tailieunhanh - Modern Analytical Cheymistry - Chapter 10

Spectroscopic Methods of Analysis Trước khi bắt đầu của thế kỷ XX, hầu hết các phân tích hóa học định lượng được sử dụng gravimetry titrimetry là phương pháp phân tích. Với phương pháp này, các nhà phân tích đã đạt được những kết quả chính xác cao, nhưng thường được giới hạn việc phân tích các chất phân tích lớn và nhỏ. Các phương pháp khác được phát triển trong thời kỳ này đã mở rộng phân tích định lượng bao gồm các chất phân tích mức độ theo dõi. Một trong những phương pháp đã được đo màu | 10 Spectroscopic Methods of Analysis B efore the beginning of the twentieth century most quantitative chemical analyses used gravimetry or titrimetry as the analytical method. With these methods analysts achieved highly accurate results but were usually limited to the analysis of major and minor analytes. Other methods developed during this period extended quantitative analysis to include trace level analytes. One such method was colorimetry. One example of an early colorimetric analysis is Nesslefs method for ammonia which was first proposed in 1856. Nessler found that adding an alkaline solution of HgI2 and KI to a dilute solution of ammonia produced a yellow to reddish brown colloid with the color determined by the concentration of ammonia. A comparison of the sampleÕs color to that for a series of standards was used to determine the concentration of ammonia. Equal volumes of the sample and standards were transferred to a set of tubes with flat bottoms. The tubes were placed in a rack equipped at the bottom with a reflecting surface allowing light to pass through the solution. The colors of the samples and standards were compared by looking down through the solutions. Until recently a modified form of this method was listed as a standard method for the analysis of ammonia in water and Colorimetry in which a sample absorbs visible light is one example of a spectroscopic method of analysis. At the end of the nineteenth century spectroscopy was limited to the absorption emission and scattering of visible ultraviolet and infrared electromagnetic radiation. During the twentieth century spectroscopy has been extended to include other forms of electromagnetic radiation photon spectroscopy such as X-rays microwaves and radio waves as well as energetic particles particle spectroscopy such as electrons and 368 Chapter 10 Spectroscopic Methods of Analysis 369 10A Overview of Spectroscopy The focus of this chapter is photon spectroscopy using ultraviolet