Gang Wang Analytical Chemistry 2 Instrumental_Week1_CH1&5-2010

8/3/2019 Gang Wang Analytical Chemistry 2 Instrumental_Week1_CH1&5-2010

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Dr.GangWang

Dr.

David

K.

RyanDepartmentofChemistryUniversityofMassachusettsLowell

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List Price $162UML Bookstore $231?Internet as low as $85 ?Fifth edition 1998

Sixth ed. just out 2007Excellent reference book


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Website

http://faculty.uml.edu/David_Ryan/84.314/

Syllabus=coursedescription

Schedule

Materials=LectureSlides, Handouts,Videosfromlast

year

4

Skoog Chapter1Introduction

BasicsofInstrumentalAnalysis

Properties

Employed

in

Instrumental

Methods NumericalCriteria

FiguresofMerit


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Nobel Prizes

William H. Bragg analysis of crystal structure by means of X-rays(physics) 1915

Francis W. Astonfor his discovery, by means of his mass spectrograph, of isotopes

(Chemistry)1922

FriderikPreglinvention of the method of micro-analysis of organic substances

(Chemistry)1923

Arne Tiselius

his research on electrophoresis and adsorption analysis, especially for

his discoveries concerning the complex nature of the serum proteins

(Chemistry)

1948

Felix Bloch

Edward M. Purcell

development of new methods for nuclear magnetic precision

measurements and discoveries (Physics)1952

Archer J P Martin

Richard L M SyngeInvention of partition chromatography (Chemistry) 1952

Jaroslav Heyrovskydiscovery and development of the polarographic methods of analysis

(Chemistry)1959

Rosalyn Yalowdevelopment of radioimmunoassays of peptide hormones (Physiology or

Medicine)1977

Kai M. Siegbahncontribution to the development of high-resolution electron spectroscopy

(physics)1981

Gerd Binnig

Heinrich Rohrerdesign of the scanning tunneling microscope (physics) 1986

Analytical Methods

Classical

Instrumental

Precipitation

Extraction

Distillation

Colors

Boiling or Melting Points

Solubilities

Odors

Optical

Gravimetric

Volumetric

Physical Properties

Conductivity

Electrode Potential

Light Absorption or Emission

Mass-to Charge ratio

Fluorescence

Chromatographic

Electrophoretic


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Instruments for Analysis


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Performance

Characteristics

Of

Instruments

Precision

The precision ofameasurementsystem,also

called reproducibility or repeatability,isthedegreetowhichrepeatedmeasurementsunderunchangedconditionsshowthesame results.

accuracy of a measurement system is the

degree of closeness of measurements of

aquantity to its actual (true) value.


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Bias Biasprovidesameasureofthesystematic,ordeterminate,error ofan

analyticalmethod. =

Where isthepopulationmeanfortheconcentrationofananalyte isthetruevalue

Sensitivity Sensitivityofamethodorinstrumentisameasureofitsabilityto

discriminatebetweensmalldifferences.

Twofactors

limit

sensitivity

Theslopeofcalibrationcurve Reproducibilityorprecisionofthemeasuringdevice S=mc+Sbl

Detectionlimit Minimumconcentrationormassofanalytecanbedetectedata

knownconfidencelevel Sm=Sbl +ksbl

Usually,k=3


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Dynamicrange

LOQlimitofquantitation

LOLlimitoflinearity

Dynamicrangeshouldbeatleastafewordersofmagnitude

Selectivity

Selectivityreferstothedegreetowhichthemethodisfreefrominterferencebyotherspeciesinsample


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Calibration of instrumental method Calibrationdeterminesthe

relationshipbetweenanalyticalresponseandanalyticalconcentration.

1.externalstandardcalibration

Nointerferenceeffects

Obtainresponsesignalasafunctionofknownanalyte

concentration

Calibration of instrumental method 2.Standard additional

methods

Addingoneormoreincrementsofstandard

solutionto

sample

aliquots

Sx=K1Cx

ST =K1(Cx+Cs)

Cx=CsSx/(ST Sx)

WhenST =0

Cx= Cs


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Calibration of instrumental method 3.internalstandard

method

Addaconstantamountofsubstancetoallsamples,blanks,andcalibrationstandard.

Plotratioofanalyte

signaland

internal

standardasafunctionofanalyteconcentration.

Homework: P23 1-10

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Skipthefollowingchapters

Chapter2 ElectricalComponentsandCircuits

Chapter3 OperationalAmplifiersinChemical

Instrumentation Chapter4 DigitalElectronicsandMicrocomputers


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SignaltoNoiseRatio(S/N) Parameterdescribingqualityofdata

Oftenreferredtoasfigureofmerit

S meanofsignal x 1 = = = N standarddeviation s RSD

RSD=relative

standard

deviation

ImpossibletodetectasignalwhenS/Nlessthan2or3

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NMR spect ra for

Progesterone

A) S/N = 4.3B) S/N = 43

Very li t t le

con f idencein ab i li ty t o

de te rmine

peaks at

low er S/N

Detect ion

L imi t


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SourcesofNoise Chemicalnoise temp,pressure,humidity,etc.fluctuations=uncontrolledvariables

Instrumentalnoise noise frominstrumentalcomponents

Thermalnoise(Johnsonnoise) thermalmotionofelectronsinloadresistor

Voltagefluctuation

vrms = 4kTRf f =1/3trNarrowbandwidthtodecreasenoise,butinstrument

willbeslower

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Instrumentalnoise

Thermalnoise

vrms = 4kTRf

vrms =rootmeansquarenoisevoltage

k=Boltzmannconstant1.38x1023J/K

T=temperature

R=resistance

f=frequencybandwidthofnoise


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Instrumental

noise Shotnoise movementof

electronsacrossajunction

irms = 2ief

irms =rootmeansquarecurrentfluctuation

i=averagecurrent

e=chargeonelectron

f=frequency

bandwidth

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Instrumentalnoise

Flickernoise anynoise

thatisinversely

proportionaltosignal

1/f

Significantatlowfrequency(


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Environmentalnoisesources(notefrequencydependence)

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ImprovingS/Nhardware&software Hardware

Grounding&shielding Faradaycage

Analogfiltering RCfiltering

Modulation

convert

DC

signal

to

high

frequency

AC

thendemodulate

Signalchopping rotatingwheeltodifferentiatee.g.IRsourcefromheat

Lockinamplifiers


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Pr imi t ive

Faraday

Cage for

sh ie ld ing

ins t rumentsfrom EM

Radiat ion

must be

grounded

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Analog Fi l t er ing

or RC Fi l ter ing

Noisy data

RC f i l t er

R

C

Fi l tered data


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Modulation

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SignalchoppinginanIRspectrophotometer


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Chopperamplifier


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ImprovingS/Nhardware&software Software

Ensembleaveraging addingspectra

Boxcaraveraging

Digitalfiltering movingwindow,slidingaverage

Correlationmethods

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Ensemble

averaging

i.e.addingoraveragingsignal


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Boxcaraveraging

Gang Wang Analytical Chemistry 2 Instrumental_Week1_CH1&5-2010

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