Nitrogen and Hydrogen as Alternate Carrier Gases for GC/MS
Authors: William Goodman, Andy Tipler, Adam Patkin, Padmaja Prabhu – PerkinElmer, Inc.
1
2
Introduction
Experimental
The PerkinElmer® Clarus® 600 GC/MS was used for the
experiments throughout this paper. The system performance
baseline was determined with the use of helium carrier gas, and
a 30 m x 0.25 mm, Elite-5MS column, as is common in GC/MS
applications. Once a baseline was established, identical method
parameters were applied to nitrogen and hydrogen. The effect
of carrier gas was noted.
The chromatographic conditions were then optimized for both
nitrogen and hydrogen. The major modifications were to the
carrier gas pressure/flow to achieve optimum efficiency and
runtime.
Nitrogen and hydrogen are commonly used and well
understood as carrier for gas chromatography with traditional
detection (FID, TCD, ECD). However, GC applications with
mass spectrometer (MS) detection are almost exclusively
performed with helium carrier gas.
As a result of a number of different factors, the price of helium
gas, has increased in recent years (Figure 1 A). Outside the
United States, the price of helium is considerably higher than
nitrogen and hydrogen (Figure 1 B).
Beyond price, there are a number of other considerations
necessary when choosing a carrier gas (Table 1). Hydrogen
and nitrogen can be generated in the laboratory. Laboratory
gas generators eliminate the need to transport high pressure
cylinders; saving time and reducing associated safety risks.
GC Method:
Injection Type –
Hot Splitless: 280 ˚C
Temperature Programmed
Splitless: 35 ˚C – 320 ˚C
GC
1.
2.
3.
Price per Metric Ton (U.S. $)
Column – Elite - 5MS
(30 m x 0.25mm ID x 0.25 µm)
(60 m x 0.25mm ID x 0.25 µm)
(20 m x 0.18mm ID x 0.36 µm)
Oven Program – 37 ˚C (0 min) –
260 ˚C @ 20 ˚C/min (0 min) –
280 ˚C @ 8 ˚C/min (0 min) –
320 ˚C @ 40 ˚C/min
A
12000
MS Method:
Full Scan Range - 50–300 Da
Transfer Line – 320 ˚C
10000
8000
6000
Scan Time - 4 Scans/Sec
Ion Source - 280 ˚C
4000
Figure 2: GC and MS conditions used throughout this experiment.
2000
0
1940
1950
1960
1970
1980
1990
2000
Regional Cost of Carrier Gas (2008)
2010
B
€ 500.00
€ 400.00
Helium
€ 300.00
N2
H2
(50 L, 2400 psi)
(50 L, 2400 psi)
A mixture of common analytes including PAHs, PCBs, phenols,
phthalates and pesticides was used as a test application. These
analytes span a wide boiling point range, allowing for the
determination of the effectiveness of a carrier gas across a
number of different specific applications.
(50 L, 2400 psi)
3
€ 200.00
Injection Method Considerations
€ 100.00
€ 0.00
USA
France
Brazil
China
Germany
Taiwan
Figure 1: (A) Cost of helium in the U.S.A over time – this reflects the transition of
government controlled vs. market prices. (B) The price of carrier gas varies widely
throughout the world – this chart demonstrates the price of 50 L in a selection of countries
in mid 2008.
Gas
Cost
Speed of
chromatography
Chromatographic
efficiency
Flow permeability
Supply
Safety concerns
Helium
Hydrogen
Nitrogen
Expensive
Medium
Low cost
Fast
Low cost
Slow
Low
Low
Pressurized
tank
Medium
High
High
Low
Pressurized tank or Pressurized tank
or nitrogen
electrolytic hydrogen
generator
generator
Highly explosive
Table 1: Necessary
considerations when
choosing a carrier gas
for GC and GC/MS.
One major consideration when choosing an alternate carrier gas
in GC/MS is that the column outlet is at vacuum rather than
ambient pressure, as it is with traditional detectors. This
dramatically reduces the column head pressure required to
provide a given column flow/linear velocity.
Table 2: Comparison of column head pressure at specific flow rates with each carrier.
