Photoacoustic IR Spectroscopy E-Book

Kirk H. Michaelian

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 598

Veröffentlichungsjahr: 2010

Beschreibung

This invaluable and up-to-date source on instruments and applications covers everything needed to employ a technique for investigating various gases and materials, including biomaterials. It includes the latest developments in light sources, signal recovery and numerical methods.
There is no other single publication that reviews the entire subject of photoacoustic infrared spectroscopy in such detail. Physicists, chemists, and spectroscopists in both academic and industrial laboratories, polymer and organic chemists, analysts in industry, forensic and government laboratories, and materials scientists will find this book to be a vital resource.

Leseprobe

Table of Contents

Cover

Table of Contents

Half title page

Related Titles

Title page

Copyright page

Dedication

Preface to the Second Edition

Preface to the First Edition

1 Introduction

1.1 Single- and Multiple-Wavelength PA Spectroscopies

1.2 Scope

1.3 Other Sources of Information

2 History of PA Infrared Spectroscopy

2.1 Early History

2.2 Multiple-Wavelength PA Infrared Spectroscopy

2.3 Arrival of PA FT-IR Spectroscopy

3 Instrumental Methods

3.1 Dispersive PA Infrared Spectroscopy

3.2 Rapid-Scan PA FT-IR Spectroscopy

3.3 Step-Scan PA FT-IR Spectroscopy

3.4 Mid-Infrared Laser PA Spectroscopy

3.5 Quartz-Enhanced PA Spectroscopy

3.6 Cantilever Enhanced PA Spectroscopy

3.7 Piezoelectric Detection

3.8 Photothermal Beam Deflection Spectroscopy

3.9 Optothermal Window Spectroscopy

4 Signal Recovery

4.1 DSP Demodulation

4.2 Lock-in Demodulation

5 Experimental Techniques

5.1 Amplitude Modulation

5.2 Phase Modulation

5.3 Synchrotron Infrared PA Spectroscopy

5.4 PA Infrared Microspectroscopy2)

5.5 Quantitative Analysis

5.6 Depth Profiling

6 Numerical Methods

6.1 Averaging of PA Data

6.2 Spectrum Linearization

6.3 Phase Analysis

7 Applications

7.1 Carbons

7.2 Hydrocarbon Fuels

7.3 Organic Chemistry

7.4 Inorganic Chemistry

7.5 Biology and Biochemistry

7.6 Medical Applications

7.7 Polymers

7.8 Catalysts

7.9 Gases

7.10 Wood and Paper

7.11 Food Products

7.12 Clays and Minerals

7.13 Textiles

Appendix 1: Glossary

Appendix 2: Literature Guide – Solids and Liquids

Appendix 3: Literature Guide – Gases

Index

Kirk H. Michaelian

Photoacoustic IR Spectroscopy

Related Titles

Everall, N., Griffiths, P. R., Chalmers, J. M. (eds.)

Vibrational Spectroscopy of Polymers

Principles and Practice

2007

ISBN: 978-0-470-01662-6

Telle, H. H., Urena, A. G., Donovan, R. J.

Laser Chemistry

Spectroscopy, Dynamics and Applications

2007

ISBN: 978-0-471-48571-1

Bordo, V. G., Rubahn, H.-G.

Optics and Spectroscopy at Surfaces and Interfaces

2005

ISBN: 978-3-527-40560-2

The Author

Kirk H. Michaelian

Natural Resources Canada

Devon, Alberta

Canada

[email protected]

Cover Photo Spieszdesign GbR, Neu-Ulm

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ISBN: 978-3-527-40900-6 ISBN: 978-3-527-63321-0 (ebk)

For Diane

Preface to the First Edition

‘Science is concerned with the rational correlation of experience rather than the discovery of fragments of absolute truth.’

