Abstract:
A method of operating a switching valve of a GC-MS apparatus is provided with installing a sample injector; connecting a first capillary column downstream of the sample injector; installing a heart-cutting unit downstream of the first capillary column; installing a first interconnecting column and a second capillary column to the heart-cutting unit respectively; connecting a switching valve to the heart-cutting unit via a first interconnecting column and a second capillary column respectively wherein the switching valve includes a plurality of ports; connecting the switching valve to an MS via a second interconnecting column; and switching ports to create different sample loops for passing compounds from the heart-cutting unit to the MS or passing compounds from the heart-cutting unit to the discharge column to be purged.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to gas chromatography-mass spectrometry (GC-MS) instrument and more particularly to a method of switching ports of a switching valve of a GC-MS apparatus. 
     2. Description of Related Art 
     A conventional gas chromatography-mass spectrometry (GC-MS) apparatus is shown in  FIG. 1  and comprises a sample injector  1 , a heart-cutting unit  3  for separating gaseous compounds carried by carrier gas from the sample injector  1  into different fractions, a first capillary column  2  interconnecting the sample injector  1  and the heart-cutting unit  3 , a flame ionization detector (FID)  7 , an interconnecting column  4  interconnecting the FID  7  and the heart-cutting unit  3 , a mass spectrometer (MS)  6 , and a second capillary column  5  interconnecting the heart-cutting unit  3  and the MS  6 . The FID  7  can be replaced with nitrogen-phosphorous detector (NPD) or one of similar detectors. 
     However, a number of drawbacks have been found in the conventional GC-MS apparatus. In detail, as sample gaseous compounds are preliminarily separated by the first capillary column  2  into different fractions, through setting different time slot and carrier gas pressure of the heart-cutting unit  3 , the simple compounds with good separation separated by the first capillary column  2  are to be sent to a detector such as FID or NPD via the interconnecting column  4  for analysis while the complex compounds which are not separated from each other completely and cannot be further separated from each other by the first capillary column  2 , are required to be sent to the second capillary column  5 , which are of different solid phase from that of the first capillary column  2 , for further separation before being sent to the MS  6  for quantitative and qualitative analysis. The simple compounds detected by the detector FID or NPD from a conventional GC-MS will only be able to be resulted in a quantitative analysis while no qualitative analysis as regards the name, structure, CAS No., etc. of such simple compounds may be concluded, thus causing inconvenience to the user. That is, different fractions cannot be sent to the MS  6  at the same time for analysis. Adding another MS to the GC-MS device can solve the problem but it will increase cost. Further, relevant software is required for control purposes. 
     Thus, the need for improvement still exists. 
     SUMMARY OF THE INVENTION 
     It is therefore one object of the invention to provide a method of operating a switching valve of a GC-MS apparatus, comprising the steps of installing a sample injector; installing a heart-cutting unit downstream of the sample injector; connecting a first capillary column to the sample injector and the heart-cutting unit; connecting a second capillary column downstream to the heart-cutting unit; connecting a switching valve downstream to the heart-cutting unit via a first interconnecting column; connecting the switching valve downstream to the heart-cutting unit via the second capillary column wherein the switching valve includes a plurality of ports; connecting the switching valve to a mass spectrometer (MS) via a second interconnecting column; and either (a) switching at least two of the ports to create a first sample loop for passing compounds from the first capillary column to the MS via the first interconnecting column, the first sample loop, and the second interconnecting column, and (b) switching the remaining ports to create a second sample loop for passing compounds from the second capillary column to the discharge column and the second sample loop; or (c) switching at least two of the ports to create a third sample loop for passing compounds from the second capillary column to the MS via the third sample loop and the second interconnecting column, and (d) switching the remaining ports to create a fourth sample loop for passing compounds from the first capillary column to a discharge column via the first interconnecting column and the fourth sample loop. 
     The above and other objects, features and advantages of the invention will become apparent from the following detailed description taken with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a conventional GC-MS apparatus; 
         FIG. 2  is a schematic diagram of a GC-MS apparatus according to the invention; 
         FIG. 3  is a view similar to  FIG. 2  with the switching valve being shown in details in its first configuration; 
         FIG. 4  is a view similar to  FIG. 3  showing a second configuration of the switching valve; 
         FIG. 5  is a chromatogram depicting retention time versus response of five distinct peaks of separated components of chemical compounds according to the conventional GC-MS apparatus which is not equipped with a switching valve; 
         FIG. 6  is a chromatogram depicting retention time versus response of two distinct peaks of separated components of chemical compounds according to the GC-MS apparatus of the invention, the components of chemical compounds being from the second capillary column after further separation and sending to the MS via the switching valve and the second interconnecting column; and 
         FIG. 7  is a chromatogram depicting retention time versus response of three distinct peaks of separated components of chemical compounds according to the GC-MS apparatus of the invention, the components of chemical compounds being from the first capillary column and sending to the MS via the first interconnecting column, the switching valve, and the second interconnecting column. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 2 to 7 , a GC-MS apparatus in accordance with the invention comprises the following components as discussed in detail below. 
