Application Note 196. Introduction

Transcription

1 pplication Note 9 Determination of Polycyclic romatic Hydrocarbons (PHs) in Edible Oils by Donor-cceptor Complex Chromatography (DCC)-HPLC with Fluorescence Detection Introduction Numerous polycyclic aromatic hydrocarbons (PHs) are carcinogenic, making their presence in foods and the environment a health concern. Regulations around the world limit levels of a variety of PHs in drinking water, food additives, cosmetics, workplaces, and factory emissions. PHs also occur in charbroiled and dried foods, and may form in edible oils by pyrolytic processes, such as incomplete combustion of organic substances. PHs in foods can also result from petrogenic contamination. The European Commission regulates the amounts of PHs in foods, and has imposed a limit of.0 µg/kg for benzo[a]pyrene (ap) in edible oils, as ap was determined to be a good indicator of PH contamination. PHs have traditionally been separated using HPLC and determined using UV, fluorescence,, electrochemical, and mass spectrometry (using atmospheric-pressure photoionization) detection methods. fter an oxygenation reaction, PHs can also be determined by LC-MS/MS. 7 These methods of determining PHs in edible oils require multiple manual sample preparation steps. One study of PHs in over a dozen edible oils used a DMSO extraction followed by three extractions with cyclohexanone and cleanup with a silica column. 8 nother study of six edible oils used solid-phase extraction, but required solvent extraction steps before SPE and evaporation afterward. 9 These manual steps consume solvent, resources, and time. In recent years, donor-acceptor complex chromatography (DCC) has gained popularity for PH analysis. 0 DCC stationary phases can be used for solid phase extraction (SPE), retaining PHs while matrix components are flushed to waste. fter elution of the analytes, solvent exchange is used to prepare the sample for HPLC analysis. Compared to traditional methods, this cleanup technique uses less solvent, is less labor intensive, and saves considerable time. However, this approach still involves several manual samplehandling steps, and therefore still requires labor and is prone to errors. In 99, Van Stijn et al. developed an automated process for oil sample preparation and analysis. The setup consists of coupling a DCC cleanup column with an HPLC analytical column. This solution does not require manual cleanup and solves the previously described challenges. However, adopting the method for routine operation is difficult and requires advanced technical know-how to optimize the system configuration. This optimization can be time consuming. Furthermore, the described solution uses the autosampler software for system control and different software for data collection, instead of using an integrated chromatography data system for system control and monitoring. This leaves room for improvement in ease of operation, process monitoring and documentation, validation, reporting, and automated diagnosis.

2 Maio et al. adapted Van Stijn's solution to create a method for automated on-line determination of PHs in edible oils that addresses the remaining challenges. This solution was performed on an HPLC system equipped with a dual-gradient HPLC pump and two switching valves, allowing on-line sample enrichment on a DCC column with HPLC analysis. On-line coupling of sample preparation and analysis eliminates the complex manual pretreatment required by traditional methods. This automation reduces unintentional errors and increases reproducibility. The analysis time per sample is approximately 80 min with the dual-gradient HPLC system, compared to 8 0 h with traditional methods. Moreover, this automated system can run h a day, significantly increasing sample throughput and making this complex analysis routine. This application note describes the setup and method for determining PHs in edible oils on-line using a Dionex UltiMate 000 Dual-Gradient HPLC platform, based on the solution described by Maio, and evaluates the method performance (i.e. linearities, detection limits, reproducibilities, recoveries, and carry over of autosampler). Equipment UltiMate 000 Dual system consisting of: DPG-00 pump with SRD-00 ir Solvent Rack WPS-000TSL autosampler TCC-00 thermostatted column compartment with two p-p valves RF000 fluorescence detector Chromeleon.80 SP Chromatography Workstation Device configurations for the online DCC cleanup with analytical HPLC are as shown in Figures to. In these figures, the upper valve is the right valve and lower valve is the left valve in the TCC-00. Reagent and Standards Deionized water from a Milli-Q Gradient 0 cetonitrile (CH CN), HPLC grade (Fisher Scientific) Isopropanol, HPLC grade, (Fisher Scientific) Charcoal, activated granular (activated carbon), chemical pure grade (Shanghai Chemical Reagent Company) Mix of PHs, EP Sample for Method 0, 00 µg/ml for each component, including phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]perylene and indeno[,,-cd]pyrene (Restek) enzo[b]chrysene, 0 µg/ml, used as an internal standard (I.S.) (ccustandard) Samples Two brands of olive oil (olive oil and from Italy and Spain, respectively), and one brand of sesame oil (from China) Conditions Columns: Column: Mobile Phases: Two SUPELCOSIL LC-PH columns,. 0 mm (Supelco Cat.# 89) ChromSpher Pi,.0 80 mm (Varian P/N: CP89). Water. cetonitrile for both loading and C. Isopropanol for loading pump ml/min 80 μl (00 μl injection loop) Flow Rate: Injection Volume: Column Temperature: 0 C utosampler Temperature: 0 C Detection: Fluorescence (Table ) Table shows the gradient for on-line solid-phase extraction (SPE) using the loading pump, and Table shows the gradient for separation using the analysis pump. Table shows the valve switching timing. ecause the maximum fluorescent responses of PHs occur at different emission wavelengths, it is necessary to change the excitation and emission wavelengths based on individual PH retention times. Table shows the program for wavelength changes. Determination of Polycyclic romatic Hydrocarbons (PHs) in Edible Oils by Donor-cceptor Complex Chromatography (DCC)-HPLC with Fluorescence Detection

