Limits of detection of polydimethylsiloxane in 29Si NMR spectroscopy

Abstract

Limits of detection for neat poly(dimethylsiloxane) (PDMS), as detected via 29Si NMR spectroscopy, were determined by the IUPAC, graphical, and propagation of errors methods from calibration curves obtained using a 7.05 Tesla superconducting magnet equipped with a magic angle spinning (MAS) NMR probe. Under conditions permitting full relaxation of the nuclear spins (recycle time > 150 sec), the limit of detection with 128 transients was 1.7, 2.2, and 3.7 mg PDMS (23, 30, and 50 μmoles elemental Si) for the IUPAC, graphical, and propagation of errors methods, respectively. A higher limit of detection results when additional sources of uncertainty are considered. From the strict dependence of the limit of detection on the inverse of the square root of the number of transients signal-averaged, it is possible to extrapolate to a limit of detection of 183 μg PDMS (2.47 μmoles elemental Si) for a 24-hr signal averaging period. This limit of detection is 3 orders of magnitude higher than silicon levels found in human blood. (C) 2000 Wiley- Liss, Inc.