Report for Analytical Chemists
33rd EXPOSITION OF CHEMICAL INDUSTRIES MANAGEMENT: INTERNATIONAL EXPOSITION CO., 200 PARK AVE., NEW YORK, N.Y. 10017 CIRCLE 81 O N READER SERVICE CARD
try in which various positions of the sample molecule are labelled, it is possible to label the reagent gas (D 2 , CD 4 , ND 3 , etc.) to determine the fate of the initially transferred proton. Preliminary experiments have been made with CD 4 {28, 47) a n d D 2 {50). For both types of experiments with deuterium-labelled compounds, it is necessary to remember that the observed ions have undergone several collisions before leaving the source, and exchange may occur between the ions and the neutral molecules {28, 50). Such exchange may greatly increase the difficulties of interpretation of the data. For some time, it has been known that polar compounds which do not have M+ ions in their conventional EI spectra may show {M -\- 1) + or higher ions at the pressures produced by large samples even in unmodified instruments {51). These ions result, of course, from ion-molecule reactions between sample ions and sample molecules. Such processes are readily observed in the tight sources of mass spectrometers modified for high-pressure operation and may be useful for the determination of molecular weights {52). The interpretation of these data is more complex than the interpretation of conventional CI data, and several experiments must be done with different size samples to differentiate between reactant and product ions. This "self-chemical ionization" mass spectrometry can be enhanced by drastically increasing the pressure of the additive until virtually all of the primary ions produced by electron impact have reacted. Such experiments were performed on optically active compounds in an unsuccessful attempt to study diasteriomeric effects {53). Another variation of this technique uses the long path lengths and large ionic residence times available from ion cyclotron resonance mass spectrometry to effect ion-molecule reactions at low pressures {54) • Acetylation reactions of CH 3 CO + produced from butanedione have been used in an effort to develop functional group analysis {55). Reactions of sample ions with sample molecules have been reported for polar compounds, "self-
New J J. Baker cala og lists over products for gas chromatography product groups: ULTREX® Standards . . . zone refined organics, organic liquids . . . most w i t h a purity of 99.95 + % . 'Baker Instra - A n a l y z e d ' ® Solvents . . . g u a r a n t e e d 99 + % by CC. Each bottle s u p p l i e d w i t h a c t u a l gas c h r o m a t o g r a m , actual U V curve, IR curve and chemical analysis. Column packing materials for liquid phases include Squalane, Cholesterol Benzoate, Silicones and Silicone Gum Rubber. Solid supports and adsorbents include M o l e c u lar Sieves, Silica Gels a n d Aluminas. Application and product information on these materials for gas chromatography is provided in Catalog 700. Carrier and laboratory gases and calibration mixtures are listed in the Baker specialty gas c a t a l o g , a v a i l a b l e o n request. For the products he needs and uses most often—the professional chooses J. T. Baker. J. T. Baker Chemical Co. 222 Red School Lane C-7 Phillipsburg, N.J. 08865
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ANALYTICAL CHEMISTRY, VOL 43, NO. 13, NOVEMBER 1971 ·
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