Characterization

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The spectronic 20 spectrophotomer is used for

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to measure ability of a liquid sample to absorb light (in a visible region of electromagnetic spectrum) at a set wavelength

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To obatin chemical or physical information you must have:

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Signal generator
input transducer
signal modifier
output transducer

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SISO for spect 20

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s-tungsten lap
I-measuring phototube
S-analog amplifier
O-analog abs meter

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Sensitivity limits

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the abilit to separate signifcant data-containing signals from meaningless noise

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define senisitivity

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change in instrument response w/change in stimulus

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fo absorption spectroscopy, sensitivity formula is

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s=da/dc=
a is sample absorbance valu
c is saple concentration

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sensitivity is affected by (3 things)

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-physical & chemical properties of the analyte
-ddetector response
-composition of sample matrix

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sensitivity is determined from...

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the slope of the calibration curve:
absorbance vs concentration

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At low concentrations, noise..

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limits the lowest concentration of analyte that can be detected. aka it has hit the detection limit.

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At high concentrations, noise..

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fixes the precision of measurements.

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for signal/noise signal enhancement, theres hardware that

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-filters-blocks out unwanted
-integrators-increases coherent nonrandom sigover random noise
-modulators-shifts import freq away from noice

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for signal/noice signal enhancement, software...

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-boxcar averaging-lots of data points
-ensemble avearaging
-fourier transformations

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define boxcar averaging

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avg of a small series of data points to get one datapoint then use to get a curve.
mosteffectve w/fast signal

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fourier transformation is used to

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-convert time domain data f(t) into frequency domain data F(v)
-much faster than old frequ domain methods

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FT's takes a single waveform and converts it into

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a single line at frequ vo w/an amp a.

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The FT conversion takes multicomponent waveforms that are generated by ____ & the sampling freq should by at least___

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superposition of individual single frequ waves
&
2x that of the highest frequ component

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define spectroscopy:

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the measurement & interpretation of electromagnetic radiation (energy)absorbed/emitted when mcules of a sample move from 1 allowed energy state to another

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electromagnetic radiation (light) has properties of:

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-a microscopic particle having a discrete energy
-a wave extending over a broad area of space

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light ineracts w/matter in only 3 fundamental ways:

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reflectoin
transmission
absorption
=all 3 happen simutaneously

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in the absorption process, the photon

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is consumed & its energy is converted into an atomic or mcular process

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in the absorption process its coverted into an atomic or mcular process meaning

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-a nucleus spins in an altered manner
-a mcule vibrates differently
-an electron changes orbit

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wavelength

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λ-is measured as distance between 2 crests

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period

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T-is time elapsed between crests
T=1/V

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frequency

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V=# of waves that pass a fixed point in a given unit of time

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amplitude

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A- is max magnitued of the displacement

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Intensity

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I=proportional to the amplitude squared

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A wave of electromagnetic radiation contains

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electric field vectors
magnetic field vectors
plane polaraized light

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electric field vectors

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have periodic maxima perpendicular to direction of propagation

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magnetic field vectors

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orthogonal to electric field vectors

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Plane polarized light

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has its periodic field oscillations occuring in a set plane

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The wavelength & frequency are related to energy E of a photon by Plank's constant,h, such that:

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E=hv

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In absorption or emission spectroscopy, the energy difference between the low energy state & high energy state is given by

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bohr frequency condition:
{}E=hv

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The only true characteristic of a particular wave of electromagnetic radiation is

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frequency

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the index of refraction depends on the

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wavelength

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frequency of electromagmetic radiation remains

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constant, meaning photon energy is constant & waveletngth shorens as wave travels through matter

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short wavelength(which means---energy) waves interact w/electrons----than long wavelength waves

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high energy, more strongly

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greater interaction of the waves gives a

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larger n-index of refraction

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monochromatic light

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contains a single wavelength (or frequency) ex color, laser light

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polychromatic light

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contains spectral range of many wavelengths (ex white light)

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constructive interference

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in phase combination increases resulting amplitude

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desturctive interference

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out of phase combination decreaes resulting amp

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the phase angle defines

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period shift in periodic wave oscillations

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define NMR

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study of molcular sturcture by means of interaciton of radio frequency of e.r.w/a collection of nuclei immersed in a magnetic field,Ho

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quantum mechanics- for a particle to absorb a photon of e.r., it must

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first be in some uniform periodic motion

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frequency of motion for e.r.must exactly match frequ of----& is true of all absorption spectroscopies

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absorbed radiation
vmotion=vphoton