SPECIATION AND QUANTITATION OF DEGRADATION PRODUCTS OF SILICONES (SILANE SILOXANE DIOLS) BY GAS-CHROMATOGRAPHY MASS-SPECTROMETRY AND STABILITY OF DIMETHYLSILANEDIOL/

Gas chromatography-mass spectrometry (GC-MS) methodology was developed to speciate and quantitate several degradation products of polydimeth ylsiloxane (PDMS) in soil. We have demonstrated that the major degrada tion product, viz., dimethylsilanediol, can be readily analyzed by GC- MS without derivatization as commonly practiced in analyzing such mate rials. A mixture of linear siloxane diols (n = 1-5, where n is the num ber of Me2SiO units), and cyclic dimethylsi loxanes (n = 4-6) was reso lved by GC-MS. We also found that peak identity of various diols requi red that GC-MS is done in the chemical ionization (CI) mode, since the electron impact (ET) ionization mode produced similar mass fragmentat ion patterns for diols and cyclics containing the same number of silic on atoms. For siloxane diols, detection limits ranged from 100 pg (for n = 1) to 1 ng (for n = 5). For cyclics, the detection limit was abou t 1 pg. Dimethylsilanediol, known to be unstable even in the solid sta te, was shown by NMR techniques to be stable in aqueous solution at <0 .1% concentration. A 100-ppm solution was stable for over a year. Puri ty check for dimethylsilanediol is best carried out by Si-29 solid-sta te NMR technique.