This short module covers the history of gas chromatography (GC) and introduces the chromatographic process and the major components of a GC instrument. The technique is compared and contrasted with other analytical techniques such as high performance liquid chromatography (HPLC). The terms and appearance of a typical chromatogram are also explained. We will outline the fundamental basis for separation in GC, and indicate the major advantages of GC and the application areas in which it is used.

At the end of this unit you will be able to identify analytes suitable for GC analysis from physicochemical data, describe the function of the various components of a gas chromatograph, explain the fundamental basis of separation in GC in terms of solubility and vapor pressure of analytes, and recognize when the use of GC might be applicable to solving analytical problems.

Topics include:

• Why is chromatography so important?
• The basics of how gas chromatography works
• Origins of gas chromatography
• Why choose gas chromatography
• Sample types suitable for gas chromatography
• Gas chromatography separation mechanism
• The gas chromatograph
• The chromatogram
• GC advantages and disadvantages
• Typical GC applications

When performing an analysis, we follow a written method. This contains all the instructions and settings by which the analysis is performed. For even a simple method, this requires a lot of knowledge and experience. In this module an experienced analyst walks you through all parts of a typical method, explaining all the important areas that require understanding and planning.

Topics include:

• GC method review and workload planning

Gas cylinders are the most common source of gases supplying a gas chromatograph. This module will present an overview of gas cylinders, regulators, and gas supplies to the GC.

Topics include:

• Gas cylinders
• Gas requirements
• Gas purity grades
• Regulators
• Leak checking regulators
• Troubleshooting regulators 

Hydrogen generators offer a cheap, reliable, and safe source of hydrogen for use with GC. This module will look at the reasons why we would need to use hydrogen generators, how hydrogen is generated, and how to select the correct generator size. As well as discussing some of the common maintenance points for these pieces of instrumentation.

Topics include:

• Why we need hydrogen generators
• How hydrogen generators work
• Essential generator maintenance
• Hydrogen generator maintenance schedule
• Choosing a generator size

Gas filters are placed in the gas lines supplying the GC to ensure a suitable purity of gas is delivered to the instrument. This module will introduce the reason for using gas filters, types of gas filter design, and correct installation and operation.

Topics include:

• Filter Designs
• Filter specifications
• Filter Types - moisture, hydrocarbon, oxygen, and combination
• Order of filter installation
• Filter operating conditions
• Installing cartridge GC gas filters

The most common inlet for capillary GC is known as the split/splitless inlet, which as the name suggests, can be operated in two modes, either split or splitless. This module will introduce the main components and gas flows required to operate this inlet. As well as introducing the differences between split and splitless injection.  

Topics include:

• Overview of the split/splitless inlet
• Split injection
• Split/splitless inlet - components and settings
• Liners for split/splitless injection
• Septa problems 

Ferrules are the small components which provide a gas-tight seal between the column and the inlet and detector fittings. These tiny items are often overlooked, but are essential in preventing leaks.

Topics include:

• Ferrule design
• Ferrule size
• Ferrule material

Practical GC tips and tricks to help improve your analyses. The benefits of using gas saver mode to reduce carrier gas consumption is the focus of this Quick Guide.

Within the gas chromatograph system, the column sits in an oven. We can accurately control the temperature of this oven, and the value we select controls retention time and peak resolution. This module will introduce the types of GC method which are run in elation to temperature - isothermal and temperature programmed methods - and how they are selected for a particular analysis.

Topics include:

• Isothermal methods
• Temperature programmed (ramp) methods

The analytical column is where the separation is actually performed. This module will introduce capillary GC columns, the most common type used for GC applications. Providing guidelines on how to prepare, install, and condition a GC column for analysis.

Topics include:

• Capillary wall coated open tubular (WCOT) GC Columns
• Column installation and conditioning

This module will provide a brief overview of GC detectors, their function, and the main characteristics that are important when considering a GC detector; such as, sensitivity, linearity, noise, and minimum detectability.

Topics include:

• GC detectors overview
• GC detectors characteristics

The flame ionization detector (FID) is the most widely used GC detector and was invented specifically for GC applications. Its high sensitivity and linear range for carbon containing compounds make it very popular in organic analyses. This module comprehensively details the working principles of this detector, giving you the knowledge and understanding to operate and optimize the detector for your analyses.

Topics include:

• The flame ionization detector (FID)
• Operating and optimizing
• Uses and performance

As part of that sequence, we perform additional injections which allow us to verify that the entire GC system is working correctly, this is system suitability. The actual parameters assessed during system suitability vary between companies, the type of analysis we are performing, and the method/compounds being used. This module outlines some of the common system suitability tests we see in GC analyses.

Topics include:

• System precision
• Retention time check
• Chromatographic profile
• Sensitivity check
• Resolution check
• Recovery check (quality control)
• Standard verification
• Calibration verification
• Peak shape verification

A step by step guide to setting up a GC instrument. From checking the cylinders, dismantling the inlet, to correctly installing a column and lighting an FID. All before shutting the instrument down correctly.

This practical module uses video filmed on a GC instrument in the lab to ensure that you get the most realistic walk through of the instrument; allowing you to correctly setup your instrument every time to get the most from it and decrease down-time by avoiding common mistakes. 

Topics include:

• Cylinders, regulators, and generators
• Gas filters
• Inlet
• Autosampler
• Column installation
• Electronic pneumatic control (EPC) setup
• Flame ionization detector (FID)
• Switching off

The correct setup of any instrument, method, or process in the lab is crucial to it performing to the best of its ability. Autosamplers are an invaluable part of chromatographic instrumentation as they are reliable and accurate and remove many of the errors associated with manual injection. However, we still need to take the time to set them up correctly. Over four short videos we will look at how to correctly setup a GC autosampler. We will consider parameters that can be changed by the user, including the syringe and needle, needle wash routines, vials, injection speed, viscosity delay, and dwell time.

Correctly setup your GC every time and achieve the optimum results with this handy checklist.

A standard is a solution of exact and known concentration that we measure to calibrate the response of our instrument/method. Preparing standards for GC creates challenges which risk introducing accuracy errors into our standards due to issues with volatility, concentration, and the complexity of mixtures that are being analyzed. This quick guide details the optimum technique for successfully preparing GC standards.

Topics include:

• Practical considerations
• Preparing known and exact concentrations
• Measure by volume or measure by weight?
• Density and relative density
• Preparing low concentrations
• Choosing a suitable solvent
• Practical technique
• Preparing volume-in-volume standards
• Preparing weight-in-volume standards
• Preparing weight-in-weight standards
• Stock solution
• Worked example

Internal standards are an approach we use to improve method precision. Although our aim during method development is to always achieve methods with the best precision we can, there are certain applications that fundamentally cannot deliver good precision. This module will consider all of the practicalities of selecting and using internal standards correctly.

Topics include:

• How do internal standards work?
• When not to use internal standards
• Choosing an internal standard
• Selecting the concentration
• Evaluating an internal standard
• Isotopically labelled standards for mass spectrometry

Learn how to carry out batch integration. We will provide you with a generic approach that can be applied to your data.

Integration of chromatographic peaks (determination of height, area, and retention time) is the first and most important step in the data analysis of HPLC and GC methods. This information is used for all subsequent calculations, including construction of calibration curves and calculation of unknown concentrations. This first installment will define what chromatographic peak integration is and the primary chromatography data system (CDS) settings which are required.

This article was written by Dr. Dawn Watson (Technical Expert, Crawford Scientific).