Analysis of Polycyclic Aromatic Hydrocarbons in …

1 Analysis of Polycyclic Aromatic Hydrocarbons in Petroleum Vacuum residues by Multiple Heart-Cutting LC. Using the Agilent 1290 In nity 2D-LC. Solution Application Note Energy and Chemicals Authors Abstract Gerd Vanhoenacker, Mieke Steenbeke, Polycyclic Aromatic Hydrocarbons (PAHs) were determined in a petroleum Frank David, Pat Sandra, and vacuum distillation residue using the Agilent Multiple Heart-Cutting (MHC). Koen Sandra 2D-LC solution. The extract was analyzed in the rst dimension by normal-phase Research Institute for Chromatography LC. Well-de ned fractions from this separation were stored in a set of sample Kennedypark 26 loops, then transferred online to the second-dimension separation where the B-8500 Kortrijk PAHs were separated from each other and from other sample constituents using Belgium reversed-phase LC on a dedicated PAH column.

2 Detection was performed with diode-array detection (DAD) as the monitor detector after the rst dimension, Udo Huber and with uorescence detection (FLD) after the second dimension. An additional Agilent Technologies, Inc. column switching valve enabled back ush of the rst-dimension normal-phase Waldbronn, Germany column to remove highly polar components. The Agilent 1290 In nity 2D-LC. solution enabled automated, selective, and quantitative Analysis of the PAHs in the complex petroleum vacuum distillation residue sample. Introduction Online LC-LC, combining NPLC with Experimental RPLC, could be an interesting approach. Polycyclic Aromatic Hydrocarbons As demonstrated by of ine approaches4,5, Samples and sample preparation (PAHs) are monitored in petroleum NPLC is able to separate Aromatic and The sample was a petroleum vacuum products because of their higher toxicity Polycyclic Aromatic Hydrocarbons from residue.

3 The sample was dissolved at and carcinogenic activity. The relative the bulk of the saturated alkanes and 200 mg/mL in iso-octane/cyclohexane concentration of PAHs in a petrochemical cycloalkanes. The fraction containing 1/9 v/v prior to injection. product such as bitumen has an the PAHs can then be transferred to important impact on the total emission RPLC, while the retained polar fraction A PAH standard stock solution (PAH-Mix of Hydrocarbons into the environment is back ushed. NPLC and RPLC offer 25, YA20952500AB, Dr. Ehrenstorfer through hydrocarbon processing, excellent orthogonality. There are, GmbH, Augsburg, Germany) containing combustion, construction (for example, however, two challenges in online 2,000 g/mL PAHs in acetone/benzene roads), accidental leakage, and so on.

4 Hyphenation of NPLC and RPLC for PAH was diluted in iso-octane/cyclohexane Recent regulations have set limits on PAH. Analysis . First, the mobile phases used in 1/9 v/v to the appropriate concentration. content in various petroleum products, both modes are different and, in theory, including vacuum distillates, vacuum not compatible. Second, the PAHs elute in Instrumentation residues , and bitumen1. a rather large window. An Agilent 1290 In nity 2D-LC solution Several methods are used for the was used. The con guration is shown in The Agilent Multiple Heart-Cutting (MHC). determination of PAHs in high-boiling Figure 1, and described in Table 1. 2D-LC solution offers a smart valve setup petroleum products. These include that enables parking of multiple fractions liquid-liquid fractionation followed by The mixer was removed in the from the rst dimension and analyzing gravimetric determination2, fractionation rst-dimension pump to reduce the delay these sequentially as soon as the second using column chromatography or SPE volume.

5 To have suf cient backpressure dimension is ready for the next Analysis . followed by GC-MS analysis3, and on the rst-dimension separation, a In this way, the wide elution window of ine size exclusion chromatography calibration capillary (G1312-67500) was from the rst-dimension separation can or normal-phase LC (NPLC), combined installed between the pump and the be split into multiple smaller fractions, with reversed-phase LC (RPLC)4,5. autosampler. thereby enhancing overall peak capacity These techniques often lack sensitivity and separation power. Moreover, this or are highly labor-intensive and Software con guration also alleviates the problem time-consuming. The determination of Agilent OpenLAB CDS ChemStation of mobile phase incompatibility. The PAHs in high-boiling petroleum fractions Edition software, revision with complete analytical process of fraction is challenging due to the complexity of Agilent 1290 In nity 2D-LC software parking and transfer onto the second the matrix (including the presence of a revision dimension is software controlled.)

