1. With Supersonic Molecular Beams Maya Kochman and Aviv Amirav
Isranalytica 2006
GCxGC – MS
With Supersonic Molecular Beams
Maya Kochman and Aviv Amirav
School of Chemistry, Tel Aviv University, Israel

2. Why Supersonic GCxGC-MS
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.
WHY GCXGC-MS

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

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

5. Diesel Fuel Analysis A. GCxGC-SMB-MS B. GC-SMB-MS Time (min) 20 40 6020 40 60 80
100
120 35
10.00
20.00 5 15 25
Diesel Fuel Analysis
A. GCxGC-SMB-MS
B. GC-SMB-MS
DIESEL FULL SCAN

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

7. Isomers Distribution Information10 20 30
RSIM 212
RSIM 226
5.00
6.00
7.00
8.00
9.00
Time (min)
RSIM 240
Isomers Distribution Information
Branched hydrocarbons isomers elutes earlier due to their slightly increased volatility but significantly lower melting points hence providing valuable information concerning jet fuels analysis.
DIESEL ISOMERS

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

9. Zoomed Scan (304-308 amu) of Diazinon in Coriander for Improved IAA
m/z
Time (min) 10 20 30
2.00
4.00
6.00
304.0
305.0
306.0
307.0
308.0
304.1
305.1
306.1
307.1
8.52
8.54
8.56
8.58 5 15 25 35
IAA confirmed
NIST identification
IAA Match = 981
Error = 0.149%
Theory
Measured
m/z
100
304
15.28
15.17
305
6.11
6.35
306
0.78
0.58
307
0.08
0.10
308
IAA DIAZINON ZOOM SCAN
Zoomed scan of 100 ppb Diazinon in the narrow mass range of amu provides clean baseline with high S/N and enables independent IAA identification of Diazinon plus the conformation of it NIST identification

10. Thionazin 500 ppb in Coriander
100
200
300
400
0.5 1
248
355 73
107
281
143
192
175
226
11.10
11.20
11.30 2 3
Time (min)
m/z 4-
128
224
193 68 4 5 6
221
147
11.00
NIST-hit #1
Match-569
R.Match-734
Prob-47.8
Thionazin
Thionazin500ppb
NIST- no hit

11. 1700
Pyrene 10 ppb SIM 202 amu
A. GCxGC-SMB-MS
Intensity
100
PYR SENSITIVITY
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.
FLOW MODULATION GCGC SMB MS VS GCGCTOF MS

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.
ADD AND DISADD OF GCGC
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