Analysis for and quantification of sulfur in crude oil, natural gas, petrochemicals, and industrial chemicals is critical to ensuring quality, process control, and safety for refinery, processors, and users. Understanding the speciation and concentration of sulfur compounds is vital in the hydrocarbon processing industry. Gas chromatography with sulfur chemiluminescence detection (GC-SCD) is one of the most powerful tools for sulfur analysis of hydrocarbons. This poster showcases the use of a new SCD for analysis according to various ASTM methods.

1. Sulfur Analysis by GC-SCD using
Shimadzu’s SCD-2030 for ASTM D5504,
D5623, and D7011
Shimadzu Scientific Instruments, Columbia, MD

2. Introduction
Analysis for and quantification of sulfur in crude oil, natural gas, petrochemicals, and
industrial chemicals is critical to ensuring quality, process control, and safety for
refinery, processors, and users. Sulfur is naturally present in raw hydrocarbon
materials and often needs to be removed to ensure processing efficiency because
sulfur can poison precious-metal catalysts. Furthermore, some sulfur species, such as
H2S present safety and health hazards to processors and end users. Finally, some
sulfur compounds are intentionally added into finished products, such as odorants in
natural gas.
For all of these reasons, understanding the speciation and concentration of sulfur
compounds is vital in the hydrocarbon processing industry. Gas chromatography with
sulfur chemiluminescence detection (GC-SCD) is one of the most powerful tools for
sulfur analysis of hydrocarbons.

3. Techniques for Sulfur Analysis
Method Advantages Disadvantages
ICP-OES • High sample throughput
• Rugged for difficult matrices
• Multi-element capability
• Sensitive into ppb range
• High initial and operating costs
• No speciation information
• May need sample digestion
• Liquid samples only
ICP-MS • High sample throughput
• Multi-element capability
• Sensitive into ppb to ppt range
• High initial and operating costs
• No speciation information
• May need sample digestion
• Spectral interferences
• Liquid samples only
XRF • Multi-element capability
• Minimal sample preparation
• Minimal laboratory infrastructure
• Solid and liquid samples without
digestion
• Slightly slower than ICP
• Lower sensitivity (10s of ppm)
• No gas samples
GC-FPD • Speciation information
• Liquid or gas sampling
• Slower throughput than ICP or X-ray
• Sensitive to matrix quenching
GC-SCD • Speciation information
• Liquid or gas sampling
• Sulfur specific
• Very sensitive for sulfur into low ppb
range
• Slower throughput than ICP or X-ray
• Only for sulfur
• Higher up-front costs
Table 1: Typical methods for sulfur analysis in petrochemical products with generalized
advantages and disadvantages.

4. ASTM Methods for Sulfur by GC-SCD
Method Title Sample Type Technique
ASTM
D5504
Determination of Sulfur Compounds in
Natural Gas and Gaseous Fuels by
Gas Chromatography and
Chemiluminescence
• Natural gas
• Air
• Digester gas
• Landfill gas
• Refinery fuel gas
• GC-SCD
ASTM
D5623
Sulfur Compounds in Light Petroleum
Liquids by Gas Chromatography and
Sulfur Selective Detection
• Distillates
• Gasoline
• Petroleum liquids
with final B.P. ~230°
• GC-SCD
• GC-FPD
• GC-PFPD
ASTM
D7011
Determination of Trace Thiophene in
Refined Benzene by Gas
Chromatography and Sulfur Selective
Detection
• Benzene • GC-SCD
• GC-FPD
• GC-PFPD
Table 2: Selected ASTM test methods for analysis of sulfur in petrochemicals using gas chromatography

5. ASTM D5504 – Sulfur in Natural Gas and
Gaseous Fuels
Sulfur compounds are commonly found in natural gas, gaseous fuels, and other high-
methane gases. Some are naturally occurring, whereas other compounds are
deliberately added to the gases due to their smell to provide an indicator of a gas leak.
The assessment of sulfur in natural gas is critical to efficient refining, meeting
environmental regulations, and for safety purposes.
ASTM D5504 provides a framework for the assessment of sulfur in natural gas using
GC-SCD. This method has also been applied to digester gas, landfill gas, refinery gas,
and atmospheric air.
Figure 1: Generalized instrument flowpath for ASTM D5504 analysis.

