tailieunhanh - Environmental Sampling and Analysis for Metals - Chapter 7

Hấp thụ nguyên tử phổ GIỚI THIỆU 7,1 phổ nguyên tử (AS) Như Bàn luận Trước đây, Như là một lớp học của các kỹ thuật phân tích nguyên tố đó việc sử dụng các bức xạ điện từ tương tác với nguyên tử hoặc ion để phát hiện sự hiện diện của các yếu tố quan tâm. | 7 Atomic Absorption Spectrometry INTRODUCTION Atomic Spectrometry AS As discussed previously AS is a class of elemental analysis techniques that use the interaction of electromagnetic radiation with atoms or ions to detect the presence of elements of interest. Atomic Absorption AA Atomic absorption occurs when a ground-state atom absorbs energy in the form of light of a specific wavelength and is elevated to an excited state. The amount of light energy absorbed at this wavelength increases as the number of atoms of the selected element in the light path increases. The relationship between the amount of light absorbed and the concentration of analyte present in known standards can be used to determine unknown concentrations by measuring the amount of light absorbed. Instrument readouts can be calibrated to directly display concentrations. Atomic Absorption Spectrometry AAS Atomic absorption spectrometry is an element analysis technique that uses absorption of electromagnetic radiation to detect the presence of the elements of interest. Molecular spectrophotometry and working techniques were discussed in Chapter 6 this chapter focuses on analytical methods using atomic spectra. This technique has been applied to the determination of numerous elements and is a major tool in studies involving trace metals in the environment and in biological samples. It is also frequently useful in cases where the metal is at a fairly high concentration level in the sample but only a small sample is available for analysis which sometimes occurs with metalloproteins for example. The first report of an important biological role for nickel was based on a determination via AA that the urease enzyme at least in certain organisms contains two nickel ions per protein molecule. Light absorption is measured and related to element concentration in both AAS and molecular spectrophotometry see Chapter 6 . The major differences lie in instrument design especially with respect