Heinz-Helmut Perkampus UVVIS Spectroscopy and Its Applications Translated by H.Charlotte Grinter and Dr.T.L.Threlfall With 78 Figures and 21 Tables Springer-Verlag Berlin Heidelberg New York London Paris Tokyo Hong Kong Barcelona Budapest
Heinz-Helmut Perkampus UV-VIS Spectroscopy and Its Applications Translated by H. Charlotte Grinter and Dr. T. L. Threlfall With 78 Figures and 21 Tables Springer -Ver lag Berlin Heidelberg New York London Paris Tokyo Hong Kong Barcelona Budapest
Preface UV-VIS spectroscopy is one of the oldest methods in molecular spectroscopy.The definitive formulation of the Bouguer-La Beer law in 1852 created the basis for the quantitative evaluation of absorption measurements at an early date.This led firstly to colorimetry,then to photometry and finally to spectrophotometry. This evolution ran parallel with the development of detectors for measuring light intensities,i.e.from the human eye via the photo- element and photocell,to the photomultiplier and from the photo- mln me mn of eomlee With the development of quantum chemistry,increasing atten- s paid to the en light abs tion a and the structur the lt that ent de t dis ssions of the theory of des a numbe (UV-VIS and c spectr spectroscopy)have been publishe Consequently,this extremely interesting as ect o mo r spec troscopy has dominated the teaching of the subject both in my own lectures and those of others.However,it is often overlooked that,in addition to the theory,applications of spectroscopic methods are of particular interest to scientists.For this reason,a lecture series about electronic spectroscopy given in the Institute for Physical Chemistry at the Heinrich-Heine-University in Dusseldorf was supplemented by one about "UV-VIS spectroscopy and its applications".This formed the basis of the present book. UV-VIS spectro opy owes its importance not least to its varied in This book to show W UV-VIS 0P2 be applied an to the kine tics of chemical reac ctions,incluc ng phot theoretical section has been kept to a minimum since,as men tioned above,excellent discussions of such matters are ava lable in the literature.The details of the equipment are also described very briefly because G.Kortum gave an outstanding discussion of this subject in volume II of the series "Anleitung fur die chemische Laboratoriumspraxis";and its basic details still apply today. In addition to the applications,a number of UV-VIS spec- troscopic techniques are discussed.However,in this case the selec- tion has been influenced by the author's own interests.In order to expe ime tal mples ous me ents ha e beer
Preface UV-VIS spectroscopy is one of the oldest methods in molecular spectroscopy. The definitive formulation of the Bouguer-LambertBeer law in 1852 created the basis for the quantitative evaluation of absorption measurements at an early date. This led firstly to colorimetry, then to photometry and finally to spectrophotometry. This evolution ran parallel with the development of detectors for measuring light intensities, i.e. from the human eye via the photoelement and photocell, to the photomultiplier and from the photographic plate to the present silicon-diode detector both of which allow simultaneous measurement of the complete spectrum. With the development of quantum chemistry, increasing attention was paid to the correlation between light absorption and the structure of matter with the result that in recent decades a number of excellent discussions of the theory of electronic spectroscopy (UV-VIS and luminescence sp,~ctroscopy) have been published. Consequently, this extremely ivteresting aspect of molecular spectroscopy has dominated the teaching of the subject both in my own lectures and those of others. However, it is often overlooked that, in addition to the theory, applications of spectroscopic methods are of particular interest to scientists. For this reason, a lecture series about electronic spectroscopy given in the Institute for Physical Chemistry at the