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13: Kinetic Methods

  • Page ID
    127243
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    There are many ways to categorize analytical techniques, several of which we introduced in earlier chapters. In Chapter 3 we classified techniques by whether the signal is proportional to the absolute amount of analyte or the relative amount of analyte. For example, precipitation gravimetry is a total analysis technique because the precipitate’s mass is proportional to the absolute amount, or moles, of analyte. UV/Vis absorption spectroscopy, on the other hand, is a concentration technique because absorbance is proportional to the relative amount, or concentration, of analyte.

    A second way to classify analytical techniques is to consider the source of the analytical signal. For example, gravimetry encompasses all techniques in which the analytical signal is a measurement of mass or a change in mass. Spectroscopy, on the other hand, includes those techniques in which we probe a sample with an energetic particle, such as the absorption of a photon. This is the classification scheme used in organizing Chapters 8–11.

    An additional way to classify analytical techniques is by whether the analyte’s concentration is determined under a state of equilibrium or by the kinetics of a chemical reaction or a physical process. The analytical methods described in Chapter 8–11 mostly involve measurements made on systems in which the analyte is at equilibrium. In this chapter we turn our attention to measurements made under nonequilibrium conditions.

    • 13.1: Kinetic Techniques versus Equilibrium Techniques
      The text discusses equilibrium and kinetic methods used in analytical chemistry. Equilibrium methods focus on the steady-state concentration of an analyte, as seen in the determination of iron in water and metal concentrations in tissue samples. Kinetic methods, on the other hand, rely on the rate of a reaction, allowing for dynamic analysis, such as measuring nitrite concentrations during a development period to obtain rate-based data.
    • 13.2: Chemical Kinetics
      The earliest analytical methods based on chemical kinetics???which first appear in the late nineteenth century???took advantage of the catalytic activity of enzymes. Despite the diversity of chemical kinetic methods, by 1960 they no longer were in common use. By the 1980s, improvements in instrumentation and data analysis methods compensated for these limitations, ensuring the further development of chemical kinetic methods of analysis.
    • 13.3: Radiochemistry
      This page explains the concept of isotopes, which are elements with the same number of protons but different numbers of neutrons, and their applications in radioactive decay analysis. It describes the types of radioactive decay particles (alpha, beta, gamma rays, and X-rays) and the role of isotopes in identifying nuclear stability. It also covers the mathematical models for radioactive decay, including first-order kinetics and half-life calculations.
    • 13.4: Flow Injection Analysis
      This chapter focuses on flow injection analysis (FIA), a technique introduced in the mid-1970s for automated sample analysis. FIA involves injecting samples into a flowing carrier stream, leading to transient signals at a detector, influenced by physical and chemical processes. The chapter outlines FIA's theory, describing components like propelling units, injectors, detectors, and transport systems. Applications span environmental and clinical analyses.
    • 13.5: Problems
      This page presents a series of problems related to chemical kinetics, enzyme catalysis, radioactive decay, and analytical chemistry techniques. These problems address the derivation of equations, determination of concentration and purity through kinetics experiments, understanding enzyme mechanisms and inhibition, and isotopic tracer analysis. Additional concepts include rate calculations, enzyme activity, flow injection analysis, standard deviation, and competitive inhibitor effects.
    • 13.6: Additional Resources
      This page provides an overview of chemical kinetic methods and flow injection analysis, highlighting several experiments and research studies that introduce students to these analytical techniques. It includes references to journal articles that describe specific experiments, such as the decomposition kinetics of hydrogen peroxide and enzyme inhibition analysis. Additionally, it mentions resources and textbooks for further reading on instrumental analysis and flow injection theory.
    • 13.7: Chapter Summary and Key Terms
      The chapter discusses kinetic methods of analysis, which determine an analyte's concentration through chemical or physical process rates. It covers chemical kinetic methods using reaction rates, radiochemical methods using radioactive decay, and flow injection methods where samples react and move with carrier streams. Chemical methods are useful for slow reactions and enzyme analysis; radiochemical methods utilize isotopes, and flow injection is ideal for fast sample processing.

    Thumbnail: Determination of a reaction’s intermediate rate from the slope of a line tangent to a curve showing the change in the analyte’s concentration as a function of time.


    This page titled 13: Kinetic Methods is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by David Harvey.

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