FAQs


What is Gas Chromatography?
How does Gas Chromatography work?
Why should I use valves?
When and Why should I work with Peak Results?

GC FAQs

What is Gas Chromatography?
Gas Chromatography is a separation science in which gas or volatile liquid mixtures are separated into individual chemical components which can be detected and quantified. Translated from Greek, chromatography literally means “color writing”. One of the earliest experiments in modern separation sciences, performed by a Russian botanist named Mikhail Tswett, resulted in individual bands of color for each component separated – hence the name: color writing or chromatography. Even though that name is a misnomer, today, it is still used as the designation for this separation science.

Back to top

How does Gas Chromatography work?

Individual chemical components separate at different rates as they transfer between a mobile gas phase (called a carrier gas) and a non-moving solid or liquid phase (called a stationary phase). The Stationary phases are contained in “columns”. Columns can consist of metal tubes packed with solids or fused silica capillaries coated with films (WCOT – wall-coated open tubular capillary) or coated with solids (PLOT – porous-layer open tubular capillary).

There are two types of separations that occur: Adsorption Gas Chromatography, in which molecules adsorb onto and desorb from a solid phase; and Partition Gas Chromatography, in which molecules diffuse into and out of a liquid phase based on the boiling point properties of the individual chemical components or the chemical affinity of the liquid phase for individual chemical components. Size Exclusion Separations are a specific sub-set of Partition Gas Chromatography. In this case, smaller molecules will travel more quickly through porous solid substrates like molecular sieves or man-made polymers than larger molecules.

In addition to the choice of column, parameters which can affect separations include the type and flow rate of the carrier gas, the length and diameter of the column, the temperature of the system, and whether and how temperature and/or flow programming is being used.

Back to top

Why should I use valves?

Gases and volatile liquids (those samples which are only liquid while under greater than ambient pressure or when chilled significantly below ambient temperature) are compressible. It is generally desirable to inject exactly the same amount of sample each time in order to make quantitation possible. It is very difficult to inject exactly the same amount of a compressible sample using a gas-tight syringe.  By using a valve, the same amount of sample may be injected every time, independent of the operator. Valves may also be used for column selection, for detector selection, for reversing flows through columns, or for obtaining more separations from more columns in a single injection cycle. Using valves, when indicated, can increase efficiency, accuracy, repeatability, and reproducibility and reduce the number of GC’s required for complete sample analysis.

Back to top

When and Why should I work with Peak Results?

If you know what you need to analyze but don’t know how to configure your gas chromatograph to perform the analysis, call and consult with us about Configuration Services. Even if you know how to configure the system, but simply do not have the time or manpower to perform the configuration or method development, let us know your design parameters, or let us propose an alternative. In either case, we will provide you with an quotation describing the scope of work which we propose to perform and the design elements which we will use. We will delineate the components which will be identified and the advantages and limitations of the proposed configuration.

We also provide Method Development Services to assist you in optimizing analyses which you may already have in your laboratory. Optimization may mean increasing separation resolution, decreasing analysis cycle times, helping you to obtain lower detection capability, changing integration parameters, or recalibrating. We want to help make your GC systems easier to operate and maintain.

Consulting and Training Services are also offered. We can evaluate your exsting GC operations and make suggestions for improvements, or assist you in planning new or remodeled facilities. Also, we offer training courses tailored to meet your specific training needs.

Finally, we provide trouble-shooting and repair services for configured GC systems, even if we have not configured the system, initially. If you provide documentation about your system, that might make diagnosis of problems faster and easier. If you have no documentation, we will work to provide you with information about how your system is plumbed and provide documentation to you, if needed. Systems Diagnostics and Repair Services are generally performed on-site and may require that you purchase additional parts from the original vendors. We will provide you with hourly rates, but we may only be able to provide estimates for a ranges of time for repair and estimated parts based on symptoms.

Back to top

  • Got peaks? If not, call us!