| Nitrate is a common contaminant in vegetables. It was content of nitrate exceeds the limit in vegetables that would cause harm to human health. With the improvement of people's living standards and food safety awareness, national food safety monitoring efforts increase, method of detecting nitrate,which is fast, accurate, low-cost, convenient to operate,has a huge market demand.This paper aims to develop a new hybrid powder method for rapid and accurate determination of nitrate content in vegetable samples. Through single factor experiment, we screened out the amount of vanadium chloride, sodium chloride dosage, the amount of amino acids, the amount of amino acid, hydrochloric acid N-Naphthylethylenediamine Dihydrochloride, reaction temperature, reaction time. Use Plackett-Burman experiment to screen out three factors which possess a significant effect on the results from experiment of seven factors. The further design of 3 factors and 3 levels of response surface experiments are studying the interaction effect among three significant factors. Model fitting and regression analysis are used for exploring the best mixing ratio of vanadium chloride powder and optimum reaction conditions. At the same time, develop pretreatment methods of vegetable sample which is suitable for the determination. Finally, based on the methodology of verification and the standard, a scheme of nitrate determination for vegetable samples is established. Specific experimental results are as follows:(1)Independently developed and mastered a quick determination of nitrate content with vanadium chloride mixing powder, sodium chloride, amino acid, hydrochloric acid, N-Naphthylethylenediamine Dihydrochloride, vanadium chloride mix with the best good ratio of 400:20:25:0.9:0.6. The total amount of the mixed powder is 0.3g. The effective use of time is two months. The determination of the mixed powder was added in 3m L sample liquid. Continue shaking until powder completely dissolved. It will be heated 30 min in 80?, and cooled. Absorbance values can be measured. Nitrate content will be obtained by the standard curve;(2)Based on vanadium chloride powder method with high sensitivity, low detection limit, and the characteristics of vegetables sample higher nitrate content. There is higher dilution in vegetable sample. So chlorophyll pigments do not interfere with the effect of color. We improved pre-treatment samples of vegetables method, without the need for sample purification liquid. Directly extracted nitrate from vegetables sample. The specific method is 5~10g vegetable homogenate with 2% acetic acid solution transfer to 250 m L. It will be shaked in 5min and then filtered. Nitrates can be rapidly extracted from vegetable samples;(3)The result of method validation is, he linear range of method, which is determination of nitrate content in vegetable samples vanadium chloride powder, is 0~2.5mg/L. The linear equation y = 0.5011x-0.0223. The correlation coefficient r is 0.999. In vegetable sample, detection limit is 0.3mg/L. Spiked recoveries of vegetable samples in the range of 97.3%~106.1%. The coefficient of variation is1.40%~7.91%. Nitrate is reduced by Vanadium chloride, whose reduction rate is 87.10%~94.10%. In summary, the calibration curves, average recoveries, precision accuracy were qualified. Vanadium chloride powder to determinate the nitrate content in vegetable samples, has high precision, good accuracy and repeatability. The result is reliable.The method is reported in the literature.Becausethe present zinc powder method is lower reduction rate, poor method accuracy issue. While using vanadiumchloride instead of zinc chloride,sodium chloride, and amino acid areacid reagent to acidic conditions. Successfully reducing agent, acidic agents, coupling agents and diazonium reagent are mixed together. The reduction rate and improve accuracy are improved, reducing the detection process steps. |
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