Exploring Chemical Analysis Fourth Edition The Analytical Process P.1

Average of the four examinations ≧ 55 Syllabus 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 Requirement Average of the four examinations ≧ 55

Reference 1 Textbook Reference 2

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

Example: analyze theobromine and caffeine in chocolate bars chocolate packs an extra punch from the stimulant caffeine and its biochemical precursor, theobromine. Theobromine Diuretic, smooth muscle relaxant, cardiac stimulant, and vasodilator Caffeine Central nervous system stimulant and diuretic

Sampling Sample Preparation The first step in any chemical analysis is procuring a representative, small sample to measure－a process called sampling 取樣. Sample Preparation Homogeneous and heterogeneous samples need different preparation procedures. Ceramic mortar and pestle used to grind solids into fine powders.

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. 離心 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.

The Chemical Analysis flows out first Chromatogram flows out latter Chromatography (層析法) column separates the analytes and measures their quantity. The column is packed with tiny particles of silica (SiO2) on which are attached long hydrocarbon molecules. flows out first Chromatogram 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. 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 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 the Results 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.

Reporting and interpretation 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

Quantitative Analytical Methods 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