The dedicated gas chromatograph for aromatic hydrocarbon analysis in finished gasoline is suitable for determining the content of benzene, toluene, ethylbenzene, xylene, C9 and above heavy aromatic hydrocarbons, and total aromatic hydrocarbons in finished automotive gasoline. The separation of aromatic hydrocarbons in finished gasoline is not affected by non aromatic interference. Non aromatic hydrocarbons with boiling points greater than n-dodecane can interfere with the determination of heavy aromatic hydrocarbons above C9. For C8 aromatic hydrocarbons, both para xylene and meta xylene flow out simultaneously, while ethylbenzene and ortho xylene are detected as single peaks. C9 and above heavy aromatic hydrocarbons are detected as a group of peaks.
The concentration range of aromatic hydrocarbons determined by the analysis system is: benzene, 0.1%~5% (volume fraction); Toluene, 1%~15% (volume fraction); C8 mono aromatic component, 0.5%~10% (volume fraction); C9 and above heavy aromatic hydrocarbons, 5%~30% (volume fraction); Total aromatic hydrocarbons, 10%~80% (volume fraction).
The common alcohol and ether compounds in gasoline do not interfere with the determination of aromatic hydrocarbons.
The instrument system fully complies with ASTM D5580, SH/T 0693-2000 "Determination of Aromatic Hydrocarbon Content in Gasoline (Gas Chromatography Method)"; It is essential to analyze the aromatic hydrocarbon content in finished gasoline. Suitable for various types of finished gasoline, with a wide range of applications. The alcohol ether compounds added to gasoline do not interfere with the determination, and the instrument can also be extended to include the determination of oxygen-containing compounds.

System flowchart:





Analysis chromatogram of aromatic hydrocarbon content in gasoline:

Figure 2 Analysis of Aromatic Hydrocarbons in Gasoline (First Analysis, Using Micro filled Pre column)
1-Benzene; 2-Toluene; 3-2-hexanone; 4- Backblowing peak (C8 and above aromatic hydrocarbons and C9 and above non aromatic hydrocarbons)

Figure 3 Analysis of Aromatic Hydrocarbons in Gasoline (Second Analysis, Using Micro filled Pre column)
1-2-hexanone; 2-Ethylbenzene; 3- p-xylene/m-xylene; 4-o-xylene; Aromatic hydrocarbons above 5-C9

Figure 4 Analysis of Aromatic Hydrocarbons in Gasoline (First Analysis, Using Capillary Pre column)
1-Benzene; 2-4-methyl-2-pentanone; 3- Toluene; 4- Backblowing peak (C8 and above aromatic hydrocarbons and C9 and above non aromatic hydrocarbons)

Figure 5 Analysis of Aromatic Hydrocarbons in Gasoline (Second Analysis, Using Capillary Pre column)
1-4-methyl-2-pentanone; 2-Ethylbenzene; 3- p-xylene/m-xylene; 4-o-xylene; Aromatic hydrocarbons above 5-C9

working principle
As shown in the above figure, the system is a dual column gas chromatography system equipped with a ten way switching valve and a hydrogen flame ionization detector. The complete analysis process requires two injections to achieve. During the first injection, the sample containing the internal standard 2-hexanone was injected into a pre cut column containing a polar stationary phase of 1,2,3-tris (2-cyanoethoxy) propane (TCEP). Non aromatic hydrocarbons smaller than C9 flow out of the pre cut column and are vented through the vent. This separation process can be monitored by a hydrogen flame detector or a thermal conductivity detector. Immediately place the pre cut column in a backflush state before the benzene flows out, and transfer the retained components into an analytical column (WCOT) containing non-polar stationary phase methyl silicone (OV-1). Benzene, toluene, and internal standard flow out of the chromatographic column in boiling point order and are detected using a hydrogen flame ionization detector. After the internal standard substance flows out, immediately blow back the analysis column and blow back the remaining components (C8 and above heavy aromatic hydrocarbons and C10 and above non aromatic hydrocarbons) out of the chromatography column into the hydrogen flame ionization detector.
During the second injection analysis, the blowback time of the pre column (TCEP) was adjusted to less than C12 for non aromatic hydrocarbons, benzene, and toluene before ethylbenzene flowed out. The retained internal standard and C8 aromatic components were introduced into the analysis column (WCOT) and flowed out in boiling point order for detection using a hydrogen flame ionization detector. When ortho xylene flows out, immediately blow back the analysis column (WCOT) and blow back the C9 or higher aromatic hydrocarbons from the chromatography column into the hydrogen flame ionization detector for detection.
Through the first analysis, the content of benzene and toluene can be obtained. Through the second analysis, the content of ethylbenzene, para/meta xylene, ortho xylene, and C9 or higher heavy aromatic hydrocarbons can be obtained. The total aromatic hydrocarbon content in the sample can be determined by two injections.
Instrument system configuration
1. Gas chromatograph (including split/non split injection ports, dual FID detection and monitoring, with automatic blowback and reset ten way switching valve)
2. Chromatographic column:
Pre cut column: a micro packed column with a length of 560mm, an outer diameter of 1.6mm, and an inner diameter of 0.38mm, filled with 20% (mass fraction) of 1,2,3-tris (2-cyanoethoxy) propane (TCEP)/chromosorb P (AW) 80-100 mesh stationary phase, or a capillary column with a length of 20m and an inner diameter of 0.35mm coated with TCEP stationary phase.
Analysis column: 30m long, 0.35mm or 0.53mm inner diameter, coated with 5.0Um or 2.6Um film thickness cross-linked methyl silicone elastic quartz capillary column.
3. Computer Workstation
4. Chromatographic gas source (high-purity nitrogen, high-purity hydrogen, pure dry air)
5. Standard samples
Mixing and cutting standard samples of iso octane solutions of benzene, ethylbenzene, o-xylene, and 2-hexanone (or 4-methyl-2-pentanone)
Qualitative standard sample of the sample
Calibration standard sample
Internal standard 2-hexanone standard sample
2,2,4-trimethylpentane (isooctane) solution of n-dodecane (for calibration)