Sir Arthur Eddington, The Philosophy of Physical Science

The continued growth of the primary scientific literature and the increased level of specialization that characterize modern physical science would both appear to require that forthcoming entries in the Chemical Analysis Series be constrained to topics somewhat narrower than those in previous volumes. The subject of photoacoustic (PA) spectroscopy is certainly not an exception to this trend. To be specific, A. Rosencwaig surveyed this then-emergent field in Volume 57, Photoacoustics and Photoacoustic Spectroscopy, a little more than two decades ago. The preparation of a similar treatise today would undoubtedly be a daunting task – one that might be expected to yield several texts. This assertion is corroborated by the 1994 publication of Air Monitoring by Spectroscopic Techniques (Volume 127, edited by M. W. Sigrist), followed in 1996 by Photothermal Spectroscopy Methods for Chemical Analysis (Volume 134, by S. E. Bialkowski). The present text, which is dedicated to the subject of photoacoustic infrared spectroscopy, is the newest volume in this continuing Chemical Analysis Series on photoacoustic and photothermal spectroscopy.

It is never inappropriate to question the need for a book on a particular analytical method. Two factors are especially pertinent with regard to the current submission. First, while several excellent review articles and book chapters on photoacoustic Fourier transform infrared (FTIR) spectroscopy already exist, much of this work is concerned with specific sample classes (e.g., polymers), numerical methods (mostly dealing with the phase of the PA signal), or instrumentation. The present volume adopts a perspective that is alternately historical and contemporary by reviewing both early and recent literature on an array of applications of PA infrared spectroscopy.

Moreover, a slightly different technological viewpoint is adopted here: This text discusses various implementations of PA spectroscopy at near-, mid- and far-infrared wavelengths, and is not restricted to the topic of ‘PA FTIR’ spectroscopy. For example, spectra of gases obtained with CO or CO2 laser radiation at discrete wavelengths, without the use of an interferometer, are included. Similarly, dispersive near- and mid-infrared PA spectra of condensed-phase materials are discussed in several contexts. This approach to the subject was taken so as to minimize the effects of the seemingly arbitrary description of PA infrared spectra that is based on the specific apparatus used to acquire them.

The second justification for the present work arises from the very significant advances in, and expansion of, PA and photothermal science in recent years. Much of the early work in this discipline consisted of research in PA spectroscopy, albeit primarily at wavelengths shorter than those considered here. On the other hand, the entire field of PA and photothermal research has now grown and diversified to the point where it is justifiable – and perhaps necessary – that its major specializations be summarized more or less independently. The ever-increasing extent of the pertinent scientific literature implies that PA infrared spectroscopy certainly merits this treatment, as do several other related topics. It is hoped that this overview and synthesis of the PA infrared literature will prove useful to readers who may require detailed information on this subject.

This book has several specific objectives. Even though PA infrared spectroscopy is well established, many infrared spectroscopists tend to regard the method as unconventional or marginal and therefore ascribe second-class status to the technique. This situation is partly attributable to the low intensities associated with many early PA spectra, a factor that has been minimized in recent years by numerous advances in instrumentation and data analysis. It also arises from the usual lack of familiarity associated with any developing method. Hence the first objective of the present work is to clearly demonstrate the viability of PA infrared spectroscopy. This is accomplished by showing its widespread acceptance and reviewing its successful utilization in a variety of disciplines.

As the relevant literature was assembled, it became apparent that a significant number of proven experimental and numerical PA infrared techniques exist. It was noted above that some of these methods have already been discussed in one or more review articles or book chapters. However, there does not appear to be a single source that attempts a more comprehensive review of the relevant literature. This goal has now been addressed: The second objective of the current work was to assemble a reference text on PA infrared spectroscopy, which discusses most of its important applications and provides the interested reader with a point of entry into the original literature on the topic.

Because this is a volume in a series on Chemical Analysis, a nonmathematical approach has been adopted where possible. On the other hand, when equations are employed, the notation of the original authors has generally been followed; this ensures that the reader will not encounter unnecessary changes when reading both the present work and the primary literature. Because symbol conventions inevitably vary, the reader may notice a few minor examples of alternative usage within the present work. Insofar as mathematical symbols are defined upon their introduction in a particular context, this situation should not cause any significant confusion.

