S$)


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&he a#sor#ance spectrum is a

graph of a sample5s a#sor#ance

at different wavelengths.


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&he spectrophotometer canmeasure the amount of a#sor#ance

or lac/ of a#sor#ance of differentcolored light for a given

molecule.


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&he concentration of moleculesin a solution affects thesolution5s a#sor#ance.

6emem#er 7 8 is a ratio 9 when wechange one num#er 9 it affects theratio

$f there are more molecules in onesolution than in another, than thereare more molecules to a#sor# thelight.


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:etermines the presence andconcentrations of samples.

:etermines the purity of asample.

Loo/ at the change ofsamples over time.


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A. Measure the absorbance of standardscontaining known concentrations of theanalyte

B. Plot a standard curve with absorbanceon the X axis and analyte concentration onthe Y axis

C. Measure the absorbance of theunknown(s

!. !eter"ine the concentration of "aterialof interest in the unknowns based on thestandard curve


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spectrophotometer 2010 ag revision

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