It is seen that using the average velocity data, the extracted value for the multi-path term is negative, which is physically impossible (for a capillary column should be zero or very close to zero). In contrast, the values obtained from data involving the exit velocity give small positive, but realistic values for the multi-path term.

In all aspects of column evaluation and column design in GC, the compressibility of the mobile phase must be taken into account or serious errors will be incurred.

Figure 10. De-Convolution of the HETP Curve Obtained Using the Average Mobile Phase Velocity