Microwaves: theoretical aspects and practical applications in chemistry

The introduction of new technologies contributes, in many cases, in the rapid changing in the way we live, learn and work. This also happened with the introduction of devices based on microwave technologies, which nowadays range from communication tools to the more common heating apparatus. In this context we can certainly assess that microwaves deeply changed the way we were. Furthermore, microwaves changed, and will still change, the way we communicate each other and work. We should be aware of this fact.Since the appearance of the first lab application, dated 1975, microwaves helped the chemists to reduce the time needed in the sample preparation, on one hand, and opened a series of new frontiers characterized by new research perspectives and knowledge on the other one.As a matter of fact, the most relevant and important acquisition with the introduction of microwaves was that people, for the first time, were able to supply and control, under certain conditions, the energy involved in reactions. Probably this was not exactly the situation at the beginning but today the new microwave devices can deliver electromagnetic radiation “when needed”. In turns, this means safer procedures and more accurate and precise analytical data. The aims of this book are mainly focused on the microwave digestion and extraction topics. State of the art examples and a deep critical discussion of the reported data are the common denominator of all the scientific contributes.Sample treatment has become an integral and fundamental part in the development process of analytical methods. Several different fields, such as physics, chemistry, geology, pharmaceutical science, nuclear science, material science, cosmochemistry, archeology, petroleum industry, pharmaceutical chemistry, forensic science, and environmental science, have benefited from the highly productive capabilities in sample preparation of this analytical technique. With the expansion of activities in instrumental analytical determinations, an impressing need is felt for time saving procedures. As far as the topics of the book are concerned, these are intended to fulfill the need of providing a well-balanced and in-depth discussion of the basic concepts and latest developments over a range of important subjects in modern sample treatment techniques by means of microwave heating devices.The idea for a new book on microwave topics was born some time ago and started from the consideration that in literature was missing a “manual” that, starting from a solid and detailed discussion on the basic principles of the wave-matter interactions, could also be used as an “operative manual” reporting the state of the art of the scientific knowledge in this field, even if excellent and valuable books are still available such as “Microwave Sample Preparation: theory and practice”, edited by H.M. (Skip) Kingston and Lois B. Jassie (1988), and “Microwave-Enhanced Chemistry: fundamentals, sample preparation and applications”, edited by H.M. (Skip) Kingston and Stephen J. Haswell (1997). Therefore, following this approach the eight chapters, which this book is constituted of, give an account of the experiences and knowledge of several Authors within this area.The material in the book has evolved from the teaching and working experiences of the researchers involved.In particular, chapter 1 deals with the description of the fundamental molecular processes, which lie behind the interaction between electromagnetic waves and the matter in the microwaves region responsible of the heating phenomena.Chapter 2 gives an overview of the chronological evolution of several MW devices with an emphasis on the vessels and pressure /temperature control apparatus.Chapters from 3 to 5 describe, with plenty of details, the multiple use and applications of the MW energy in several area and the recent results in the biological field for the trace and ultra trace element determination, respectively.In the majority of cases, the introduction of microwaves permits a huge time saving in the analytical procedure. Although time and cost saving have been for long time the main strengths of this technique, nowadays scientists probably more appreciate the possibility of an energy delivery control following the philosophy of “energy when necessary”. In this context it becomes crucial the optimization of the factors that play a fundamental role on the yield of processes, namely the solvent composition, the temperature, the time, etc. Therefore, chapter 6 gives an overview of the potentialities of the Design of Experiment approach in the optimization of digestion procedure for the metals recovery in real matrices. Finally, in chapters 7 and 8, the advantages introduced by the implementation of the microwaves in extraction apparatus is deeply discussed and compared with alternative procedures. It is hoped that the book will be also a good teaching tool of the principles of microwave-matter interaction and applications to undergraduate and graduate students as well as to those with no background in sample preparation topics. The practitioner of microwave devices at all levels should also enjoy reading the book.A special acknowledgment is due to all the CEM people: for their help, suggestions and encouragement during the realization of the book.Finally, I lack the words to express my full appreciation to all the Authors that joined this project with their invaluable contribution.