Bintoro V P, Cantin-Esnault D, Alary J
Laboratory of Analytical Chemistry, Faculty of Pharmaceutical Sciences, Grenoble, Domaine de la Merci, La Tronche, France.
Analyst. 1995 Nov;120(11):2747-53. doi: 10.1039/an9952002747.
A rapid, simple and direct visible spectrophotometric method, based on the quantitative nitration of 2-sec-butylphenol in concentrated sulfuric acid, is described for the determination of nitrate in milk. The nitration product was extracted into toluene and the yellow nitrophenoxide compound formed in alkaline aqueous solution was determined at 418 nm. Carrez reagents were used for protein precipitation. Interference from lactose, chloride and nitrite ions and the effect of reagent concentration was controlled. The calibration graph was linear over the range 0.5-5 micrograms ml-1 NO3-; y = -0.0019 + 0.0681 x; r = 0.9997. The limits of detection and quantification were found to be 0.18 and 0.5 microgram ml-1 NO3-, respectively. The accuracy of the method did not depend on nitrate content in spiked milk. The mean recovery of the spiked milk was found to be 99.81% with the confidence limits of 0.67%, a relative standard deviation (RSDr) of 1.79% for repeatability and an RSDR value of 1.90% for reproducibility. Adequate agreement was found between results obtained by the nitration method and those of the French official reduction spectrophotometric reference method (AFNor). For the Indonesian dry (powdered) milk sample studied the nitrate levels were in the range 10.7-29.5 mg kg-1 NO3-.
本文描述了一种基于浓硫酸中2-仲丁基苯酚定量硝化反应的快速、简单且直接的可见分光光度法，用于测定牛奶中的硝酸盐。硝化产物用甲苯萃取，碱性水溶液中形成的黄色硝基酚盐化合物在418nm处进行测定。使用Carrez试剂沉淀蛋白质。控制了乳糖、氯离子和亚硝酸根离子的干扰以及试剂浓度的影响。校准曲线在0.5 - 5微克/毫升NO₃⁻范围内呈线性；y = -0.0019 + 0.0681x；r = 0.9997。检测限和定量限分别为0.18和0.5微克/毫升NO₃⁻。该方法的准确度不取决于加标牛奶中的硝酸盐含量。加标牛奶的平均回收率为99.81%，置信限为0.67%，重复性相对标准偏差（RSDr）为1.79%，再现性RSDR值为1.90%。硝化法所得结果与法国官方还原分光光度参考方法（AFNor）的结果有充分的一致性。对于所研究的印度尼西亚干（粉末状）牛奶样品，硝酸盐含量在10.7 - 29.5毫克/千克NO₃⁻范围内。
