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The Analytical ProcessThe Analytical Process

ExploringExploring ChemicalChemical AnalysisAnalysis

Fourth Edition

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Syllabus

Requirement

Class 1 ch 0 + 1 + 2

Class 2 ch 3 + 4 + 5

Classes 3 ~ 5 spectroscopy in ch 18-20 and supplementary material

Class 6 ch 21 + exam 1

Classes 7 ~ 8 chromatography in ch 21-23

Class 9 exam 2

Classes 10 ~ 13 titration in ch 6-13 (skip ch 12)

Class 14 exam 3

Classes 15 ~ 17 electric chemistry in ch 14-17

Class 18 exam 4

Average of the four examinations 55≧

TextbookReference 1

Reference 2

Skoog

Analytical chemistry is applied throughout industry, medicine, and all the sciences.

chocolate packs an extra punch from the stimulant caffeine and its biochemical precursor, theobromine.

TheobromineDiuretic, smooth muscle relaxant, cardiac stimulant, and vasodilator

Caffeine Central nervous system stimulant and diuretic

Example: analyze theobromine and caffeine in chocolate bars

SamplingSampling The first step in any chemical analysis is pro

curing a representative, small sample to measure－ a process called sampling 取樣 .

Sample PreparationSample Preparation

Ceramic mortar and pestle used to grind solids into fine powders.

Homogeneous and heterogeneous samples need different preparation procedures.

Figure 0-2

Extracting fat from chocolate to leave defatted solid residue for analysis.

Substances being measured - caffeine and theobromine in this case - are called analytes.

Centrifugation and filtration are used to separate undesired solid residue from the aqueous solution of analytes.

The cloudy, tan, supernatant liquid (liquid above the packed solid) was then filtered in a further attempt to remove tiny particles of solid from the liquid.

Sample preparation transforms sample into a state that is suitable for analysis.

離心

The Chemical Analysis The Chemical Analysis Chromatography (層析法 ) column separ

ates the analytes and measures their quantity.

The column is packed with tiny particles of silica (SiO2) on which are attached long hydrocarbon molecules.

Chromatogram of 20.0 mL of dark chocolate extract. A 4.6-mm-diameter× 150-mm-long column, acked with 5-mm particles of Hypersil DS, was eluted (washed) with water:methanol: acetic acid (79: 20: 1 by volume) at a rate of 1.0 mL per minute.

Chromatogram

flows out first

flows out latter

qualitative analysis: Identifying what is in an unknown

quantitative analysis: Identifying how much is present

In the chromatogram, the area under each peak is proportional to the quantity of that component passing through the detector.

Calibration CurvesCalibration Curves A graph showing detector response as a function of analyte

concentration is called a calibration curve or a standard curve.

To construct a calibration curve, standard solutions containing known concentrations of pure theobromine or caffeine were prepared and injected into the column, and the resulting peak heights were measured.

Interpreting theInterpreting the ResultsResults

A can of soft drink or a cup of tea contains about one-quarter to one-half of the caffeine in a small cup of coffee.

Quality Assurance ( 品質保證 ) Professional analysts follow a set of practices,

called quality assurance, intended to give themselves and their customers confidence in the quality of their results.

General Steps in a Chemical Analysis Formulating the question Translate general questions into specific questions to be

answered through chemical measurements.

Selecting analytical procedures Search the chemical literature to find appropriate or, if

necessary, devise new procedures to make the required measurements.

Sampling Select representative material to analyze.

Sample preparation Sample preparation is the process of converting a representative

sample into a form suitable for chemical analysis, which usually means dissolving the sample.

Analysis Measure the concentration of analyte in several identical

aliquots (portions).

Reporting and interpretation Deliver a clearly written, complete report of your results,

high-lighting any special limitations that you attach to them.

Drawing conclusions Once a report is written, the analyst might not further

participate in what is done with the information.

Skoog

Gravimetric methods ----- chapter 7

determine the mass of the analyte

Volumetric method ----- chapters 6, 8, 9, 10, 11, 13 measures the volume of a solution containining the analytes

Electroanalytical methods ----- chapters 14, 15, 16, 17

determine the electrical properties as potential, current, resistance, and quantity of electrical charge of analytes

Spectroscopic methods ----- chapters 18, 19, 20

measurement of the interaction between electromagnetic radiation and analyte atoms or molecules or on the production of such radiation by analytes.

Chromatography ----- chapters 21, 22, 23 separates the analytes from a mixture and measure the quantity of analytes

Quantitative Analytical Methods