3 Time Table. Gradient Program for Flow rate (ml/min) Solvent Solvent Solvent C Curve (%) Time Table. Gradient Program for Separation Flow rate (ml/min) Solvent Solvent Curve (%) Table. Valve Switching Programs for the Left and Right Valves Time (min) Left Valve Right Valve No Movement -. - No Movement 7 - No Movement. No Movement - Time (min) Table. Wavelength Changes for RF000 Fluorescence Detector Excitation Wavelength (nm) Emission Wavelength (nm) Preparation of Standards and samples Purification of Olive Oil Used as lank and Matrix dd g activated carbon to 0 g olive oil, heat for h at 0 C while stirring, then filter through a pleated filter. Pass filtrate through a membrane filter (0. µm, PTFE, Millex -LCR, Millipore) and store the resulting purified oil sample at C. Preparation of Olive Oil Containing I.S. Used as Matrix To prepare a 0. µg/ml stock I.S. solution, add 99 µl isopropanol using a -ml pipette to a -ml vial, and add µl of 0 µg/ml I.S. oil using a 0-µL syringe. dd 0 µl of the 0. µg/ml stock I.S. solution, using a 0-µL syringe, to about 0 g of the purified olive oil used as blank and matrix. The concentration of I.S. in the oil matrix is about µg/kg. In the work presented in this application note, the I.S. working standard was added to g of the purified olive oil sample. The resulting I.S concentration in the matrix was 0.99 µg/kg. Preparation of Working Standards (Olive Oil as Matrix) To prepare a µg/ml stock standard solution, add 99 µl isopropanol, using a -ml pipette, and µl of the 00 µg/ml standard solution, using a 0-µL pipette, to a -ml vial. The stock standard solution is used to prepare working standards as described in Table. Table. Preparation of the Working Standards (Oil as Matrix) Vial # (. ml) Volume of µg/ml PH stock standard solution (µl) Volume of isopropanol (µl) Concentration of PHs (µg/ml) Vial # (. ml) Volume of Diluted Standard (Vial or Vial ) or Stock Standard (µl) dded weight of the cleaned olive oil used as matrix (containing I.S.) (g) Final concentration of PHs Final concentration of I.S. Vial Vial Vial Vial Vial Vial 0 µl, Vial 0 µl, Vial 0 µl, stock standard 0 µl, stock standard pplication Note 9