6. Method ASTM D5504 Results
Three gas samples were prepared for analysis: 1) 14 sulfur compounds in nitrogen at 1
ppm, 2) blank nitrogen, 3) sulfur-free natural gas. Standards were prepared by diluting
Gas 1 with blank nitrogen at 50, 100, 500, and 1000 ppb (v/v). The sulfur-free natural
gas was also spiked with sulfur compounds at 50 ppb. The samples were analyzed
according to Table 4. Linearity of the calibration curves was calculated as well
as %RSD for five repeat analyses of the 1 ppm standard.
Instrument: Nexis GC-2030 with AOC-20i plus
Valve: 6-port valve from Restek
Sample Loop Volume: 1 mL
Injector: SPI
Column: SH-Rtx™-WAX (60 m × 0.53 mm I.D., df = 7 μm)
Post Column: Deactivated Fused Silica Tubing (0.3 m × 0.32 mm)
Detector: Nexis SCD-2030
Injection Mode: Split
Sample Introduction: 1 : 9
Injector Temperature: 150° C
Carrier Gas: Helium
Carrier Gas Control: Constant Column Flow – 6.00 mL/min
Column Temperature: 30° C (1.5 min. hold)  Ramp 10° C/min  200° C (3 min. hold)
Interface Temperature: 200° C
Furnace Temperature: 850° C
Detector Gases: H2 100 mL/min; N2 10 mL/min; O2 12 mL/min; O3 25 mL/min
Table 3: Analytical conditions for ASTM D5504.

7. Method ASTM D5504 Results
1) Nitrogen w/ 14 sulfur compounds 2) Nitrogen
Component Conc. Component Conc.
Balance Nitrogen 99.999% Balance Nitrogen 99.9995%
1 Hydrogen sulfide 0.93 ppm
2 Carbonyl sulfide 0.96 ppm 3) Natural Gas Standard
3 Methyl mercaptan 0.99 ppm Component Conc.
4 Ethyl mercaptan 0.98 ppm Balance Methane 86.595%
5 Dimethyl sulfide 1.00 ppm 1 Nitrogen 0.10%
6 Carbon disulfide 1.02 ppm 2 Carbon dioxide 0.30%
7 2-Propanethiol 0.95 ppm 3 Ethane 8.50%
8 t-Butanethiol 1.09 ppm 4 Propane 3.50%
9 1-Propanethiol 1.00 ppm 5 n-Hexane 0.05%
10 Methyl ethyl sulfide 0.98 ppm 6 Isopentane 0.05%
11 Thiophene 1.02 ppm 7 n-Pentane 0.05%
12 Diethyl sulfide 0.99 ppm 8 Isobutane 0.40%
13 n-Butanethiol 0.95 ppm 9 n-Butane 0.40%
14 Dimethyl disulfide 0.97 ppm 10 Oxygen 0.06%
Table 4: Composition of gas samples.

8. Method ASTM D5504 Results
Component
Linearity
(r2)*
Repeatability
(%RSD)**
1 Hydrogen sulfide 0.9999 1.09
2 Carbonyl sulfide 0.9999 0.35
3 Methyl mercaptan 0.9998 0.91
4 Ethyl mercaptan 1.0000 0.90
5 Dimethyl sulfide 0.9998 0.68
6 Carbon disulfide 1.0000 0.29
7 2-Propanethiol 0.9998 1.39
8 t-Butanethiol 0.9999 0.51
9 1-Propanethiol 0.9994 2.15
10 Methyl ethyl sulfide 0.9995 0.68
11 Thiophene 0.9998 1.06
12 Diethyl sulfide 0.9996 0.85
13 n-Butanethiol 0.9997 2.31
14 Dimethyl disulfide 0.9997 0.87
*
Linearity of 4-point calibration curve (50 ppb, 100 ppb, 500 ppb, 1000 ppb)
**
%RSD of 1 ppm standard (n=5)
Table 5: Linearity and repeatability results for ASTM D5504 analyses.
Table 5 demonstrates linearity and repeatability for all compounds that are within the
prescribed limits for ASTM D5504 validation.

