Do các nguyên tử NHẤT Atom có thể hấp thụ các yếu tố không tồn tại trong một trạng thái tự do tại mặt đất nhiệt độ phòng, nhiệt Must Be dụng để phá vỡ các nguyên tử và phát hành trái phiếu miễn phí. Các nguyên tử được sản xuất bởi Cung cấp năng lượng đủ để làm nóng các mẫu để phân tách các hợp chất vào nguyên tử miễn phí. Chỉ có một yếu tố, thủy ngân (Hg), là một ngoại lệ. Bởi vì tự do có thể tồn tại nguyên tử Hg ở nhiệt độ phòng,. | 10 Cold-Vapor Atomic Absorption Spectrometry GENERAL DISCUSSION Because the atoms of most atomic absorption elements cannot exist in a free ground state at room temperature heat must be applied to break the bonds and release free atoms. The atoms are produced by supplying enough heat energy to the sample to dissociate the compounds into free atoms. Only one element mercury Hg is an exception. Because free Hg atoms can exist at room temperature Hg can be measured by atomic absorption without a heated device. This process is called the cold-vapor technique. In the cold-vapor technique the Hg is reduced by the addition of a stannous Sn2 compound which is a strong reducing agent. The volatile-free Hg is taken from the reaction vessel by bubbling air through the solution Hg atoms go through the tubing to the absorption cell which is placed in the light path of the AA spectrometer. As the Hg atoms pass into the sampling cell measured absorbance rises indicating the increasing concentration of Hg atoms in the light path. The highest absorbance observed during the measurement is taken as the analytical signal. The procedure is based on the absorption of radiation at nm by mercury vapor. The absorbance is measured as a function of Hg concentration and recorded in the usual manner. Advantages One of the advantages of the cold-vapor technique is high sensitivity which is achieved through a 100 sampling efficiency. Because all mercury contained in the sample is released for measurement increasing the sample volume means that more mercury atoms are available to be transported to the sample cell and measured. Limitations The cold-vapor technique is limited to Hg determination because no other element offers the possibility of chemical reduction to a volatile-free atomic state at room temperature. In addition to inorganic forms of Hg organic mercurials may also be present. These organo-mercury compounds will not respond to the cold-vapor technique unless