The organization of this text is based on the straightforward division of the published literature into several categories. To begin, Chapters 1 and 2 provide an introduction and historical review of PA infrared spectroscopy, with particular emphasis on early work. After this perspective is established, Chapter 3 discusses a series of seven different experimental PA methods that have been employed by researchers during the last two decades.

One of the most important capabilities of PA infrared spectroscopy – depth profiling – is described in Chapter 4. In this discussion the principles that underlie several relevant experimental techniques are explained and typical results are presented. Chapter 5 then outlines three important numerical methods that pertain to PA spectroscopy. The phase of the PA signal (which is distinct from the instrumental phase that affects all FTIR spectra) plays a key role in several of these manipulations.

A thorough reading of the appropriate scientific literature confirms that the disciplines in which PA infrared spectroscopy has been applied are particularly diverse. Many analysts may be familiar with one or more specific uses of the technique; in all likelihood, very few will be acquainted with the entire array of research topics in which it has been successfully utilized. Chapter 6, which describes a total of 15 different applications of PA infrared spectroscopy, was written to address this situation. Each section is meant to convey a sense of the research carried out in a specific area and to guide the reader who may wish to pursue the subject in more detail. Typical spectra (reproduced from the published literature or measured in the author’s laboratory) are presented in each section of this chapter.

As a spectroscopic technique matures, its use for quantitation generally becomes more viable. The status of PA infrared spectroscopy with regard to quantitative analysis is reviewed in Chapter 7. Indeed, while the majority of the literature on PA spectra of solids and liquids describes qualitative or semi-quantitative studies, this discussion shows that many successful experiments in quantitative analysis have also been carried out.

Finally, Chapter 8 discusses two emerging techniques: PA infrared microspectroscopy and synchrotron infrared PA spectroscopy. Very recent experiments thus demonstrate that the field of PA infrared spectroscopy continues to advance after several decades of active research by a particularly wide community of spectroscopists.

The main part of the book is followed by two appendices. Appendix 1 provides definitions of a number of relevant terms used in the PA literature. Appendix 2 is an alphabetical listing of publications (including journal articles, book chapters, and conference proceedings) on PA infrared spectra of solids and liquids; the particular application(s) discussed in each article are indicated using a classification scheme similar to that in Chapter 6. This information has been collected as an aid to the reader who wishes to consult the original literature on PA infrared spectroscopy of condensed-phase samples.

It is usual to conclude preliminary remarks such as these with a series of acknowledgments. In this regard, the support of Natural Resources Canada during this research and the preparation of this manuscript is greatly appreciated. Similarly, I have benefited considerably from continued cooperation and collaboration with Bruker Optics in the implementation of PA infrared spectroscopy at CANMET during the last two decades. My entry into this field came about as the result of a prescient suggestion approximately 20 years ago. The use of rather tentatively worded acknowledgments is often effected stylistically or deferentially; in this case, however, it is literally necessary. Specifically, I would like to thank Dr. J. C. Donini for ensuring my involvement in PA spectroscopy, but cannot; his sudden passing five years ago has made this impossible.

Kirk H. Michaelian

Edmonton, Alberta, Canada

November, 2002

1

Introduction

This book discusses the experimental technique known as photoacoustic (PA) infrared spectroscopy. Research and applications in this field have enjoyed more or less continual development since its emergence over 30 years ago: a substantial body of literature – comprising more than one thousand publications – on PA infrared spectra exists today. The present work attempts to review and synthesize this literature, a principal objective being to summarize the current status of the technique. Recent advances in this field are also described. The assembled information will allow spectroscopists and researchers in specific disciplines to determine whether the method is appropriate for their needs.

PA infrared spectroscopy can be viewed from several perspectives. For example, it can be regarded as one of a large number of photoacoustic and photothermal (PT) methods used by physicists, chemists, and other researchers to characterize condensed matter and gases. It should be noted that both optical and thermophysical properties of materials can be investigated by these methods. From this viewpoint, PA infrared spectroscopy is a specialization within a much broader field, made possible by the development and application of transducers and optical instrumentation that operate in the infrared region of the electromagnetic spectrum. Of course some might suggest that this (obviously valid) interpretation tends to ascribe a secondary status to PA infrared spectroscopy.

