Determination of trace sulfur in cathode copper by resistance combustion-infrared absorption method
The content of sulfur in cathode copper has a significant influence on the conductivity,heat con-ductivity and plastic processing property of copper.Therefore,the accurate determination of its content is of great significance.The standard sample series of cathode copper for spectral analysis and chemical anal-ysis(GSB 04-2554-2010)as well as self-made reference samples prepared by mixing these standard sam-ples,in which the sulfur content had certain gradient and enough span,were used as calibration samples to prepare the calibration curves.The unknown samples were calculated by combining the calibration curve and daily correction factor.The determination of trace sulfur in cathode copper by resistance combustion-infrared absorption method was realized.The experimental conditions such as sampling amount,combus-tion temperature and integration time were optimized:1.00 g of sample was accurately weighed;the com-bustion temperature and integration time were controlled at 1 200 ℃ and 150 s,respectively.It was found that the release curve of sulfur in standard sample had tailing peak.Moreover,the results were abnormally high.These problems were analyzed and discussed.The results showed that it was possibly caused by the water vapor in air.Therefore,the anhydrous magnesium perchlorate purification column was added before determination to dry the combustion mixture gas.The flow rate of oxygen had significant interference with the determination,and the optimal flow rate in experiments was 2.3 L/min.The blank values of porcelain boat before and after treatment were investigated.The results showed that the blank value of porcelain boat could be significantly reduced after treatment.Therefore,the porcelain boat was immersed in 20％hydrochloric acid(volume fraction)overnight,and then burned in muffle furnace at 1 200 ℃ for 2 h.The calibration sample series were determined under the selected instrumental conditions,and the calibration curve was drawn using the sulfur mass as the horizontal axis and the corresponding integral area as the ver-tical coordinate.The correlation coefficient of the calibration curve was 0.999 9.The limit of detection and limit of quantification was 0.1 μg/g and 0.3 μg/g,respectively.The contents of sulfur in standard cathode copper sample and production samples with various content levels were determined for 11 times in parallel according to the experimental method.The result showed that the found results were consistent with the standard values for the standard sample,and the relative standard deviation(RSD,n=11)was less than 2.0％.For the production samples,the measurement results were consistent with those obtained by high frequency combustion infrared absorption method or iodometry in GB/T 467-2010,and the RSDs(n=11)were between 1.6％and 5.3％.
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