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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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