Vibrational (infrared and Raman) spectroscopists1) will almost certainly approach PA infrared spectroscopy in a different way. For these scientists, PA detection of infrared spectra can be described as an enabling technology, significantly increasing the number and type of samples for which viable data can be obtained. The reader will soon recognize that the viewpoint of the infrared spectroscopist is adopted in this book. In fact PA detection of infrared absorption spectra, using modern equipment and radiation sources, offers several well-known advantages. The most important of these are the following:

Minimal sample preparation is required.The technique is suitable for opaque materials.Depth profiling can be effected for inhomogeneous or layered solids.PA spectroscopy is nondestructive (the sample is not consumed).

It is not an exaggeration to assert that these characteristics are critical in many circumstances: for example, samples exhibiting various problematic characteristics may be encountered in industrial laboratories on a daily basis. These include, but are not limited to, viscous liquids, semisolids, and dispersions; metal powders, carbonaceous solids, and granular materials; polymers and layered solids with physical structures or chemical compositions that may be altered by grinding. Traditional infrared sample preparation methods are often inappropriate or have deleterious effects on these substances. Hence the minimization of sample preparation in PA infrared spectroscopy can be considered its most important attribute. Examination of the scientific literature confirms that the majority of spectroscopists using this technique implicitly agree with this statement. The use of PA infrared spectroscopy for the characterization of problematic, even ‘intractable’, samples is discussed throughout this book.

Notwithstanding these statements, the capacity for PA depth profiling is an almost equally important feature: this experimental technique has been utilized extensively to study layered polymers, adsorption on substrates, and surface oxidation of hydrocarbon fuels or other species. Thus the PA spectroscopist also possesses the capability for analysis of surface and subsurface layers (in this context, ‘surface’ implies depths on the order of micrometers, while ‘subsurface’ regions extend tens of micrometers), a goal that surely can be said to be the dream of many chemists and physicists.

PA spectroscopy – frequently referred to by the acronym PAS – is sometimes described as an ‘unconventional’ infrared technique. The very significant number of publications in the primary scientific literature reporting research-quality PA spectra belie this somewhat pejorative description. It is hoped that the present account adequately demonstrates the wide-ranging applicability of the technique and makes a convincing argument for its increased future use.

1.1 Single- and Multiple-Wavelength PA Spectroscopies

PA spectroscopy can be divided into two broad categories. The first can be described as single-wavelength spectroscopy, since only one wavelength of light impinges on the sample of interest. Signal generation in a gas-microphone cell can be used to illustrate this technique. Three steps can be identified. First, modulated radiation from a laser or other suitable source impinges on the condensed-phase sample; second, the absorbed radiation is converted to heat by radiationless processes; and third, the heat generated within the sample is transferred to its cooler surroundings. Periodic heating of the boundary layer of carrier gas adjacent to the warm surface creates a pressure (acoustic) wave that is detected by the transducer (microphone). This experiment can be extended to include measurement of wavelength (wavenumber) dependence of optical absorption by systematically changing the wavelength of the incident radiation to build up a PA spectrum. Sequential observation of PA signals can be effected by selecting different lines from a multiple-wavelength laser or by use of an optical filter, such as a grating monochromator, in conjunction with broad-band radiation. These techniques were used to obtain PA infrared spectra by several research groups, particularly in the 1970s and early 1980s when PA spectroscopy enjoyed a rapid increase in popularity. Currently, multi-line gas (CO2 and CO) and solid-state mid- and near-infrared lasers are used for specific PA applications, an important example being trace gas detection. This implementation of single-wavelength PA infrared spectroscopy is discussed in later chapters.

