Method for reducing the ambiguity of comprehensive two-dimensional chromatography retention times

Comprehensive two-dimensional chromatography generates a two-dimensional chromatogram from a one-dimensional signal array. This process can only be done unambiguously when the range of secondary retention times is less than the modulation period. However, complex samples often produce wider ranges of secondary retention times. Peaks with retention times that exceed the modulation period are said to be wrapped-around . A simple algorithm has been developed that determines absolute retention times when wrap-around occurs. A sample is first analyzed under standard modulation conditions and then re-analyzed with a modulation period that is increased by an integer fraction of the original modulation period. Retention shifts along the secondary axis are used to determine absolute retention times. A theoretical analysis has been performed to optimize the implementation conditions and characterize the technique limitations. The efficacy of this algorithm has been tested through a series of isothermal GC x GC separations. This method has been found to be particularly useful during the initial stages of method development

Comprehensive two-dimensional gas chromatography with a simple fluidic modulator

The use of a comprehensive two dimensional gas chromatography (GC) with a simple in-line fluidic modulator to demonstrate modulator performance is discussed. The in-line fluidic modulator produces 2-D separations that are similar to those produced by previously described differential flow modulators. The in-line fluidic modulator maintains optimal performance over a wider range of differential flow ratios than the dual-loop fluidic modulator. The main challenge of developing a differential flow modulator is to generate a device that can effectively combine the primary effluent and the auxiliary flow without additional peak broadening and without diminishing the primary separation. The simplicity and the low resource requirement of the modulation strategy decreases the difficulty of implementing comprehensive 2-D gas chromatography and can potentially lead to the broader adoption of the GC×GC technique

Comprehensive two-dimensional gas chromatography analysis of high-ethanol containing motor fuels

A comprehensive 2-D GC (GC x GC) instrument equipped with a flow-switching modulator was used to determine the concentration of ethanol and eight other alcohols in a retail pump sample of E85 fuel. E85 is a mixture of ethanol and gasoline where the ethanol concentration can range from 70 to 85 vol%. The increased peak capacity and selectivity generated by GC x GC analysis allowed the alcohols to be fully resolved from the gasoline hydrocarbons. GC x GC analysis was compared to the performance obtained with the standard analytical method for determining ethanol in fuel ethanol (ASTM D5501) and the standard method for determining oxygenate concentrations in gasoline (ASTM D4815). The GC x GC analysis required 14 min while the combined ASTM D5501 and ASTM D4815 analyses required more than 60 min. The ethanol concentration obtained by GC x GC was in excellent agreement with the value obtained by the D5501 method. Poorer agreement was observed between the GC x GC and D4815 concentrations for the other alcohols present in E85. In all cases, the differences could be attributed to deficiencies in the D4815 method that led to coelutions between the alcohols and gasoline hydrocarbons

Microfluidic Deans Switch for Comprehensive Two-Dimensional Gas Chromatography

A microfluidic Deans switch was used as a comprehensive two-dimensional gas chromatography (GCxGC) modulator. The simplicity and wide temperature range of the Deans switch make it a promising alternative to existing modulation techniques. However, the Deans switch is a low duty cycle modulator; that is, it samples only a small portion of the primary column effluent. Like all low duty cycle modulators, the Deans switch produces inconsistent transfer of components from the primary to the secondary column if the primary peaks are undersampled. Theoretical simulations and experimental studies show that the relative standard deviation (RSD) of the fraction of material transferred from the primary column to the secondary column is less than 1% if the modulation ratio is greater than 2.5. But the RSDs increase rapidly as the modulation ratio is decreased below 2.5. Deans switch GCxGC was validated by analyzing the aromatic content of gasoline. A fast analysis (\u3c10 min) produced narrow primary peaks and a modulation ratio of 1.7. The quantitative results were in good agreement with results obtained with differential flow modulation GCxGC and GC/MS, but the RSDs of single-component levels were approximately three times greater. The Deans switch modulator was also used for a slower gasoline analysis (33 min run time) that produced modulation ratios near 5. In this case, the quantitative results and RSDs were in excellent agreement with the differential flow GCxGC and GC/MS results. These studies demonstrate that a Deans switch can be an effective modulator provided that modulation ratios greater than approximately 2.5 are employed

Comprehensive two-dimensional gas chromatography for the separation of fatty acids in milk

Comprehensive two-dimensional gas chromatography (GC x GC) is a recent technique, rapidly gaining importance for the analysis of complex samples. Here, we evaluate the potential of GC x GC for the analysis of the fatty acid profile of milk from dairy cows fed either a control diet or the control diet supplemented with marine algae. Fatty acids were separated using two column combinations, a nonpolar/polar arrangement and a polar/nonpolar arrangement. Due to the difference in separation mechanism of the two columns, GC x GC resulted in an improved separation compared with analysis on the same column set without the use of the modulator. Displaying the peaks in a 2-D contour plot showed a well-ordered structure of fatty acids according to their number of carbon atoms and degree of unsaturation, facilitating identification of known and unknown compounds. Based on these relations, identification of carbon number and degree of unsaturation of several 22-fatty acids was possible. The large difference between the 22-fatty acids from milk fat of cows fed the control and the marine algae-containing diet suggest that rumen hydrogenation of 22:6 n-3 results in a similar complex profile of hydrogenation intermediates as observed for 18:2 n-6 and 18:3 n-3. In conclusion, this experiment suggests GC x GC to be a powerful technique for the analysis of fatty acids. Nevertheless, further research on the optimization of GC x GC is needed to increase separation of trans- and cis-18:1 isomers, which may require a longer and/or more selective 1 D column

Trends in data processing of comprehensive two-dimensional chromatography: state of the art

The operation of advanced chromatographic systems, namely comprehensive two-dimensional (2D) chromatography coupled to multidimensional detectors, allows achieving a great deal of data that need special care to be processed in order to characterize and quantify as much as possible the analytes under study. The aim of this review is to identify the main trends, research needs and gaps on the techniques for data processing of multidimensional data sets obtained from comprehensive 2D chromatography. The following topics have been identified as the most promising for new developments in the near future: data acquisition and handling, peak detection and quantification, measurement of overlapping of 2D peaks, and data analysis software for 2D chromatography. The rational supporting most of the data processing techniques is based on the generalization of one-dimensional (1D) chromatography although algorithms, such as the inverted watershed algorithm, use the 2D chromatographic data as such. However, for processing more complex N-way data there is a need for using more sophisticated techniques. Apart from using other concepts from 1D chromatography, which have not been tested for 2D chromatography, there is still room for new improvements and developments in algorithms and software for dealing with 2D comprehensive chromatographic data.publishe