Biomedical subjects

James Harynuk

Publications and source records attributed to James Harynuk.

9 recordsLinked to original sources

PubMed2006

Modulation ratio in comprehensive two-dimensional gas chromatography.

Comprehensive two-dimensional chromatography employs a serially coupled two-column arrangement where effluent from the first column is collected or sampled and then introduced to the second column according to a chosen modulation period. This is effected by use of a modulator at or near the column junction. One of the considerations in applying the technique is the period of the modulator, which determines the sampling duration of the first column effluent. Here, we propose that the sampling rate can be most effectively described by a new term, called the modulation ratio (MR). This is defined as the ratio of 4 times the first column peak standard deviation (4sigma) divided by the modulation period (PM) or 1.6985 times the half-height width of the peak (wh): MR = 4sigma/PM = wb/PM = (wh x 1.6985)/PM. The 4sigma value is more commonly recognized as the peak base width (wb). The use of 4sigma as the numerator is preferred to simply sigma because when the PM value used for an experiment is equal to sigma, then the MR value is calculated to be 4, implying that the primary peak will be modulated approximately 4 times as is normally recommended for a comprehensive multidimensional separation. The less well-defined term of modulation number (NM) has been previously used and proposed as the number of modulations per peak and, therefore, is intended to convey the manner in which the primary column peak is sampled; this is a subjective and not well-characterized value. The use of MR should provide users with a meaningful and strictly defined value when reporting experimental conditions. The utility of MR is demonstrated through a mathematical model of the modulation process for both Gaussian and tailing peaks, supported by an experimental study of the modulation ratio. It is shown that for the analysis of trace compounds where precise quantitative measurements are being made, the experiment should be conducted with an MR of at least 3. Conversely, for semiquantitative methods or the analysis of major components, an MR of approximately 1.5 should suffice.

Journal Article↗

PubMed2006

Fast GCxGC with short primary columns.

A novel approach to comprehensive two-dimensional gas chromatography (GCxGC) separations is presented, which operates in a new region of the "GCxGC optimization pyramid". The technique relies on the use of short primary columns to decrease elution temperatures (Te) of analytes from the primary column, with a Te reduction of up to 50 degrees C illustrated. This in turn has implications that will expand the areas where GCxGC can be used, as decreased elution temperatures will allow GCxGC to be applied to mixtures of less volatile compounds or permit the use of less thermally stable stationary phases in the column ensemble. As well, it will allow GCxGC to be applied to thermally labile compounds through a reduction in elution temperature. With short primary columns, resolution and efficiency in the first dimension is sacrificed, but speed is gained; however, the second column in GCxGC provides additional resolution and separation of compounds of differing chemical properties. Thus, it is possible to recover some of the analytical separation power of the system to provide resolution of target analytes from sample impurities. As an example, a case study using short primary columns for the separation of natural pyrethrins, which degrade above 200 degrees C, is described. Even with the sacrifices of overall separation power that are made, there is still sufficient resolution available to separate the six natural pyrethrins from each other and the complex chrysanthemum extract matrix. The use of cold-on-column injection, a short primary column, and a high carrier gas flow rate allow the pyrethrins to be eluted below 200 degrees C, with separation in 17 min and complete resolution from sample matrix.

Journal Article↗

PubMed2005

Comparison of comprehensive two-dimensional gas chromatography in conventional and stop-flow modes.

A new mode of operation for comprehensive two-dimensional gas chromatography (GC x GC), stop-flow GC x GC, was introduced recently. In this technique, the flow in the primary column is stopped for a brief period of time during each modulation cycle, allowing for a secondary separation time that is longer than would otherwise be permitted by the modulation period in conventional GC x GC. This allows the modulation period and the secondary separation time to become independent variables, and greatly increases the flexibility of the system. In this paper, separations obtained under similar conditions for both conventional and stop-flow GC x GC are presented, demonstrating the advantages that stop-flow GC x GC provides over conventional GC x GC for certain separations.

Benzene Derivatives↗

PubMed2005

Effect of first-dimension column film thickness on comprehensive two-dimensional gas chromatographic separation.

