不同制样方法对直流辉光放电质谱法测定氮化硼中27种杂质元素的影响

讨论了3种制样方法对直流辉光放电质谱法(dc-GDMS)检测氮化硼中的Na、Mg、Al、Si等27种杂质元素的影响。3种制样方法分别如下所示:方法1,直接把氮化硼压在铟薄片上;方法2,把氮化硼压在铟薄片上后,再盖上一层铟罩;方法3,把压碎后的氮化硼放在针状钽勺上。在优化的辉光放电参数下对比了3种不同制样方法对基体信号强度的影响。试验表明:在方法1中,当氮化硼尺寸约为3mm×3mm,厚度小于1mm时,基体¹¹B的信号可达1.8×10⁷ cps;在方法2中,选择铟孔大小合适的铟罩,基体¹¹B的信号可达1.0×10⁷ cps;方法3获得基体信号强度比方法1、方法2高一个数量级。大部分元素在中分辨率下可获得较好的结果,而对于在高分辨率下也较难分离的元素,可选择丰度较低的同位素在中分辨率下进行测定,如Ge选择⁷⁰Ge⁺,Se选择⁸²Se⁺,Cd选择¹¹¹Cd⁺,Sn选择¹¹⁹Sn⁺,Ag选择¹⁰⁹Ag⁺,Pt选择¹⁹⁴Pt⁺。氮化硼中的杂质元素含量可通过样品片中待测元素含量减去来自于铟薄片或钽勺中该元素贡献的含量来计算获得。将样品平行测定5次,相对标准偏差均在20%以内。对于Al、Si、Ti等元素的测定,3种制样方法的测定结果基本一致;方法1、方法2中检测到的In含量较大,使得铟中的Ni、Cu对氮化硼的测定值影响较大;方法3由于钽中Fe、Cu的贡献导致氮化硼中Fe、Cu的检测值较大,但方法3获得的基体信号强度大,可降低部分元素的检出限,如Cr、Mn、Ga、Ge等。综上所述,方法3为优选方法。

Effect of sample preparation method on the determination of twenty-seven impurity elements in boron nitride by direct current glow discharge mass spectrometry

The influence of three sample preparation methods on the determination of twenty-seven impurity elements (including Na, Mg, Al, Si, etc) in boron nitride by direct current glow discharge mass spectrometry (dc-GDMS) was discussed. Three sample preparation methods were described as below. Method 1: the boron nitride was directly pressed on the thin sheet of indium; Method 2: after pressing boron nitride on the thin sheet of indium, a layer of indium cover was added; Method 3: the crushed boron nitride was placed on the needle-like tantalum spoon. The influence of three sample preparation methods on the signal intensity of matrix was compared under optimized glow discharge parameters. The results showed that: for Method 1, when the size of boron nitride was about 3mm×3mm with thickness less than 1mm, the signal intensity of matrix (¹¹B) was up to 1.8×10⁷ cps; for Method 2, if the hole size of indium cover was appropriate, the signal intensity of matrix (¹¹B) reached 1.0×10⁷ cps; for Method 3, the signal intensity of matrix was one order of magnitude higher than above two methods. The analytical results were good for most elements under moderate resolution mode. For the elements which were difficult to be separated at high resolution, the isotopes with low abundance could be selected for determined at moderate resolution mode, for example, ⁷⁰Ge⁺ for Ge, ⁸²Se⁺ for Se, ¹¹¹Cd⁺ for Cd, ¹¹⁹Sn⁺ for Sn, ¹⁰⁹Ag⁺ for Ag, and ¹⁰⁴Pt⁺ for Pt. The content of impurity elements in boron nitride could be calculated by subtracting the results of impurities measured from the indium sheet or tantalum spoon. The sample was determined independently for five times, and the relative standard deviations (RSD) were all less than 20%. The analysis results of Al, Si and Ti were basically consistent for three sample preparation methods. In Method 1 and Method 2, the content of detected indium was relatively high, leading to high influence of Ni and Cu in indium on the determination of boron nitride. In Method 3, due to the contribution of Fe and Cu in tantalum, the detected values of Fe and Cu in boron nitride were relatively high. However, the signal intensity of matrix in Method 3 was high, which could reduce the detection limits of some elements such as Cr, Mn, Ga and Ge. Therefore, the Method 3 was the preferred method.