- Spectrophotometric determination method of soil available phosphate in Lancaster extracting solution by separately adding molybden compound-bismuth subcarbonate mixed reagent and ascorbic acid

摘要

PURPOSE: A measuring method of effective phosphorus acid of soil with a spectrophotometer is provided to promote simple measuring of effective phosphorus acid in soil by measuring absorbance with a spectrophotometer after coloring the effective phosphorus acid in soil with molybdic acid-bismuth subcarbonate and ascorbic acid. CONSTITUTION: To produce molybdic acid-bismuth subcarbonate used as a coloring agent, bismuth subcarbonate is dissolved in sulfuric acid of high concentration, ammonium molybdate, molybdic acid, sodium molybdate or potassium molybdate are additionally dissolved in distilled water. The two kinds of solutions are mixed. After the molybdic acid-bismuth subcarbonate is produced, the liquid type molybdic acid-bismuth subcarbonate and powder type ascorbic acid are additionally added to soil sampling liquid and standard solution respectively to color the solutions. The sampling liquid is colored by additionally adding the molybdic acid-bismuth subcarbonate and the ascorbic acid. Then, the optimum absorbance wavelength for measuring phosphorus acid in soil is decided. The coloring agent is added to the standard phosphorus acid solution, and the absorbance thereof is measured to obtain a standard curved graph. The content of effective phosphorus acid in soil is obtained by the existing method and the current method. The measured content of effective phosphorus acid in soil is compared and analyzed. If molybdic acid-bismuth subcarbonate not containing ammonium is used as a coloring agent, the treatment cost of waste agent is reduced.