Development of a high-performance liquid chromatographic–inductively coupled plasma method for speciation and quantification of silicones: from silanols to polysiloxanes

The speciation and quantification of organosilicon compounds at sub-ppm levels in environmental and industrial samples require the separation of the compounds of interest coupled with a sensitive, selective detector. The combination of high-performance liquid chromatography (HPLC) for separation and inductively coupled plasma atomic emission spectrometry (ICP-AES) for detection is ideal for the determination of a wide variety of organosilicon compounds. The HPLC–ICP combination was used in two modes: separation of non-polar, high molecular mass poly(dimethylsiloxane) polymers by size-exclusion chromatography with tetrahydrofuran or xylene as the mobile phase, and separation of polar, low molecular mass silanols by reversed-phase HPLC with water–acetonitrile as mobile phase. Samples analysed included water and extracts of sludge and soils. The coupled system detection limit for poly(dimethylsiloxane) is approximately 4–5 ng of Si, depending on the molecular mass distribution. The detection limit for a series of methylsilanediols is 1–4 ng of Si. An important feature of this work is that the analyses were performed using commercial HPLC and ICP equipment, with no modifications to hardware or software, and routinely employed solvents that are traditionally considered ‘difficult’ for ICP-AES. The equipment was interfaced and operating daily in less than 2 weeks from the beginning of the project. The ease of coupling readily available commercial equipment makes HPLC–ICP a viable technique for routine use in industrial and commercial analytical laboratories.