Instrumental Analysis Gas chromatography Jack Lee E.P. Department

Introduction GC: Gas Chromatography GC was invented by A. J. P. Martin. The first gas chromatographic separation was a series of fatty acids. A more sophisticated GC was constructed by James and Martin in 1955.

The Modern GC The modern gas chromatograph is a really complex instrument mostly computer controlled. The samples are mechanically or manually injected. The analytical results are automatically calculated and printed out.

Block diagram of GC structure

The first unit It provides all the necessary gas supplies. A minimum of three different gases would be required. (FID) Three flow controllers, three flow monitors would be required. A microprocessor is employed to monitor flow rates, adjust individual gas flow rates. Use gas generators instead of gas tanks.

The second unit It contains a manual (1. 2. 3)or an automatic injector. It is situated inside a thermostatically controlled enclosure. We use a syringe to inject sample onto the column. Automatic injector(carousel) can carry out a series of sample preparation procedures before injecting the sample onto the column.

The third unit It contains the column and an oven. The column is the essential device to achieve the necessary separation. The oven is used to control the column temperature. The column has two kinds: Packed column Capillary column

The fourth unit It contains the detector which is situated in its own oven. There is a wide range of detectors available each having unique operating parameters and its own performing characteristics. The output of detector is electronically modified.

The detectors Types of the detectors: TCD: Thermal Conductivity Detector FID: Flame Ionization Detector ECD: Electron Capture Detector FPD: Flame Photometric GC Detector NPD: Nitrogen Phosphorus Detector Principles of the detectors

TCD: Thermal Conductivity Detector

The bridge circuit for TCD detector

FID: Flame Ionization Detector

ECD: Electron Capture Detector

FPD: Flame Photometric GC Detector

NPD: Nitrogen Phosphorus Detector