Analysis of Nitrate in Liquid Milk and Milk Powder
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摘要: 采用固相萃取-离子色谱法和国家标准中化学法(镉柱还原光度法)分析石家庄市售110份液态乳及奶粉中硝酸盐含量。离子色谱法中将制备好的样品加入适量乙酸沉淀蛋白，离心取上清液，通过固相萃取柱去除脂肪等疏水性化合物，采用AS11-HC型阴离子色谱柱进行分析,同时对液态乳样品采用镉柱还原法进行比对实验。两种方法测得液态乳中硝酸盐的平均含量分别为10.05 mg/kg和9.95 mg/kg，奶粉中硝酸盐的平均含量分别为25.74 mg/kg和25.66 mg/kg。经t检验分析，显示t=0.07，P>0.05，即无显著性差异，研究结果证实了离子色谱法的准确性，实验过程也进一步验证了离子色谱法的简易性。依据我国目前对乳粉中硝酸盐的限量要求，所测乳粉中的硝酸盐均在限量规定范围内，对食用的安全性不产生负面影响；而液态乳中的硝酸盐进行污染评价发现，超标率大约为14%。Abstract: Solid Phase Extraction-Ion Chromatography and the national standard chemical method (cadmium column reduction method) were used for the determination of nitrate in liquid milk and milk powder sold in Shijiazhuang. The Ion Chromatography method was achieved by adding acetic acid to precipitate protein in the prepared samples. After being centrifuged, the top clear solution was loaded to the DIONEX OnGuard RP solid phase extraction column to remove fat and other hydrophobic compounds. The AS11-HC anion chromatographic column was used for analysis. All samples were analyzed by the cadmium column reduction method for comparison. The average contents of nitrate in liquid milk were 10.05 mg/kg and 9.95 mg/kg, respectively. The average contents of nitrate in the milk powder were 25.74 mg/kg and 25.66 mg/kg, respectively. T test analysis it showed revealed that no significant difference was observed (t=0.07, P>0.05). The results support the accuracy of ion chromatography and the convenience of the procedure, which is in concordance with literature. The method of Ion Chromatography was easy to operate. According to the requirements on nitrate in milk powder in China, the evaluated results were within the prescribed limits. Meanwhile, the unqualified ratio of nitrate in liquid milk was about 14%.
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Key words:
- liquid milk /
- milk powder /
- nitrate /
- Ion Chromatography /
- cadmium column reduction method
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表 1 液态乳及奶粉样品中硝酸盐含量
Table 1. Content of nitrate in liquid milk and milk powder
测定方法 液态乳中硝酸盐含量
(现无国标限量值)
w(NO3-)/(mg·kg-1)乳粉
(国标限量值100 mg/kg)测定平均值 含量范围 测定平均值 含量范围 离子色谱法 10.05 2.96～16.6 25.74 9.9~46.8 国标化学法 9.95 3.02~16.3 25.66 10.1~47.2 
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表 2 离子色谱法测定乳粉中硝酸盐的回收率试验
Table 2. Recovery results of nitrate in milk powder by ion chromatography
加标浓度w
(NO3-)/(mg·kg-1)m/μg 平均回收率/%(n=6) RSD/% 加入量 平均测定值 10.0 10.0 7.83 78.3 6.3 20.0 20.0 8.08 80.8 10.8 30.0 30.0 11.1 111.0 9.3
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