Rapid determination of silicone oil lubricant in elastomeric closures by ICP-OES

Abstract

A rapid method for determination of silicone oil in elastomeric closures of injection syringes by inductively coupled plasma optical emission spectrometry (ICP-OES) is presented. The silicone oil was extracted from the intact closure using a mixture of methyl isobutyl ketone and 1-pentanol, no further sample treatment was necessary. Quantitation was based on response from Si(I) at 288.158 nm using external calibration with standard solutions of silicone oil dissolved in the same extraction mixture. A supplemental flow of oxygen was used to decrease background interference, providing a detection limit (3s, n = 10) of 0.05 mg of silicone per L. The LOQ (10s, n = 10) was 0.15 mg silicone per L, equivalent to 3.8 μg silicone/sample of elastomeric closure, based on 25 mL of extraction solvent per closure. The same samples were also analyzed by high-resolution flame atomic absorption spectrometry (HR-CS F-AAS), providing results similar to those obtained by ICP-OES. Spike recoveries of 97–104% demonstrated the accuracy of the methodology. Precision, expressed as the relative standard deviation, was 0.7–3.0% under conditions of repeatability and 0.7–3.3% for reproducibility. This simple procedure has been adopted by the Institute of Technology of Paraná – TECPAR (Curitiba, Brazil).