Optimization Of Determination Method Of Total Arsenic In Chinese Cabbage

Chinese cabbage,a popular vegetable crop has been seriously polluted by arsenic in recent years.The current national standard test method is GB5009.11-2014 " Determination of Total Arsenic and Inorganic Arsenic in Food Safety National Standard Food".The key link includes two parts,namely sample pretreatment and instrument selection.In this paper,the two steps are optimized to find the best conditions and on this basis,the optimized experimental method is used for sample detection to compare the differences of sample determination before and after optimization.In this experiment,microwave digestion method was used to pretreat the sample and atomic fluorescence spectrometer was used to determine the total arsenic in Chinese cabbage.The test contents and results are as follows:(1)Optimization of pretreatment method of total arsenic.Microwave digestion method was used to pretreat total arsenic in vegetables and response surface methodology was used to optimize various parameters of pretreatment of total arsenic.The optimized pretreatment conditions were determined as follows: nitric acid addition 9.60 m L,sulfuric acid addition0.80 m L,acid catching temperature 132 ?,acid catching time 6.0 h,the recovery rate of total arsenic was the best.(2)Optimization of parameters of atomic fluorescence spectrometer.The instrument parameters were optimized by orthogonal test.The optimized instrument conditions were negative high voltage 290 V of photomultiplier tube,lamp current 60 m A and carrier gas flow rate 400 m L / min.Under these conditions,the instrument's condition is optimal.(3)Research on the degree of precision and uncertainty.Under the optimized conditions,through 20 times of data determination of Chinese cabbage samples,calculation precision and drawing of the quality control chart,it can be concluded that the measured values of this test method are all within the warning line of the quality control chart,indicating that the stability of the data determination results of this method and the reproducibility of the test are good.The expanded uncertainty was 0.0051 mg / kg by calculating the uncertainty of the standard material of Chinese cabbage.The measured final result(0.00595 0.0051)mg / kg,within the given result range of the standard substance,expanded uncertainty of 0.0051,the value is small,indicating high accuracy of the test.The drawing of quality control chart and the calculation of the degree of uncertainty in this test show that the data measured under the optimized conditions of this test method are highly reliable.(4)Validation test of total arsenic in Chinese cabbage.The samples of Chinese cabbage were collected and analyzed by microwave digestion method,dry ashing method and wet digestion method respectively.By comparing the recovery rate,it was found that themicrowave digestion method had a higher recovery rate with an average value of about 95 %,and at the same time,it would not cause harm to human body in the pre-treatment process.Through the optimization of analysis conditions and calculation and analysis of data results,it can be concluded that the microwave digestion method has good results and high stability for the determination of arsenic in vegetables and simple operation provides a new method for the total arsenic digestion of vegetables.