title: Practical aspects of shimming a high resolution magic angle spinning probe.
abstract: High resolution magic angle spinning (HRMAS) has become an extremely versatile tool to study heterogeneous systems. HRMAS relies on magic angle spinning of the sample to average out to zero magnetic susceptibility differences in the sample and to obtain resonance linewidths approaching those of liquid state NMR. Shimming such samples therefore becomes an important issue. By analyzing the different sources of magnetic field perturbations present in a sample under MAS conditions, we propose a simple protocol to obtain optimum shim settings in HRMAS. In the case of aqueous samples, we show that the lock level cannot be used as a reliable indicator of the quality of the shims at high spinning speeds. This effect is explained by the presence of temperature gradients imparted by the sample rotation.
authors.affiliation: Institut de Chimie, FRE 2446, 4 rue Blaise Pascal, Université Louis Pasteur, 67084 Strasbourg, France. martial.piotto@bruker.fr
authors.forename: Martial
authors.initials: M
authors.lastname: Piotto
authors.forename: Karim
authors.initials: K
authors.lastname: Elbayed
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Wieruszeski
authors.forename: Guy
authors.initials: G
authors.lastname: Lippens
mesh_terms: D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation*; D011138:Polytetrafluoroethylene / Q000737:chemistry; D012815:Signal Processing, Computer-Assisted; D013696:Temperature; D014867:Water / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
chemical_list: D014867:Water; D011138:Polytetrafluoroethylene; D015040:Zirconium