Application Note
Energy and Chemicals

Analysis of Tetrahydrothiophene(THT) in Natural Gas Using theAgilent 990 Micro GCAuthor
Jie Zhang
Agilent Technologies, Inc.

Introduction
Natural gas, as a source of energy, is widely used for heating, cooking, and electricity
generation. When it leaks and the concentration in air reaches the explosive limit, it iseasy to ignite. Natural gas is odorless, so to detect a leak at an early stage, odorantis added as a leak indicator and warning agent.
Tetrahydrothiophene (THT) is an odorant that is widely used in Europe and China.
THT is easily detected by a person with a normal sense of smell, and it is stable anddoes not corrode the transport pipeline. However, there are odorant-fading factorsthat impact the real concentration or intensity of odorants over time, for example,
the adsorption or absorption to pipelines and contaminants in natural gas that mask
the odorant. The frequent and consistent monitoring of odorants is vital to maintaintheir effectiveness.
Controlling the concentration of THT at the lowest level while remaining effectiveis important for cost savings. In China, the THT limit is 20 mg/m3 (approximately5.6 ppm) by CJJ/T 148-2010. In Europe, the range is 10 to 40 mg/m3.
A previous work has shown that THT in natural gas can be analyzed on theAgilent 490 Micro GC.1 The same is true for the Agilent 990 Micro GC. The work
here demonstrated that the 990 Micro GC equipped with a CP-Sil 19CB channel caneffectively monitor trace‑level THT in simulated natural gas with good signal-to-noise
ratio (S/N).

Experimental

0.5The Agilent 990 Micro GC is equippedwith a 6 m, CP-Sil 19CB straight channel
for THT analysis.

0.4

Channel AnalyticalConditions

n-C9mv

Table 1. Test conditions for THT on anAgilent CP-Sil 19CB channel.

0.3
THT
0.2

0.1

n-C6n-C8

TBM n-C7

Setpoints

Column Pressure

200 kPa

Column Temperature

90 °C

Carrier Gas

HeliumInjection Time

255 ms00.175

0.275

0.375

0.475

Concentration (ppm)

Table 3. RT and area repeatability of 4 ppm
THT analyzed by the Agilent 990 Micro GC.

n-C6
tert-Butyl mercaptan

5.17

Injection no.10

RT (min)

Area (mv × s)

THT

4.0110.827

0.022

n-C9

3.94

20.8270.022

30.827

0.021

4

0.827

0.022

50.8270.023

60.827

0.022

7

0.827

0.022

80.8270.023

90.8270.022

100.827

0.022

Average

0.827

0.022

RSD%

0.019

2.5

Figure 1 shows the chromatogram of4 ppm THT on the CP-Sil 19CB channel.
The THT elutes at 49.6 seconds, octane
elutes at 31.3 seconds, and nonane
elutes at 52.7 seconds. The resolution
between THT and n-c9 is 2.1. The S/Nfor the 4 ppm THT peak is greater than
20 at applied test conditions, which isgood enough for trace-level THT analysis
in natural gas. Repeatability evaluation
was based on 10 injections of 4 ppm
THT. The area repeatability is 2.5%, andthe retention time (RT) repeatability is0.019%.

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© Agilent Technologies, Inc. 2019
Printed in the USA, June 24, 20195994-1042EN

0.775

0.875

0.975

1.075

1.175

Figure 1. Measurement of 4 ppm THT on an Agilent CP-Sil 19CB column.

4.95

Results and discussion

0.675RT (min)-0.1

Table 2. THT standard sample.
Compound0.575

Conclusion
An Agilent CP-Sil 19CB straightchannel can resolve THT fromother hydrocarbons in natural gas.
This midpolarity column has lessretention capability on the heavierhydrocarbons such as nonane, which
effectively improves the analysis speed
to approximately one minute. The
RT RSD% (<0.02%) and area RSD% (<3%)
demonstrates the excellent repeatabilityof THT analysis, which proves that
Agilent 990 Micro GC is an ideal platformfor THT analysis in natural gas.

Reference1.

Van Loon, R. Analysis of
Tetrahydrothiophene (THT) in
Natural Gas Using Agilent 490
Micro GC, Agilent Technologies
Application Note, publication number
5990‑8528EN, 2011.