提出了一种基于双波长光谱法快速测定低污染水样的化学需氧量(COD)的方法。 结果表明: 对低COD样品采用440和560 nm双波长的测定方法可有效地提高可靠性和检测灵敏性。 该法的灵敏度(即定量检测下限)为8.6 mg·L-1； 在低COD范围标样(≤100 mg·L-1)的准确性对比测定相对标准误差在2%～15%的范围内。 另外, 该方法不需要用标准样品进行校正, 可以通过光谱法检测消解液中重铬酸根的消耗直接计算出样品的COD值, 使实验步骤得到了进一步的简化。

The present paper reports a dual wavelength spectroscopic method for the determination of chemical oxygen demand(COD) of low content samples, based on the absorption measurement at 440 and 560 nm. Since the absorptivities of Cr3+ at these two wavelengths are the same, a net absorption from dichromate ions can be determined by subtracting the absorption at 560 nm(only contributed by Cr3+) from the absorption at 440 nm. The results showed that the detection limit of quantification is 8.6 mg·L-1 and the relative standard deviations are in the 2%～15% range for the low COD standard samples (≤100 mg·L-1) in this proposed method. Further more, the method does not require calibration based on the standard samples. The present method is simple, reliable, and accurate; it is suitable for the application in a mass testing for low COD samples.