4 Edible Oil Sample Preparation Prior to injection, filter oil through a 0.-µm membrane (PTFE, Millex-LCR, Millipore). Results and Discussion Description of the On-Line DCC-HPLC Method The flow scheme, shown in Figure, couples the DCC cleanup directly with the analytical HPLC run, using a second gradient pump and two column-switching valves. Figure shows the valve positions at the time of the injection. The filtered and undiluted oil is injected directly, using isopropanol (IP) to transfer the sample onto the enrichment column (DCC column). The analytical separation column is equilibrated with the second pump at the same time. fter the analytes are bound to the DCC column, the right valve switches to flush out the oils and IP, in a backflow mode, with acetonitrile/water (Figure ). When all IP and oils have been removed, the system switches the enrichment column into the analytical flow path (Figure ). Reproducibility, Detection Limits, and Linearity Method reproducibility was estimated by making seven replicate injections of olive oil sample spiked with the PHs standard mix (vial # in Table ) (Figure ). Table summarizes the retention time and peak area precision data. Calibration linearity for the determination of PHs was investigated by making five replicate injections of a mixed standard of PHs prepared at four different concentrations. The internal standard method was used to calculate the calibration curve and for real sample analysis. Table 7 reports the data from this determination as calculated by Chromeleon software. PH method detection limits (MDLs) are also listed in Table 7. Pump Figure. Flow scheme for on-line sample preparation and analysis. The valves are positioned for injection of the sample on the enrichment column. Pump Enrichment Column Column Figure. Isopropanol is flushed out of the enrichment column in backflow mode. Pump utosampler utosampler utosampler Waste Waste Enrichment Column Enrichment Column Waste Pump Column Pump Column Fluorescence Detector 70 Fluorescence Detector 7 Fluorescence Detector Pump 7 Figure. The enrichment column is switched into the analytical flow path, eluting the PHs onto the analytical column for gradient separation followed by fluorescence detection. Determination of Polycyclic romatic Hydrocarbons (PHs) in Edible Oils by Donor-cceptor Complex Chromatography (DCC)-HPLC with Fluorescence Detection

5 Table. Reproducibility of Retention Times and Peak reas a PH RT RSD rea RSD Phenanthrene nthracene Fluoranthene Pyrene enzo[a]anthracene Chrysene enzo[b]fluoranthene enzo[k]fluoranthene enzo[a]pyrene Dibenzo[a,h]anthracene enzo[g,h,i]perylene Indeno[,,-cd]pyrene a Seven injections of olive oil sample spiked with 0 µg/kg mixed PH standards. Detection: Fluorescence Column: ChromSpher Pi,.0 80 mm Sample: Mixture of PHs standard Peaks: µg/kg Columns: Two Supelco PH columns. Phenanthrene 0. 0 mm for separation. nthracene 0 Eluent: ) water,. Fluoranthene 0 ) acetonitrile for both loading and. Pyrene 0. enzo[a]anthracene 0 C) isopropanol forloading pump. Chrysene 0 Flow Rate: ml/min 7. enzo[b]fluoranthene 0 8. enzo[k]fluoranthene 0 Temperature: 0 ºC for column, 9. enzo[a]pyrene 0 0 ºC for autosampler 0. Dibenzo[a,h]anthracene enzo[g,h,i]perylene 0. Indeno[,,-cd]pyrene 0. enzo[b]crysene (added as I.S.) Table 7. Calibration Data for the PHs Phenols Equations r (%) MDL Phenanthrene =.09 C + 7. nthracene =.87 C + 9. Fluoranthene =.99 C Pyrene =.080 C +.00 enzo[a]anthracene =.7 C Chrysene =.0 C +. enzo[b]fluoranthene = C enzo[k]fluoranthene = 89. C + 8. enzo[a]pyrene =.97 C Dibenzo[a,h]anthracene =. C +. enzo[g,h,i]perylene =.7 C +.0 Indeno[,,-cd]pyrene =.908 C The single-sided Student s test method (at the 99% confidence limit) was used for estimating MDL, where the standard deviation (SD) of the peak area of seven injections of olive oil sample spiked with µg/kg mixed PHs standard is multiplied by. (at n = 7) to yield the MDL Figure. Overlay of chromatograms of seven serial injections of olive oil sample spiked with a PH standard mixture (0 µg/kg). 0 pplication Note 9