In comprehensive two-dimensional gas chromatography (GC x GC), samples experience two-dimensional separation implemented by a modulator which helps preserve the first-dimension separation and facilitates the second-dimension separation by periodically collecting, focusing and launching the material from the primary column onto the secondary column with a different stationary phase. Column overloading in GC x GC is a considerable problem, aggravated by the fact that two columns are involved. Broad first-dimension peaks of an analyte help produce smaller fractions of the analyte in the second-dimension, reducing the chance of secondary column overloading. One of the means to generate broad peaks in the first-dimension is to use thick film primary columns. A series of primary columns of various film thickness were tested in the study, and the results indicate that when other conditions are kept constant, 1 microm film columns often provide better resolution in both first and second-dimension but at the expense of a much longer separation time; 0.1 microm is clearly inadequate for GC x GC separation; 0.5 and 0.25 microm film columns seem to be the best compromises.

Alkanes↗

PubMed2005

Flow model for coupled-column gas chromatography systems.

One of the challenges in performing comprehensive two-dimensional gas chromatographic separations is being able to predict the average linear velocities of the carrier gas in the two columns, especially when they have different diameters. The problem is compounded for loop-type modulators, where two thermal trapping zones that switch from hot to cold and back simultaneously are separated by a delay loop. If the linear velocity in the loop is not tuned to the length of the loop and the modulation period, the dual-stage modulation may cease to work properly. A model has been developed that calculates the flow rates in the columns and predicts appropriate delay loop dimensions for a given set-up. Additionally, the model determines the pressure ramp that needs to be used in order to maintain constant average linear velocity within the modulator loop throughout the course of the separation.

Chromatography, Gas↗

PubMed2005

Overloading of the second-dimension column in comprehensive two-dimensional gas chromatography.

Comprehensive two-dimensional gas chromatography (GC x GC) is based on a coupling of two GC columns of different characteristics by means of a device that allows portions of the effluent from the primary column to be injected onto the second dimension column for an additional separation. The time available for the separation in the second-dimension column is very short. Thus, this separation should be very efficient. The vast majority of GC x GC practitioners use very narrow bore columns for the second dimension. While this approach is justified in principle, if peaks in the second dimension overload this column, its peak capacity is severely reduced. A series of second-dimension columns of varying internal diameters, but similar phase ratios, were used to study these effects. The results indicate that 250 microm columns often provide comparable second dimension peak widths to 100 microm columns, while at the same time being less prone to overloading, indicating that they may often be a better choice than smaller diameter columns in the second dimension of GC x GC systems.

Chromatography, Gas↗

PubMed2004

Comprehensive two-dimensional gas chromatography in stop-flow mode.

The theory and proof of concept of a new mode of operation for comprehensive two-dimensional gas chromatography (GC x GC) is presented. In current GC x GC interface designs, the modulation period defines the separation time allowed in the second dimension. In the stop-flow GC x GC mode, flow in the primary column is periodically stopped for brief periods of time. Consequently, the modulation period for the primary column and the amount of time available for second dimension separation become independent variables. This allows the separations in both the primary and secondary dimensions of the GC x GC system to be carried out under more optimised conditions, allowing extended periods of time for second dimension separations without sacrificing the separation in the primary dimension. This new technique has the potential to offer increased separation power and overall resolution as it is further developed.

Journal Article↗

PubMed2004

The evolution of comprehensive two-dimensional gas chromatography (GC x GC).

For a technology little over a decade old, comprehensive two-dimensional gas chromatography (GC x GC) has quickly reached the status of one of the most powerful analytical tools for volatile organic compounds. At the heart of any GC x GC system is an interface, which physically connects the primary and the secondary columns and acts to preserve the separation obtained in the first dimension (first column) while allowing additional separation in the second dimension. The paper presents a review of the technology, including fundamental principles of the technique, data processing and interpretation and a timeline of inventive contributions to interface design. In addition, applications of the technique are presented, with a more detailed discussion of selected examples.

Journal Article↗

PubMed2003

New liquid nitrogen cryogenic modulator for comprehensive two-dimensional gas chromatography.

A new liquid nitrogen (LN2) jet-based thermal modulator for performing comprehensive two-dimensional (2D) gas chromatographic (GC x GC) separations has been designed and constructed. Temperature measurements of the trapping zone, a segment of uncoated fused silica capillary, show that it can be cooled to -196 degrees C in about 300 ms. A film of liquid nitrogen develops on the outside of the trapping capillary even when the oven temperature is in excess of 200 degrees C. Compounds as volatile as propane can be trapped by the modulator and held for periods of at least 1 min without breakthrough. The peak widths for n-alkanes are on the order of 80 ms at half height after passing through an 80cm second dimension column. Repeated analysis of gasoline demonstrated excellent run-to-run reproducibility of the system.

Chromatography, Gas↗