Using a Novel Heartcut Device for Multidimensional GC Peak Sectioning to Reveal Small Peaks Otherwise Obscured by Large Peaks in Mass Chromatograms Daniel Pentek, Andrew Tipler, William D. Goodman, Adam J. Patkin, PerkinElmer Life and Analytical Sciences, Shelton, CT, United States . 1 Methylenechloride _NoCut_ 092 Deans’ Switch Figure 2. Installing the wafer in the holder Scan EI+ 35_150 5.00e7 100 5.47 3.30 4.56 6.16 7.19 1.98 2.87 100 0.00 0.50 1.00 1.50 2.00 2.5 0 3.14 3.33 3. 00 2.72 3 .50 4 .00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 Time 8.00 3 0.00 0.50 1.00 1.50 2.00 2.50 3.00 The final analytical data is obtained by combining the results from all the chromatograms shown in Figures 10 and 12. Table 3 lists each impurity detected in each of the 5 DCM samples. In each case there would have been co-elution of some peaks if the sidecutting and heartcut sectioning techniques were not deployed. 3.67 1.63 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 Time 8.00 Table 3. Tentative MS assignment of compound identities in DCM samples using the solvent side cutting and heartcut sectioning technique. DCM Sample Figure 3. Wafer mounted in the threaded holder Figure 4. The holder containing the wafer mounted inside the GC oven Figure 7. FID chromatogram of DCM Sample 3 showing small impurity peaks. restrictor restrictor Scan EI+ 35_150 5.00e7 100 Split/splitless injector D-Swafer D-Swafer Retention Time, min Scan EI+ TIC 2.00e10 100 Scan EI+ TIC 2.00e10 100 3.30 All sample transferred to Column 2 4.56 5.48 30m x 0.25mm x 1.0µm Elite-Wax % MS MS 30m x 0.25mm x 1.0µm Elite-Wax 6.17 Figure 6. 6 Wafer heartcut system with effluent from primary column cut to secondary column. Figure 5. 5 Wafer heartcut system with effluent from primary column directed to mid-point FID. 3 Experimental Conditions Tables 1 and 2 give details of the analytical system and method applied to examine 5 samples of dichloromethane (DCM). Table 1. Analytical System. Setting Clarus 600 Oven Temperature p Heartcut device D-Swafer in D4 configuration Carrier Gas Split/Splitless Injector 225°C Carrier Gas Pressure (P1) 23psig (159kPa) Split Flow 100mL/min 15m x 0.25mm x 1.0m Elite-1 Midpoint Pressure (P2) Column 2 30m x 0.25mm x 1.0µm Elite Wax Detector 1 (FID) Temperature Restrictor 58cm x 0.10mm deactivated fused silica Air Flow rate 450mL/min Hydrogen Flow Rate 45mL/min Range x20 Attenuation Detector 2 (MS) Temperature Mass Range 250°C x64 200°C 15 to 150 Da 0.2s Interscan delay 0.1s Sample Injection 1µL by Autosampler in Fast Mode Swafer Switching Valve (V4) Timed Events See Results Section S l t Sid tti Solvent Sidecutting In Figures 7 and 8 we see the solvent peak dominates the chromatography around it and probably obscures some smaller peaks. The large amount of solvent entering the MS system also raises some concerns. A run was made with the heartcut switched to the second column at the start of the run and switched to the FID during the solvent peak elution then switched back again. This sidecutting technique has the effect of removing a large fraction of the solvent yet allowing the rest of the sample to g 9 shows enter the second column and the MS detector. Figure a chromatogram run this way. Inspection of Figure 9 shows that much of the solvent has been removed by the sidecutting method. This removal is better illustrated by Figure 10 which shows the two chromatograms at a larger scale. This is a highly effective technique for keeping solvent away from the MS detector. 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 Time 8.00 0 1 00 1.00 2 00 2.00 3 00 3.00 4 00 4.00 5 00 5.00 6 00 6.00 7 00 7.00 8 00 8.00 Time 9 00 9.00 Figure 10. Chromatograms shown in Figures 8 and 9 plotted together at a larger scale to show the efficacy of sidecutting for solvent removal. branched chain pentene* √ 3.68+ dichloroethylene* √ 4 5 √ 3 √ √ √ √ √ √ 3.75 branched chain hexane* 3.87 acetone 3.90 branched chain hexane* √ √ √ √ √ branched chain hexene* 4.56 dichloroethylene* 4.65 ethanol 4.70 isopropanol 4.91# trimethyl oxirane 5.31 1-chlorobutane 5.48 2-chloro-2-methylbutane 5.79 cyclohexene y √ √ √ √ √ √ √ √ √ √ √ √ √ √ 6.02 acetonitrile 6.17 2-butanone √ 7.08 hexyl alcohol* √ √ 7.19 chloroform √ √ √ √ Solvent Sectioning 6 Methylenechloride_1-78_099 100 100 % 0 1 2 3 4 5 Scan EI+ 35_150 5.00e7 5.06 6 6 Methylenechloride_1-76_098 6 5 7 Methylenechloride_1-74_097 100 % 4 Scan EI+ 35_150 5.00e7 3.46 7 Methylenechloride_1-72_096 100 % % Scan EI+ 35_150 5.00e7 3 7 Methylenechloride_1-70_095 100 % Scan EI+ 35_150 5.00e7 2 3.68 7 Methylenechloride_1-68_094 100 % Scan EI+ 35_150 5.00e7 1 3.41 3.68 7 Methylenechloride_1-66_093 100 % 1.67 1.68 1.69 1.70 1.71 1.72 1.73 1.74 1.75 1.76 1.77 1.78 1.79 1.80 1.81 1.82 1.83 1.84 1.85 Figure 11. Sectioning the DCM solvent peak into six 0.02-minute heartcuts. Time Scan EI+ 35_150 5.00e7 0 7 1.00 This time would be needed to fully y map p the obscured components. In the samples examined here, only two additional peaks were found in the sectioned chromatograms and so the method could be optimized just to apply heartcuts to the affected sections and so reduce the number of runs necessary. Scan EI+ 35_150 5.00e7 100 % Summary Thi side-cut This id t and dh heartcut t t ttechnique h i provides a comprehensive and reliable method of revealing the low-level impurities of solvents using MS as the detection system. Although the solvent peak sectioning process entails several repeat chromatograms of the same sample, these runs are fairly short and isothermal and so the total analytical time is just 50 minutes. 