pressure gradient correction factor

in gas chromatography
A factor that corrects for the compressibility of the carrier gas. The values of the measured quantities obtained after multiplication by the factor j are independent of the pressure drop in the column. If p i, p o are respectively the pressures of the carrier gas at the inlet and outlet of the column, then j is given by: \[j=\frac{3\ [(\frac{p_{\text{i}}}{p_{\text{o}}})^{2}- 1]}{2\ [(\frac{p_{\text{i}}}{p_{\text{o}}})^{3}- 1]}\]
Orange Book, 2nd ed., p. 101 (