D. Harvey - Modern Analytical Chemistry (794078), страница 3
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Any solid impurities that remain areremoved by filtration before continuing with the analysis.In a typical total analysis method, the procedure mightreadAfter dissolving the sample in a beaker, remove anysolid impurities by passing the solution containingthe analyte through filter paper, collecting thesolution in a clean Erlenmeyer flask. Rinse the beakerwith several small portions of solvent, passing theserinsings through the filter paper, and collecting themin the same Erlenmeyer flask. Finally, rinse the filterpaper with several portions of solvent, collecting therinsings in the same Erlenmeyer flask.For a typical concentration method, however, the proceduremight stateStandardization—External standards, standard additions,and internal standards are a common feature of manyquantitative analyses.
Suggested experiments using thesestandardization methods are found in later chapters. A goodproject experiment for introducing external standardization,standard additions, and the importance of the sample’syymatrix is to explore the effect of pH on the quantitativeanalysis of an acid–base indicator. Using bromothymol blueas an example, external standards can be prepared in91Ga pHSUGGESTEDREADINGSbuffer and used to analyze samples buffered to different pHsin the range of 6–10. Results can be compared with thoseThe role of analytical chemistry within the broader discipline ofobtained using a standard addition.chemistry has been discussed by many prominent analyticalchemists. Several notable examples follow.Baiulescu, G. E.; Patroescu, C.; Chalmers, R.
A. Education andTeaching in Analytical Chemistry. Ellis Horwood: Chichester,1982.Hieftje, G. M. “The Two Sides of Analytical Chemistry,” Anal.Chem. 1985, 57, 256A–267A.Kissinger, P. T. “Analytical Chemistry—What is It? Who Needs It?Why Teach It?” Trends Anal. Chem.
1992, 11, 54–57.Laitinen, H. A. “Analytical Chemistry in a Changing World,”Anal. Chem. 1980, 52, 605A–609A.Laitinen, H. A. “History of Analytical Chemistry in the U.S.A.,”Talanta 1989, 36, 1–9.Laitinen, H. A.; Ewing, G. (eds). A History of AnalyticalChemistry. The Division of Analytical Chemistry ofthe American Chemical Society: Washington, D.C.,1972.McLafferty, F. W. “Analytical Chemistry: Historic and Modern,”Acc. Chem. Res.
1990, 23, 63–64.1H REFERENCES1. Ravey, M. Spectroscopy 1990, 5(7), 11.2. de Haseth, J. Spectroscopy 1990, 5(7), 11.3. Fresenius, C. R. A System of Instruction in Quantitative ChemicalAnalysis. John Wiley and Sons: New York, 1881.4. Hillebrand, W. F.; Lundell, G. E. F. Applied Inorganic Analysis, JohnWiley and Sons: New York, 1953.5. Van Loon, J. C. Analytical Atomic Absorption Spectroscopy. AcademicPress: New York, 1980.6. Murray, R.
W. Anal. Chem. 1991, 63, 271A.7. For several different viewpoints see (a) Beilby, A. L. J. Chem. Educ.1970, 47, 237–238; (b) Lucchesi, C. A. Am. Lab. 1980, October,4. A sample was analyzed to determine the concentration of ananalyte. Under the conditions of the analysis, the sensitivity is17.2 ppm–1. What is the analyte’s concentration if Smeas is 35.2and Sreag is 0.6?5.
A method for the analysis of Ca2+ in water suffers from aninterference in the presence of Zn2+. When the concentrationof Ca2+ is 50 times greater than that of Zn2+, an analysis forCa2+ gives a relative error of –2.0%. What is the value of theselectivity coefficient for this method?6. The quantitative analysis for reduced glutathione in blood iscomplicated by the presence of many potential interferents.In one study, when analyzing a solution of 10-ppbglutathione and 1.5-ppb ascorbic acid, the signal was 5.43times greater than that obtained for the analysis of 10-ppbglutathione.12 What is the selectivity coefficient for thisanalysis? The same study found that when analyzing asolution of 350-ppb methionine and 10-ppb glutathione thesignal was 0 906 times less than that obtained for the analysis113–119; (c) Atkinson, G.
