News
Resolving quadrupolar nuclei by NMR Approximately two-thirds of the magnetically active nuclides found in the periodic table have a half-integer spin number > 1. NMR of solid samples containing these nonspherical quadrupolar nuclei leads to anisotropic interactions and broad, difficult-to-resolve peaks. Several techniques, such as magic-angle spinning (MAS), have been developed to improve the resolution. Lucio Frydman and coworkers at the University of Illinois at Chicago have discussed the theoretical and experimental aspects of multiple-quantum magic-angle spinning (MQMAS) NMR and demonstrated its application to spin 3/2 nuclei Unlike MAS NMR, this method removes second-order quadrupolar effects. MQMAS yields two-dimensional spectra, which, by inspection, provide isotropic chemical and quadrupolar shifts for different chemical sites in powdered samples. In addition, say the authors, the resolved anisotropic lineshapes are almost unaffected by excitation distortions, and can be used to discern the site's quadrupolar coupling constant and asymmetry parameter. (J. Amerr Chem. Soc. 1995, 117,12779-787)
Better and best: comparison between the static, MAS, and MQMAS 23Na NMR spectra of A/a2S03. 166 A
GOVERNMENT
EPA tries flexibility A major effort to introduce "flexibility" into the analytical methods of EPA's Office of Water is being discussed at a series of public meetings being held around the United States. In addition, the Office of Water is exploring ways to streamline procedures for adopting new methods, dumping outdated methods, and unifying competing methods of various program offices for the same analytes. According to William Telliard of the Office of Science and Technology, the effort has the support of Robert Perciasepe, head of the Office of Water, and could lead to a "strawman" proposal by the end of this year. Flexibility, says Telliard, would give environmental laboratories freedom to modify analytical methods within the structure of an existing method, thereby taking advantage of newer technologies. Labs adopting modified methods would need to demonstrate at least equivalent performance. For example, labs could modify an extraction step for a GC analysis, but not substitute LC/MS for the GC technique. As such, the proposal stops short of performance-based methods, which would allow using any methods that meet certain criteria. Currently, analytical methods for environmental measurements in water (as well as air) are prescribed in great detail by EPA. In addition, complementary programs, such as those for drinking water and wastewater, can have different methods for the same analyte. EPA's flexible method proposal joins other attempts by Congress and the National Environmental Laboratory Accreditation Conference (see Anal. Chem. Feb. 1,1996, pp. 82 A-84 A) to revamp the agency's approach to analytical methods.
Analytical Chemistry News & Features, March 1, 1996
The issue is further complicated by the need to gain the support of state and local governments, which have the responsibility to oversee compliance with federal environmental laws. Telliard says that the flexibility proposal would not interrupt EPA's methoddevelopment research for specialized needs such as the analysis of off-shore drilling muds. Routine methods development would be left to groups such as the American Society for Testing and Materials, he added.
U.K.'s Laboratory of the Government Chemist to privatize The government of the United Kingdom plans to privatize the Laboratory of the Government Chemist (LGC) through a trade sale. The preferred bidder will be a consortium of LGC management and staff, the Royal Society of Chemistry, and an investment company. The consortium will continue all activities of LGC and maintain it as a national center for excellence in chemical measurement. The official Government Chemist will continue to be appointed from the laboratory.
European standards guide NIST and the Commercial Service at the U.S. Mission to the European Union have jointly published NIST special publication 891, "Standards Setting in the European Union Standards Organizations and Officials in EU Standards Activities." The document provides information on the harmonization of standards in the EU and should be useful to manufacturers, exporters and government officials. Information for the guide was provided by the EU Commission, the European Committee on Standardization the EuroCommittee for Electrotechnical Standardization and the European Telecommunications Standards Institute Included are lists of directives other NIST publications and sources for standards SP 891 (stock no 003003-03369-3) is available for $5 from the U S Government Printing Office Washington DC 20402 (202-512-1800)
