溶液阴极辉光放电结合标准加入法和背景去除法分析水溶液中的Ca和Mg

溶液阴极辉光放电发射光谱法易受水体样品中的基体效应影响,而且对于实际水体样品组份相对复杂,含有多种元素,受基体效应干扰更加明显,导致金属元素浓度预测精度降低。为了减少溶液阴极辉光放电发射光谱法中水体样品基体效应的影响,常常利用定量分析方法对金属元素进行分析。这些定量分析方法中,标准加入法尤其适合于待测物质基体效应较为显著或者含有干扰物质等情况,然而标准加入法容易受到背景信号的干扰,使测量结果产生误差,因此在进行标准加入法之前需要消除光谱数据的背景干扰。最简单的谱线干扰消除法是离峰校正法,此法扣除线峰左右两侧的背景强度值,以达到消除背景干扰的目的;小波变换法同样也适用于消除背景干扰,并且具备普适性,利用此法对小波进行多尺度分层,而后对小波低频系数进行处理,获得校正后的数据。在独立开发的溶液阴极辉光放电发射光谱系统上,利用基于标准加入法的离峰校正法和小波变换法对水溶液样品中Ca和Mg含量进行预测。实验结果比较发现,基于传统的标准加入法,测得5, 10和20 mg·L-1浓度的Ca样品的相对误差分别为157.0%, 105.1%和47.0%, Mg的相对误差分别为20.1%, 3.1%和2.8%。然而,结合标准加入法和离峰校正法后, Ca的相对误差分别降低至15.4%,-8.8%和3.3%, Mg的相对误差分别降低至14.5%, 0.1%和0.8%。采用小波变换算法消除背景干扰后的标准加入法, Ca元素的相对误差分别降至13.2%,-7.6%和-1.4%, Mg的相对误差分别降至13.4%,-0.4%和0.5%。结果表明,离峰校正法和小波变换法结合标准加入法测量Ca和Mg的准确度显着提高,两种方法能有效地消除背景干扰,降低基体效应,使预测精度升高。其中,小波变换法结合标准加入法可用于多种类型的背景校正场合,无需选择合适的背景校正点,而且预测精度更高,相比离峰校正法具有一定的优势。

Ca and Mg Analysis in Solution by Solution Cathode Glow Discharge Combined with Standard Addition Method and Background Removal

Solution cathode glow discharge atmosphere emission spectrometry(SCGD-AES) is affected by the matrix effect in aqueous solution. Moreover, actual water contains many elements and the components are relatively complex, which makes matrix effect more serious and leads to a decrease in accuracy of metal element concentration prediction. In order to reduce matrix effect of aqueous solution in SCGD-AES, quantitative analysis methods are often used to analyze metal elements. Among these methods, standard addition method is especially suitable for the situation that matrix effect or interfering substance is relatively significant. However, standard addition method is vulnerable to background interference, resulting in the error of results. Therefore, the background interference must be eliminated before standard addition method is carried out. The simplest method to eliminate the interference is off-peak correction method, which deduces the background intensity value measured at the left and right of the linear peak, so as to eliminate the background interference. Wavelet transform method is also applicable to eliminate background interference and it is universal. This method is applied to multi-scale stratification of wavelet, and then the low-frequency coefficient of wavelet is processed to obtain the corrected data. Here, Ca and Mg content in solution were predicted by off-peak correction and wavelet transform method based on standard addition method in a homemade SCGD-AES system. For the traditional standard addition method, the relative error of the Ca samples with concentrations of 5, 10 and 20 mg·L-1 were measured as 157.0%, 105.1% and 47.0%, respectively. The REs of Mg in the three groups of samples were 20.1%, 3.1% and 2.8%, respectively. However, when the standard addition method and off-peak correction were combined, REs of Ca were reduced to 15.4%,-8.8% and 3.3%, and REs of Mg were reduced to 14.5%, 0.1% and 0.8%, respectively. When standard addition method by wavelet transform to eliminate background interference was employed, REs of Ca decreased to 13.2%,-7.6% and-1.4% respectively, and REs of Mg decreased to 13.4%,-0.4% and 0.5% respectively. The experimental results show that the accuracy of Ca and Mg measurement is significantly improved by off-peak and wavelet transform method. The two methods can effectively eliminate background interference, reduce matrix effect and improve the prediction accuracy. The wavelet transform combined with standard addition method can be used for various background correction occasions, without selecting appropriate background correction points, and the prediction accuracy is higher, which has advantages compared with off-peak correction method.