Can I Build My Own Gas Chromatography Instrument?

Perhaps you are interested in gas chromatography (GC)? Maybe you’d even like one of your own? Sounds impossible, right? Perhaps not… How simple would it be to build one in the shed at home though? Let's find out! 

How does GC work?

GC is a method of separating components from mixtures. It is used to separate compounds from a mixture and to identify the components; both qualitative and quantitative analysis can be carried out. A commercial GC instrument uses a carrier gas to carry a sample from a heated injection port to a column. The sample passes through the column to a detector — where the output is taken and displayed on a screen.

Components in a GC

A GC instrument essentially has four components:

• Carrier Gas

Known as the mobile phase it carries the sample through the column. Carrier gases must be inert, so they do not react with the sample — helium and nitrogen are used in commercial instruments.

• Injection Port

The usual way to introduce a sample to the system is through a heated injection port. The injection port is heated to a temperature that immediately vaporizes the sample so that it enters the carrier gas as a gas.

• Heated Column

In commercial GC’s, the column is housed in an oven. The oven is used to increase the temperature of the column. This changes the conditions at the interface between the sample molecules and the stationary phase. Two factors influence the retention of the sample onto the column — the volatility of the sample, and the attractive forces between the sample and the stationary phase.

• Detector

The detector has to somehow react to the molecules as they leave the column.

Homemade GC

So how to replicate the commercial GC. The column would be relatively straightforward; copper tubing is used in commercial GCs, so a simple copper pipe with some dried silica gel as the stationary phase would be a good approximation to a GC column. A small fan heater controlled from a temperature probe using a feedback loop would provide heat to change the column conditions. This would allow you to see the effect of different temperatures on a compound by measuring the retention time on the column.

A simple aquarium pump and tubing could be used to introduce air, your carrier gas, to the copper pipe.

If the sample is a gas, no need for a heated injection port, and if the sample is a volatile liquid, a small drop allowed to vaporize would allow some sample to be introduced into the system.

A more difficult problem is detection, especially if you want some quantification. A small flame burning at the end of the column could be induced to change colour with the right sample; for example a haloalkane will burn in air with a bright coloured flame — the change in brightness could be detected by a light sensitive resistor. A simple FID detector.

A simple system? To give you some idea of the thought processes necessary to build your GC have a look at this article: Optimisation of Column Parameters in GC.

Image Source: Workman Screwdriver via Paul Wilkinson