The second category is multiple-wavelength (multiplex) PA spectroscopy, as practiced with Fourier Transform infrared (FT-IR) spectrometers. Most readers already know, of course, that these spectrometers have attained very wide acceptance in analytical, research, and teaching laboratories during the last four decades. In the present context, the most important attribute of an FT-IR spectrometer is its capability for simultaneous measurements at a range of wavelengths; spectral coverage is determined mainly by the optical characteristics of the beamsplitter, the window material in the sample accessory, and the detector. An optical detector is not required in conventional PA FT-IR spectroscopy, and the accessible wavelength interval depends only on the beamsplitter and the window fitted on the gas-microphone cell. This technique has been used extensively for about three decades and is the source of the majority of the literature discussed in this book. Signal generation in the PA FT-IR experiment can be described in terms similar to those in the previous paragraph. Modulation is provided by the moving mirror in the interferometer or by use of an external device such as a chopper. This is discussed in more detail in Chapter 3.

1.2 Scope

As noted in the previous section, PA infrared spectroscopy has long been practiced with lasers, scanning monochromators, and FT-IR spectrometers. Indeed, the ongoing use of many types of instrumentation in PA spectroscopy demonstrates the breadth of the field. Although many workers today naturally associate infrared spectroscopy with FT-IR spectrometers, it should be emphasized at the outset that PA FT-IR spectroscopy is, in fact, a specialization within the broader discipline of PA infrared spectroscopy. This book adopts the wider definition of the field and examines a number of relevant PA infrared techniques from both historical and modern perspectives.

Spectroscopists are well aware that definitions of wavelength regions tend to differ for reasons that may be either historical, technological, or a combination of the two. Near-, mid-, and far-infrared PA spectroscopies are discussed in this book. Unless otherwise stated, these regions are demarcated as follows: near-infrared, 4000–12 500 cm−1 (wavelengths 2.5–0.8 µm); mid-infrared, 400–4000 cm−1 (25–2.5 µm); and far-infrared, 50–400 cm−1 (200–25 µm). It should be noted that this division of the electromagnetic spectrum, although not uncommon, is somewhat arbitrary; for example, the low-wavenumber limit given for the far-infrared region is based on the few published PA far-infrared spectra rather than more con­ventional far-infrared limits that encompass lower wavenumbers and longer wavelengths.

1.3 Other Sources of Information

Many review articles and conference proceedings dealing with PA spectroscopy have been published during the last three decades. Some literature reviews provide an overview of PA methods and emphasize work at shorter wavelengths (ultraviolet and visible) that is not discussed in this book. Mid-infrared PA spectroscopy receives very limited attention in most of these articles; some, however, discuss near-infrared spectroscopy and are therefore relevant to specific sections of this text. The early work of Adams (1982) is a typical example. Similarly, Vargas and Miranda (1988) published a detailed summary of PA and PT techniques that contains a short section on PA spectroscopy in the near- and mid-infrared regions. Further references discuss PA spectroscopy and its relationship to PA and PT methods (Pao, 1977; Rosencwaig, 1978, 1980; Tam, 1986; Almond and Patel, 1996).

Initial work in mid-infrared PA spectroscopy was summarized by Vidrine (1982) and Graham, Grim, and Fateley (1985). McClelland (1983) discussed several aspects of signal generation and instrumentation in an important survey of PA spectroscopy that emphasized the infrared region. The latter article is considered to be authoritative and continues to be cited by many practitioners who utilize PA infrared spectroscopy. Numerical methods, specifically phase correction and signal averaging, were discussed a few years later by the present author (Michaelian, 1990).

Two research groups made major contributions to the advancement of PA infrared spectroscopy and should be particularly noted with regard to review publications. R. A. Palmer of Duke University, together with many students and other collaborators, published extensively on research topics including PA infrared spectra of polymers, the role and significance of the PA phase, and the development of step-scan FT-IR PA spectroscopy. Consistent with this research effort, a review on PA spectroscopy of polymers by Dittmar, Palmer, and Carter (1994) contains a useful summary of the history and principles of PA infrared spectroscopy. Numerous other publications by this research group are referred to in later chapters.

