Phosphoric Acid Content Detection By Ammonium Molybdate Spectrophotometry Is Established And Preliminary Application

Majority of cane sugar factories in China adopt phospho-sulphitation process,with industry phosphoric acid as auxiliary agent for clarifying agent in the process. The process of sugaring demand the quantity of effective P2O5was about300～400mg/kg, while cane juice had the quantity of P2O5just ahout100mg/kg.Hence it need to add industry phosphoric acid as supplement. The volume of addition was determined according to the content of industry phosphoric acid.The indetermination of the volume of industry phosphoric acid would effect the addition of phosphoric acid consequently effecting the clarification result.The determination methods of gravimetric method and volumetric method were the two national standards for the detection of the content of phosphate.The gravimetric method need higher operant level to the operations personnel for the requirements of washing and transfering,which time consuming and could not adapt to the need of the fast-tempo production of sugar mills with continuous Production Mode; the volumetric method, being simple to operate、consuming less time, is the most popular measuring method in cane sugar mills at present. Its principle is through determining the concentration of H+by acid-base neutralization in order to determine the content of phosphate,but it found that there were other acid resulting in the measurement deviation in the actual measurement process. Therefore, it is immediacy that finding a faster and accurate measuring method to resovle the problem of the determination methods of phosphate.Ammonium molybdate spectrophotometric method could satisfy the measuring of the content of phosphorus in industry phosphoric acid, so it could get the content of industrial phosphoric acid by verifying the content of phosphorus.This paper explored the experimental conditions of ammonium molybdate spectrophotometric method for industrialfor the determination of phosphate content;national standard method validation of ammonium molybdate spectrophotometric method was used;comparison of several phosphate content detection method which were in common use.Application of new methods in sugar mill was explored.The conclusion as follows:(1) Exploring the experimental conditions of ammonium molybdate spectrophotometric method on detection of industry phosphoric acid.Sample was without digestion process because the main ingredient of industrial phosphoric acid was orthophosphate.Experimental researches showed that when ascorbic acid as reducing agent was used,the dosage of ascorbic acid was about1.Oml;the dosage of molybdate was about2.0ml;the pH of coloration was3.5;the reaction temperature of water bath was about20～30℃reaction time was20min;the wavelength of determination was about700nm;can get the better experiment effect.(2) Ammonium molybdate spectrophotometric method detected Phosphorus Standard Solution with the concentration of0.20mg/L was used.The measurement results were under two-tailed and one-tailed t testing:the result of two-tailed testing showed that t=2.388less than t(0.005,9)=3.250and the probability of two-tailed was0.020>0.01, which meant that the operation of the new method was without systemic error:one-tailed testing showed that t=2.388>0,t=2.388<t (0.01,9)=2.821ans the probability of one-tailed was0.041>0.01which meant that the testing result of the new method did not have statistical differences with standard values.(3) Combining the criterion of ISO/IEC17025-2005《Testing and calibration laboratory criteria for recognition》 with 《ICH Harmonised Tripartite Guideline》 for the new method is validated:the adding standard recovery of sample was between100%～109%;the relative standard deviation of the precision of test results was lesser than4.0%; the concentration of phosphorus of sample had a preferablelinear correlation in the range of0.02～0.72mg/L, method for synthesis of uncertainty was about1.8041%; specificity experiments shown that phosphoric acid with impurity did not affect the accuracy of measurement.(4) F and t test were uesed to verify the results of four kinds of phosphate detection method quinoline phosphomolybdate respectively gravimetric methods volumetric method、 ion chromatography method and ammonium molybdate spectrophotometric method.The results showed that the four kinds of phosphate detection method did not have difference among the average in the same sample.The variance of the measuring reuslts of gravimetric method and volumetric method were greater than the ammonium molybdate spectrophotometric methods’which meant that the precision of ammonium molybdate spectrophotometric method was higher than gravimetric method and volumetric method.Ammonium molybdate spectrophotometric method had the closet measuring results to the the ion chromatography method by comparing the results of several samples.The average recovery rate of ion chromatography method was about100.42%,in order to ion chromatography method as a reference, ammonium molybdate spectrophotometric method had a higher veracity than national standard method.(5) Put the new building method of the ammonium molybdate spectrophotometric into practical use of sugar cane sugar mill industrial phosphoric acid test, the result showed that the the new method has a better treatment efficiency in cane mill in practical application,the adding standard recovery is between103%to105%.