tailieunhanh - Soil and Environmental Analysis: Modern Instrumental Techniques - Chapter 3

Trong số các thông số điện nhiều có thể đo được, chỉ có ba cần được xem xét ở đây là tiềm năng quan trọng thực tế, hiện tại, và dẫn, do đó mở đường cho ba kỹ thuật mà thực sự có một cái gì đó để cung cấp trong lĩnh vực phân tích môi trường, nơi các mẫu luôn luôn phức tạp và các yếu tố quyết định sự quan tâm thường xuất hiện ở nồng độ rất thấp. Phí điện, đo trong kỹ thuật được gọi là coulometry, thực sự có những ứng dụng phân tích quan. | 3 Electroanalytical Methods in Environmental Chemical Analysis Iain L. Marr The University of Aberdeen Aberdeen Scotland I. BACKGROUND Of the many electrical parameters that can be measured only three need be considered here as of practical importance potential current and conductivity thus opening the way to three techniques that really have something to offer in the area of environmental analysis where samples are always complex and determinants of interest usually are present at very low concentrations. Electrical charge measured in the technique known as coulometry does indeed have important analytical applications especially in the Karl Fischer determination of water but not often in the field of environmental analysis and therefore will not be discussed further. The potential of an electrode may be related to the concentration of a particular species if a number of conditions are met the clever chemistry of electrode membrane manufacture makes it possible to construct probes with useful sensitivity and selectivity to individual species in solution. While the tendency for a chemical reaction to proceed is measured no current is actually allowed to flow. Potentiometry using ion selective electrodes is the technique in question and using the glass electrode for the measurement of pH is one special and the best known example. A great deal more information can be obtained by electroanalytical methods if one parameter is varied and a second measured so-called twodimensional measurement. In this case a signal pattern rather than one measured value is used to identify as well as quantify one or more species in a solution. The current can be monitored as the potential across a cell is MARCH Copyright n 2 0 04 by Marcel Dekker Inc. All Rights Reserved. scanned the approach is termed amperometry. When the current is controlled by diffusive processes in solution the technique is termed polarography and while few people will have any time for a dropping mercury electrode