S. G. Kadarmandalgi Karnatak University Dharwor-3, India
Spot Test for Detection of Manganese
Certain reagents including sodium b i s muthate,' potassium p e r i ~ d a t e ,and ~ ammonium per~ulfate~ have , ~ been suggested for the detection of manganese in qualitative analysis. Among these reagents, sodium bismnthate is not so sensitive (limit of identification being 25 ~ g ) . Potassium periodate and ammonium persnlfate are fairly sensitive, but reducing elements must be absent. If ammonium persulfate is used, silver ions are to be used as catalysts, and chloride, bromide, iodide and other anions that precipitate silver should be absent. During the study of resacetophenone oxime as an analytical reagent it was observed that resacetophenone oxime can be used advantageously for the detection of manganese. This reagent is fairly sensitive and does not require any oxidizing or catalytic reagent. A stock solution of manganese chloride was prepared in distilled water containing few ml of concentrated
' YOGEL,A. I., "Textbook of Maoro and Semi-micro Qualita-
tive Analysis," 4th ed., Longmans Green and Company, London, 1959, p. 289.
2 W ~ ~H. IH.,~ AND ~ GREATHOUSE, ~ ~ , L. H., J. Am. Chem. SOC.,39,2366(1917). MARSHALL, H., Z. anal. Chem., 43,418 (1904). MARSHALL, H., Z. physik Chem., 37, 255 (1901).
HC1. The manganese content was determined by usual gravimetric and volumetric methods. Dilute solutions were prepared by dilution from the stock solution. All other chemicals employed in this iuvestigation were of analytical reagent quality. The preparation of resacetophenone oxime5 has been communicated earlier. A 0.2y0 solution of reagent was prepared by dissolving 0.2 g of oxime in 10 ml of ethyl alcohol and diluting to 100 ml with distilled water. The solution was stored in amber colored bottle. Manganese(I1) does not react with the reagent in acidic medium but gives yellowish-brown color in alkaline medium (pH 7-11). If the concentration of the manganese is very low, pale yellow color is obtained. I n ammonia and ammonium chloride buffer medium, results are far more satisfactory. The color is stable even if excess of ammonia or sodium hydroxide is added; color fades on adding concentrated mineral acids. Procedure for spot test. A drop of test solution is placed on the white spot plate followed by 1-2 drops of 10% ammonium chloride solution, 1 drop of dilute ammonia (4-6 N) and 2 drops of reagent. (The addi-
' KADARMANDALQI, S. G.,Cuwmt Sn'. (India), 33,175, (1964)
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tion of ammonium chloride prevents the precipitation of manganese hydroxide.) Yellow or yellowish-brown color develops within one minute. Limit of identification is 0.5 fig of Mn++. Ions of alkali metals and alkaline earths, cerium(III), iron(II), tungsten(V1) and the anions chloride, bromide, iodide, nitrate, sulphate, acetate, citrate do not interfere. Zinc and magnesium do not interfere if a large excess of ammonium chloride is added, copper, iron(lll), nickel, thorium, lead, aluminium, chromium, tin, mercury interfere by causing either precipitation or coloration. Phosphate, borate, carbonate, fluoride, oxalate, and chromate anions also interfere in the above detection.
438 / Journal o f Chemical Education
Manganese i n presence of zinc. I t was observed that zinc does not react with the reagent if large excess of ammonium chloride is present. So the solution containing manganese and zinc ions (chloride) is treated with 3-4 of alnmonium chloride, 2-3 drops of (4-6 N ) and excess of reagent. The production of yellowish-brown or pale yellow color indicates the presence of manganese in the test solution; zinc does not react under these conditions. Thus resacetophenone oxime can be advantageously used for the detection of manganese in presence of zinc in qualitative analysis. Thanks are due to Professor S. Siddappa and Dr. N. S. Biradar for their interest and encouragement.
