THEORETICAL APPROXIMATIONS FOR THE LINEAR FLOW OF CARRIER GAS THROUGH A RECTANGULAR GC COLUMN

摘要

The ability of a gas chromatographic (GC) column to separate two compounds is determined by its analytical resolution. The height equivalent to a theoretical plate (HETP) is given by HETP=2D_g/u+C_su+C_Mu where D_g is the diffusion coefficient in the gas phase, and C_s and C_M are the resistances to mass transfer in the gas and liquid phases, respectively. For a rectangular column, the average linear velocity u is given by u=1/(8bd)_(-b-d)∫∫~(+b+d)[((x~2-b~2)(y~2-d~2))/((x~2-b~2)+(y~2-d~2))]dxdy1/η(dP)/(dz) where 2b and 2d are the width and height of the column, η is the viscosity of the carrier gas, and dP/dz is the pressure gradient along the column. Whenever bd, u can be approximated by u=-[A_1(b~2d~2)/(b~2+d~2)+A_2(b~4d~4)/((b~2+d~2)~3)+...+A_n(b~(2n)d~2n)/((b~2+d~2)~(2n-1))+...]1/η(dP)/(dz) where A_n are constants whose values depend on the type and level of approximation.