chapter 1.2-the analytical approach
TRANSCRIPT
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Analytical Methods
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TOPIC 1.2:Sample Preparation
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An analysis involves severalsteps and operations whichdepend on:• the particular problem• your expertise• the apparatus orequipment available.
The analyst should beinvolved in every step.
An analysis involves severalsteps and operations whichdepend on:• the particular problem•
your expertise• the apparatus orequipment available.
The analyst should beinvolved in every step.
Steps in a typical quantitative
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Steps in a Typical Analysis
1. Define the problem2. Select a method
3. Obtain a representative sample4. Prepare the sample for analysis5. Perform any necessary chemical separations
6. Perform the measurement. !alculate the results and report
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(1) Defne the Problem
• What is the problem – hat needs to be !ound"#ualitative and$or quantitative
• What ill the in!ormation be used !or" Who illuse it"
• When ill it be needed"• %o accurate and precise does it have to be"• What is the bud&et"• 'he analyst ( the problem solver ) should consult
ith the client to plan a use!ul and e cientanalysis includin& ho to obtain a use!ul sample*
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(+) Select a Method• Sample size• Size of sample• Sample preparation
needed• Concentration and range
(sensitivity needed• Selectivity needed
(interferences• Acc!racy"precision
needed
• Tools"instr!mentsavaila#le
•
$%pertise"e%perience• Cost• Speed• &oes it need to #e
a!tomated'• Are met ods availa#le in
t e c emical literat!re'• Are standard met ods
availa#le'
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(,) -btain a .epresentativeSample
• Sample type " homo#eneity " si$e
• Samplin# statistics " errors
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(/) Prepare the Sample !or Analysis
• Solid " li%uid " #as&• Dissolve&• 'sh or di#est&•
!hemical separation or mas(in# of interferencesneeded&
• )eed to concentrate the analyte&• )eed to chan#e *derivative+ the analyte for detection&• )eed to ad,ust solution conditions *p- add rea#ents+&
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(0) Per!orm Any ecessary 2hemicalSeparations• Distillation• Precipitation• Solvent e/traction• Solid phase e/traction• !hromato#raphy *may be done as part of the
measurement step+• 0lectrophoresis *may be done as part of the measurement
step+
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(3) Per!orm the Measurement
• !alibration•
alidation " controls " blan(s• eplicates
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(4) 2alculate the .esults and .eport• Statistical analysis *reliability+
• eport results ith limitations " accuracyinformation
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