Atomic masses early research

During the time of early research on the atom, even before any subatomic particles were identified, some chemists searched for an order among elements. In 1869, two men found an order, independently of each other. Dmitri Mendeleev and Lothar Meyer observed that when elements are arranged according to their atomic masses, certain properties repeat at regular intervals. 

Early in the 20th century chemists began to research and exploit physical properties of the analyte properties, such as conductivity, electrode potential, light absorption or emission, mass-to-charge ratio and fluorescence for solving analytical problems. Classical principles remain useful in modem analytical instruments and methods. In comparison to classical methods the output of instrumental methods is a signal from which the result of the analyses is calculated. Instrumental analysis is most useful for elemental determinations at minor and trace levels (about 1% all the way down to 1 atom)—in this range classical analysis does not perform well. 

ISOTOPE. An isotope is one of nvo or more nuclides ibal have the same number of protons in iheir nuclei. An> two isotopes have ihe same aiuniic number. However. their mass numbers, A. differ. Isotope is a term that stems from the Greek words, isos tsume) and topos (place , to designate substances having different atomic weights and vei having chemical properties so much alike I hat in the early days ol research ii was nor possible to perform ti chemical separation ol the isotope of a given element. 

By far the most common type of plasma used for speciation analysis is the inductively coupled plasma (ICP) with mass spectrometry (MS) or atomic emission spectrometry (AES) detection. The performance of the ICP-MS system has been well documented since its development in the early 1980s by the Gray and Houk research groups [14,15], and it is now used for a wide variety of applications such as environmental, clinical, geological, food, and industrial analysis. 

Over 30 years of liquid chromatography-mass spectrometry (LC-MS) research has resulted in a considerable number of different interfaces (Ch. 3.2). A variety of LC-MS interfaces have been proposed and built in the various research laboratories, and some of them have been adapted by instmment manufacturers and became commercially available. With the advent in the early 1990 s of interfaces based on atmospheric-pressure ionization (API), most of these interfaces have become obsolete. However, in order to appreciate LC-MS, one carmot simply ignore these earlier developments. This chapter is devoted to the older LC-MS interfaces, which is certainly important in understanding the histoiy and development of LC-MS. Attention is paid to principles, instrumentation, and application of the capillary inlet, pneumatic vacuum nebulizers, the moving-belt interface, direct liquid introduction, continuous-flow fast-atom bombardment interfaces, thermospray, and the particle-beam interface. More elaborate discussions on these interfaces can be found in previous editions of this book. 

Later research done along the same lines as Rutherford s early work found that protons in a nucleus have a mass over 1800 times that of an electron. In fact, the positively charged nucleus of the atom that contained most of its mass was very dense and took up only a tiny part of an atom s total space. 

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