6 Polar fraction) and the low level of PAHs that need to be detected (< 1 mg/kg). The power of the Agilent MHC 2D-LC. Online multidimensional chromatographic solution is demonstrated by the Analysis techniques can be of interest here. of PAHs in a petroleum vacuum residue. Comprehensive GC GC has been used The method was validated (calibration, for group type separation of PAHs in repeatability) for a selection of PAHs that petrochemicals, including high-boiling also were quanti ed. fractions6,7. With the GC GC approach, PAHs fraction can be separated from the alkane or monoaromatic fraction, but Analysis of trace levels of individual PAHs in a bulk of high-boiling alkanes is dif cult. 2. 1 D-Detector 1260 In nity Fluorescence Detector Spectra Agilent 1290 In nity Thermostatted Column Compartment 1 D-Column 2 D-Column Agilent Polaris 3 NH2 Agilent ZORBAX Eclipse Plus PAH.

7 3 5 4. 1. 6 Waste 2. 5 6 2. Capillary dimensions 1 D-DAD 3. 1 1. 400 mm 3 Agilent 1290 In nity 4 Diode Array Detector 2. 50 mm 3. 100 mm 4 4. 40 mm 2 8 5. 200 mm 6. 200 mm Agilent 1290 In nity 5. 7. Autosampler 6. 2 D-Column 1. 2. 6 5. 1 4 . 3 . 3 IN 2 . 1 . 4. OUT. 5. 6. 1 D-Pump 2 D-Pump Agilent 1260 In nity Agilent 1290 In nity Binary Pump Binary Pump Figure 1. Con guration for multiple-heart cutting 2D-LC. Capillary dimensions: Table 1. Instrumental con guration. Instrument Part number Agilent 1260 In nity Binary Pump ( rst dimension) G1312B. Agilent 1290 In nity Binary Pump (second dimension) G4220A. Agilent 1290 In nity Autosampler G4226A. Agilent 1290 In nity Thermostatted Column Compartment with 2-position/6-port valve G1316C. Agilent 1290 In nity Valve Drive G1170A.

8 Agilent Multiple Heart-Cutting Single Upgrade Kit G4242A. Six-column selector valve, 1200 bar (equipped with six loops of 40 L) 5067-4142. 3. Results and Discussion Method For the determination of PAHs in a Parameter Value complex hydrocarbon matrix such as First dimension NPLC. vacuum distillation residues or bitumen, Column Agilent Polaris 3 NH2, 150 mm, 3 m (p/n A2014150x020). a combination of NPLC and RPLC was Solvent Heptane used. Figure 2 shows the separation of a standard mixture of PAHs in NPLC mode. Flow rate 120 L/min Table 2 gives the identity of the peaks. Temperature 30 C. On the aminopropyl column, PAHs are Flow direction 0 to 18 minutes, normal direction (valve in TCC port 2 > 1, 3 > 4, 6 > 5). separated according to the number of 18 to 55 minutes, back ush direction (valve in TCC port 2 > 3, 1 > 6, 4 > 5).

9 Rings. Also, some separation is observed DAD detection 254/4 nm (Reference off). according to ring fusion within a group Peak width > minutes (5 Hz). of PAHs with the same number of Injection 2 L (with needle wash, ush port, 3 seconds, isopropanol/methanol Aromatic rings. Benzo(a)anthracene is, for Loop lling instance, partly separated from chrysene. Valve and loop 6+1 loops (cocurrent). con guration 40 L loops This NPLC separation alone is, however, Time segments Timing varied according to targeted PAHs not suitable for the determination of Four fractions of minutes wide were taken PAHs in complex petroleum fractions. Second dimension RPLC. Figure 3 shows the overlay of the UV. trace obtained for the Analysis of a Column Agilent ZORBAX Eclipse Plus PAH, 100 mm, m (p/n 959961-918).)

10 Vacuum distillate residue and the PAH Solvent A Water test mixture. In NPLC, the bulk of the Solvent B Acetonitrile Hydrocarbons elutes unretained (fraction Flow rate mL/min eluting before naphthalene, not visible in Idle ow rate 2 mL/min UV). For the sample, a large unresolved Gradient 0 minutes, 20 to 40 %B. hump is detected, eluting between 11 minutes, 40 to 100 %B. 4 and 18 minutes. This is the Aromatic 11 minutes, 100 %B. and polyaromatic hydrocarbon fraction. minutes, 20 %B. In addition, the sample also contains Temperature 30 C. a polar fraction that is not eluted with FLD detection Multi-emission mode 100 % heptane, but is back ushed. Peak width > minutes ( Hz). This back ush option is possible due to PMT Gain: 10. the installation of an extra valve in the Detector wavelength varied according to targeted PAHs system (see Figure 1).