Instrumental Analytical Chemistry

An Introduction

James W. Robinson, Eileen M. Skelly Frame, George M. Frame II

• Editore: CRC Press
• Anno: 2021
• ISBN:
  9781315301136
• Edizione: 1
• Argomento: Ciencias físicas
• Categoria: Química

Analytical chemistry today is almost entirely instrumental analytical chemistry and it is performed by many scientists and engineers who are not chemists. Analytical instrumentation is crucial to research in molecular biology, medicine, geology, food science, materials science, and many other fields. With the growing sophistication of laboratory equipment, there is a danger that analytical instruments can be regarded as "black boxes" by those using them. The well-known phrase "garbage in, garbage out" holds true for analytical instrumentation as well as computers. This book serves to provide users of analytical instrumentation with an understanding of their instruments.

This book is written to teach undergraduate students and those working in chemical fields outside analytical chemistry how contemporary analytical instrumentation works, as well as its uses and limitations. Mathematics is kept to a minimum. No background in calculus, physics, or physical chemistry is required. The major fields of modern instrumentation are covered, including applications of each type of instrumental technique.

Each chapter includes:

• A discussion of the fundamental principles underlying each technique
• Detailed descriptions of the instrumentation
• An extensive and up-to-date bibliography
• End of chapter problems
• Suggested experiments appropriate to the technique where relevant

This text uniquely combines instrumental analysis with organic spectral interpretation (IR, NMR, and MS). It provides detailed coverage of sampling, sample handling, sample storage, and sample preparation. In addition, the authors have included many instrument manufacturers' websites, which contain extensive resources.

Concepts of Instrumental Analytical Chemistry1

1.1 Introduction: What is Instrumental Analytical Chemistry?

Perhaps the most functional definition of analytical chemistry is that it is “the qualitative and quantitative characterization of matter”. The word characterization is used in a very broad sense. It may mean the identification of the chemical compounds or elements present in a sample to answer questions such as “Is there any vitamin E in this shampoo as indicated on the label”? or “Is this white tablet an aspirin tablet”? or “Is this piece of metal iron or nickel”? This type of characterization, to tell us what is present is called qualitative analysis. Qualitative analysis is the identification of one or more chemical species present in a material. Characterization may also mean the determination of how much of a particular compound or element is present in a sample, to answer questions such as “How much acetylsalicylic acid is in this aspirin tablet”? or “How much nickel is in this steel”? This determination of how much of a species is present in a sample is called quantitative analysis. Quantitative analysis is the determination of the amount of a chemical species present in a sample. The chemical species may be an element, compound, or ion. The compound may be organic or inorganic. Characterization can refer to the entire sample (bulk analysis), such as the elemental composition of a piece of steel, or to the surface of a sample (surface analysis), such as the identification of the composition and thickness of the oxide layer that forms on the surface of most metals exposed to air and water. The characterization of a material may go beyond chemical analysis to include structural determination of materials, the measurement of physical properties of a material, and the measurement of physical chemistry parameters like reaction kinetics. Examples of such measurements are the degree to which a polymer is crystalline as opposed to amorphous, the temperature at which a material loses its water of hydration, how long it takes for antacid “Brand A” to neutralize stomach acid, and how fast a pesticide degrades in sunlight. These diverse applications make analytical chemistry one of the broadest in scope of all scientific disciplines. Analytical chemistry is critical to our understanding of biochemistry, medicinal chemistry, geochemistry, environmental science, forensic science, atmospheric chemistry, polymer chemistry, metallurgy, and many other scientific disciplines.

For many years, analytical chemistry relied on chemical reactions to identify and determine the components present in a sample. These types of classical methods, often called “wet chemical methods”, usually required that a part of the sample be taken, dissolved in a suitable solvent if necessary, and the desired reaction carried out. The most important analytical fields based on this approach were volumetric and gravimetric analyses. Acid-base titrations, oxidation-reduction titrations, and gravimetric determinations, such as the determination of silver by precipitation as silver chloride are all examples of wet chemical analyses. These types of analyses require a high degree of skill and attention to detail on the part of the analyst if accurate and precise results are to be obtained. They are also time-consuming and the demands of today's high-throughput pharmaceutical development labs, forensic labs, commercial environmental labs, and industrial quality control labs often do not permit the use of such time-consuming methods for routine analysis. In addition, it may be necessary to analyze samples without destroying them. Examples include evaluation of valuable artwork to determine if a painting is really by a famous “Old Master” or is a modern forgery, as well as in forensic analysis, where the evidence may need to be preserved. For these types of analyses, non-destructive analysis methods are needed. Wet chemical analysis is still used in specialized areas of analysis, but many of the volumetric methods have been transferred to automated instruments. Classical analysis and instrumental analysis are similar in many respects, such as in the need for proper sampling, sample preparation, assessment of accuracy and precision, and proper record-keeping. Some of the topics discussed briefly in this chapter are covered at greater length in more general texts on analytical chemistry and quantitative analysis. Several of these types of texts are listed in the bibliography.

Most analyses today are carried out by instrumental analytical chemistry, using specially designed electronic instruments controlled by computers. These instruments make use of the interaction of electromagnetic radiation and matter, or of some physical property of matter, to characterize the sample being analyzed. Often these instruments have automated sample introduction, automated data processing, and even automated sample preparation. To understand how instrumentation operates and what information it provides requires knowledg...