9. Method ASTM D5504 Results
Figure 2: Chromatograms of sulfur compounds in nitrogen (black), sulfur compounds in natural gas (red),
and sulfur-free natural gas (blue).
The chromatograms shown in Figure 2 demonstrate selectivity for sulfur in nitrogen
and natural gas matrices. There are no erroneous peaks generated in the natural gas
matrix. Furthermore, the identical height and retention times of the nitrogen and
natural gas matrices demonstrate that no matrix quenching occurs during detection.

10. ASTM D5623 – Sulfur in Light Hydrocarbon
Liquids
Sulfur compounds are also found in liquid hydrocarbon fuels, such as gasoline, and
need to be minimized largely due to environmental regulations. When gasoline is
burned, sulfur compounds are oxidized and expelled into the atmosphere with the
exhaust and other combustion byproducts. These oxidized sulfur compounds react
with atmospheric water to form dilute sulfuric acid, or acid rain. As a result, the sulfur
content of gasoline is limited to 10 ppm by the U.S. EPA’s Tier 3 standards.
ASTM D5623 outlines the methodology for analysis of sulfur in hydrocarbon liquids
with final boiling point < ~230°C, including gasoline.

11. Method ASTM D5623 Results
Nineteen sulfur compounds were separated into two groups for optimal
chromatographic separation and diluted in toluene or n-Hexane. Diphenyl sulfide was
added at 1 ppm (w/w) as an internal standard. The samples were analyzed according
to Table 6. Linearity of the calibration curves was calculated as well as %RSD for five
repeat analyses of the 1 ppm standard. Long-term stability of signal was assessed
over 16 days using a standard containing all 19 compounds at 10 ppm (w/w sulfur)
and making repeated injections.
Instrument: Nexis GC-2030 with AOC-20i plus
Column: SH-Rxi™-1MS (30 m × 0.32 mm I.D., df = 4 μm)
Detector: Nexis SCD-2030
Injection Volume: 1 μL
Injection Mode: Split
Sample Introduction: 1 : 9
Injector Temperature: 275° C
Carrier Gas: Helium
Carrier Gas Control: Constant Column Flow – 2.80 mL/min
Column Temperature: 40° C (3 min. hold)  Ramp 10° C/min  2500° C (16 min. hold)
Interface Temperature: 200° C
Furnace Temperature: 850° C
Detector Gases: H2 100 mL/min; N2 10 mL/min; O2 12 mL/min; O3 25 mL/min
Table 6: Analytical conditions for ASTM D5623.

12. Method ASTM D5623 Results
Figure 3: Chromatograms for 19 compounds dissolved in different matrices.
Figure 3 demonstrates the separation and detection of the 19 sulfur compounds
without interference from the matrix itself.

13. Method ASTM D5623 Results
Figure 4: Relative response factors for 4 compounds over 16 day period.
The long-term repeatability study over 16 days (Figure 4) shows a relative response
factor of 1.2 to 1.6 %RSD, demonstrating long-term repeatability of analyses of
compounds with low and high boiling points.

14. Method ASTM D5623 Results
Component 0.1 ppm 1 ppm 10 ppm 100 ppm
Linearity
(r2)*
1 Methyl mercaptan 7.1% 1.8% 5.1% 3.0% 0.9999
2 Ethyl mercaptan 6.5% 1.5% 3.7% 2.3% 0.9999
3 Dimethyl sulfide 6.8% 1.3% 3.7% 2.4% 0.9999
4 Carbon disulfide 7.3% 1.9% 4.4% 2.7% 0.9999
5 2-Propanethiol 6.7% 1.4% 2.9% 2.0% 0.9999
6 2-Methyl-2-propanethiol 9.7% 2.8% 2.5% 1.9% 0.9999
7 1-Propanethiol 6.3% 1.4% 2.9% 1.9% 0.9999
8 Ethyl methyl sulfide 7.7% 1.8% 2.8% 2.2% 0.9999
9 Thiophene 6.7% 1.7% 2.8% 2.0% 0.9999
10 2-Butanethiol 8.5% 3.4% 1.7% 2.4% 0.9999
11 2-Methyl-1-propanethiol 8.5% 3.1% 1.7% 2.3% 0.9999
12 Diethyl sulfide 4.8% 2.9% 1.9% 2.3% 0.9999
13 1-Butanethiol 9.1% 3.8% 1.8% 2.4% 0.9999
14 Methyl disulfide 1.9% 2.6% 2.1% 2.3% 1.0000
15 2-Methylthiophene 9.7% 3.2% 1.8% 2.3% 0.9999
16 3-Methylthiophene 6.0% 2.8% 1.5% 2.4% 0.9999
17 Diethyl disulfide 3.7% 2.8% 1.8% 2.4% 0.9999
18 5-Methylbenzothiophene 9.4% 1.5% 1.9% 1.8% 0.9999
19 3-Methylbenzothiophene 9.6% 4.1% 1.7% 2.5% 0.9999
Table 7: Linearity and repeatability results for ASTM D5623 analyses.
Linearity and repeatability (Table 7) are within the parameters of ASTM D5423, with
linearity in particular being excellent for all compounds.

