Methods and systems for characterizing a sorbent tube
View Patent ↗Disclosed are systems and methods that include providing a vessel having an adsorbent disposed therein, the vessel having an inlet and an outlet for communicating a carrier gas through the vessel; determining a differential pressure between the inlet and the outlet for a known flow rate at the outlet; and, determining a geometric measure for the vessel based on a ratio of the known flow rate and the differential pressure. In some embodiments, the methods and systems can include a viscosity in the ratio, determining a flow rate at ambient pressure using a factor based on a ratio of a gas pressure at the output and ambient pressure, and/or, determining a flow rate at ambient temperature using a factor based on a ratio of a temperature at the output and ambient temperature.
1. A method, comprising:
providing a vessel having an adsorbent disposed therein, the vessel having an inlet and an outlet for communicating a carrier gas through the vessel;
determining a differential pressure between the inlet and the outlet for a known flow rate at the outlet; and,
determining a geometric measure for the vessel based on a ratio of the known flow rate and the differential pressure.
2. The method of claim 1 , wherein determining a differential pressure includes providing at least one sensor to provide measurements related to the differential pressure.
3. The method of claim 1 , where determining a geometric measure includes factoring a viscosity of the carrier gas in the ratio.
4. The method of claim 1 , wherein said vessel comprises an adsorbent trap.
5. The method of claim 1 , wherein the vessel comprises a sample tube.
6. The method of claim 1 , further comprising at least one of:
determining a flow rate at ambient pressure using a factor based on a ratio of a gas pressure at the output and ambient pressure, and,
determining a flow rate at ambient temperature using a factor based on a ratio of a temperature at the output and ambient temperature.
7. The method of claim 1 , further wherein the step of determining the geometric measure of the vessel comprises calculating k in accordance with the equation
F
a
=
k
·
(
p
i
-
p
o
)
η
·
p
o
p
a
·
T
a
T
o
where (p i −p o ) is the differential pressure between the inlet and the outlet, F a is the flow rate at ambient pressure and temperature, p a is the ambient absolute pressure, T a is the ambient absolute temperature, p o is the absolute gas pressure at the tube outlet, and T o is the absolute temperature at the tube outlet.
8. A chromatographic system, comprising:
a carrier gas inlet for supplying carrier gas;
a chromatographic column for receiving the carrier gas;
a flow path through which the carrier gas is communicated from said carrier gas inlet to said chromatographic column;
a vessel disposed in said flow path, said vessel having an adsorbent disposed therein for adsorbing and desorbing analytes to be measured;
wherein said vessel includes an inlet and an outlet for communicating the carrier gas through said vessel;
at least one sensor in communication with said flow path adjacent at least one of the vessel inlet and vessel outlet for measuring either the pressure drop or the flow rate of the gas communicated through said vessel;
at least one computer connect to said sensor;
software executing on said computer for comparing the measured pressure drop or flow rate to the expected pressure drop (p i −p o ) or expected flow rate F a , respectively, of the gas communicated through said vessel calculated in accordance with the equation
F
a
=
k
·
(
p
i
-
p
o
)
η
·
p
o
p
a
·
T
a
T
o
where p a is the ambient absolute pressure, T a is the ambient absolute temperature, p o is the absolute gas pressure at the tube outlet, T o is the absolute temperature at the tube outlet, and k is the permeability factor of said vessel.
9. The system of claim 8 , wherein said at least one sensor comprises at least one pressure transducer for measuring the pressure drop across said vessel.
10. The system of claim 8 , wherein said at least one pressure transducer comprises a differential pressure transducer in communication with said flow path adjacent the vessel inlet and adjacent the vessel outlet for measuring the pressure drop across said vessel.
11. The system of claim 9 , further comprising a flow controller disposed in said flow path for controlling the flow rate of the carrier gas.
12. The system of claim 11 , wherein said flow controller is positioned between the vessel outlet and said chromatographic column.
13. The system of claim 8 , wherein said at least one sensor comprises at least one flow sensor in communication with said flow path for sensing the flow rate of the gas communicated through said vessel.
14. The system of claim 13 , further comprising at least one pressure regulator disposed in said flow path for establishing a pressure drop across said vessel.
15. The system of claim 14 , wherein said at least one pressure regulator comprises a forward pressure regulator disposed in said flow path between said carrier gas inlet and the vessel inlet, further comprising a valve disposed in said flow path between the vessel outlet and said chromatographic column for venting the carrier gas to the atmosphere.
16. The system of claim 14 , wherein said at least one pressure regulator comprises:
a forward pressure regulator disposed in said flow path between said carrier gas inlet and the vessel inlet; and
a back pressure regulator disposed in said flow path between the vessel outlet and said chromatographic column.
17. The system of claim 14 , further comprising a differential pressure transducer in communication with said flow path adjacent the vessel inlet and adjacent the vessel outlet for verifying the pressure drop across said vessel.
18. The system of claim 8 , further comprising a sample container for supplying the analytes to said flow path, wherein said vessel comprises an adsorbent trap for receiving the analytes supplied by said sample container and pre-concentrating the analytes before the analytes are communicated to said chromatographic column.
19. The system of claim 8 , wherein said vessel comprises a sample tube for collecting the analytes before said vessel is disposed in said flow path.
20. The system of claim 19 , further comprising:
a second vessel disposed in said flow path, said second vessel having an adsorbent disposed therein for receiving the analytes supplied by said sample tube and pre-concentrating the analytes before the analytes are communicated to said chromatographic column;
wherein said second vessel includes an inlet and an outlet for communicating the carrier gas through said second vessel; and
at least one additional sensor in communication with said flow path adjacent at least one of the second vessel inlet and the second vessel outlet for measuring either the pressure drop or the flow rate of the gas communicated through said second vessel.
21. A method of performing a chromatographic analysis, the method comprising:
providing a carrier gas inlet for supplying carrier gas;
providing a chromatographic column for receiving the carrier gas;
providing a vessel having an adsorbent disposed therein for adsorbing and desorbing analytes to be measured, the vessel having an inlet and an outlet for communicating carrier gas through the vessel;
communicating carrier gas from the carrier gas inlet, into the vessel through the vessel inlet, and out of the vessel through the vessel outlet;
measuring either the pressure drop or the flow rate of the gas communicated through the vessel; and
comparing the measured pressure drop or flow rate to the expected pressure drop (p i −p o ) or the expected flow rate F a , respectively, of the gas communicated through said vessel calculated in accordance with the equation
F
a
=
k
·
(
p
i
-
p
o
)
η
·
p
o
p
a
·
T
a
T
o
where p a is the ambient absolute pressure, T a is the ambient absolute temperature, p o is the absolute gas pressure at the tube outlet, T o is the absolute temperature at the tube outlet, and k is the permeability factor of said vessel.