Analytical chemists in Belgium have developed a direct solid sampling method for the analysis of metal impurities in high-purity semiconducting polymers. 

Martín Resano and co-workers at Ghent University, Belgium, were asked by Solvay Research and Technology, an international chemical and pharmaceutical group headquartered in Brussels, to assist in their routine analysis of metal impurities in fluoropolymers. Resano said the challenge to develop a faster and simpler method 'was a very interesting application, very well suited for the characteristics of electrothermal vaporisation ICP-MS'. 

To be used as in the semiconductor industry, these polymers must be extremely pure. Metallic impurities are normally monitored using inductively coupled plasma mass spectrometry (ICP-MS). However, because ICP-MS requires a dilute aqueous sample, the polymers need to be pre-treated, which is often time-consuming and can result in analyte losses and contamination.

To avoid this, Resano used electrothermal vaporisation (ETV) for sample introduction. Small pieces of the polymer are loaded into a graphite tube and placed inside a furnace which is heated electrothermally. The matrix is completely removed at 800°C prior the volatilisation of the seven metal analytes of interest. This enables extremely sensitive multi-element analysis by a simple external calibration with aqueous standard solutions. 

'Such a straightforward analysis of solid samples is not readily possible by laser ablation, which in any case does not allow in situ separation of the analytes from the matrix,' said Diane Beauchemin of Queen's University, Kingston, Canada. 'This technique has great potential since it should be applicable to aqueous and solid samples where analyte levels would be high enough for direct detection by ICP-MS but interference arising from the matrix precludes direct analysis'.

Antonio Martín-Esteban, a scientist at the National Institute for Agriculture and Food Research and Technology, Madrid, agreed that 'this work gives an excellent confirmation of the potential of solid-sampling ETV-ICP-MS being more than a promising alternative to the laborious procedures currently used in multi-elemental analysis of complex samples'.

Debora Giovanelli