15. ASTM D7011 – Analysis of Trace
Thiophene in Benzene
High-purity benzene is a precursor used in many chemical manufacturing processes,
particularly as a building block for the synthesis of other aromatic compounds. The
majority of thiophene is removed from benzene, typically, through a sulfuric acid
“washing” procedure, but traces will remain. As is the case for sulfur compounds in
fuels, even low levels of thiophene can poison catalysts used in the synthesis process,
thereby rendering synthesis inefficient and reducing yields.
ASTM D7011 is used as a methodology for assessing trace levels of thiophene in
benzene and is crucial for process control in the chemical manufacturing industry.

16. Method ASTM D7011 Results
Standard solutions were made by diluting thiophene in thiophene-free benzene at
various concentrations ranging from 10 to 1000 ppb (v/v). Additionally, so-called “high
purity” benzene was used as a comparison to thiophene-free benzene. Details of the
analytical conditions within the GC and the SCD are provided in Table 8.
Instrument: Nexis GC-2030 with AOC-20i plus
Column: SH-Rtx™-WAX (30 m × 0.32 mm I.D., df = 1 μm)
Detector: Nexis SCD-2030
Injection Volume: 1 μL
Injection Mode: Split
Sample Introduction: 1 : 5
Injector Temperature: 125° C
Carrier Gas: Helium
Carrier Gas Control: Constant Column Flow – 2.00 mL/min
Column Temperature: 40° C (2 min. hold)  Ramp 10° C/min  100° C (1 min. hold)
Interface Temperature: 200° C
Furnace Temperature: 850° C
Detector Gases: H2 100 mL/min; N2 10 mL/min; O2 12 mL/min; O3 25 mL/min
Table 8: Analytical conditions for ASTM D7011

17. Method ASTM D7011 Results
The stacked chromatograms in Figure 5 demonstrate the elution and detection of
thiophene in benzene. Of note is the presence of thiophene even in so-called “high-
purity” benzene.
Figure 5: Comparison of high-purity benzene, showing
contamination, to thiophene-free benzene, and spike
samples of thiophene in benzene.

18. Method ASTM D7011 Results
Concentration
(ppb)
Retention
Time RSD
(%)
Area
RSD
(%) S/N Average
10 0.027 9.47 5.37
50 0.006 0.58 30.0
100 0.015 0.39 57.9
500 0.011 0.57 280
1000 0.013 0.51 544
Figure 6: Stacked chromatograms of standards and blank solvent showing minor sulfur
components in solvent and no peak at the time of benzene elution.
Table 9: Retention time and peak area RSDs and
signal-to-noise ratios for thiophene in benzene.
Table 9 shows the excellent repeatability of both retention time and peak area for trace
levels of thiophene in benzene as well as the signal to noise ratios. The stacked
chromatograms in Figure 6 show the presence of thiophene in benzene, as well as
trace levels of other sulfur compounds eluting at~1.65 minutes. Note that there is no
peak generated when benzene elutes off of the column.

19. Conclusions
• GC-SCD is one of the most powerful analytical techniques for analysis of sulfur,
particularly in petrochemicals and hydrocarbon matrices.
• The SCD-2030 is compliant with common ASTM test methods for sulfur in
petrochemicals, and meets or exceeds method specifications for ASTM D5504,
D5623, and D7011.
• Its large redox cell allows for complete oxidation and reduction of sulfur
compounds, yielding excellent sensitivity and selectivity for sulfur.
• Other features of the SCD-2030 provide for an easy-to-use and maintain
detector, such as the horizontally-mounted redox cell providing easy access to
consumable components and software automation functions that simply
operation.

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