Application Note. Author. Abstract. Energy & Chemicals - Petrochemicals. Edgar Naegele, Agilent Technologies, Inc. Waldbronn, Germany

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1 Determination of Aromatic Hydrocarbons in Petroleum Middle Distillates with the Agilent Infinity Binary HPLC System with RID Detection According to IP9()/ASTM D9 Application Note Energy & Chemicals - Petrochemicals Author Edgar Naegele, Agilent Technologies, Inc. Waldbronn, Germany Abstract This Application Note shows the determination of aromatic hydrocarbons under normal phase conditions with the Agilent Infi nity Binary LC system with RID detection in compliance with the IP9()/ASTM D9 methods. Nagesh Babu and Sumitra Sankar Gulf Bio Analytical, United Arab Emirates, Dubai

2 Introduction The IP9()/ASTM D9 methods cover the determination of mono-aromatic (MAH), di-aromatic (DAH), and poly-aromatic hydrocarbon (TRI+) contaminants in petroleum middle distillates and diesel fuels boiling in the range from C to C, for example gas oil. The aromatic hydrocarbon content of motor diesel fuel is a factor that can affect exhaust emissions and fuel combustion characteristics, as measured by the cetane number. Using this instrumental setup, it is possible to determine mono and di-aromatic hydrocarbons according to IP/ASTM D79. It is also possible to determine the total aromatic hydrocarbons and total saturates according to ASTM D79. This Application Note shows the possibility to determine aromatic hydrocarbons under normal phase conditions with RID detection by using the Agilent Infinity binary LC system while complying with the IP9()/ ASTM D9 methods. Experimental Instruments Agilent Infi nity LC System Agilent Infinity Binary Pump (GB) with Agilent Infinity Standard Degasser (GA) Agilent Infinity Standard Autosampler (G9B) with Agilent 9 Infinity Thermostat (GB) Agilent Infinity Thermostatted Column Compartment (GA) with Agilent Infinity Series Quick-Change -postition/-port valve (G A). Agilent Infinity Refractive Index Detector (GA) Software Agilent OpenLAB CDS ChemStation Edition for LC & LC/MS Systems, Rev. C.. Columns Agilent ZORBAX NH,. mm, µm (p/n ) Agilent ZORBAX NH, Guard Cartridges,.. mm, µm (p/n 89-98) Agilent ZORBAX High Performance Guard Fittings Kit (p/n ) Reagents Mobile Phase: Heptane, HPLC Grade Standards System Performance Standard (SPS) - ASTM-P--PAK: cyclohexane ( mg/ml), o-xylene ( mg/ml, MAH), dibenzothiophene ( mg/ml, DAH), 9-methylanthracene ( mg/ml, TRI+). Calibration Standard: ASTM-P--SET Std. Std. Std. Cyclohexane o-xylene (MAH).. Debenzothiophene (DAH).. 9-Methylantracene (TRI+).. Std.

3 LC method RID Peak width >. minutes ( second response time) (.8 Hz) Temperature. C Column compartment Initial valve position Port & Temperature. C Change valve position 7.8 minutes: Port & Sampler Injection mode Standard injection Injection volume. μl Needle wash in vial with heptane Binary pump Flow. ml/min Stop time. min Solvent A Heptane, isocratic Valve operation (Figure ) In the OFF position, the sample is injected into the column through the autosampler. Once the DAH is eluted from the column, the valve is switched to the ON position, which reverses the flow in the column, backflushing the TRI+ aromatics to the RID detector. The time B (seconds) for switching to backflush is calculated based on an injection of the System Performance Standard (SPS) without valve switching using the following equation: B = t A +. (t B t A ) A Pump Autosampler B Pump Autosampler NH-column NH-column Detector Where: t A is the retention time of dibenzothiophene (DAH), in seconds. t B is the retention time of 9-methylanthracene (TRI+), in seconds. Detector Figure. Valve configuration for the IP 9 method. A) OFF Position & is the loading position. B) After switching to ON position & the compounds are eluted and analyzed in backflush.

4 Sample preparation Place between.9 g to. g of sample, to the nearest. g, into a -ml volumetric flask and fill to the mark with n-heptane. Shake thoroughly to mix, and filter the sample to remove the particulate matter. RID, Refractive index signal Non-aromatics. Mono-aromatics.97 Di-aromatics.8 Results and Discussion With the final method, all four calibration standards were measured (Figure ). The measurement showed a good separation of the inherent compounds, a clear separation of the aromatic compounds from the aliphatic cyclohexane, and a separation of the poly nuclear aromatic hydrocarbons to a much higher retention time. This is necessary for their determination in real samples. For the non-aromatic as well as aromatic compounds (MAH, DAH, TRI+), individual calibration curves were created. They ranged from to mg/ml for cyclohexane,. to mg/ml for MAH and DAH, and. to mg/ml for TRI+ aromatics (Figure ). All calibration curves for the aromatic hydrocarbons showed linearity coefficients better than To determine the limit-of-detection (LOD), the signals and the noise were measured for a / dilution of Standard. The typical LOD for aromatic compounds is µg/ml (calculated for a signal-tonoise ratio of ). Statistical evaluation of retention time and area for the aromatic compounds by multiple injection of calibration standard level showed RSD values typically below. % and. %, respectively (Table ). nriu tri+-aromatics Time (min) Figure. Overlay of IP9 Calibration standard (ASTM-P--SET), cyclohexane (non-aromatics), o-xylene (MAH), dibenzothiophene (DAH), 9-methylanthracene (TRI+). A Non-aromatics, RID A = *Amt 97.7 Correlation:.997,, C Di-aromatics, RID A =.*Amt Correlation:.99997,,, Figure. Calibration curves for the four compounds tested. B Mono-aromatics, RID A =.878*Amt +. Correlation:.99987,,, 8 D Tri+-aromatics, RID A =.88*Amt Correlation:.9998,,, Table. Statistical evaluation of retention time and area for the aromatic compounds by multiple injection (n = ) of calibration standard level. Mono-aromatics Di-aromatics Tri+-aromatics RT (min).7.. RT RSD (%)... RSD (%)... LOD (µg/ml).7

5 Figure displays a RI chromatogram of a real sample. This sample shows approximately. mg/ml of tri+aromatic compounds. Conclusion This Application Note demonstrates the use of the Agilent Infinity Binary LC in combination with the Agilent Infinity RI Detector for the determination mono-aromatic (MAH), di-aromatic (DAH), and tri+-aromatic (TRI+) contaminants in petroleum middle distillates and diesel fuels according to IP 9()/ASTM D9. The calibration of the RID showed excellent linearity for MAH, DAH, and TRI+ aromatics. The retention time RSD is typically below. % and the area RSD is typically below. %. nriu RID, Refractive index signal Non-aromatics Mono-aromatics Di-aromatics 8 Time (min) Figure. Real diesel oil sample showing aromatic compounds. Tri-aromatics References. IP9()/ASTM D9, Standard Test Method for Determination of Aromatic Hydrocarbon Types in Middle Distillates High Performance Liquid Chromatography Method with Refractive Index Detection.. D9.htm. Agilent Application Note, Publication number 99-7EN. Agilent Application note, Publication number 99-7EN

6 This information is subject to change without notice. Agilent Technologies, Inc., Published in the USA, December, 99-7EN