Determination Of Nitrate In Milk Tea By Ion Chromatography And Its Risk Assessment

Milk tea was well-loved as a long-established and widely popular beverage.As the main component of milk tea,tea and milk have contained a certain amount of nitrate,and nitrate,as an environmental pollutant,has been widely present in water bodies and food,and also it has been one of the most prevalent chemical pollutants.Nitrate was reduced to nitrite in human mouth and intestine,and nitrite nitrogen,as an intermediate product of nitrogen cycle,can induce cancer in human digestive system and had certain toxic effects on human health.The analysis of nitrate content in milk tea was conducive to better control the quality control process of its production process,so that the production of milk tea can be improved in the direction of more conducive to nutrition and health.The determination of nitrate has been generally determined by spectrophotometric and chromatographic methods,in addition to electrochemical methods,quick test method,etc..The current spectrophotometric method for the determination and analysis of nitrate content,its pre-treatment steps were cumbersome,and the reproducibility of the results obtained was not good;electrochemical method for the detection of nitrate,the precision of the results was slightly poor;fast detection method compared to the mature detection technology,the method was not perfect,the precision of the results was not good.In the actual sample,the chemical components of milk tea have been complex,which contains a variety of organic and inorganic molecules,the existing standards lacked of analytical methods for nitrate in milk tea,the use of GB5009.33-2016 for the analysis of milk tea samples,because of the complexity of its matrix led to inaccurate results,with certain limitations.It is important to establish an effective analytical method for the risk assessment of nitrate in milk tea samples.In this study,a method was developed for the determination of nitrate in milk tea using ion chromatography,and a risk assessment of nitrate in milk tea was performed.The daily intake of milk tea was calculated based on the results of nitrate content in milk tea,and a reasonable intake recommendation was made.The main results of the study are as follows:1.The sample pretreatment method and chromatographic conditions were optimized.5 g of sample volume(accurate to 0.001 g)was used as the sample volume for this method,8 m L of acetonitrile was added as the precipitant,and the sonication time was 20 min without passing through the Ag and Na columns;200 ?L was used as the injection volume,and the conductivity detector and the online generation system of the eluent were used to shorten the pretreatment time for the determination of nitrate and save the experimental cost,and make the sample solution is more clarified,and the chromatogram baseline noise is small,and the nitrate peak shape is more ideal.2.In this experiment,retention time characterization was used,and the relative standard deviation of 1.2% was obtained by six replicate determinations of nitrate content in the samples,and the linear equation y=0.3896x+0.0002 with a correlation coefficient of 0.9993,which showed good precision of the results.The method was used for the determination of milk tea samples,and the spiked recoveries were calculated to be 92.1%?101.2%.The method showed ideal results,high precision and good response,and can be widely applied to the determination of nitrate in milk tea samples.3.Based on the results of the determination of nitrate content in 120 milk tea samples from 6 milk tea stores sold in Jinan and Tai'an,the dietary exposure levels of nitrate in milk tea samples were calculated to be 1.42% to 12.5%,and the risk factor was taken as 100%,which means that the risk factor of nitrate in the sampled brand milk tea samples was low;thus,the preliminary risk assessment of nitrate in milk tea,the nitrate in sampled milk tea The distribution of nitrate content in sampled milk teas was: 1 in 10.0-15.0 mg/L,31 in 15.0-30.0mg/L,30 in 30.0-45.0 mg/L,34 in 45.0-60.0 mg/L,14 in 60.0-75.0 mg/L,and 10 in 75.0-90.0mg/L.Referring to the limit value of nitrate content in packaged drinking water in the standard "GB 2762-2017 Food Safety National Standard Limits of Contaminants in Food",45mg/kg was set as the limit value of nitrate in this study,and with reference to this value,the number of exceedances in the statistical sampling milk tea was 58 in total,accounting for48% of the total.And the safe daily intake of milk tea was estimated to be about 2.4L.