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Rapid Photometric Determination of Exchangeable Potassium and Sodium
Author(s) -
Attoe O. J.,
Truog E.
Publication year - 1947
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1947.036159950011000c0042x
Subject(s) - citation , library science , potassium , mathematics , computer science , information retrieval , chemistry , organic chemistry
ONE of the most striking characteristics of potassium is the brilliant violet color produced when its salts are heated in a flame. Likewise, sodium salts produce a very intense and characteristic yellow flame. No other element commonly found in appreciable amounts in soils gives these same flame tests. From time to time, investigators have attempted with varying degrees of success to make quantitative determinations by means of these flame characteristics. Through the use of a spectroscope, Lundegardh (4) photographed the intensity of the light emitted by a number of metallic elements when solutions containing them were sprayed into an acetylene flame. The calculation of the results for quantitative purposes involved plotting the ratio of the line transparency to that of the background against the concentration of the standard solution used. In making determinations of exchangeable bases in soils, Ells and Marshall (3) found this method to give an accuracy within about 5%. In the determination of potassium' and sodium, Barnes, et al. ( i) employed a simplified apparatus called the flame photometer. In the operation of this instrument, the solution of potassium or sodium is atomized under controlled conditions and fed with the air supply into a Meker burner. A direct photoelectric measurement of the intensity of the light produced is then made. The instrument is calibrated by means of a reference solution having a known concentration of the element being analyzed. These investigators obtained an accuracy of about 3% when analyzing solutions relatively free from foreign salts or acids. However, Berry, et al. (2) obtained low results with this instrument when analyzing solutions containing. appreciable amounts of various salts and other extraneous substances. In an attempt to reduce the error due to'this cause, they used an "internal standard" consisting of lithium sulfate. Instead of determining potassium or sodium directly, they actually measured photo-electrically the ratio of sodium or potassium to lithium. In the analysis of pure solutions of potassium and sodium salts by this method, they reported an accuracy of ±1.01% for potassiumand ±1.24% for sodium. Also, they report this method to be less subject to interference from the presence of salts, acids, and other foreign substances. The present investigation was undertaken for the purpose of finding' out if the flame photometer, model 18, manufactured by the Perkin-Elmer Corporation, might be used for the determinations of exchangeable potassium and sodium in soils. Details of its construction and operation are given by Barnes, et al. (i) . In the operation of this instrument, the supply of gas, air, and current must be kept uniform in order that the solution containing the potassium or sodium may be atomized at a uniform rate. This can be done within satisfactory limits and without the use of elaborate control devices. The presence of dissolved substances in the solutions being analyzed may also seriously affect the rate or degree of atomization by influencing certain physical properties, such as surface tension and viscosity. Since unknown solutions may contain a considerable number of dissolved substances, and often in greater concentration than that of the element being tested, an investigation of the influence of these substances on the determination of potassium and sodium seemed desirable to start with.