Heinrich-Heine-University in Dusseldorf was supplemented by one about "UV-VIS spectroscopy and its applications". This formed the basis of the present book. UV-VIS spectroscopy owes its importance not least to its varied applications in chemistry, physics and biochemistry. This book aims to show how UV-VIS spectroscopy can be applied to analytical problems, to the investigation of chemical equilibria and to the kinetics of chemical reactions, including photokinetics. The theoretical section has been kept to a minimum since, as mentioned above, excellent discussions of such matters are available in the literature. The details of the equipment are also described very briefly because G. KortUm gave an outstanding discussion of this subject in volume II of the series "Anleitung fUr die chemische Laboratoriumspraxis"; and its basic details still apply today. In addition to the applications, a number of UV-VIS spectroscopic techniques are discussed. However, in this case the selection has been influenced by the author's own interests. In order to obtain experimental examples, numerous measurements have been
VI Preface made which might also be set as practical work for students of ad- chemis like my colleagues for making these measure. ments,and rawing grams The English translation of the s onddition of this volume is due to the stimulating interest of the "Ultra iolet Spectrometry Group",London,to whom I am very gratefu Mrs.Charlotte Grinter undertook the translation with great in terest and engagement,professionally supported by Dr.T.L. Threlfall and Dr.Grinter.I would like to express my sincere thanks to Mrs.Grinter and the colleagues mentioned above for their hard labors. A few additions have been made to the first edition,i.e.the brief section "Chemometrics"was added by the English colleagues, me have e been changed,others are new and the cited ated w y.Here also the English ed to be very helpful for ich vould like to ex press my thank Thanks are also due to Dr.Enders of the Springer -Verlag interest and support of the publication of the English Dusseldorf,June 1992 HEINZ-HELMUT PERKAMPUS
VI Preface made which might also be set as practical work for students of advanced physical chemistry. I would like to thank my colleagues for making these measurements, and drawing the diagrams. The English translation of the second edition of this volume is due to the stimulating interest of the "Ultraviolet Spectrometry Group", London, to whom I am very grateful. Mrs. Charlotte Grinter undertook the translation with great interest and engagement, professionally supported by Dr. T. L. Threlfall and Dr. Grinter. I would like to express my sincere thanks to Mrs. Grinter and the colleagues mentioned above for their hard labors. A few additions have been made to the first edition, i.e. the brief section "Chemometrics" was added by the English colleagues, some figures have been changed, others are new and the cited literature has been updated where necessary. Here also the English colleagues proved to be very helpful for which I would like to express my thanks. Thanks are also due to Dr. Enders of the Springer-Verlag for his interest and support of the publication of the English edition. Dusseldorf, June 1992 HEINZ-HELMUT PERKAMPUS
Contents 1 Introduction 1 Principles .。4”4。4 2.2 Primary Photophysical Processes . 5 2.3 Vibrational Structure of Electronic Spectra. 6 2.4 Electronic Spectra and Molecular Structure . 8 References. Photometers and Spectrophotometers. o 3.1 Photometers. 11 3.2 Spectrophotometers. 12 3.3 The Stray Light Error 17 3.3.1 General Observations 3.3.2 The Stray Light Error of Transmission and Absorbance and Its Measurement 19 3.4 Light Sources for UV-VIS Spectroscopy . 21 References 24 Analytical Applications of UV-VIS Spectroscopy 26 4.1 Photometric Determination of a Single Substance 26 4.1.1 Photometric Det mination of Ei lements by Means of Co omp Ag 29 4.1.2 metric Determ in f Anions and Amm 4.1.3 Photometric Water Analyses 4.1.4 Photometric Determination of Organic Compounds. 。,。,。 4.1.5 Enzymatic Analysis and Enzyme Kinetics. 4.2 2. Multicomponent Analysis +。 Basic Equa tions 42 An Example of a Multicomponent Analysis . 886 43 Identification and Structure Determination. 68
