Hans-Gerd Janssen, Unilever Research and Development Vlaardingen, the Netherlands 

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Chromatography is an excellent and extremely powerful separation technique. It is fast, simple, sensitive and usually requires little sample.

Hans-Gerd Janssen, Unilever Research and Development Vlaardingen, the Netherlands 

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In order to separate two sample components during a chromatographic separation, there must be a difference in their retention behavior. All retention parameters are described and explained in this chapter and their effect is illustrated in animations.

Nico Vonk, Avans+, Breda, The Netherlands

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The efficiency of a column is affected by a number of variables:

Column length
Column diameter (open-tubular columns)
Particle size (packed columns)
Packing and coating quality
Linear velocity (flow)
Instrument quality (dead, void or hold-up volume)
Retention factor k

Various equations have been developed to describe the influence of these variables on the column efficiency:

1. The Van Deemter equation for packed GC columns
2. The Golay equation for capillary columns

Nico Vonk, Avans+, Breda, The Netherlands

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The analyte peak has a certain width, which becomes wider traveling further distances along the column after the injection. The chance of overlap will be much smaller with narrow peaks, so that even with small differences in retention there will be a complete, baseline separation.

Nico Vonk, Avans+, Breda, The Netherlands

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In the previous sections the effects of column and system parameters on the separation have been discussed. The separation result is not the only important parameter in practice. This chapter touches on a number of other parameters e.g. the analysis time and optimisation.

Nico Vonk, Avans+, Breda, The Netherlands

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A qualitative analysis involves the identification of a component by means of peak data on the chromatogram. The retention of a component is the result of a specific interaction of that component with the stationary phase and the mobile phase. Since the retention time is a specific property of a component, it may be used as a means to identify the component.

Nico Vonk, Avans+, Breda, The Netherlands

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Henk Lingeman, Free University, Free University, Netherlands

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A number of separation systems can be used to determine organic compounds in complex matrices. The most important techniques are LC, GC and CE. In order to develop an adequate analytical method / procedure, the combination of SP/ST, separation and the reaction/detection procedure is more critical than the separation mode itself. To choose the best option from the large number of possibilities you need clear guidelines. The most suitable method can be found by answering the questions given in the following tables. These questions are related to the physico-chemical properties of the analyte and of the matrix as well as the objectives of the overall method.

Nico Vonk, Avans+, Breda, The Netherlands

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This chapter shows a series of GC chromatograms with some common problems and their solutions.

Harold McNair, Virginia Tech, USA

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This chapter discusses the most frequently asked questions on GC practice.

Nico Vonk, Avans+, Breda, The Netherlands

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Considering the stringent requirements of the user and the sensitivity of the equipment, slight deviations can quickly lead to unacceptable chromatographic results. Thus, every GC user must be prepared to troubleshoot problems. This, in turn, requires an understanding of the entire analytical method, as well as the GC apparatus. Without this knowledge disturbances can set off a random and highly inefficient search for the source of the problem, e.g. randomly turning switches on and off, replacing parts which may or may not be defective, and generally interpreting the facts incorrectly. Obviously, a random, uninformed search is a waste of time, energy and money, making a structured search crucial in resolving GC problems.

Nico Vonk, Avans+, Breda, The Netherlands

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Gas Chromatography is a very complex and sensitive technique and is therefore sensitive to disturbances and has a high risk to have trouble. The demands on the instruments and columns are high in terms of sensitivity, accuracy, reproducibility. Trouble shooting is therefore a part of our job. To become a good – fast and efficient - trouble shooter, one must understand the separation itself as well as the instrument. A chaotic search for the problem can result in damaging the instrument, breaking or replacing parts without a plan and an wrong interpretation of the observed problems.

This chapter will help you to interpret the observations and bring structure in your troubleshooting efforts.

Nico Vonk, Avans+, Breda, The Netherlands

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Abstract The problems encountered in the gas system, the components of the carrier gas system, tubing, connectors, and detectors are listed and discussed in detail.

Detailed information about injection techniques for capillary GC are described in the chapter " Injection modes, Principles & Hardware - Injection principles of capillary GC".

Every column has a limited lifetime.
Good resolution can be completely ruined by a loss in efficiency of a damaged or dirty column, which can be the result of improper handling of the column.
 
Typical GC column problems are:

• Incorrect installation of the column (dead volume; wrong cut)
• Incorrect connecton to a splitter
• Leaking of column couplings
• Incorrect use of the column
• wrong polarity
• wrong temp settings
• Incorrect oven temperature Wrong storage of the column
• Overloading by mass or volume
• Contamination of the column
• Incorrect carrier gas velocity 
• Breakage 
• Ageing (oxidation, pollution, bleeding)

Nico Vonk, Avans+, Breda, The Netherlands

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Possible sources for detector problems are discussed, examples of effects are given as well as how to prevent and solve problems.

Possible GC detector problem areas are:

• Detector response (R)
• Detector sensitivity (S)
• Linear dynamic range (LDR)
• Noise level (N)
• Instrumental band broadening 

A good detector for the gas chromatography should comply with a number of requirements:

• Universal or selective. Dependent on the application, a detector should detect all chemical components which emerge from the column or should detect only a specific group. 
• Sensitivity. Small amounts of sample (nanogram or picogram amounts) should be 'observed'. 
• Accurate. Deviant signals, given by the detector, should stay within acceptable limits. 
• Reproducibility. A detector should give a similar signal if two identical components in the same amounts pass through the detector independent of the time of measurement. 
• Speed. Components pass, after they leave the column, the detector rapidly. This should not cause any problems regarding the accuracy and the separation. 
• Reliability. One should be able to rely on a detector.

