tailieunhanh - Modern Analytical Cheymistry - Chapter 12

Chromatographic and Electrophoretic Methods Vẽ từ một kho vũ khí của các kỹ thuật phân tích, nhiều người trong số đó là chủ đề của bốn chương trước, các nhà hóa học phân tích đã thiết kế phương pháp để phân tích các chất phân tích ở nồng độ ngày càng thấp hơn và trong ma trận ngày càng phức tạp hơn. Mặc dù sức mạnh của những kỹ thuật này, họ thường bị thiếu chọn lọc. Vì lý do này, nhiều thủ tục phân tích bao gồm một bước để tách các chất phân tích từ interferents tiềm năng. Một. | Chapter 12 Chromatographic and Electrophoretic Methods rawing from an arsenal of analytical techniques many of which were the subject of the preceding four chapters analytical chemists have designed methods for the analysis of analytes at increasingly lower concentrations and in increasingly more complex matrices. Despite the power of these techniques they often suffer from a lack of selectivity. For this reason many analytical procedures include a step to separate the analyte from potential interferents. Several separation methods such as liquid-liquid extractions and solid-phase microextractions were discussed in Chapter 7. In this chapter we consider two additional separation methods that combine separation and analysis chromatography and electrophoresis. 543 544 Modern Analytical Chemistry 12A Overview of Analytical Separations In Chapter 7 we examined several methods for separating an analyte from potential interferents. For example in a liquid-liquid extraction the analyte and interferent are initially present in a single liquid phase. A second immiscible liquid phase is introduced and the two phases are thoroughly mixed by shaking. During this process the analyte and interferents partition themselves between the two phases to different extents affecting their separation. Despite the power of these separation techniques there are some significant limitations. The Problem with Simple Separations Suppose we have a sample containing an analyte in a matrix that is incompatible with our analytical method. To determine the analyte s concentration we first separate it from the matrix using for example a liquid-liquid extraction. If there are additional analytes we may need to use additional extractions to isolate them from the analyte s matrix. For a complex mixture of analytes this quickly becomes a tedious process. Furthermore the extent to which we can effect a separation depends on the distribution ratio of each species in the sample. To separate an .