Similarly, J. F. McClelland and co-workers at Iowa State University made a very considerable contribution to PA infrared spectroscopy during the last three decades. These investigators have a substantive history in instrumentation that culminated in the successful manufacture of commercial sample accessories for FT-IR spectrometers. McClelland and his colleagues published several detailed review articles, including a summary of the PA FT-IR technique that discusses signal generation and demonstrates a series of qualitative and quantitative applications (McClelland et al., 1992). Other reviews discussed sample handling in PA FT-IR spectroscopy (McClelland et al., 1993) and the implementation of PA spectroscopy with step-scan and rapid-scan spectrometers (McClelland et al., 1998). PA FT-IR spectroscopy was reviewed in Volume 2 of Handbook of Vibrational Spectroscopy (McClelland, Jones, and Bajic, 2002) with particular reference to signal generation, instrumentation and sampling. These publications will be of considerable use to investigators who require an introduction to PA infrared spectroscopy.

Note

1) The author of this text is included in this group.

References

Adams, M.J. (1982) Photoacoustic spectroscopy. Prog. Analyt. Atom. Spectrosc., 5, 153–204.

Almond, D. and Patel, P. (1996) Photothermal Science and Techniques, Chapman & Hall, London.

Dittmar, R.M., Palmer, R.A., and Carter, R.O. (1994) Fourier transform photoacoustic spectroscopy of polymers. Appl. Spectrosc. Rev., 29 (2), 171–231.

Graham, J.A., Grim, W.M., and Fateley, W.G. (1985) Fourier transform infrared photoacoustic spectroscopy of condensed-phase samples, in Fourier Transform Infrared Spectroscopy, vol. 4 (eds J.R. Ferraro and L.J. Basile), Academic Press, New York, pp. 345–392.

McClelland, J.F. (1983) Photoacoustic spectroscopy. Anal. Chem., 55 (1), 89A–105A.

McClelland, J.F., Luo, S., Jones, R.W., and Seaverson, L.M. (1992) A tutorial on the state-of-the-art of FTIR photoacoustic spectroscopy, in Photoacoustic and Photothermal Phenomena III (ed. D. Biani), Springer-Verlag, Berlin, pp. 113–124.

McClelland, J.F., Jones, R.W., Luo, S., and Seaverson, L.M. (1993) A practical guide to FTIR photoacoustic spectroscopy, in Practical Sampling Techniques for Infrared Analysis (ed. P.B. Coleman), CRC Press, Boca Raton, pp. 107–144.

McClelland, J.F., Bajic, S.J., Jones, R.W., and Seaverson, L.M. (1998) Photoacoustic spectroscopy, in Modern Techniques in Applied Molecular Spectroscopy (ed. F.M. Mirabella), John Wiley & Sons, Inc., New York, pp. 221–265.

McClelland, J.F., Jones, R.W., and Bajic, S.J. (2002) Photoacoustic spectroscopy, in Handbook of Vibrational Spectroscopy, vol. 2 (eds J.M. Chalmers and P.R. Griffiths), John Wiley & Sons, Ltd, Chichester, pp. 1231–1251.

Michaelian, K.H. (1990) Data treatment in photoacoustic FT-IR spectroscopy, in Vibrational Spectra and Structure, vol. 18 (ed. J.R. Durig), Elsevier Science Publishers B.V., Amsterdam, pp. 81–126.

Pao, Y.-H. (ed.) (1977) Optoacoustic Spectroscopy and Detection, Academic Press, New York.

Rosencwaig, A. (1978) Photoacoustic spectroscopy. Adv. Electron. Electron Phys., 46, 207–311.

Rosencwaig, A. (1980) Photoacoustics and Photoacoustic Spectroscopy, Chem. Anal., vol. 57, John Wiley & Sons, Inc. (Interscience), New York.

Tam, A.C. (1986) Applications of photoacoustic sensing techniques. Rev. Mod. Phys., 58 (2), 381–431.

Vargas, H. and Miranda, L.C.M. (1988) Photoacoustic and related photothermal techniques. Phys. Rep., 161 (2), 43–101.

Vidrine, D.W. (1982) Photoacoustic Fourier transform infrared spectroscopy of solids and liquids, in Fourier Transform Infrared Spectroscopy, vol. 3 (eds J.R. Ferraro and L.J. Basile), Academic Press, New York, pp. 125–148.