Stuart P. Cram

Splitless sampling for capillary-column gas chromatography

Abstract The experimental aspects of the “Grob splitless” sampling technique are discussed in terms of the sampling time, purge activation time, solvent type, sample size, column temperature, injector temperature and column flow-rate. Guidelines are developed for using and simplifying splitless sampling. Optimized experimental parameters are given from the results of optimization by simplex. Precision data for retention times and peak areas are shown to be 0.05 and 1% respectively, for an automated splitless capillary system.

Instrumental contributions to band broadening in gas chromatography : I. Development of a model

Abstract The principles of superposition of the first and second moments are applied to a model gas chromatographic system in order to develop the equations necessary to describe the instrumental contributions to band broadening. The total first moment is obtained from an equation which gives a straight line when the pressure drop across a capillary column is small. The expression for the time-based second moment is given by a hyperbola with an inverse dependence on the carrier gas flow-rate. For the volume-based second moment, the hyperbolic equation predicts a direct dependence on the carrier gas flow-rate. For systems in which the mixing volumes and the detector-electrometer time constants are small, the equations are linearized to give the same slopes as the asymptotes of the hyperbola and nearly the same intercepts.

Effects of digital filters on chromatographic signals

Abstract Digital filters are quantitatively evaluated for their effects on chromatographic digital data. Changes in peak-shape parameters for Gaussian and asymmetrical chromatographic peaks are described by the error levels introduced. Reductions in baseline noise are discussed in terms of reducing the amplitude and the frequency response. An example of the practical considerations and trade-offs in implementing digital filters in a microprocessor-based data system is presented, so as to minimize peak distortion, and enhance peak detection and signal-to-noise ratio.

Instrumental contributions to band broadening in gas chromatography : II. Experimental evaluation

Abstract A precision gas chromatograph under the control of a digital data acquisition and control system is described which was designed to evaluate the band broadening contributions of a model system. The zeroth, first, and second moments of a non-sorbed peak are reported and the band-broadening contributions from the sample, mixing volumes, effective detector volume, and electronic time constants have been measured. Excellent agreement was found between the predicted values and the experimental results.