Emission-based detector for capillary gas chromatography
An emission-based detector for use in conjunction with capillary chromatography or other applications involving a gas sample having a small volume is provided. The detector is based on optical emission from a plasma medium. An optical cartridge or other detection and/or processing means may be provided to receive and analyse the emitted radiation and thereby obtain information on the gas to be analysed. The emission-based detector includes a gas inlet, a gas outlet and a capillary channel which is in fluid communication with the gas inlet and gas outlet. The capillary channel acts as the plasma chamber. Preferably, the capillary channel has transversal dimensions of the same order as the cross-section of typical chromatography capillary columns and defines a winding path within the detection area. A multi-cell emission-based detector and a method of analysing a gas sample using multiple detection cells are also provided.
1. A method of analysing a gas sample including multiple time-spaced impurity peaks, the method comprising:
a. providing multiple detection cells each configured to generate a plasma from said gas sample and to collect optical emissions from said plasma, each detection cell being configured to measure optical properties associated with a corresponding one of said impurity peaks;
b. successively circulating the gas sample through each of said detection cells;
c. adding a different doping agent to the gas sample between circulation of said gas sample through consecutive ones of said multiple detection cells, each doping agent enhancing detection of the one of said impurity peaks associated with the next detection cell; and
d. measuring the optical properties of the optical emissions collected from each of said detection cells.
2. The method according to claim 1 , wherein the measuring of step d. comprises measuring an impurity peak in said gas sample that is negatively affected by the doping agent using a detection cell through which the gas sample circulates prior to the adding of said doping agent.
3. The method according to claim 1 , further comprising controlling a generator associated with each one of said multiple detection cells to generate a plasma therein only during the circulating of the associated impurity peak therethrough.
4. The method according to claim 1 , wherein, in the providing of step a., each detection cell comprises a detection area having a gas inlet, a gas outlet and a capillary channel in fluid communication with the gas inlet and gas outlet to allow circulation of the gas sample therebetween.
5. The method according to claim 4 , wherein, in the providing of step a., the capillary channel of each detection cell has a cross-section area between about 0.01 mm 2 and 0.20 mm 2 .
6. The method according to claim 5 , wherein, in the providing of step a., the capillary channel of each detection cell defines a plasma chamber following a winding path within the detection area.
7. The method according to claim 6 , wherein, in the providing of step a., the capillary channel of each detection cell has a length within the detection area such that a path of the gas sample within said detection area substantially corresponds to a width of an impurity peak in said gas sample.
8. The method according to claim 6 , wherein, in the providing of step a., each detection cell comprises a plasma-generating mechanism configured to apply a plasma-generating field across the plasma chamber so as to generate a plasma from said gas sample.
9. The method according to claim 6 , wherein, in the providing of step a., each detection cell comprises a detector window allowing the optical emissions from said plasma to exit the plasma chamber.
10. The method according to claim 1 , wherein, in the providing of step a., each detection cell comprises an optical cartridge provided with an optical filter selected in view of the optical properties of the impurity peak associated with said detection cell.