Inorganic Analysis Chromatography Molecular Spectroscopy Thermal/Elemental Analysis Informatics Gas Chromatography MS Vent Enhancement to the PreVent System to Optimize Operation with the TurboMass, TurboMass Gold, and Clarus 500 GC/MS Systems P R O D U C T N O T E www.perkinelmer.com Introduction MS Vent is a technical enhancement to the PreVent system and can be used with the PerkinElmer TurboMass, TurboMass Gold, and the Clarus 500 GC/MS systems. Figure 1 shows the basic PreVent configuration with the MS detector. The MS Vent hardware, when added to an existing PreVent system, not only retains the functionality of PreVent but provides some significant additional technical capabilities. Figure 1. Basic PreVent Configuration. MS Vent offers the following practical benefits: Ability to remove and change columns without cooling and venting the MS. Ability to backflush a single capillary column (TimeSaver mode). Ability to perform large volume injections (ELVI). Ability to perform injector maintenance without cooling and venting the MS. Ability to use any capillary column at any carrier gas flow rate and deliver a fixed flow rate into the detector (equivalent to an open split interface). Ability to connect vented column effluent to a second detector for dual signal capability. Key Capabilities Column replacement without cooling and venting the MS Perform injector maintenance without cooling and venting the MS Ability to use any column and flow rate Column effluent can be split to a second detector for dual signal capability Perform large volume injections
Design The MSVent design uses the standard PreVent hardware and minimal additional components to effect a solution similar to that of the Zero- Dilution Liner (ZDL) recently introduced for the PerkinElmer headspace systems. Figure 2 shows a schematic diagram of the system. MS transfer line From midpoint pressure regulator F/M/M T-piece Restrictor/vent Slot Column The design components comprise a standard F/M/M T-piece. This is connected to the end of the standard PreVent adapter using an O-ring to seal a short length of Glass-Lined Tubing (GLT) tubing within the T-piece. The tube acts as a guide for capillary columns of up to 0.53mm i.d. so that the column may be threaded right through into the glass hourglass. The restrictor within the MS transfer line is of wider outer diameter than the normal PreVent restrictor so that it is sealed and retained within the hourglass. The column is pushed up against the hourglass constrictor, directly opposite to the end of the restrictor and then back to leave a ~1-mm gap as shown in Figure 3. Fused silica restrictor Figure 2. The MS Vent interface. Restrictor to Turbomass Standard PreVent injector adapter Hourglass Standard hourglass O-ring 0.85-mm i.d. glass-lined tube Column This gap allows gas to escape from between column and restrictor. The escaping gas passes out of the hourglass, along the GLT tubing, through the slot and out through the restrictor/vent. This flow of gas can be fed to a second detector for simultaneous monitoring. If the flow of gas eluting from the column is less than the flow rate of gas into the MS transfer line, then carrier gas will enter through the gap in the hourglass to make up the flow rate. Thus the flow rate of gas entering the detector is always constant excess flow from the column will be vented; insufficient flow will be made up. Seal Figure 3. Internal detail of hourglass with restrictor and column installed. Allows gas venting or makeup. Restrictor inside transfer line Injector PreVent device Midpoint gas supply Gap New T-piece Vent to second detector Detector Figure 4 shows the MS Ion Source interface, with MS Vent installed into the GC oven. Figure 4. MS Ion Source Interface with MS Vent installed into the GC oven.
