The pyrethrin contents of undried flowers,chrysanthemum cinera-riaefolium, determined by extraction with petrol ether
✍ Scribed by Edwards, M. G.
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1948
- Weight
- 508 KB
- Volume
- 67
- Category
- Article
- ISSN
- 0368-4075
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✦ Synopsis
In the presence of 10 pg. of molybdenum the intensity of the colour developed was identical, within the limits of accuracy of the determination, whether any additional element was present or not. The results obtained on actual determinations on plants (Table ) supported this and showed clearly t h t none of these elements interfered significantly with the determination of . molybdenum.
Summary
I. A method has been developed for the determination of microgram quantities of molybdenum in plant materials. The method involves preliminary extraction of molybdenum with cupferron and chloroform and the subsequent formation of the complex of molybdenum with dithiol (4-methyl-I : z-dimercaptobenzene).
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The optimum conditions for the extraction of molybdenum from acid solutions containing citrate have been investigated and it has been shown that quantitative recoveries of microgram quantities can be obtained readily, by cxtraction with cupferron and chloroform at pll o to 0.5.
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Thc optimum conditions for the formation of the molybdenum-dithiol complex havc also been investigated. It has been found that precipitation in sulphuric acid solution, 15-qy~ by volume, prevented interference by tungsten if present, while amyl acetate was superior to amyl alcohol for the extraction of the molybdenum complex. In amyl acetate the complex was stable for more than 24 hours.
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The spectral transmission curve of molybdenum-dithiol complex showed that strong absorption occurred at 6700-6900 A. and at ~~O O -~O O
A. The former wave band was found to be the more suitable for its photometric determination in the presence of other elements. 5. Determinations carried out by the new method have shown that small amounts of molybdenum added to plant samples were recovered quantitatively, while determinations made by different analysts yielded highly concordant results. Values obtained for molybdenum by the new method also agreed closely with those obtained by Dick and Bingley's modification of the thiocyanate method.
- Tungstcn, titanium, vanadium, zirconium, thorium and uranium, although extractable by cupferron and chloroform, did not interfere with the determination of molybdenum when present in amounts up to at least 100 pg. Iron and tin caused a small amount of interference under some conditions but in the method finally adopted, the amounts of these elements normally present in plants did not introduce a significant error.