Set Up Ion Chromatography Method For Simultaneous Determination Of Nitrate Nitrite And Thiocyanide In Dairy Food

Through the experiment, this study set up and optimization Ion Chromatography method for simultaneous determination of Nitrate,Nitrite and Thiocyanide in dairy food. After the experiment of sample procedure, instrument method and precision evaluation results are as follows:Milk sampling procedure: 10mL milk was added to 50mL polypropylene centrifuge tube and 15mL acetonitrile was added. After intensive shaking, the mixture was centrifuged at the speed of 10000r/min for 5 minute. 5mL the supernatant was taken out and 45mL ultrapure water was added to it and mixed them together. Then, the mixed solution was transferred to a centrifugal filter unit and was centrifuged at the speed of 4000r/min for at least 10 minute. If the filtrate was less than 10mL after this centrifugation,the centrifugation time should be extended or the centrifugation step should be repeated once more. Then, the centrifugal filter unit was taken off and 15mL Trichloromethane was added into the centrifugal cell to mix with the filtrate together. After intensive shaking, the mixture solution was centrifuged at the speed of 4000r/min for 5 minute. Finally, the supernatant was passed through 0.22μm water system filter, OnGuard RP column and OnGuard Ag/H column one by one to get the sample solution for final examination by ion chromatography.Milk powder sampling procedure: 2g milk powder was added to 50mL polypropylene centrifuge tube. Then 10mL water was added to dissolve the milk powder. The dispersion liquid was transferred into a 15mL acetonitrile. The following procedure for sampling the milk powder was same as milk sampling procedure mentioned (mentioned) above.The optimized working conditions of ion chromatography:The analytical column, IonPac AS19, was used for this ion chromatography. The flow rate of Mobile phase was 1mL/min. The injection volume of sample was 100μL. The column temperature was 30℃. The self-regenerating suppressor electric current was 174mA.The KOH gradient elution was done as following: firstly,23mM KOH hold 12min,then increased to 78mM within 5min, and then decreased to 23mM within 5min, after balance with 23mM KOH for 8min,the next sample could be injected.The standard samples of Nitrate, nitrite and thiocyanide were separated well in the chromatogram map of ion chromatography. The coefficients correlation of linear regression equation were 0.99977, 0.99950, 0.99930 respectively for the three ions. For the market milk and milk powder sample, the analysis precision of nitrate, nitrite and thiocyanide were 0.886%, 1.704%, 0.562% respectively. For the market milk, the adding standard recovery of the three salts were 92.990%, 98.116%, 94.728% respectively. For the market milk powder, the adding standard recovery of the three salts were 91.570%, 94.892%, 94.756% respectively. Compare with the spectrophotometry and HPLC methods the ion chromatography method had better reproducibility.The sample preparation is simple .This method was high sensitive, accuracy, low detection limit and suitable for the determination of nitrate, nitrite and thiocyanide in milk and milk powder.