Two stage thermal modulator for gas chromatography with thermally matched grounding point
Disclosed herein are two stage thermal modulators that are useful in the separation of the components of an analyte sample in an analytical method, such as gas chromatography. In some embodiments, the thermal modulators described herein include a modulator column coupled to at least one ground point so as to define a plurality of stages that may be independently temperature modulated. In some cases, the modulator column (or stages thereof adjacent to a ground point) and the ground point are thermally matched, so as to limit or eliminate the formation of a temperature differential between the modulator column and a ground point.
1. A two stage thermal modulator, comprising:
a housing;
a cavity in said housing, the cavity configured to contain a coolant;
a modulator column comprising a chilled region disposed within said cavity so as to be in contact with said coolant;
a ground point coupled to said modulator column and within said chilled region, said ground point operable to connect said modulator column to electrical ground; and
at least one power supply coupled to said modulator column at a first point and a second point along said modulator column, said at least one power supply operable to resistively heat a first stage of said modulator column and a second stage of said modulator column, said first stage being between said first point and said ground point, said second stage being between said ground point and said second point;
wherein:
said modulator column has a resistivity R1, a thermal mass TM1, and a cross sectional area CSA1;
said ground point has a resistivity R2, a thermal mass TM2, and a cross sectional area CSA2; and
at least two of the following relationships are true:
R2 differs from R1 by less than or equal to about 5%;
TM2 differs from TM1 by less than or equal to about 5%; and
CSA1 differs from CSA2 by less than or equal to about 5%.
2. The two stage thermal modulator of claim 1 , wherein all of the following relationships are true:
R2 differs from R1 by less than or equal to about 5%;
TM2 differs from TM1 by less than or equal to about 5%; and
CSA1 differs from CSA 2 by less than or equal to about 5%.
3. The two stage thermal modulator of claim 2 , wherein said ground point comprises at least one of a knot and a plate.
4. The two stage thermal modulator of claim 1 , wherein at least one of the following relationships is true:
R2 differs from R1 by less than or equal to about 1%;
TM2 differs from TM1 by less than or equal to about 1%; and
CSA1 differs from CSA2 by less than or equal to about 1%.
5. The two stage thermal modulator of claim 1 , wherein at least two of the following relationships are true:
R2 differs from R1 by less than or equal to about 1%;
TM2 differs from TM1 by less than or equal to about 1%; and
CSA1 differs from CSA2 by less than or equal to about 1%.
6. The two stage thermal modulator of claim 1 , wherein all of the following relationships are true:
R2 differs from R1 by less than or equal to about 1%;
TM2 differs from TM1 by less than or equal to about 1%; and
CSA1 differs from CSA2 by less than or equal to about 1%.
7. The two stage thermal modulator of claim 1 , wherein at least one of the following relationships is true:
R2=R1;
TM2=TM1; and
CSA1=CSA2.
8. The two stage thermal modulator of claim 1 , wherein at least two of the following relationships are true:
R2=R1;
TM2=TM1; and
CSA1=CSA2.
9. The two stage thermal modulator of claim 1 , wherein all of the following relationships are true:
R2=R1;
TM2=TM1; and
CSA1=CSA2.
10. The two stage thermal modulator of claim 1 , wherein said modulator column and said grounding point are made of the same material.
11. The two stage thermal modulator of claim 1 , wherein said ground point comprises at least one of a knot and a plate.
12. A method for temperature modulation in gas chromatography comprising:
introducing a sample into a modulator column of a two stage thermal modulator, the modulator column comprising a chilled region disposed within a cavity of a housing so as to thermally contact a coolant disposed within said cavity;
wherein said two stage thermal modulator comprises:
a ground point coupled to said modulator column and within said chilled region, said ground point operable to connect said modulator column to electrical ground;
a power supply electrically coupled to said modulator column at a first point and a second point along said modulator column, said power supply operable to resistively heat a first stage of said modulator column and a second stage of said modulator column, said first stage being between said first point and said ground point, said second stage being between said ground point and said second point;
and wherein:
said modulator column has a resistivity R1, a thermal mass TM1, and a cross sectional area CSA1;
said ground point has a resistivity R2, a thermal mass TM2, and a cross sectional area CSA2;
and at least two of the following relationships are true:
R2 differs from R1 by less than or equal to about 5%;
TM2 differs from TM1 by less than or equal to about 5%; and
CSA1 differs from CSA2 by less than or equal to about 5%.
13. The method of claim 12 , wherein all of the following relationships are true:
R2 differs from R1 by less than or equal to about 5%;
TM2 differs from TM1 by less than or equal to about 5%; and
CSA1 differs from CSA2 by less than or equal to about 5%.
14. The method of claim 13 , wherein said ground point comprises at least one of a knot and a plate.
15. The method of claim 12 , wherein at least one of the following relationships is true:
R2 differs from R1 by less than or equal to about 1%;
TM2 differs from TM1 by less than or equal to about 1%; and
CSA1 differs from CSA2 by less than or equal to about 1%.
16. The method of claim 12 , wherein at least two of the following relationships are true:
R2 differs from R1 by less than or equal to about 1%;
TM2 differs from TM1 by less than or equal to about 1%; and
CSA1 differs from CSA2 by less than or equal to about 1%.
17. The method of claim 12 , wherein all the following relationships are true:
R2 differs from R1 by less than or equal to about 1%;
TM2 differs from TM1 by less than or equal to about 1%; and
CSA1 differs from CSA2 by less than or equal to about 1%.
18. The method of claim 12 , wherein at least one of the following relationships is true:
R2=R1;
TM2=TM1; and
CSA1=CSA2.
19. The method of claim 12 , wherein at least two of the following relationships are true:
R2=R1;
TM2=TM1; and
CSA1=CSA2.
20. The method of claim 12 , wherein all of the following relationships are true:
R2=R1;
TM2=TM1; and
CSA1=CSA2.
21. The method of claim 12 , wherein said modulator column and said ground point are made of the same material.
22. The method of claim 12 , wherein said ground point comprises at least one of a knot and a plate.
23. A modulator column for use in a two stage thermal modulator, the modulator column comprising a ground point, a first stage proximal to the ground point, and a second stage distal to the ground point, wherein:
said modulator column has a resistivity R1, a thermal mass TM1, and a cross sectional area CSA1;
said ground point has a resistivity R2, a thermal mass TM2, and a cross sectional area CSA2:
at least two of the following relationships are true:
R2 differs from R1 by less than or equal to about 5%;
TM2 differs from TM1 by less than or equal to about 5%; and
CSA1 differs from CSA2 by less than or equal to about 5%; and
when an electric current is passed through the first stage and the grounding point or the second stage and the grounding point, the ground point exhibits a temperature that is less than about 5% different from the temperature of the first stage or the second stage, respectively.