Roland F. Hirsch

Effects of restricted mass transfer on the efficiency of micellar chromatography

Abstract A model treating restricted mass transfer in micellar chromatography based on the kinetics of adsorption—desorption of the solute on the stationary phase and entrance—exit rates from micelles in the mobile phase is proposed. This model provides an explanation for the lower chromatographic efficiency of micellar mobile phases relative to conventional mobile phases. Based on our studies, the efficiency of micellar chromatography can be optimized by use of elevated temperatures, low flow-rates and minimal micelle concentrations. All of these experimental variables are targeted at maximizing the kinetic rate parameters.

Gas-solid chromatography on cation-exchange resins: Darc topological analysis of the behavior of alkenes on nickel ions

Abstract Retention indices of 44 alkenes in gas-solid chromatography were determined on the Ni2+ form of a cation-exchange resin and on the corresponding unsulfonated copolymer matrix. The Ni2+ form was prepared from a sulfonated Porapak Q ethylvinylbenzene-divinylbenzene copolymer. DARC topological analysis (DTA) was applied to the Kovats retention indices determined at 175°C. DTA helps to delineate the evolution of specific π bond-Ni2+ ion interactions with progressive variations of the structural effects of the alkenes.

Liquid Ion Exchanger Membrane Electrode Sensitive to Perrhenate and Thiocyanate; U-Shaped Potentiometric Titration Curves

Abstract The Orion Perchlorate Ion Activity Electrode also is sensitive to perrhenate and thiocyanate activities. Response is Nernstian over several orders of magnitude, with detection limits about 10−6 F for perrhenate and 10−5 F for thiocyanate. Titrations can be carried out with ±0.5% relative standard deviations at the 10−1 to 10−2 F concentration level. Titration curves for addition of mercury (II) to thiocyanate, chloride, bromide, and iodide are U-shaped. The electrode appears to be highly sensitive to the anionic mercury-halide complexes formed in the early stages of these titrations. The data are consistent with the stabilities of the complexes.

Quantitative study of structural parameters of specific adsorption of alkenes on zinc ions using gas—solid chromatography and topological data-processing techniques

Abstract Gas—solid chromatography can provide information on the adsorption processes involved in heterogeneous catalysis. Retention indices of a set of 44 alkenes on the zinc form of a sulfonated porous polymer are analyzed to evaluate the polar and steric contributions to adsorption on this metal ion. DARC/PELCO topological analysis is used to evaluate the effect of each carbon atom in the environment of the double bond on the overall retention of a compound by adsorption.

Reliability of factor analysis in the presence of random noise or outlying data

Abstract Hirsch, R.F., Wu, G.L. and Tway, P.C., 1987. Reliability of factor analysis in the presence of random noise or outlying data. Chemometrics and Intelligent Laboratory Systems , 1: 265–272. The influence of random and determinate error on abstract factor analysis is investigated. A Monte Carlo study of the effect of random error in data from NMR and GC-MS experiments indicates that the eigenvalue ratio test and Malinowskis indicator function are more accurate that the imbedded error function in determining the number of significant factors or components. Outliers affect the analysis, but the level of deviation of a single outlier can be considerably larger than the random experimental error in the data before the effect is significant.

Specific interactions of alkenes with different metal ion forms of ion exchangers in gas solid chromatography

SummaryThe gas chromatographic selectivity of K+, Zn2+, Ag+, Ni2+, and Cd2+ forms of a cation exchange packing have been determined for a set of 44 C2 to C8 alkenes. The retention characteristics of each ion are broken down into electronic (charge-transfer) and steric effects associated with the alkene sub-populations of each carbon number. Almost every pair of alkenes tested can be separated on at least one of these packings. Retention is much stronger on the ion exchangers than on metal-ion containing packings in gas-liquid chromatography, even with shorter columns and higher temperatures.

75 years of the Division of Analytical Chemistry of the American Chemical Society.

The Division of Analytical Chemistry is celebrating the 75th anniversary of its founding in 1938. We celebrate the continuing high importance of our discipline for all aspects of chemical science and for its applications in so many aspects of everyday life. We especially celebrate the accomplishments of our fellow analytical chemists through the years, and the impact we have had on the profession. This article is a short history of the Division within the context of the parallel development of our profession and our science.