     A sample injector  10  is provided to allow carrier gas to pass through to carry chemical compounds. A heart-cutting unit  30  is provided to separate the gaseous compounds, carried by the carrier gas from the sample injector  10  and preliminarily separated by the first capillary column  20 , into different fractions which are to be further sent to a first interconnecting column  40  and a second capillary column  50  respectively. A first interconnecting column  40  interconnects the heart-cutting unit  30  and the switching valve  60  (e.g., 6-port switching valve). A second capillary column  50  interconnects the heart-cutting unit  30  and the switching valve  60 . A second interconnecting column  70  interconnects the switching valve  60  and a mass spectrometer (MS)  80 . 
     The switching valve  60  as the subject of the invention comprises first, second, third, fourth, fifth and sixth ports  61 ,  62 ,  63 ,  64 ,  65  and  66 . The first interconnecting column  40  is connected to one of the ports, the second capillary column  50  is connected to another one of the ports, a discharge column  90  is connected to still another one of the ports, and the third interconnecting column  70  is connected to further another one of the ports as detailed below. 
     For introducing components of the chemical compounds separated from the heart cutting unit  30  (i.e. the first and the second vaporized compounds) to the MS  80 , an individual may set the retention time and carrier gas pressure of the heart-cutting unit  30  and rotate the switching valve  60  to switch ports into a configuration as shown either in  FIG. 3  or in  FIG. 4 . 
     In  FIG. 3 , a first sample loop consisting of the fifth, fourth, second, and third ports  65 ,  64 ,  62 , and  63  is created in the switching valve  60 . As a result, the first vaporized compounds may travel from the first interconnecting column  40  to the MS  80  for analysis via the first sample loop and the second interconnecting column  70 . Moreover, the second vaporized compounds may travel from the second capillary column  50  to the discharge column  90  to be purged from the GC-MS apparatus via a second sample loop consisting of the first and sixth ports  61  and  66 . 
     In  FIG. 4 , an individual may rotate the switching valve  60  to switch ports into a configuration as shown. A third sample loop consisting of the sixth, first, third, and second ports  66 ,  61 ,  63 , and  62  is created in the switching valve  60 . As a result, the second vaporized compounds may travel from the second capillary column  50  to the MS  80  for analysis via the third sample loop and the second interconnecting column  70 . Moreover, the first vaporized compounds may travel to the discharge column  90  to be purged from the GC-MS apparatus via the first interconnecting column  40  and a fourth sample loop consisting of the fourth and fifth ports  64  and  65 . 
     Referring to  FIG. 5 , it is a chromatogram depicting retention time versus response (i.e., base peak intensity) of five distinct peaks (i.e., labeled  1 ,  2 ,  3 ,  4  and  5 ) of separated components of chemical compounds according to the conventional GC-MS apparatus. However, its retention time is short (e.g., first peak having a retention time of 7.90-8.30 minutes, second peak having a retention time of 9.72-9.90 minutes, third peak having a retention time of 9.98-10.10 minutes, fourth peak having a retention time of 11.24-11.60 minutes, and fifth peak having a retention time of 12.30-12.60 minutes) and its responses are not strong. 
     As shown in the chromatogram of  FIG. 6 , two distinct peaks of separated components of chemical compounds (i.e., labeled  2  and  5 ) according to the GC-MS apparatus of the invention are shown in which the second vaporized compounds from the first capillary column  20  are sent to the MS  80  via the second capillary column  50 , the switching valve  60  and the second interconnecting column  70 . 
     As shown in the chromatogram of  FIG. 7 , three distinct peaks of finely separated components of chemical compounds (i.e., labeled  1 ,  3  and  4 ) according to the GC-MS apparatus of the invention are shown in which the first vaporized compounds from the first capillary column  20  are sent to the MS  80  via the first interconnecting column  40 , the switching valve  60 , and the second interconnecting column  70 . 
     As a comparison with the conventional chromatogram of  FIG. 5 , it is found that retention time is increased and response is stronger according to the GC-MS apparatus of the invention. 
