Determination of iodine in polyamide by inductively-coupled plasma/mass spectrometry

A method was developed for the determination of iodine in polyamide (PA). This method is needed as PA containing iodine (such as CuI/KX (X = I or Br) heat stabilizing agent), may represent a risk of corrosion for electronic parts in the automotive industry. The method involved a microwave assisted digestion method using nitric acid followed by inductively coupled plasma mass spectrometry (ICP-MS) analysis. A dilution in 0.5% NH₃ was needed prior to ICP-MS analysis to suppress memory effect. The limit of quantification was estimated to be 0.9 mg kg^-1 which allows the control of very low iodine content PA used for applications in sensitive electronic parts. Spiking with iodide at 50 mg kg^-1 gave recovery factors of 100 ± 0.8%. The acid digestion method was compared with microwave assisted extraction of PA with 5% NH₃ solution. Alkaline extraction gave slightly lower results (10% below). Finally, the acid digestion method was applied to the analysis of raw materials PA pellets and molded parts (used or not). Obtained iodine contents were ranged from < 0.9-1000 mg kg^-1 with relative standard deviation (RSD) on samples in the range 2.2-4.5%.