AUTOMATIC ON-LINE INTERNAL STANDARD ADDITION SYSTEM FOR DETERMINATION OF METALS BY INDUCTIVELY COUPLED PLASMA OPTICAL EMISSION SPECTROMETRY

Abstract

A new automatic on-line system that consisted of a 6-port valve equipped with a sample loop and a 2-channel syringe pump was developed for the addition of internal standard solution to sample solution before the determination by inductively coupled plasma optical emission spectrometry (ICP-OES). By the dual syringe pump, the carrier solution was pushed, simultaneously with the internal standard solution, to deliver the sample solution to mix with the internal standard solution. The mixture was consecutively directed to ICP-OES. The solution introduction flow rate at 1.50 mL/min was used in the determination of metals in aqueous samples and oil samples. The oxygen additional gas flow rate of 0.10 L/min was used in the analysis of oil samples. Under the suitable operating conditions using 4-mL sample volume, the sample throughput for the analysis of metals ions in aqueous solution and oil were 11 and 14 samples per hour, respectively. In the determination of Cr, Cu, Mn and Ni in spiked aqueous samples, the recoveries of metals were in the range of 98.9-111.5 % for samples having metal concentration lower than 10 µg/L level, 93.3-112.2 % for 10-100 µg/L level, and 85.9–108.0 % for the concentration higher than 100 µg/L level. The limits of detection were in the range of 2.5-6.4 µg/L. In the determination of Al, Cr, Cu, Fe, Pb, and Sn in spiked oil samples, the recoveries of metals were in the range of 89.46–104.74 %. The limits of detection were in the range of 0.22-2.71 µg/g. When the results of the sample analysis by the proposed method were compared to those from direct injection using the ICP-OES peristaltic pump, it was found that the recoveries and %RSD of the results obtained from the proposed method were in acceptable ranges and better than another method. The accuracies of the determination of metals in certified reference aqueous samples (ERM-CA022a) and certified oil samples (WM-11-NMS-5X-1) were evaluated and the proposed methods provided the results with high and acceptable accuracy. Moreover, the automatic on-line solution addition system can be applied to determine chromium (VI) by coupling the system to ultraviolet-visible spectrophotometer. The suitable solution introduction flow rate was 2.00 mL/min. The system provided an acceptable performance in the measurement of chromium (VI). This method provided the acceptable accuracies.