Rapid determination of small amounts of copper as a tramp element in steel scraps by laser induced plasma spectrometry

A quantitative analysis of copper in steel scraps was investigated by using laser induced plasma spectrometry. A Nd:YAG laser at a wavelength of 532 nm was employed to generate the plasma under reduced argon atmospheres. Several experimental parameters, such as an argon pressure, a gate width and a delay time of the spectrometer were optimized to obtain a calibration curve having higher sensitivity and better linearity. Several line pairs of copper and iron were also investigated as a candidate of the analytical line for measuring the intensity ratio converted into the atomic ratio of copper to iron in steel scraps. The Cu 1 324.754-nm line was more suitable for the analytical line than the Cu 1 327.396-nm line due to its higher intensity. Line pairs of Cu 1 324.754 nm to several iron lines, Fe 1 381.583 nm, Fe 1 382.043 nm, and Fe 2 276.750 nm, were measured to compare criteria of their calibration curves, such as a slope, an intercept and a regression coefficient. As a result, it was recommended that a calibration curve for the intensity ratio of Cu 1 324.754 nm/Fe 2 276.750 nm could be employed in the actual application because it had a regression coefficient of almost unity over a concentration range up to 1.0 mass% Cu in standard reference samples of iron-copper binary alloy. The limit of detection, based on three times the standard deviation of the emission intensity at 324.75 nm in a pure iron sample, was estimated to be the Cu/Fe atomic ratio of 0.00059.