The Shimadzu GC-2010 is perfectly suited for Fast GC as it meets all the requirements for a Fast GC system:

• high pressure carrier gas supply
• high split ratios
• high oven heating rates
• constant linear velocity mode
• high maximum detector data acquisition rate (adjustable according to application)
• small minimum detector filter time constant (adjustable according to application)

The benefits of Fast Gas Chromatography are appealing to every laboratory: saving of valuable analysis time and reduction of costs of e.g. carrier gas and also manpower. Important for the successful application of Fast GC are the instrument parameters.

Fast GC uses short columns with small inner diameters. This gives short retention times and at the same time high resolution. As small inner diameter columns deliver a high back pressure, a high pressure should be available for the carrier gas in the GC. But the option to use high split ratios to avoid overloading of the column should also be available. To avoid band broadening of the peaks after injection, the heating rates of the oven should be fast.

The separation efficiency (resolution) of a capillary column is a function of the carrier gas linear velocity. During a GC temperature program the viscosity of the carrier gas increases and the linear velocity of the carrier gas decreases accordingly, so the optimal conditions for chromatographic resolution are no longer present. The GC should therefore offer a constant linear velocity mode enabling an automatic increase in the pressure to keep the linear velocity constant and in the optimum range.

Figure 1: Definition of filter time constant τ

Last but not least the detector should be fast enough to acquire the data on a sharp peak of only several ms. The response characteristics of the detector, here the filter time constant (Fig 1), are very important for obtaining good results.

Figure 2: FID signal of chlorodecane. The filter time constant τ was changed from 4 to 200 ms. The sampling frequency was 250Hz in all cases.

Fig. 2 shows the effect of the filter time constant on the peak shape. If the filter time constant chosen is too large, the peaks are distorted and qualitative as well as quantitative analysis cannot be performed.

Figure 3: Chromatograms relative to a kerosene sample at a filter time constant τ of 100 ms and 10 ms respectively

Fig. 3 illustrates a chromatogram with the same data acquisition rate, but different filter time constants. If the filter time constant is too large (meaning the detector is too slow) the resolution of the chromatogram is poor. On the other hand, if the filter time constant is too small (meaning the detector is too fast) too much noise is recorded, thereby decreasing the detection limit of a peak. So it is important that the filter time constant can be chosen according to the peak width in the chromatogram.

You will find all information about Fast GC and its application in our Application Book Fast GC/GCMS which can be downloaded from our web site at http://eu.shimadzu.de/info/applicationbook/vol1.aspx

For further details visit our web page at www.shimadzu.de