Atomic mass determination chemical method

Determination of atomic weights by chemical methods by yse of the mass spectrograph by the X-ray method. 

When applied precisely, the gas density method may be used for atomic mass determinations, particularly for the lighter elements. Even crude gas density experiments may be used, in conjunction with chemical composition data and known atomic masses to establish the molecular mass, and hence the molecular formula of a gaseous compound. 

Until recently almost all atomic-mass determinations were made by the chemical method. This method consists in determining the amount of the element that will combine with one gram-atom of oxygen or of another element with known atomic mass. One example, which was important in the development of the theory of radioactivity, follows. 

Metals contained in samples are determined by a wide variety of analytical methods. Bulk metals, such as copper in brass or iron in steel, can be analyzed readily by chemical methods such as gravimetry or electrochemistry. However, many metal determinations are for smaller, or trace, quantities. These are determined by various spectroscopic or chromatographic methods, such as atomic absorbance spectrometry using flame (FAAS) or graphite furnace (GFAAS) atomization, atomic emission spectrometry (AES), inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), x-ray fluorescence (XRF), and ion chromatography (IC). 

The chemical method of accurately determining atomic weights involves the determination of stoichiometric ratios. The procedure is illustrated by the examples given below and the problems at the end of the chapter. In addition to this method, extensive use is made of the method of gas densities, and, in recent years, of the mass-spectro-graphic method. The gas-density method is discussed in Chapter 8, and the mass-spectrographic method in the section following this one. 

The great accuracy of modern mass spectrographs makes the mass-spectrographic method of determining atomic weights about as useful and important at present as the chemical method. 

The long-term goal of the chemistry of atmospheric aerosols is to establish analytical methods for determining the chemical composition of particular submicrometric particles. At the present time, this requirement is partially satisfied by two methods— electron and ion microprobes, which are based on the analysis of a point-concentrated electron or ion beam. By use of the ion microprobe it is possible to determine essentially all the elements, whereas the electron microprobe is suitable only for elemeiits with a greater atomic mass than sodium. 

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