Robert H. Shapiro

Quantitative analysis by various g.l.c. response-factor theories for partially methylated and partially ethylated alditol acetates☆

Results are presented which demonstrate that the molar flame-responses of partially methylated partially ethylated alditol acetates should be calculated on an effective carbon response (e.c.r.) basis. The relative responses of 2,3,4,6-tetra-O-ethyl-D-glucitol 1,5-diacetate, 2,3,6-tri-O-ethyl-D-glucitol 1,4,5-triacetate, hexa-O-ethyl-D-glucitol, hexa-O-methyl-D-glucitol, α-D-galactopyranose pentaacetate were measured and compared to the predicted values from three theories: equal molar response, equal weight response, effective carbon response. The observed values agree very well (±0−6%) with the e.c.r.-calculated values. The other theories of relative response can result in as much as 100% error in quantitation. The e.c.r-calculated relative response-factors for all commonly found partially methylated partially ethylated alditol acetates are presented, and their use is suggested for accurate quantitation.

A convenient method for the accurate estimation of concentrations of alkyllithium reagents

Abstract 1,3-Diphenyl-2-propanone tosylhydrazone in tetrahydrofuran solvent is shown to be an effective reagent for the determination of concentrations of alkyllithium reagents. A sharp color change is observed at equivalence, the solution becoming orange upon initial production of the tosylhydrazone dianion. 1,3-Diphenyl-2-propanone tosylhydrazone is conveniently prepared, stored and handled, and is non-hygroscopic.

Partially ethylated alditol acetates as derivatives for elucidation of the glycosyl linkage-composition of polysaccharides

Abstract The use of partially ethylated alditol acetates for the analysis by gas-liquid chromatography of the components of polysaccharides, and the glycosidic linkages of these components, is described. The derivatives are prepared by procedures analogous to those for the synthesis of partially methylated alditol acetates. Derivatization requires two successive ethylations and more-strenuous conditions of hydrolysis and reduction than for the methyl analogs. The partially ethylated alditol acetates are formed in nearly quantitative yield and give single, sharp peaks on gas chromatography. Retention-time data, relative to two internal standards, are given for 79 glycosidic linkage-isomers of mannose, galactose, glucose, arabinose, xylose, rhamnose, and fucose, on four g.l.c. columns. One of these columns is a newly developed, highly polar, capillary column. Direct comparisons of these retention times to retention times of partially methylated alditol acetates are made. The ethyl analogs are eluted sooner that the corresponding methyl derivatives, and the amount of this shift in elution time is dependent upon the number of alkyl groups in the derivative. This change in elution time allows separation of many polysaccharide components by g.l.c. that are not separable as their partially methylated alditol acetates. Others, separated as their O-methyl derivatives, are coeluted as their partially ethylated alditol acetates. The two derivatives thus provide excellent complementary procedures because of their differential chromatographic separation and because of the similarity of their preparation.

Correlation of excited electronic states of organic ions and mass-spectral fragmentation patterns☆

Abstract In a recent paper, the authors presented a new method of measuring parent-ion-fragmentation rate constants as a function of energy in a mass spectrometer source. Charge-exchange ionization was used to provide nearly monoenergetic excitation. The fragmentation rate constant curves obtained in this way were shown to have an experimental correlation with the photoelectron spectrum (PES) of the compound. A brief argument was presented to explain this observed correlation theoretically. However, the proposed explanation of the effect was incorrect. An alternative explanation of the observed correlation is now proposed. This does not invalidate use of the correlation in assigning the electronic states from which fragmentations occur.

Distribution function data and the electronic states for parent ion fragmentation of some simple organic compounds

Abstract Equations based on those originally derived by Hills, Futrell and Wahrhaftig are solved to evaluate the first fragmentation rate constant in the mass spectrometer source. The results so obtained are related to the distribution function for the parent ion in the source, and thus are also related to photoelectron spectra of the compound. Hence, some identification of which energy states are leading to the fragmentation at a given energy can be made. This is applied to carbon disulfide, acetone and several simple alcohols, and distribution function data curves are given for those.