Solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry for the direct determination of traces of iodine

Abstract

In this work, the possibilities of electrothermal vaporization-inductively coupled plasma mass spectrometry for the direct determination of I at the ppm and sub-ppm level in solid samples have been evaluated. Five reference materials of different natures (NIST SRM 1549 and BCR CRM 150 Milk Powder, BCR CRM 129 Hay Powder, NIST SRM 1548a Typical Diet and NIST SRM 2709 San Joaquín Soil) were selected for this study.The importance of the use of pre-reduced Pd in the analysis of biological materials was demonstrated. The use of this chemical modifier results in a better stabilization of the analyte (up to 700 °C), enabling complete removal of the organic matrices without analyte losses. Moreover, for those samples for which some matrix effects were still observed (milk powder materials), the use of the Pd signal as internal standard permitted correction for these effects, allowing accurate results to be obtained. A detection limit of 8 ng g⁻¹ and a sample throughput of 20–25 min per determination were estimated for these biological materials. The potential of the technique for inorganic samples was also evaluated with a soil material (NIST SRM 2709). For this sample, an alternative approach was developed. By taking advantage of the volatility of the analyte in the absence of any modifier and of the refractory nature of most matrix components, it was possible to selectively vaporize I at 1500 °C, ensuring the absence of significant matrix effects. A higher sample throughput of 10 min per determination (due to the faster temperature program) and a higher detection limit (30 ng g⁻¹, due to the absence of Pd) were calculated for this material. In all cases, external calibration with aqueous standards was possible and RSD values were in the vicinity of 10%.