Carrier
Gas
Type
Column Column
Length Diameter
(m)
(µm)
GC Start
Temperature
(˚C)
Chromatographic performance
Beyond the scope of cost reduction, there are
advantages to using hydrogen as a carrier gas, with
regard to reducing the chromatographic run time.
Figure 3 demonstrates the effect of head pressure on a
splitless injection of methylene chloride. At high temperature,
the solvent expands rapidly; the high head pressure of helium
mitigates the problem, while the low pressure of a hydrogen
injection results in uncontrolled solvent expansion and severe
solvent tailing. The issue of solvent expansion can be over
come by selecting a different column geometry, such as 60 m,
which achieves a head pressure with hydrogen which will
control solvent expansion (Figure 3 C) or by using a different
injection technique such as temperature programmed
injection, TPI, (Figure 3 D).
051508he_03
Inlet
Outlet
Flow
Velocity Pressure
Pressure (mL/min) (cm/sec)
(psig)
Helium
Hydrogen
Nitrogen
Helium
Hydrogen
Nitrogen
Helium
Hydrogen
Nitrogen
30
30
30
60
60
60
20
20
20
250
250
250
250
250
250
180
180
180
37
37
37
37
37
37
37
37
37
Vacuum
Vacuum
Vacuum
Vacuum
Vacuum
Vacuum
Vacuum
Vacuum
Vacuum
1
2
1
1
1.5
0.5
0.75
0.75
0.5
36.3
76.1
38.2
25.7
46.6
19.1
38.5
57.1
33.1
7.1
6
6
16.2
10.8
6
15.1
5.4
8.4
Helium
Hydrogen
Nitrogen
Helium
Hydrogen
Nitrogen
Helium
Hydrogen
Nitrogen
30
30
30
60
60
60
20
20
20
250
250
250
250
250
250
180
180
180
37
37
37
37
37
37
37
37
37
Ambient
Ambient
Ambient
Ambient
Ambient
Ambient
Ambient
Ambient
Ambient
1
2
1
1
1.5
0.5
0.75
0.75
0.5
25.1
51.3
25.7
20.5
34.6
12.9
30.4
37.8
23.5
11.6
10.8
10.7
19.5
14.7
10.7
18.5
10.2
12.7
Figure 3: Demonstration
of the effect of head
pressure on a splitless
injection.
Chromatogram A:
helium carrier achieves
expected
chromatography
Chromatogram B:
hydrogen carrier,
demonstrates severe
solvent tailing
Chromatogram C:
hydrogen with increased
column length (60 m)
Chromatogram D:
nitrogen with TPI.
4
6.82
10.17 10.43
11.58
4.10
4.51
21.53
18.93
4.72
12.00
17.00
10.47
11.23
15.75 15.98
13.70
14.23
12.63 13.18
14.87
Scan EI+
TIC
4.26e8
5.80
7.48
Hydrogen
8.84 9.09
%
10.53
5.57
4.55
4.99
6.66
7.28
6.11
7.85
9.21
8.61
10.70
10.03
4.26
11.73 12.09
11.06
12.63
13.82 14.11
0
051408n2_08a
6.93
5.81
8.66
7.54
10.06
6.73
4.03
4.57
5.61
6.04
6.64
7.87
7.22
8.56
Nitrogen
10.32
8.95 9.42 9.76
10.37
11.85
11.80
11.96
11.19
13.53
15.61 15.86
13.03
14.06 14.28
13.08
14.08
0
22.00
4.08
5.08
6.08
7.08
8.08
9.08
10.08
11.08
12.08
Scan EI+
TIC
1.33e8
15.08
Time
16.08
27.00
16.79
4.09
8.09
6.38
16.32
10.25 11.43
%
8.91
19.70
13.59
13.21
21.95
18.79
Figure 5: Comparison of the time for chromatography with helium, hydrogen,
and nitrogen as carrier gas.
