Analysis and fractionation of silicone and fluorosilicone oils for intraocular use

Silicone oil (SiO) and fluorosilicone oil (FSiO) are useful in difficult cases of retinal detachment surgery. Unidentified low-molecular-weight components (LMWC) and residual catalysts in SiO and FSiO have been implicated in the adverse reactions of the oils in the eye. The authors analyzed LMWC of SiO and FSiO using a gas chromatograph (GC) equipped with a 6-ft x 2-mm column packed with 3% SP-2250 and a flame-ionization detector. By commercially available standards and a homologous series plot, MD3M to MD23M (linear LMWC) and D4 to D30 (cyclic LMWC) were positively identified in commercial-grade 1000-centistokes (cs) SiO. Commercial-grade 12,500-cs SiO contained GC-detectable LMWC (up to MD28M and D30) at higher concentrations than commercial-grade 1000 cs SiO, although the weight percent of acetone-extractable LMWC (including those larger than MD28M and D30) was less in the former than in the latter. The GC-detectable LMWC in most medical-grade SiO were less than those in commercial-grade SiO. Tetramethylammonium siloxanolate (a residual catalyst) and tributylphosphine oxide (a heat-decomposition product of a polymerization catalyst) were tentatively identified in commercial- and medical-grade 12,500-cs SiO, respectively. Commercial-grade 1000- and 10,000-cs FSiO also contained LMWC, including F3 and/or F4 (cyclic LMWC). To eliminate LMWC from the oils, the authors developed a solvent fractionation method using acetone for SiO and hexane for FSiO. After continuous solvent extraction of SiO for 2 weeks and FSiO for 3 weeks, all measurable LMWC were eliminated from the oils.