6 Carryover Performance Carryover performance for the WPS 000TSL autosampler was investigated by serial injections of 00 μg/kg of benzo[b]crysene (I.S.) and a purified olive oil sample prepared as a blank. Figure shows exceptional carryover performance with external needle wash by acetonitrile both before and after the injection. There was no cross contamination observed when using the WPS 000TSL autosampler for this application. Column: ChromSpher Pi,.0 80 mm Columns: Two Supelco PH columns,. 0 mm for separation Eluent: ) water ) acetonitrile for both loading and C) isopropanol forloading pump Flow Rate: ml/min Temperature: 0 ºC for column, 0 ºC for autosampler Detection: Fluorescence Flow Rate: Column: ChromSpher Pi,.0 80 mm Columns: Two Supelco PH columns,. 0 mm for separation Detection: Eluent: ) water ) acetonitrile for both loading and C) isopropanol for loading pump, ml/min Temperature: 0 ºC for column, 0 ºC for autosampler Fluorescence Peaks:. enzo[b]crysene (added as I.S.) Figure. Carryover test on the WPS-000 autosampler. ) Purified olive oil spiked with 00 μg/kg of benzo[b]crysene (I.S.). ) Purified olive oil prepared as blank, analyzed immediately after ) Figure. Overlay of chromatograms of ) untreated olive oil, and ) purified olive oil used as a blank. 9 Sample nalysis Two olive oil samples and one sesame oil sample were analyzed. The results are summarized in Table 8. Figure 7 shows chromatograms of the oil samples. Spike recoveries for these PHs were in the ranges from 70% to %. Some PHs were found in the edible oil samples. Five PHs, phenanthrene, anthracene, benzo[a] anthracene, chrysene and benzo[a]pyrene, existed in all of the three samples and phenanthrene was obviously the most abundant PH. 70 Effect of the Purified Olive Oil Used as lank and Matrix One brand of olive oil was prepared as a blank and to serve as a matrix according to the procedure specified above. Figure is an overlay of chromatograms of the original and purified olive oils, from which we observe that many ingredients were eliminated from the original olive oil. However, impurities persisted in the prepared olive oil used as a blank and matrix, which might have affected determination of some PHs. To overcome this effect, the baseline of the purified olive oil blank was subtracted during data processing with Chromeleon software. Determination of Polycyclic romatic Hydrocarbons (PHs) in Edible Oils by Donor-cceptor Complex Chromatography (DCC)-HPLC with Fluorescence Detection

7 Column: ChromSpher Pi,.0 80 mm Columns: Two Supelco PH columns. 0 mm for separation Eluent: ) water, ) acetonitrile for both loading and C) isopropanol for loading pump Flow Rate: ml/min Temperature: 0 ºC for column, 0 ºC for autosampler 0 Detection: Fluorescence Peaks:. Phenanthrene. Pyrene. enzo[a]anthracene. Chrysene 7. enzo[b]fluoranthene 8. enzo[k]fluoranthene 9. enzo[a]pyrene. enzo[g,h,i]perylene. Indeno[,,-cd]pyrene Column: ChromSpher Pi,.0 80 mm Columns: Two Supelco PH columns,. 0 mm for separation Eluent: ) water ) acetonitrile for both loading and C) isopropanol forloading pump Flow Rate: ml/min 0 Temperature: 0 ºC for column, 0 ºC for autosampler Detection: Fluorescence Sample: Mixture of PHs standard C Figure 7. Overlay of chromatograms of ) olive oil, ) olive oil, and C) sesame oil samples. Ruggedness of the SPE Column The tolerance of the SPE column used in this online analysis of PHs in edible oils was investigated by comparing the separation of PHs using two different SPE columns. One of these columns already had extracted over 00 injections of an edible oil sample; the other was nearly new. Figure 8 shows an overlay of chromatograms of PHs using these two SPE columns. Final results of the PH analyses are very similar, despite the different exposure levels of the two columns. Precautions Contaminants in solvents, reagents, glassware, and other sample processing hardware may cause method interferences, so glassware must be scrupulously cleaned. Use high-purity reagents and solvents to minimize interference problems. Figure 8. Separation of PHs in olive oil using different SPE columns. ) SPE column with 00 prior injections; ) new SPE column. Table 8. Results for Olive Oil, Olive Oil, and Sesame Oil PH Olive Oil Olive Oil Detected dded Recovery (%) Detected Sesame Oil Detected Phenanthrene 7 0. nthracene Fluoranthene.0 ND ND Pyrene.. ND enzo[a]anthracene Chrysene. 0.. enzo[b]fluoranthene ND 90 ND ND enzo[k]fluoranthene ND 8 ND ND enzo[a]pyrene Dibenzo[a,h]anthracene ND 8 ND ND enzo[g,h,i]perylene ND 70 ND. Indeno[,,-cd]pyrene ND 8 ND ND One sample and one spiked sample were prepared, and two injections of each were made. pplication Note 9 7

