吸收光谱异常的工业废水六价铬检测方法探讨

Detection Method of Hexavalent Chromium in Industrial Wastewater with Abnormal Absorption Spectrum

参照标准检测方法《水质六价铬的测定二苯碳酰二肼分光光度法》(GB/T 7467—1987)中的氢氧化锌共沉淀-酸性高锰酸钾消解法预处理后的六价铬工业废水样品,仍存在消解不完全或难以消解的干扰物,显色后生成干扰吸收光谱的棕色,导致结果偏高或定性失误。选择存在明显吸收光谱干扰的印染废水1和无明显干扰的印染废水2,采用光谱吸收曲线-线性拟合斜率-分光光度法(SAC-LFS-S)进行定量分析,基于降低或消除上述干扰的目的,筛选出消解空白、样品结果、加标回收率等准确度指标和方法检出限均良好的测定波长段518~523 nm,以及对应的参比波长段(554~569、542~577、539~579、540~580和534~584 nm)。同时对单波长法(即标准检测方法,测定波长540 nm)、双波长法(测定波长540 nm,参比波长660 nm)和优化后SAC-LFS-S法的定量结果进行比较。结果显示,单波长法和双波长法在检测吸收光谱存在明显干扰的印染废水1(8.2~8.9μg/L,加标回收率<80.0%)和垃圾填埋场废水3(3.7~4.0μg/L,加标回收率<90.0%)时,均存在准确度欠佳问题,而优化后SAC-LFS-S法测得结果均低于方法检出限(1.5~1.8μg/L),加标回收率分别介于85.0%~86.0%和93.0%~93.5%。优化后SAC-LFS-S法测得其他4个无吸收光谱干扰的印染废水结果介于2.3~13.3μg/L(回收率为87.5%~94.5%),与双波长法结果无显著性差异,但明显低于单波长法。经参比波长段校正后的SAC-LFS-S法,适用于经氢氧化锌共沉淀-酸性高锰酸钾消解法预处理后工业废水的定量分析,尤其是存在明显吸收光谱干扰的样品。

After pretreatment with zinc hydroxide coprecipitation-acid potassium permanganate digestion method specified in Water Quality-Determination of Chromium(Ⅵ)-1,5 Diphenylcarbohydrazide Spectrophotometric Method(GB/T 7467-1987),the samples of industrial wastewater containing hexavalent chromium still have interferences which are incomplete or difficult to be digested,and the absorption spectrum is brown after color development,resulting in higher detection results or qualitative errors.The two printing and dyeing wastewater samples with and without obvious absorption spectrum interferences were quantitatively analyzed by spectral absorption curve-linear fitting slop-spectrophotometry(SACLFS-S).The measuring wavelength in the range of 518-523 nm and the corresponding reference wavelength ranges(554-569 nm,542-577 nm,539-579 nm,540-580 mm and 534-584 nm)with good accuracy indexes such as digestion blank,sample results and recoveries and detection limits were selected,so as to reduce or eliminate the interferences.The quantitative results of single-wavelength method(standard detection method with measuring wavelength of 540 nm),dual-wavelength method(measuring wavelength of 540 nm and reference wavelength of 660 nm)and the optimized SAC-LFS-S method were compared.Both the single-wavelength and dual-wavelength methods had poor accuracy in detecting No.1 printing and dyeing wastewater(8.2-8.9μg/L,standard recovery less than 80%)and No.3landfill wastewater(3.7-4.0μg/L,standard recovery less than 90%)with obvious interference in absorption spectrums.However,the results of the optimized SAC-LFS-S method were all lower than the detection limits(1.5-1.8μg/L),and the recoveries were 85.0%-86.0%and 93.0%-93.5%,respectively.After optimization,the results of other 4 printing and dyeing wastewater without absorption spectrum interference measured by SAC-LFS-S method ranged from 2.3μg/L to 13.3μg/L with recoveries between 87.5%and 94.5%,which had no significant difference with the results detected by the dual-wavelength method.However,the result was significantly lower than that detected by singlewavelength method.The SAC-LFS-S method corrected by reference wavelength band was suitable for quantitative analysis of industrial wastewater pretreatment by zinc hydroxide coprecipitation-acid potassium permanganate digestion,especially the samples with obvious absorption spectral interference.