23+16psig 100mLsplit 1.68 Cut, 04-Feb-2009 + 20:32:17 Methylenechloride_NoCut_092 80 2 + Peak co-eluting with solvent in Column 1 # Peak co-eluting with solvent in Column 2 * Isomer not determined Although this sidecutting technique allows the sample to be processed on the MS without the potential damage and interference from the solvent peak, it does not take into account any peaks which will co-elute with the solvent on the primary column – these peaks would not enter the secondary column or be seen by the MS. Close examination of Figure 9 reveals that two peaks are missing from this chromatogram at approximately 3.42 and 3.67 minutes that were present in Figure 8. These clearly must co-elute with the solvent on the primary column. To enable these (and possibly other) peaks that co-elute with the solvent to be transferred to the second column for separation, a peak sectioning technique was used to deliver time-incremented narrow heartcuts of the solvent peak from sample Figure 11 shows successive runs of the same DCM sample. how the solvent peak was sectioned into six 0.02-minute heartcuts that each produced chromatograms shown in Figure 12. This approach allows the area under the solvent peak on the first column to be fully mapped by the second without exposing the MS detector to large amounts of solvent. 16psig (110kPa) Scan Time 1.00 5 Helium Temperature Flame Ionization Clarus 600 MS 4 0.50 Value Detector 2 Column1 5 0.00 Figure 9. MS TIC with DCM solvent peak sidecut. The switching valve was turned off between 1.68 and 1.80 minutes but was on for the rest of the run. 60°C isothermal for 8 minutes Detector 1 7.19 2.72 Table 2. Analytical Conditions. Description GC 3.41+ 4.56 0 Methylenechloride_Total_119 % P1 P1 1 2-methylbutane % 5.08 15m x 0.25mm x 1.0µm Elite-1 15m x 0.25mm x 1.0µm Elite-1 MS Identification 3.30 23+16psig 100mLsplit Nosolvent, 05-Feb-2009 + 10:23:10 Methylenechloride_NoSolvent_118 Solvent eliminated by sidecutting Solvent peak largely removed P2 P2 Figure 8. MS total ion chromatogram (TIC) of DCM Sample 3. 23+16psig 100mLsplit Nosolvent, 05-Feb-2009 + 10:35:34 Methylenechloride_NoSolvent_119 FID FID Split/splitless injector Injector For this work, a D-SwaferTM microchannel pneumatic switch was used as shown in Figures 1 to 4. This device is about the same size as a nickel coin. The internal microchannels are fabricated using laser etching. They are fully chemically deactivated to handle reactive analytes. In this instance the wafer was configured in a classical heartcutting configuration (Deans’ switch) to enable sample cuts to be directed from the effluent of the first column into the inlet of the second column as shown in Figures 5 and 6. The cutting operation is controlled through a solenoid valve programmed by GC timed events to apply a switching gas to direct the primiary column effluent between the wafer two outlets. Methylenechloride_Total_119 % % Component Figure 1. The D-Swafer Deans’ switching microchannel wafer A: F ID 5.38e5 100 Solvents are widely used in the pharmaceutical and food industries for a variety of purposes. It is important that such solvents are carefully QC tested prior to use to ensure that no unsafe levels of impurities are present. GC is normally the preferred technique for the determination of impurities in solvents. The inclusion of a mass spectrometric detector enables the identities and quantification of trace-level impurities to be established. Because many solvents are produced by fractional distillation, their impurities will have similar boiling points to that of the solvent. Thus in GC, the retention times will be similar to that of the solvent and the risk of co-elution can be high. Furthermore, if the MS is kept active during solvent elution, contamination of the ion source or analyzer may result and the risk of filament damage is greatly increased. This poster describes a heartcutting technique that allows the entire injected sample to reach the detector and yet resolve the issues with solvent peak resolution and potential detector damage. 2 23+16psig 100mLsplit Total, 05-Feb-2009 + 11:55:02 23+16psig 100mLsplit No Cut, 04-Feb-2009 + 20:07 :30 Introduction 2.00 3.00 4.00 5.00 6.00 7.00 Figure 12. Chromatograms from successive 0.02-minute heartcuts 8.00 9.00 Time Although we have shown the application of this technique just to samples of dichloromethane, dichloromethane the same approach could be extended to other solvents or any sample where there is an interest in identifying and quantifying compounds at low levels that co-elute with other relatively large peaks. PerkinElmer, Inc., 940 Winter Street, Waltham, MA USA (800) 762-4000 or (+1) 203 925-4602 www.perkinelmer.com