基于水内标的NO-3，SO2-4，ClO-4拉曼光谱定量分析研究

拉曼光谱由于重现性差，在进行定量分析时往往需要内标。在水溶液中，水在2 700~3 900 cm-1范围伸缩振动拉曼峰很强，有作为内标的可能性，但水与溶质的相互作用会导致水伸缩振动拉曼峰形状发生变化，此外水的占比也会随着溶质浓度的变化而变化，当溶质浓度较高时需要对水的含量进行校正。将这两点因素考虑在内，研究了以水为内标，采用拉曼光谱法测量水溶液中NO-₃，SO2-₄和ClO-₄浓度的适用性。不同浓度NaNO₃，Na₂SO₄和NaClO₄溶液的拉曼光谱显示随着盐浓度的升高水在2 700~3 900 cm-1范围内的拉曼峰呈现出左肩下降右肩上升的变化趋势。将三种盐溶液拉曼光谱中酸根离子拉曼峰面积（A_盐）和水的拉曼峰面积（A_H2O）的比值（Ｒ_S=A_盐/A_H2O）与溶液中酸根离子和水的含量的比值（c_盐/c_H2O）作图，均呈现出良好的线性关系，拟合得到三条相关曲线的R2分别为0.999 1，0.999 1和0.999 4，说明酸根离子和水的拉曼散射系数均未发生变化或者在同比例变化。虽然水拉曼峰的形状发生了改变，但并不会影响水作为内标的可行性。在引入水的含量修正后，经理论推导c_盐与R_S符合关系式：c_盐=AR_S/(1+BR_S)。在0.1 mol·L-1到近饱和的宽浓度范围内，将R_S对c_盐作图，通过数据拟合获得的NaNO₃，Na₂SO₄和NaClO₄的工作曲线分别为c_NaNO3=18.8R_S/(1+0.6R_S) (R2=0.999 1)，c_Na2SO4=20.2R_S/(1+1.0R_S) (R2=0.998 8)，c_NaClO4=15.0R_S/(1+0.7R_S) (R2=0.999 8)。NaNO₃，Na₂SO₄和NaClO₄的检出限分别为0.008 0，0.005 2和0.007 3 mol·L-1。在水拉曼峰形状变化不影响其作内标可行性的基础上，当溶液中同时存在两种阴离子时，通过在水含量修正部分加入干扰离子对水含量的影响，可以在单盐溶液定量工作曲线中加入校正项来消除溶液中干扰离子对待测离子分析结果的干扰，但当干扰离子浓度较大而待测离子浓度较小时，干扰离子拉曼峰强度过大会影响到待测离子拉曼峰面积的准确性，从而使得校正的效果下降。

Quantitative Analysis of NO3-, SO2-4 , ClO4- With Water as Internal Standard by Raman Spectroscopy

Internal standard is often required when using Raman spectroscopy for quantitative analysis due to the poor reproducibility of the Raman spectrum. In aqueous solutions, the stretching vibration Raman peak of water at 2 700~3 900 cm-1 has a strong intensity and may be used as an internal standard, but the interaction of water and solute will cause the shape of the water stretching vibration Raman peak to change. In addition, the concentration of water will also change with the change the solute concentration. When the solute concentration is high, the water concentration needs to be corrected. Taking these two factors into consideration, quantitative analyses of NO-₃, SO2-₄, ClO-₄ in aqueous solutions with Raman spectroscopy are investigated, focusing on evaluating water as an internal standard. The Raman spectra of different concentrations of NaNO₃，Na₂SO₄，NaClO₄ solutions show that with the increase of salt concentration, the Raman peak of water in the range of 2 700~3 900 cm-1 presents a trend that the left shoulder drops and the right shoulder rise. However, there exists a good linear relationship between A_salt/A_H2O and c_salt/c_H2O in NaNO₃，Na₂SO₄，NaClO₄ solutions, where A represents the area of the Raman peak and c represents the concentration, and the R2 of the three fitting curves are 0.999 1, 0.999 1, 0.999 4, respectively. This indicates that the Raman scattering coefficients of acid ions and water do not change or change in the same proportion. So, although the shape of the water Raman peak having changed, the feasibility of water as an internal standard is not affected. After introducing the correction of the concentration of water, it is theoretically deduced that c_salt and conform to the relationship: c_salt=AR_S/(1+BR_S), where R_S=A_salt/A_H2O. In a wide concentration range from 0.1 mol·L-1 to near saturation, the standard working curves for NaNO₃, Na₂SO₄, and NaClO₄ are obtained to be c_NaNO3=18.8R_S/(1+0.6R_S) (R2=0.999 1), c_Na2SO4=20.2R_S/(1+1.0R_S) (R2=0.998 8), and c_NaClO4=15.0R_S/(1+0.7R_S) (R2=0.999 8), respectively. The limit of detection (LOD) of NaNO₃, Na₂SO₄ and NaClO₄ are found to be 0.008 0, 0.005 2 and 0.007 3 mol·L-1, respectively. On the basis that the shape change of the water Raman peak does not affect its feasibility as an internal standard, when there are two salts in a solution, a water concentration correction for the second salt can be made to improve the quantitative analysis based on the standard curves for the single salt solutions. However, the correction result is limited when the second salt concentration is too large, and the first salt concentration is relatively small because the accuracy of the Raman peak area of the first salt will be affected due to the too large Raman intensity of the second salt.