Example Chromatography 1. Basic chromatographic performance Figure 5 shows a Test Mixture on a directly coupled column. Figure 6 shows a comparison of the same Test Mixture run with MS Vent installed. The two chromatograms are very similar indicating that the introduction of the MS Vent system into the sample flow-path does not degrade performance. The retention times are slightly different in this case because of the differences in applied pressure. 2. Excess column effluent can be split to a conventional detector. If the carrier gas pressure in the injector is raised to a level where the carrier gas flow rate through the column is higher than that through the MS transfer line restrictor, this excess flow will pass out of the system through the fused silica vent restrictor on the MS Vent adapter. This restrictor may be connected to a second detector, such as a Flame Ionization Detector (FID) to provide a second means of monitoring the chromatography. Figure 7 show a FID trace produced simultaneously with the chromatogram shown in Figure 6. This feature may be used for improved quantitative performance or for signal monitoring purposes when it is undesirable to heat the detector filament (e.g., to monitor sample solvent elution). Figure 5. Test Mixture on directly coupled column. Inlet Pressure = 2 psig, Outlet Pressure = Vacuum (inside MS). Figure 6. Test mixture with MS Vent installed Inlet Pressure = 27 psig, Outlet Pressure = 15psig (MS Vent midpoint pressure). Figure 7. Column effluent split to FID.
3. Column Backflushing. Figure 8 shows a Petrochemical Intermediates Sample without backflush and Figure 9 shows the same sample with backflush. This technique enables the chromatographic system to handle samples containing significant unwanted heavy material. Backflushing is a very effective means of removing such material from the system: it reduces analysis time, eliminates the need for extended temperature programming and helps keep the column and detector clean. 4. Injector maintenance or column replacement can be carried out while the MS is active. Figure 8. Petrochemical Intermediates Sample without backflush. Figure 10 shows the MS detector trace during column change. These data were collected by scanning upwards from 15 amu and so the background signal associated with air and water could be directly monitored. The traces show no evidence of leakage of air or water into the system as the column is removed. In fact the only indication that the change is being made is a slight step in the signal as the pressure inside the MS Vent adapter drops as the column is removed. Figure 9. Petrochemical Intermediates Sample with backflush. Figure 10. MS signal background during column removal.
5. Rapid column replacement. Because the column may be removed and replaced with the MS still active, changing columns becomes much faster and more convenient. Figure 11 shows a Petrochemical Intermediates Sample run on one column. This column was removed and replaced with a second column of the same type. Figure 12 shows the Petrochemical Intermediates Sample run on the new column 20 minutes after the first chromatogram has finished. There is some lumpiness near the end of the second trace but this would be removed by normal column conditioning. It should be noted that column conditioning may be performed with the column fully installed. Applying backflush conditions will ensure that none of the column bleed occurring during the conditioning process will enter the MS detector. Figure 11. Petrochemical Intermediates Sample. Finally, Figure 13 shows the same sample run on the new column with backflush. Figure 12. Petrochemical Intermediates Sample on new column. Figure 13. Same sample on new column with backflush.
6. Constant carrier flow rate can be applied to the MS regardless of column flow rate. The flow rate of carrier gas through the MS Vent restrictor in the MS transfer line is controlled by the mid-point pressure set inside the MS Vent adapter. It is completely independent of the flow rate through the column. If the column flow rate is greater, then the excess is vented (perhaps to a second detector). If the column flow rate is less, then the midpoint gas supply will make up the difference in flow through the restrictor. This means that any column with any flow rate can be used with MS Vent and the flow rate into the detector will remain at its optimum without the need for fine "tweaking". Figure 14. Petrochemical Intermediates Sample on a 0.53-mm i.d. column. The column used to produce the chromatogram shown in Figures 12 and 13 was removed and replaced with a wider-bore column to produce the chromatogram shown in Figure 14. Conclusion MS Vent not only extends the capabilities of PreVent, but also provides significant benefits to the user reduction in downtime and increased productivity. PerkinElmer Life and Analytical Sciences 710 Bridgeport Avenue Shelton, CT 06484-4794 USA Phone: (800) 762-4000 or (+1) 203-925-4600 www.perkinelmer.com 2002 PerkinElmer, Inc. All rights reserved. PerkinElmer is a trademark of PerkinElmer, Inc. MS Vent, TurboMass and Clarus are trademarks of PerkinElmer Instruments LLC. PerkinElmer reserves the right to change this document at any time and disclaims liability for editorial, pictorial, or typographical errors. D-6672A KG110205 Printed in USA