Limits of detection of polydimethylsiloxane in Si-29 NMR spectroscopy

Limits of detection for neat poly(dimethylsiloxane) (PDMS), as detected via Si-29 NMR spectroscopy, were determined by the IUPAC, graphical, and propa gation of errors methods from calibration curves obtained using a 7.05 Tesl a superconducting magnet equipped with a magic angle spinning (MAS) NMR pro be. Under conditions permitting full relaxation of the nuclear spins (recyc le time > 150 sec), the limit of detection with 128 transients was 1.7, 2.2 , and 3.7 mg PDMS (23, 30, and 50 mu moles elemental Si) for the IUPAC, gra phical, and propagation of errors methods, respectively. A higher limit of detection results when additional sources of uncertainty are considered. Fr om the strict dependence of the limit of detection on the inverse of the sq uare root of the number of transients signal-averaged, it is possible to ex trapolate to a limit of detection of 183 mu g PDMS (2.47 mu moles elemental Si) for a 24-hr signal averaging period. This limit of detection is 3 orde rs of magnitude higher than silicon levels found in human blood. (C) 2000 W iley-Liss, Inc.