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在用发射光谱法测定微量元素时,往往找不到合适的标准样品,但可在试样中加入一定量的待测元素,以求出试样中的未知含量,这种方法称为增量法。常用的增量法之一是曲线逼直法。在原有含量为c的数份试样中,加入一系列增量c_1、c_2……,绘制增量的lgc-lgR曲线。在该曲线的高含量部分,由于增量远大于原有含量c,所以具有线性关系;而在低含量部分,由于增量接近原有含量c,该曲线将逐渐向上弯曲。为求得准确的工作曲线,将偏离直线点移到高含量增量所确定的直线上查得相应含量c,减去该增量即得一次近似值c_1,将各个增量点所得的c_1平均后,加入诸增量中,重复上述手续,得二次近似值c_2。如此重复几次,直到工作曲线变成直线,这种作法需反复绘制工作曲
In the determination of trace elements by emission spectrometry, often can not find a suitable standard sample, but the sample can be added to a certain amount of test elements to determine the unknown content of the sample, this method is called incremental law. One of the commonly used incremental methods is the curve straightforward method. In the original content of c several samples, add a series of increments c_1, c_2 ......, draw incremental lgc-lgR curve. In the high content part of the curve, since the increment is much larger than the original content c, it has a linear relationship; in the low content part, the curve will gradually curve upwards because the increment is close to the original content c. In order to obtain the accurate working curve, the deviation from the straight line to the high content of the increase in the line identified by the corresponding content c, subtracting the increment was an approximation c_1, the incremental points obtained after c_1 average , Add the increments, repeat the above procedure, the second approximation c_2. Repeat a few times until the working curve into a straight line, this practice needs to be drawn repeatedly work song