Patent ID: 7396386

Claim:
A method for obtaining reproducibility of the retention times of the components of a mixture to be analysed in an apparatus for gaschromatographic analysis provided with a capillary column, when one or more of the following variations occurs: a variation in the length of the column, or alternatively replacement of the column with a column having identical real specifications with the exception of the length, and/or a variation in the output pressure from said column, given that the pneumatic resistance KC old =K(L old ) of said column is known, the analytical expression of which is: K ⁡ ( L old ) = 256 · L old π · d 4 · η 0 · P ref T ref 1 + α ( 9 ) where: d is the diameter of the column; Pref, Tref are, respectively, the reference pressure and the reference temperature (referred to standard conditions); η0 is the viscosity of the carrier gas at the reference conditions; L old is the initial length of the column; α is the coefficient depending upon the type of carrier gas used; and in which the temperature of said capillary column is maintained equal, instant by instant, starting from the introduction of the mixture into the apparatus, for each analysis of said mixture before and after one of said variations, characterized by the following steps: measuring, prior to said variations, the pressure p i,old of the carrier gas at the input section of the column, and the pressure p o,old of the carrier gas at the output section of the column; following upon said variations, measuring the new pneumatic resistance KC new K(L new ) of the column, the analytical expression of which is: K ⁡ ( L new ) = 256 · L new π · d 4 · η 0 · P ref T ref 1 + α ( 5 ) wherein: L new is the new length of the column; selecting, after said variations, the new pressure p o,new at output from the column; calculating a new input pressure p i,new or a new mass flow F new (referred to standard conditions) of the carrier gas, using the relation: λ = j old j new · g · p o , new p o , old ⁢ ⁢ where ⁢ : ( 1 ) g = K ⁡ ( L new ) K ⁡ ( L old ) = L new L old ( 2 ) j new = 3 2 · ( p i , new p o , new ) 2 - 1 ( p i , new p o , new ) 3 - 1 ( 3 ) j old = 3 2 · ( p i , old p o , old ) 2 - 1 ( p i , old p o , old ) 3 - 1 ( 4 ) setting, after said variations, said new input pressure p i,new or said new mass flow F new of the carrier gas into said apparatus for gaschromatographic analysis in correlation to λ.