B
23.22 25.49
15.38
0
Time
7.00
100
12.00
17.00
9.89 11.08 11.72
22.00
27.00
32.00
37.00
12.90
8.95
C
14.83
7.88
14.00
17.11
15.76
7.06
18.90
20.10
21.35
22.98
29.12
27.32
0
Time
8.25
10.25
100
4.93
%
11.96
12.11
9.86
10.70
5.60
Time
%
9.24
8.36
6.39
100
22.62
0
100
8.67
7.32
6.17
%
17.13 17.90
16.49
7.00
7.86
6.13 6.59
5.70
5.35
0
051408h2_04
A
15.21
14.14
4.24
4.03
Helium
13.03
9.78 10.41 12.68
6.61 7.63 8.60
6.42
%
8.76
%
12.25
6.94
5.81 6.73
7.55
14.25
16.25
18.25
20.25
4.03 4.43
5.62
6.50
7.23
24.25
26.25
28.25
D
10.32
3.53
7.87
22.25
8.67
11.85
11.96
8.95 9.76
15.86
13.55 14.07
11.19
0
As expected, it is possible to reduce run times while
maintaining efficiency when using hydrogen carrier gas. In
this example, without modifying GC oven parameters, the
analytical time was reduced from approximately 16 minutes
with helium to approximately 14.25 minutes with hydrogen.
Additional gains can be made with further changes to GC
oven program and column dimensions.
Time
4.75
6.75
8.75
10.75
12.75
14.75
16.75
6
MS System Performance
Following the optimization of the GC parameters, it is
necessary to consider the effect of alternate carrier gas on
the MS system. The most notable difference is with nitrogen
as carrier. Changes must be made to the instrument tuning
to achieve maximum sensitivity, details are presented in
table 3). The tuning of the MS for helium and hydrogen was
similar.
Helium/ Hydrogen
Nitrogen
EI+
EI+
250
320
70
100
1
5
100
10.5
11.5
1.5
1
400
250
320
70
100
1
1
100
14
11
0.5
1
400
S/N:RMS=1360.48
100 9.04
A common challenge throughout each of these techniques is
the low head pressure as a result of the low viscosity of
hydrogen and low optimal flow of nitrogen. A possible
workaround is to choose a column with different geometry,
smaller I.D. or increased length. Additionally, tools such as
temperature-programmed injection and solvent purge can
be used to reduce the impact of solvent expansion.
A
%
9.69
0
Time
9.10
9.30
9.50
9.70
9.90
S/N:RMS=489.25
7.85
100
B
%
8.48
7.54
0
Time
7.60
7.80
8.00
8.20
C
%
9.94
0
Time
9.10
9.30
9.50
9.70
After optimization, hydrogen carrier gas is suitable for
GC/MS analysis. It will reduce run times and maintain
resolution. It has demonstrated similar sensitivity in realworld applications, but requires extra safety precautions.
8.40
S/N:RMS=352.00
100
Conclusion
Many common GC/MS techniques have been optimized with
helium carrier gas. As a result, there are a number of
challenges when trying to duplicate these techniques with
alternate carrier gases. Discussed in this presentation are:
hot, splitless injection and pressure pulse injection.
Table 3: Comparison of optimized tune conditions with the use of helium
and hydrogen as carrier and nitrogen carrier.
Polarity
Source Temp (C)
GCLine Temp (C)
Electron Energy
Trap Emission
Repeller
Lens 1
Lens 2
LM Resolution
HM Resolution
Ion Energy (V)
Ion Energy Ramp
Multiplier (V)
7.64
5.90
5.01
4.92
100
Scan EI+
TIC
1.35e9
7.03
100
100
Carrier Gas – Helium, Hydrogen,
Nitrogen
14000
1930
5
Injection Volume – 1 µL
Utilizing an alternate carrier gas in GC/MS introduces a
number of unique challenges into the method design. The
focus of this presentation is to look at the practical application
of nitrogen and hydrogen as carrier gas in GC/MS.
United States Helium Cost vs. Year
The reduction of head pressure required to reach an optimal
flow/velocity has an effect on the injection performance,
especially if a hot splitless injection is performed. Hot,
splitless injection is commonly used to maximize sensitivity in
GC/MS applications, often in combination with a pressure
pulse to further sharpen chromatographic peaks.
9.90
Figure 4: Comparison of the phthalate response of the GC/MS system with each
carrier gas. Carrier gas and MS tune parameters were optimized in each example:
chromatogram A, helium; chromatogram B, hydrogen; and chromatogram C, nitrogen.
Nitrogen carrier gas has limited applicability to GC/MS
applications, but is suitable for analyses where high
sensitivity is not needed. It does, however, require
modifications to tune parameters to optimize MS
performance.
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