对光度法的几点新认识

Some New Understandings on Spectrophotometry

摘要: 以碳钢、高锰钢、锰铁中锰的高锰酸光度法测定为例，介绍了在严格遵循“精密度法则”，即“保持影响测量的各因素对同一测定系列各个样品(包括标准样品)影响的一致性”条件下，对光度法的7点新认识：1) 方法的“校准曲线”区间，实际就是入射光的值域区间。在此区间内，吸光度改变量ΔA与吸光物质含量的改变量ΔC成正比：ΔA = KΔC，而不是A = KC；2) 造成光度法实际与朗伯–比尔定律不符的原因，不是入射光的“非单色性”。光度计不应追求入射光的单色性，反而应采用“非单色性”的入射光，以提它的测定灵敏度；3) 光度法测定结果的相对误差与透光率无关，最佳测定范围的相对误差不会是1%；4) 在方法的“校准曲线”范围内，所有样品含量和它吸光度的坐标点(C, A)，都必然会落在同一ΔA = KΔC的直线上。所以，标准样品上、下限两个坐标点的连线，即是样品含量的“测定线”，而无需采用多标准样品绘制“校准曲线”；5) “吸收谱带”是化学物质基态内不同量子能级量子化吸收的反映，所以它的不同波长都可用于相关物质含量的测定，并不只是它的峰值；6) 每个方法所给定的含量范围，实际是相应含量入射光的吸光度范围。不同含量的样品，只要制成入射光吸光度范围的样品，都可以用原方法实施测定；7) 光度法测定结果的不确定度：U₉₅=0.67R/√n、k_p=2，U₉₉=R/√n、k_p=3 (R是样本极差，n是样本容量)，简明而切合实际。新认识简化了光度法的操作和不确定度评定，并把光度法的测定含量扩大至任意含量，同时也为光度计研制提供了新思路。

Abstract: Taking the spectrophotometric determination of manganese in carbon steel, high manganese steel and ferromanganese as an example, seven new understandings of photometry are introduced under the condition of strictly following the “precision rule”, i.e. “to maintain infection consistency of each factor for each sample (including standard sample) in the same measurement series”: 1) The “calibration curve” interval of the method is actually the domain of the incident light. In this interval, the difference ΔA of absorbance is proportional to the difference ΔC of the matter that absorbs light: ΔA = KΔC , not A = KC; 2) The reason for the discrepancy between the photometric method and Lambert-Beer’s law is not the “non-monochromaticity” of incident light. Photometer should not pursue the monochromaticity of incident light, which should adopt the “non-monochromatic” incident light to improve its sensitivity. 3) The relative error of spectrophotometric results is independent of the transmittance, and the relative error of the optimum measurement range will not be 1%. 4) Within the “calibration curve” of the method, all the sample content and its absorbance coordinate points (C, A) will inevitably fall on the same line of ΔA = KΔC. Therefore, the connection between the upper and lower coordinate points of the standard sample is the “determination line” of the sample content, without the need to draw “calibration curve” with multi-standard samples. 5) The “absorption band” is the reflect of quantized absorption of different quantum levels in the ground state of chemicals, so its different wavelengths can be used to determine the content of related matter, not just its peak value. 6) The content range given by each method is actually the absorbance range of the incident light with the corresponding content. Samples with different contents can be determined by the original method as long as they are made into samples within the range of incident light absorbance. 7) The uncertainty of photometric determination results:U₉₅=0.67R/√n、k_p=2，U₉₉=R/√n、k_p=3(R is sample range, n is sample capacity), which are simple, clear and realistic. The new understanding simplifies the operation and uncertainty evaluation of spectrophotometry, expands the determination content of spectrophotometry to any content, and provides a new idea for the development of photometer.