Contents 1 2 2.1 2.2 2.3 2.4 Introduction Principles . . The Bouguer-Lambert-Beer Law and Its Practical Application . . Primary Photophysical Processes . . Vibrational Structure of Electronic Spectra Electronic Spectra and Molecular Structure . . 1 3 3 5 6 8 References . 9 3 3.1 3.2 3.3 3.3.1 3.3.2 3.4 Photometers and Spectrophotometers . . Photometers . . Spectrophotometers . . The Stray Light Error . . General Observations . . The Stray Light Error of Transmission and Absorbance and Its Measurement . . Light Sources for UV-VIS Spectroscopy . . 10 11 12 17 17 19 21 References . 24 4 4.1 4.1.1 4.1.2 4.1.3 4.1.4 4.1.5 4.2 4.2.1 4.2.2 4.3 Analytical Applications of UV-VIS Spectroscopy Photometric Determination of a Single Substance Photometric Determination of Elements by Means of Complexing Agents . . Photometric Determination of Anions and Ammonia . . Photometric Water Analyses . . Photometric Determination of Organic Compounds . . Enzymatic Analysis and Enzyme Kinetics . . Multicomponent Analysis . . Basic Equations . . An Example of a Multicomponent Analysis . . Identification and Structure Determination . . 26 26 29 38 43 44 49 58 58 65 68
VIII Contents 4.4 Chemometrics 六 References . 76 5 Recent Developments in UV-VIS Spectroscopy. 8 5.1 Dual-Wavelength Spectroscopy 。+，。+ 81 5.2 Derivative Spectroscopy. 5.3 Reflectance Spectroscopy 9 5.4 Photoacoustic Spectroscopy 。,。4.4。年。4。，。g: 5.4.1 Principles of PAS . 181 5.4.2 PAS Applications. 110 5.5 Luminescence-Excitation Spectroscopy ·。” 120 References . . 128 6 Investigation of Equilibria 3 61 General. 131 6.2 Protolytic Equilibria;pK-Values ，。，。，。÷。4.4944。 132 6.3 Complex-Forming Equilibria 142 63, As ation. 143 6.3 EDA 149 +”4。年”年”年”中年车”卡”中”·。”。 6.3.3 Metal Complexes 年年。+。+4++4年44。”。”*”。卡” 158 References 162 Investigation of the Kinetics of Chemical Reactions. 165 7. Fundamental Equations of Kinetics 165 11.1 Introduction of Absorbance a meas 165 7.1.2 sific of Other Types of Reaction 167 7.1.2.1 2nd o 167 年。卡年无，8”卡”卡”卡”中”中”卡” 7.1.2.2 3rd Order 169 00年卡年卡+”年9年。，。年。” 7.1.2. 3 Pseudo 1st Order Reactions ▣0。t0t。t。t”年”+”4”4 171 7.1.2.4 Consecutive Reactions . 172 7.1.2.5 Parallel Reactions., 173 7.2 The Number of Linearly Independent Partial Reactions. 175 7.3 Evaluation of Kinetic Measurements .179 7.4 Examples,.,。.。,.,。.。,。,.,。 183 Fast Reactions 190 Flow Method opped-Flov 190 Spectroscopic Relaxation Techniques. 193
VIII .Contents 4.4 Chemometrics 75 References . 76 5 5.1 5.2 5.3 5.4 5.4.1 5.4.2 5.5 Recent Developments in UV-VIS Spectroscopy . . Dual-Wavelength Spectroscopy . . Derivative Spectroscopy . . Reflectance Spectroscopy . . Photoacoustic Spectroscopy . . Principles of PAS . . PAS Applications . . Luminescence-Excitation Spectroscopy . . 81 81 88 95 101 101 110 120 References . 128 6 Investigation of Equilibria . 131 6.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 6.2 Protolytic Equilibria; pK-Values . . 6.3 Complex-Forming Equilibria . . 6.3.1 H-Bond Association . . 6.3.2 EDA Complexes . . 6.3.3 Metal Complexes . . References . . 7 Investigation of the Kinetics 132 142 143 149 158 162 of Chemical Reactions . 165 7.1 Fundamental Equations of Kinetics. . . . . . . . . 165 7.1.1 Introduction of Absorbance as a Measurement Parameter . 165 7.1.2 Classification of Other 'JYpes of Reaction . 167 7.1.2.1 2nd Order Reactions . 167 7.1.2.2 3rd Order Reactions . 169 7.1.2.3 Pseudo 1 st Order Reactions . 171 7.1.2.4 Consecutive Reactions . 172 7.1.2.5 Parallel Reactions . 173 7.2 The Number of Linearly Independent Partial Reactions . 175 7.3 7.4 7.5 7.5.1 7.5.2 Evaluation of Kinetic Measurements . . Examples . . Fast Reactions . . Flow Methods: The Stopped-Flow Technique . . Spectroscopic Relaxation Techniques . . 179 183 190 190 193