ML Magnuson | PubMed Health

PubMed2000

Microextraction of nine haloacetic acids in drinking water at microgram per liter levels with electrospray-mass spectrometry of stable association complexes

Haloacetic acids are disinfection byproducts of the chlorination of drinking water. This paper presents the analysis of all nine chloro and bromohaloacetic acids (HAA9) at the submicrogram per liter level by microextraction with detection by electrospray-mass spectrometry. The haloacetic acids are extracted from acidified water through a microscale liquid-liquid extraction. Perfluoroheptanoic acid is added to the extracts, and the haloacetic acids are detected with electrospray-mass spectrometry. Confidence in the selective quantification of the haloacetic acids is achieved by observing the stable association complexes that are formed between the haloacetic acids and perfluoroheptanoic acid. The method detection limits for the haloacetic acids are less than 1 microg L(-1), depending on the haloacetic acid. Standard addition is used to quantify the haloacetic acids in several water matrixes.

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PubMed1996

Line Narrowing in Solid-State Proton NMR with Acquisition Delay

Organic solids have extensive proton-proton dipolar interactions, and their 1H NMR linewidths are very large even with magic-angle spinning at moderate speeds. Recently it has been shown that substantial narrowing of the proton linewidths of organic solids can be achieved by using single-pulse excitation with acquisition delay or spin echo [S. Ding and C. A. McDowell, J. Magn. Reson. A 111, 212 (1994); 115, 141 (1995); 117, 171 (1995)]. This interesting line-narrowing phenomenon has been further examined through the study of several amino acids, their deuterated analogs, and some aromatic compounds. The results confirm that narrow proton peaks are observed with long acquisition delay, and the peaks appear in the appropriate chemical-shift ranges for organic protons (0-10 ppm with respect to tetramethylsilane). However, except for some special cases, the observed peaks cannot be assigned to individual types of protons based on chemical-shift considerations only. To explore the reason for the line narrowing, the effect of acquisition delay on the 19F linewidth of CaF2 was also studied and compared with that on the 1H linewidths of organic solids. It is suggested that the broad proton peak in an organic solid is a superposition of numerous transitions. These transitions have different linewidths, and the narrow peaks in the spectrum remain observable with long acquisition delays.

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