8 References ) Commission Regulation (EC) No. 88/00 of 9 December 00, Setting Maximum Levels for Certain Contaminants in Foodstuffs. Official Journal of the European Union 00, 9, L,. ) Saravanabhavan, G.; Helferty,.; Hodson, P. V.; rown, R. S. Multi-Dimensional High Performance Liquid Chromatographic Method for Fingerprinting Polycyclic romatic Hydrocarbons and Their lkyl- Homologs in the Heavy Gas Oil Fraction of laskan North Slope Crude. J. Chromatogr., 007,,. ) Zuin, V. G.; Montero, L.; auer, C.; Popp, P. Stir ar Sorptive Extraction and High-Performance Liquid Chromatography-Fluorescence Detection for the Determination of Polycyclic romatic Hydrocarbons in Mate Teas. J. Chromatogr., 00, 09, 0. ) Pino, V.; yala, J. H.; fonso,.m.; González, V. Determination of Polycyclic romatic Hydrocarbons in Seawater by High-Performance Liquid Chromatography with Fluorescence Detection Following Micelle-Mediated Preconcentration. J. Chromatogr., 00, 99, 9 99 ) ouvrette, P.; Hrapovic, S.; Male, K..; Luong, J. H. nalysis of the Environmental Protection gency Priority Polycyclic romatic Hydrocarbons by High Performance Liquid Chromatography-Oxidized Diamond Film Electrodes. J. Chromatogr., 00, 0, 8. ) Itoh, N.; oyagi, Y.; Yarita, T. Optimization of the Dopant for the Trace Determination of Polycyclic romatic Hydrocarbons by Liquid Chromatography/ Dopant-ssisted tmospheric-pressure Photoionization/Mass Spectrometry. J. Chromatogr., 00,, ) Lintelmann, J.; Fischer, K.; Matuschek, G. Determination of Oxygenated Polycyclic romatic Hydrocarbons in Particulate Matter Using High- Performance Liquid Chromatography-Tandem Mass Spectrometry. J. Chromatogr., 00,, 7. 8) Pandey, M.K.; Mishra, K.K.; Khanna, S.K.; Das, M. Detection of Polycyclic romatic Hydrocarbons in Commonly Consumed Edible Oils and Their Likely Intake in the Indian Population. J. m. Oil Chem. Soc. 00, 8,. 9) arranco,.; lonso-salces, R. M.; akkali,.; errueta, L..; Gallo,.; Vicente, F.; Sarobe, M. Solid-Phase Clean-Up in the Liquid Chromatographic Determination of Polycyclic romatic Hydrocarbons in Edible Oils. J. Chromatogr., 00, 988, 0. 0) ogusz, M. J.; El Hajj, S..; Ehaideb, Z.; Hassan, H.; l-tufail, M. Rapid Determination of enzo(a) pyrene in Olive Oil Samples with Solid-Phase Extraction and Low-Pressure, Wide-ore Gas Chromatography-Mass Spectrometry and Fast Liquid Chromatography with Fluorescence Detection. J. Chromatogr., 00, 0, 7. ) arranco,.; lonso-salces, R. M.; Corta, E.; errueta, L..; Gallo,.; Vicente, F.; Sarobe, M. Comparison of Donor cceptor and lumina Columns for the Clean-Up of Polycyclic romatic Hydrocarbons from Edible Oils. Food Chem. 00, 8, 7. ) van Stijn, F.; Kerkhoff, M..; Vandeginste,. G. Determination of Polycyclic romatic Hydrocarbons in Edible Oils and Fats by On-Line Donor-cceptor Complex Chromatography and High-Performance Liquid Chromatography with Fluorescence Detection. J. Chromatogr., 99, 70, 7. ) Maio, G.; rnold, F.; Franz, H. nalysis of PHs in Edible Oils by DCC-HPLC Coupling with Fluorescence Detection, Poster Presented at the th International Symposium on Chromatography, Paris, France, Oct. 8, 00. LPN, Dionex Corporation, Sunnyvale, C. com/en-us/webdocs/70_summit_x_poster_pah_ application_isc0_sep0.pdf or search for PH on SUPELCOSIL is a trademark of Sigma-ldrich Co. Millex is a trademark and Milli-Q is a registered trademark of Millipore Corporation. Chromeleon, Summit, and UltiMate are registered trademarks of Dionex Corporation. Passion. Power. Productivity. Dionex Corporation North merica Europe sia Pacific 8 Titan Way P.O. ox 0 U.S. (87) Canada (90) 8-90 ustria () enelux () () 9 Denmark () France () Germany (9) 99 0 Sunnyvale, C Ireland () 00 Italy (9) 0 7 Switzerland () 0 99 Taiwan (88) 87 South merica United Kingdom () 7 97 razil () 7 0 (08) ustralia () 90 China (8) 8 8 India (9) 7 7 Japan (8) 88 Korea (8) 80 Singapore () LPN 998 PDF 0/ Dionex Corporation