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Achieving Faster GC |
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Achieving Faster GC
By Hans-Gerd Janssen, Ph.D., Unilever Food and Health Research Institute
Numerous articles have been published in the scientific literature regarding faster methods for gas chromatography (GC), yet confusion remains on how best to speed up separations. A significant source of this confusion is the fact that authors often neglect to define the terms "analysis speed" and "analysis time". Does the analysis time include sample preparation time? Or is it just the run time between injection and last time point on the chromatogram? Does it include reconditioning, paperwork, or interpretation? Is it the instrument time or the operator time? Numerous questions often are left unanswered and it is these questions that are to blame for the chaos in fast GC. Here I will try to clarify this confusion.
A chromatographic analysis consists of four steps: sample preparation, chromatographic separation, detection, and data interpretation. Clearly these steps are related and can not be considered in isolation. Changes in the sample preparation might affect the performance of the separation, and more sensitive and selective detectors may allow simpler sample preparation. It is these very strong interactions among the four steps that make it very difficult to describe the consequence of a change somewhere in the procedure on the total analysis time.
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Quality Control in Metabolomics |
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Quality Control in Metabolomics
Dr. Oliver Fiehn, UC Davis Genome Center
Comprehensive analysis of small molecule metabolites (30-1500 Da) is a challenging task for quality control. Metabolites are found in very different concentrations in complex biological matrices, from which they have to be extracted without compromising the structural integrity and relative abundances. There are metabolites which are transformed extremely rapidly if enzymatic activity is not stopped completely at the time of sample collection, such as the ratio of the energy metabolites ATP to ADP. Similarly, redox carriers such as NADH and NADPH are very sensitive to oxidative degradation during sample preparation. Consequently, quality control in metabolomics means more than just taking care of chromatographic or mass spectrometry parameters. Quality control is an attitude towards gaining reliable data, rather than an automatic procedure implemented in instrument software.
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Using Guard Columns and Retention Gaps in GC (Part 2) |
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Using Guard Columns and Retention Gaps in GC (Part 2)
Jaap de Zeeuw, International GC Consumables Specialist, Restek Corporation
Guard columns and retention gaps are used widely in gas chromatography (GC). Many users have difficulty understanding the difference between these two products, even though there is a significant difference in application. In Part 1 of this article we reviewed retention gaps, which mainly are used for focusing the sample components when introducing a large (liquid) sample directly onto the column. In contrast, guard columns are used to protect the analytical column from contamination. Guard columns and retention gaps both must be coupled to the analytical column, and this connection introduces a potential point of risk. A new approach is to integrate the retention gap directly into the analytical column tubing. By applying a "segment" coating technology the stationary phase can be deposited only in a certain part of the column allowing a deactivated section at the beginning. Column coupling is not required and maintenance is greatly simplified. Here we will review guard columns and discuss the new segment coating technology.
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Using Guard Columns and Retention Gaps in GC (Part 1) |
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Using Guard Columns and
Retention Gaps in GC (Part 1)
Jaap de Zeeuw, International GC Consumables Specialist, Restek Corporation
Guard columns and retention gaps are used widely in gas chromatography (GC). Many users have difficulty understanding the difference between these two products, even though there is a significant difference in application. Retention gaps mainly are used for focusing the sample components when introducing a large (liquid) sample directly onto the column. Guard columns are used to protect the analytical column from contamination. When using a retention gap system, the retention gap will also act as a guard column, but its primary function is to create a focusing effect.
Guard columns and retention gaps both must be coupled to the analytical column, and this connection introduces a potential point of risk. A new approach is to integrate the retention gap directly into the analytical column. By applying a “segment” coating technology the stationary phase can be deposited in a certain part of the column allowing a deactivated section at the beginning. Column coupling is not required and maintenance is greatly simplified. In Part 1 of this article we will explore retention gaps and build a foundation for a comparison to guard columns. In Part 2, we will review guard columns and discuss the new segment coating technology.
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Retention Cross-over Phenomenon in Gas Chromatography |
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Retention Cross-over Phenomenon in Gas Chromatography — Can the Mystery be Revealed?
Werner Engewald, Ph.D., Professor Emeritus, University of Leipzig, Institute of Analytical Chemistry, Leipzig, Germany;
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Have you ever faced changes in elution order after modifying the column temperature or the heating rate in the temperature program of the GC analysis of complex samples? This so-called cross-over phenomenon, which can lead to problems in peak identification, has been a well-known mystery in GC for decades.1 But, so far, the physico-chemical background is still not well understood.
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