tailieunhanh - Environmental Sampling and Analysis for Metals - Chapter 12

Trong AES, mẫu phải chịu nhiệt độ cao đủ để gây ra không chỉ phân ly nguyên tử vào mục đích Ngoài ra khoản tiền đáng kể kích thích collisional (và ion hóa) của các nguyên tử mẫu. Một khi các nguyên tử và ion đang ở trong trạng thái kích thích của họ, họ có thể phân hủy thành thấp hơn các quốc gia thông qua quá trình chuyển đổi nhiệt hoặc phóng xạ năng lượng (khí thải). (Xem thảo luận về khí thải tại mục .) Trong AES, cường độ của ánh sáng thải ra IS đo tại. | Inductively Coupled Plasma Atomic Emission Spectroscopy ATOMIC EMISSION SPECTROSCOPY AES In AES the sample is subjected to temperatures high enough to cause not only dissociation into atoms but also significant amounts of collisional excitation and ionization of the sample atoms. Once the atoms and ions are in their excitation states they can decay to lower states through thermal or radioactive emission energy transition. See discussion of emission in Section . In AES the intensity of the light emitted is measured at specific wavelengths and used to determine the concentrations of the elements of interest. Thermal excitation sources can populate a large number of different energy levels for several different elements at the same time. Consequently all excited atoms and ions can emit characteristic radiation at nearly the same time. In general three types of thermal sources are used in analytical atomic spectrometry to dissociate sample molecules into free atoms flames furnaces and electrical discharges. The first two types are hot enough to dissociate most types of molecules into free atoms. Electrical discharges the third type are also called plasmas. Plasmas Plasma is a state of matter usually consisting of highly ionized gas that contains an appreciable fraction of equal numbers of ions and electrons in addition to neutral atoms and molecules. Plasmas conduct electricity and are affected by magnetic fields. The plasma source has a high degree of stability to overcome interference effects. Plasma is capable of exciting several elements that are not excited by flames and has increased sensitivity to flame AES. The low detection limits freedom from interferences and long-line working ranges prove that it is a superior technique for AES. For more detail about plasmas see Appendix J. The electrical plasmas used in AES work are highly energetic ionized gases and are usually produced in inert gases. The plasma source for analytical AES is argon-supported