Chromatographic column having stationary phase thickness gradient

A method of peak focusing in a gas chromatography device, comprising:

• introducing two or more target analytes into an inlet of a chromatographic column comprising a stationary phase deposited inside the chromatographic column and having a positive thickness gradient, wherein the stationary phase extends from the inlet to an outlet and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet of the chromatographic column, wherein the second thickness is at least about 10% greater than the first thickness;
• separating two or more target analytes in the chromatographic column;
• and
• eluting the two or more target analytes from the outlet of the chromatographic column.

A method of verifying peak focusing in a gas chromatography device, comprising:

• conducting a forward operation by introducing two or more target analytes into an inlet of a chromatographic column comprising a stationary phase deposited inside the chromatographic column and having a positive thickness gradient, wherein the stationary phase extends from the inlet to an outlet of the chromatographic column and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet, wherein the second thickness is at least about 10% greater than the first thickness;
• separating the two or more target analytes in the chromatographic column;
• eluting the two or more target analytes from the outlet of the chromatographic column;
• conducting a reverse operation by introducing the two or more target analytes into the outlet of the chromatographic column comprising the stationary phase;
• separating the two or more target analytes in the chromatographic column;
• eluting the two or more target analytes from the inlet of the chromatographic column;
• and
• comparing chromatographic resolutions from the forward operation and the reverse operation, wherein a peak focusing rate for at least one corresponding pair of two peaks from two target analytes is greater than 5%.