Gas Chromatography Detectors - The Nitrogen Phosphorus Detector (NPD) > Page 45

Figure 21. The Separation of a PIANO Standard Mixture

The sensor was held at 250oC (50oC) above the maximum column temperature to avoid condensation in the jet and conduits. The sample size was 0.1 ml, which was split 100-1, giving a total charge of about 1 mg. Helium was used as the carrier gas at a linear velocity of 20 cm/sec. It is seen that the baseline is extremely stable despite the temperature program, and that the high sensitivity and wide dynamic range of the FID make it invaluable for quantitative analysis.

Anothertype of analysis frequently carried by the hydrocarbonindustryistheparaffin, isoparaffin, aromatic, naphthalene and olefin estimation(the so-called PIANO analysis), an example of which is shown in figure 21. The column was fused silica, 50 m long and 0.5 mm I.D., and the stationary phase was also Petrocol DH 50.2. The column temperature was held at 35oC for 5 minutes and then programmed up to 200oC at 2o/min. The carrier gas was helium and its velocity through the column 20 cm/sec.

The Nitrogen Phosphorus Detector (NPD)

The nitrogen phosphorus detector (NPD) (sometimes called the thermionic detector) is a very sensitive, specific detector the design of which, is based on the FID. Physically the sensor appears to be very similar to the FID but, in fact, operates on an entirely different principle. A diagram of an NPD detector is shown in figure 22.