GCxGC – MS With Supersonic Molecular Beams

1. Isranalytica 2006 GCxGC – MS With Supersonic Molecular Beams Maya Kochman and Aviv Amirav School of Chemistry, Tel Aviv University, Israel Email: kochman@tau.ac.il, amirav@tau.ac.il

2. What is GCxGC? GCxGC is a gas chromatographic technique which offers superior resolution and separation power compared to conventional gas chromatography (GC). Unlike GC, which consists of only one column, GCxGC consists of two columns, the first is typically non polar, separating the sample according to its volatility, while the second is a polar column for further orthogonal sample separation in time according to its polarity. These two columns are serially coupled, with a modulation mechanism at their junction (thermal or flow). An important advantage of flow modulation is its ability to tune the second column injection bandwidth with the second column flow rate. As a result, one can choose ~0.3 sec second column injection bandwidth that enables (with a minor traded second GC column separation) the use of quadruple mass analyzer with its limited scan speed such as 10 Hz for 350 amu mass range . Why Supersonic GCxGC-MS Supersonic GC-MS provides enhanced molecular ion which is always present together with ultimate amount of mass spectral information. Consequently, Supersonic GCxGC-MS could serve for the provision of ultimate sample information through a combination of best GC separation and MS information techniques.

3. Flow Modulation GCxGC Supersonic -MS Originally developed by John Seeley (Oakland University, Rochester MI) as a low cost reliable GCxGC method.

4. Rotary 200 l/min Turbo Make-up gas 70 l/s Calibration Cluster CI Pulse Generator agent agent 3-way solenoid valve Turbo injector 250 l/s EFC Gas Y-union Mixing 1st col 1 2 3 Sample loop Skimmer SGE union 4 2nd col Supersonic Nozzle Transfer Line GC Temp. GC oven Fly-Through Controlled EI Ion Source Y-Vu-union connector Restek (2) Y-Vu-union connector Restek (1) 2nd col GCxGC-SMB-MS System EPC (in) MS HSI Surface & Ion Mirror Y-Vu-unionconnector Restek (3) SGE Inlet Splitter(4) 1st col Sample loop B Sample loop A 0.5 m megabore

5. 120 Diesel Fuel Analysis 100 80 A. GCxGC-SMB-MS 60 40 20 0 35 B. GC-SMB-MS 25 15 5 0 5 15 10.00 20.00 Time (min)

6. 161 176 160 GCxGC-SMB-MS OF DIESEL FUEL 147 104 117 133 91 190 131 300 100 200 100 200 300 154 142 212 182 127 300 226 115 m/z 300 100 200 100 200 Time (min) 4.86 4.90 4.94 4.98 Note the separation according to polarity - thus reduce mass over the time

7. Isomers Distribution Information 30 RSIM 212 20 10 0 30 RSIM 226 20 10 30 RSIM 240 20 10 Time (min) 5.00 6.00 7.00 8.00 9.00 Branched hydrocarbons isomers elutes earlier due to their slightly increased volatility but significantly lower melting points hence providing valuable information concerning jet fuels analysis.

8. 304 179 A. GCxGC-SMB-MS NIST Hit # 1 Match: 674 R.Match:714 Prob.:93.9 16 152 199 276 137 14 227 57 248 97 12 m/z 100 200 300 10 8 6 4 2 8.40 8.50 8.60 0 Time (min) 304 B. GC-SMB-MS 10 250 NIST Hit # 1 Match: 463 R.Match:551 Prob.:48.2 179 203 218 152 95 278 135 8 100 200 300 62 m/z 6 4 Time (min) 8.50 8.60 8.70 Diazinon 100 ng/g in Coriander GCxGC helps to clean the mass spectra, and as a result, the chromatographic separation is superior.

9. 30 35 25 15 5 0 8.52 8.54 8.56 8.58 20 304.1 20 10 305.1 306.1 307.1 10 304.0 305.0 306.0 307.0 308.0 m/z 0 Time (min) 2.00 4.00 6.00 Zoomed Scan (304-308 amu) of Diazinon in Coriander for Improved IAA IAA confirmed NIST identification IAA Match = 981 Error = 0.149% Zoomed scan of 100 ppb Diazinon in the narrow mass range of 304-8 amu provides clean baseline with high S/N and enables independent IAA identification of Diazinon plus the conformation of it NIST identification

10. 355 281 248 73 221 147 m/z 4- 6 1 5 3 107 3 143 4 128 224 175 193 68 2 0.5 3 m/z 2 2 1 1 1 0 0 100 200 300 400 100 200 300 400 0 200 300 400 100 0 Time (min) 248 11.30 11.00 11.20 11.10 355 73 107 281 143 192 3 226 175 m/z 2 1 0 Time (min) 11.10 11.20 11.30 Thionazin 500 ppb in Coriander NIST-hit #1 Match-569 R.Match-734 Prob-47.8 Thionazin NIST- no hit

11. Pyrene 10 ppb SIM 202 amu 1700 A. GCxGC-SMB-MS Intensity 100 B. GC-SMB-MS Intensity Time (min) 10.90 11.00 11.10 GCxGC provides better sensitivity. In this case the tailing pyrene (due to prolong pesticide analysis) sensitivity was improved by 17 times.

12. Flow Modulation Supersonic GCxGC-MS versus Thermal Modulation GCxGC-TOF-MS Supersonic GC- MS provides enhanced molecular ion and ultimate mass spectral information. In contrast, GC- MS with Time of Flight MS provides reduced molecular ion and mass spectral information (in comparison with standard GC- MS) due to its use of an ion detector without high voltage conversion dynode, and especially since the fast ion source response time needed for the very narrow thermal modulation GCxGC peaks requires about 80ºC hotter ion source temperature (20ºC for each factor of two faster ion source response time). As a result, the molecular ion is significantly reduced (in GCxGC-TOF) and is often absent, hence MS based sample identification is compromised. Supersonic GCxGC- MS provides ultra-fast ion source response time regardless to sample volatility, combined with enhanced molecular ion and confidence level in sample identification.

13. Flow modulation GCxGC – MS • Advantages • Unique compatibility with SMB-MS due to the need of high flow rate in the second column. • 2. Unique compatibility with quadruple SMB-MS in view of the ability to tune the second column injection bandwidth according to the first and second columns flow rates ratio. • 3. The GCxGC-SMB-MS combination benefits from the superior characteristics of SMB-MS: • a. Highest Level of Information -Enhanced molecular ion, extended isomer and structural information, exact isotope abundance and elemental information, tunable fragmentation and improved library identification. • b. Lowest Detection Limits -Enhanced molecular ion for minimal matrix interference and best RSIM sensitivity for difficult molecules, ion source tailing free peaks. • 4. The flow modulator is simple, inexpensive, durable, and has no inherent temperature limitations. • Disadvantages • Limited first column flow rate of about 1ml/min. • Reduced separation in the 2nd column (verses thermal modulation) due to high flow rate. • 3. Non-flexible flow modulator in terms of dimensions, flow rates and columns selection, thus tedious to optimize. • 4. The modulator, the main core of the system, is constructed from four unions that may generate problems of leaks and dead volume. GCxGC-SMB-MS Ultimate sample information with 2DGC separation and improved MS