     Above can be further ascertained by the following two experiments: 
     Experiment I 
     For introducing components of the chemical compounds (i.e., labeled  2  and  5 ) into the second capillary column  50  for further separation, an individual may set the retention time of the heart-cutting unit to cut the components consisting the compounds labeled  2  and rotate the switching valve  60  at the time of 9.5 minutes to switch ports into a configuration as shown in  FIG. 4  for introducing the compounds labeled  2  into GC-MS  80  via the second capillary column  50 ; and then set the retention time of the heart-cutting unit to turn off channel between the heart-cutting unit and the second capillary column  50  at the time of 10.5 minutes but the still maintain the configuration of the ports of the switching valve as shown in  FIG. 4 . Further, for introducing components of the compounds labeled  5  into the second capillary column  50  for further separation, an individual may first set the retention time of the heart-cutting unit to cut the components consisting the compounds labeled  5  and rotate the switching valve  60  at the time of 12.2 minutes to switch ports into a configuration as shown in  FIG. 4  for introducing the compounds labeled  5  into GC-MS  80  via the second capillary column  50 ; and then set the retention time of the heart-cutting unit to turn off channel between the heart-cutting unit and the second capillary column  50  at the time of 13.0 minutes but the still maintain the configuration of the ports of the switching valve as shown in  FIG. 4 . 
     As a result, components of the chemical compounds (i.e., labeled  2  and  5 ) can be introduced into the second capillary column  50 . Thereafter, the separated components of the chemical compounds labeled  2  and  5  may travel from the second capillary column  50  to the MS  80  for analysis via the third sample loop consisting of the sixth, first, third and second ports  66 ,  61 ,  63 , and  62  in the switching valve  60  and the second interconnecting column  70 . Moreover, the components of the chemical compounds separated from the first capillary column  20  (i.e., labeled  1 ,  3  and  4  in  FIG. 5 ) may travel to the discharge column  90  to be purged from the GC-MS apparatus via the first interconnecting column  40  and the fourth sample loop consisting of the fourth and fifth ports  64  and  65 . 
     Experiment II 
     For introducing components of the chemical compounds (i.e., labeled  1 ,  3  and  4  in  FIG. 5 ) separated from the first capillary column  20  to the MS  80  directly, an individual may set the retention time of the heart-cutting unit to cut the components consisting the compounds labeled  1  and rotate the switching valve  60  to switch ports into a configuration as shown in  FIG. 3  at the time of 7.5 minutes for introducing the compound labeled  1  into GC-MS  80  via the first interconnecting column  40 ; and then set the retention time of the heart-cutting unit to turn off channel between the heart-cutting unit and the first interconnecting column  40  at the time of 8.5 minutes but the still maintain the configuration of the ports of the switching valve as shown in  FIG. 3 . Further, For introducing components of the compounds labeled  3  and  4  to the MS  80 , an individual may first set the retention time of the heart-cutting unit to cut the components consisting the compounds labeled  3  and  4  and rotate the switching valve  60  to switch ports into a configuration as shown in  FIG. 3  at the time of 9.95 minutes for introducing the compound labeled  3  and  4  into GC-MS  80  via the first interconnecting column  40  and the second interconnecting column  70 ; and then set the retention time of the heart-cutting unit to turn off channel between the heart-cutting unit and the first interconnecting column  40  at time of 12.0 minutes but the still maintain the configuration of the ports of the switching valve as shown in  FIG. 3 . 
     As a result, components of the chemical compounds (i.e., labeled  1 ,  3  and  4 ) can be introduced into the first interconnecting column  40 . Thereafter, the separated components of the chemical compounds may travel from the first interconnecting column  40  to the MS  80  for analysis via the second interconnecting column  70  and the first sample loop consisting of the fifth, fourth, second and third ports  65 ,  64 ,  62 , and  63  in the switching valve  60  (see  FIG. 3 ). Moreover, the components of the chemical compounds separated from the first capillary column  20  (i.e., labeled  2  and  5 ) may travel to the discharge column  90  to be purged from the GC-MS apparatus via the second capillary column  50  and the second sample loop consisting of the first and sixth ports  61  and  66 . 
     By injecting the same complex sample twice into the injector and performing the steps as stated in Experiment I and Experiment II, full quantitative and qualitative information such as the name, structure, CAS No., etc. may be concluded for such complex sample. 
     It is found that co-eluting interferences in the chromatogram according to the conventional GC-MS apparatus (see  FIG. 5 ) have been greatly eliminated by the invention when comparing with the chromatogram according to the GC-MS apparatus of the invention in either  FIG. 6  or  FIG. 7 . As a result, a more accurate analysis can be made by the invention. 
     While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims.