X射线荧光光谱法测定奶粉中的营养元素

Determination of Mineral Nutrients in Milk Powder by X-Ray Fluorescence Spectrometry

采用粉末压片制样,波长色散X射线荧光光谱法测定奶粉中的氮、钠、镁、磷、氯、钾、钙。从仪器的X射线光管铍窗厚度、电流强度、测量时间和样品制样压力等方面优化了N元素的测定参数。选择不同种类的奶粉,由标准方法定值,采用标样建立校准曲线,理论α影响系数法校正基体效应。研究发现,铍窗厚度是制约N元素测定的主要因素,而电流强度的影响较小;手工研磨可较好地实现样品的均质处理;X射线辐照可以引起奶粉褐变,形成类似美拉德反应的外观和气味,并严重破坏内部蛋白质,P,Cl,K,Ca等元素测量结果均发生有规律的变化。该方法对N元素的检出限和相对标准偏差(RSD,n=9)分别为900 mg/kg和2.9%,其它元素的检出限和RSD分别小于10 mg/kg和3.0%,测定结果与标准方法一致。

A method was developed for the determination of N,Na,Mg,P,Cl,K,Ca in milk powder by wavelength dispersive X-ray fluorescence spectrometric method with pressed powder pellets. Effects of experimental conditions,including X-ray tube Beryllium window thickness,current intensity of instrument,measurement time,and sample preparation,on the determination of nitrogen were studied. Different kinds of milk powder samples were chosen and determined firstly by reference methods,then calibration curves were drawn using both the milk powder samples with known contents and reference materials. To eliminate the effect,the theoretical α influence coefficient method was used to correct matrix effects. It was found that manual grinding could better realize the homogeneous treatment of the sample. Thickness of beryllium window was the main factor restricting the nitrogen determination,but influence of the current intensity of fluorescence intensity was limited. X-ray irradiation could cause milk powder browning,forming the color and smell similar to that of maillard reaction. Furthermore,internal protein also suffered severe damage,and multiple interference could make the contents of P,Cl,K,Ca change according to a certain rule. For nitrogen,limit of detection and RSD（ n = 9） were 900 mg / kg,2. 9%,respectively,and for other elements,limits of detection and RSDs were less than 10 mg / kg,3. 0%,respectively. The measurement results were consistent with the reference method.