F. J. Chem. Educ. 1982, 59, 201–202;(d) Pardue, H. L.; Woo, J. J. Chem. Educ. 1984, 61, 409–412;(e) Guarnieri, M. J. Chem. Educ. 1988, 65, 201–203; (f) de Haseth, J.Spectroscopy 1990, 5, 20–21; (g) Strobel, H. A. Am. Lab. 1990,October, 17–24.8. Hieftje, G. M. Am. Lab. 1993, October, 53–61.9. See, for example, the following laboratory texts: (a) Sorum, C. H.;Lagowski, J.
J. Introduction to Semimicro Qualitative Analysis, 5th ed.Prentice-Hall: Englewood Cliffs, NJ, 1977.; (b) Shriner, R. L.; Fuson,R. C.; Curtin, D. Y. The Systematic Identification of OrganicCompounds, 5th ed. John Wiley and Sons: New York, 1964.ProblemsA variety of problems, many basedon data from the analytical literature,provide the student with practicalexamples of current research.xi1400-Fm 9/9/99 7:38 AM Page xiiPrefaceAPrefaces currently taught, the introductory course in analytical chemistry emphasizesquantitative (and sometimes qualitative) methods of analysis coupled with a heavydose of equilibrium chemistry. Analytical chemistry, however, is more than equilibrium chemistry and a collection of analytical methods; it is an approach to solvingchemical problems.
Although discussing different methods is important, that discussion should not come at the expense of other equally important topics. The introductory analytical course is the ideal place in the chemistry curriculum to exploretopics such as experimental design, sampling, calibration strategies, standardization,optimization, statistics, and the validation of experimental results. These topics areimportant in developing good experimental protocols, and in interpreting experimental results.
If chemistry is truly an experimental science, then it is essential thatall chemistry students understand how these topics relate to the experiments theyconduct in other chemistry courses.Currently available textbooks do a good job of covering the diverse range of wetand instrumental analysis techniques available to chemists.
Although there is somedisagreement about the proper balance between wet analytical techniques, such asgravimetry and titrimetry, and instrumental analysis techniques, such as spectrophotometry, all currently available textbooks cover a reasonable variety of techniques. These textbooks, however, neglect, or give only brief consideration to,obtaining representative samples, handling interferents, optimizing methods, analyzing data, validating data, and ensuring that data are collected under a state of statistical control.In preparing this textbook, I have tried to find a more appropriate balancebetween theory and practice, between “classical” and “modern” methods of analysis,between analyzing samples and collecting and preparing samples for analysis, andbetween analytical methods and data analysis.
Clearly, the amount of material in thistextbook exceeds what can be covered in a single semester; it’s my hope, however,that the diversity of topics will meet the needs of different instructors, while, perhaps, suggesting some new topics to cover.The anticipated audience for this textbook includes students majoring in chemistry, and students majoring in other science disciplines (biology, biochemistry,environmental science, engineering, and geology, to name a few), interested inobtaining a stronger background in chemical analysis.
It is particularly appropriatefor chemistry majors who are not planning to attend graduate school, and who oftendo not enroll in those advanced courses in analytical chemistry that require physicalchemistry as a pre-requisite. Prior coursework of a year of general chemistry isassumed. Competence in algebra is essential; calculus is used on occasion, however,its presence is not essential to the material’s treatment.xii1400-Fm 9/9/99 7:38 AM Page xiiiPrefaceKey Features of This TextbookKey features set this textbook apart from others currently available.• A stronger emphasis on the evaluation of data. Methods for characterizingchemical measurements, results, and errors (including the propagation oferrors) are included.
Both the binomial distribution and normal distributionare presented, and the idea of a confidence interval is developed. Statisticalmethods for evaluating data include the t-test (both for paired and unpaireddata), the F-test, and the treatment of outliers. Detection limits also arediscussed from a statistical perspective. Other statistical methods, such asANOVA and ruggedness testing, are presented in later chapters.• Standardizations and calibrations are treated in a single chapter. Selecting themost appropriate calibration method is important and, for this reason, themethods of external standards, standard additions, and internal standards aregathered together in a single chapter.
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