Kory Kelly, Phenomenex, U.S.A 

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 “Why won’t my FID light or stay lit?”

This problem is much more common when using newer instruments that have an EPC (electronic pressure control) device because these utilize “smart software,” which tries to alert you of potential system problems.

The instrument determines that it has succeeded in lighting the flame when the FID signal (pA) stays above the offset value (usually 2-3pA). If unexpected signal variations occur that could indicate a leak or other FID related problems, the instrument will shut itself down and alert you of the problem. In such cases, the flame may initially light, however the instrument will shut off the detector after the problem is detected.

Nico Vonk, Avans+, Breda, The Netherlands 

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This chapter shows a series of GC chromatograms with some common problems and their solutions.

Tailing.You see the result of two manual split injections of some methane (natural gas) on a standard apolar column.

Base line driftA sample of high boiling analytes was separated on a thin film apolar column, in combination with on-column injection and temperature programming.

Nico Vonk, Avans+, Breda, The Netherlands

Abstract This chapter shows a series of GC chromatograms with some common problems and their solutions.

LevelBasic

Tailing

You see the result of two manual split injections of some methane (natural gas) on a standard apolar column.

What could be the reason for the tailing of the peak in result A? Answer?

Base line drift

A sample of high boiling analytes was separated on a thin film apolar column, in combination with on-column injection and temperature programming.

Mohamed Adahchour, Omegam Laboratoria B.V., the Netherlands

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Abstract In all the literature published so far, very impressive contour and colour plots have been shown demonstrating the power of GC×GC. These plots not only show the high separation power of GC×GC at enhanced sensitivities, but also exhibit the clustering and grouping of chemically related compounds, a valuable help in identification of separated components. Nevertheless, it is important not to overlook the peak shapes of individual peaks in GC×GC chromatograms. As is the case in 1D-GC, observing peak shapes in the chromatogram can help in understanding the separation phenomena under consideration, in optimizing the separation and in troubleshooting.

KeywordsThis article was written in cooperation with Jan Beens.

Jan Beens, Vrije Universiteit Amsterdam, the Netherlands

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Multidimensional gas chromatography (MDGC) can be defined as any GC separation process carried out with an integrated (switching) system of two or more columns. Multidimensional systems in which the columns are combined by column switching can optimize the separation capabilities of the different columns. There are numerous possibilities for MDGC ranging from simple two column arrangements, to complex systems involving several columns and precisely timed switching facilities. However MDGC is not a widely utilized technique in general, because it is thought to be complex in operation. Nevertheless there are practical situations, which can benefit from the use of combined columns and some of these will be discussed.

Jan Beens, Vrije Universiteit Amsterdam, the Netherlands

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One of the most sophisticated forms of multidimensional GC is comprehensive two-dimensional GC (GC×GC). Separation and analysis in two dimensions is much more powerful than in one. A retention plane has much more peak capacity than a retention line and so can accommodate much more complex mixtures. Component identification is potentially more reliable because each substance has two identifying retention measures rather than one. Separations are likely to be more structured in two dimensions, leading to recognizable patterns characteristic to the mixture source.

Mohamed Adahchour, Omegam Laboratoria B.V., the Netherlands

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GCxGC was introduced in 1991 by John B. Philips and has been rapidly gaining interest over the last decade, especially during the past five years. There are several reasons for that. The GCxGC-hardware (which was initially very fragile) has become much more robust and reliable, and dedicated software for processing the GCxGC-data has become available. In addition, an increasing number of applications has been published in the scientific journals which greatly simplify method development.

Still, there are currently many conventional one-dimensional GC applications in use which can be improved by ‘adding a second dimension’.


KeywordsThis article was written in cooperation with Jan Beens.

Jan Beens, Vrije Universiteit Amsterdam, the Netherlands

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Nomenclature and conventions for further use in GCxGC technique

Comprehensive Two-Dimensional Gas Chromatography, nomenclature, conventions

Henk Lingeman, Free University, Free University, Netherlands

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A number of separation systems can be used to determine organic compounds in complex matrices. The most important techniques are LC, GC and CE. In order to develop an adequate analytical method / procedure, the combination of SP/ST, separation and the reaction/detection procedure is more critical than the separation mode itself. To choose the best option from the large number of possibilities you need clear guidelines. The most suitable method can be found by answering the questions given in the following tables. These questions are related to the physico-chemical properties of the analyte and of the matrix as well as the objectives of the overall method.

Henk Lingeman, Free University, Free University, Netherlands

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Sample treatment (ST) is the bottleneck in most chromatographic / electrophoretic separations.
The main ST objectives discussed in this Topic are:

1. Learn technologies and techniques:
· How do they work,
· What are the applications,
· What are the advantages and limitations,
2. Possibilities to improve laboratory operations:
· Cost (labour intensive),
· Errors (accuracy, precision),
· Time,
3. Productivity issues:
· Automation,
· Parallel versus serial processing,
· On-line versus off-line,
4. Help to make the transition from SOP’s to (new) techniques a successful one:
· Criteria for choosing sample treatment techniques.

Sampling and sample preparation in analytical chemistry will be presented in a practical way to provide the analytical chemist with the necessary tools to determine low- and high-molecular-weights compounds in a variety of matrices using chromatographic / electrophoretic, spectroscopic or immunological methods.
Method development procedures will be based on the physico-chemical properties of the analyte(s) and the matrices in which these compounds are present

This chapter provides a general introduction. The upcoming chapters will provide the necessary detail.

Henk Lingeman, Free University, Free University, Netherlands

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A (bio-)analytical procedure is used to obtain qualitative and/or quantitative information on a sample. In this “Introduction” section an overview will be given on the different stages of the process emphasizing on sampling and sample preparation (SP).