The challenging extraction of non-polar contaminants out of a non-polar vegetable oil sample

Transcription

1 The challenging extraction of non-polar contaminants out of a non-polar vegetable oil sample Presented by Michael Ye ExTech, 2014 sigma-aldrich.com/analytical 1

2 Agenda 1. Background; why and how analyze PAHs in edible oils 2. A new approach dual layer SPE; EZ-POP NP 3. Summary of method using EZ-POP NP for olive oil 4. Experimental data GC-MS background PAH recoveries GC Method ruggedness Comparison to other SPE methods 5. Conclusions 2

3 The Issue Why analyze PAHs in edible oils? Contamination from environmental exposure and processing Air pollution Combustion gases produced during processing/production of oils EU Commission Regulation No. 835/2011: 2 ng/g MCL for benzo[a]pyrene 10 ng/g total benzo[a]pyrene, benzo[b]fluoranthene, chrysene and benzo[a]anthracene combined 3

4 How to analyze PAHs in edible oils? ISO methods Benzo[a]pyrene only, uses large alumina column (30 cm x 1.5 cm) for extraction 16 PAHs (light to heavy), uses LLE and 2-step cleanup with C18 and Florisil Other methods LLE followed by GPC Silica gel or florisil SPE using large, glass columns Molecularly imprinted polymer (MIP) SPE Final analysis done by GC-MS/SIM or HPLC-FLD Issues with current methods GPC Silica gel/florisil (lg. column SPE) MIP SPE expensive, time consuming expensive, inadequate cleanup for GC Poor recoveries of lighter PAHs 4

5 How to analyze PAHs in edible oils? A new approach - EZ-POP NP SPE Dual-layer SPE cartridge containing Florisil and Z-Sep/C18 mix. Florisil - retains background constituents with polar functionality such as fatty acids. Z-Sep/C18 mixture - retains fatty matrix through both Lewis acid/base and hydrophobic interactions. Easy sample preparation methodology using minimal volume of solvent. Final sample extracts compatible with GC or HPLC. 5

6 What is Z-Sep / C18? A mixture of a proprietary HybridSPE zirconia-coated silica and C18 functionalized silica: ZrO ZrO Zr ZrO ZrO ZrO ZrO ZrO C18 C18 C18 C18 C18 C18 C18 C18 Zirconia acts as a Lewis acid, binding electron donating groups such as OH found in mono and diacylglycerols. C18 binds fats through hydrophobic interaction. Used with zirconia, it produces a synergistic effect in enhancing fat retention. 6

7 Extraction of PAHs from Olive Oil Using EZ-POP NP Condition SPE cartridge with 10 ml acetone using gravity elution. Dry cartridge at -10 to -15 Hg for 10 min. Weigh 0.5 ml olive oil onto top of SPE cartridge. Add internal standard. Add 15 ml of acetonitrile in 2 x 7.5 ml increments. Pull through SPE cartridge at a drop rate of approximately 1 drop/second. Collect all eluent. Florisil layer Evaporate eluent at 40 C under 5 psi nitrogen (do not allow to go dry). Z-Sep&C18 layer Adjust the final volume of the extracts to required final volume using acetonitrile Proceed with HPLC/FLD and/or GC-MS/SIM analysis. EZ-POP NP dual-layer cartridge during extraction of PAHs from 7 olive oil.

8 Background extract of 0.5 gm olive oil sample Background remaining in a 1mL olive oil extract; evaluated by GC-MS in scan mode abundance 0.00E E E Time (min) Silica gel SPE (5 gm/10 ml), FV=1 0.00E E E+07 EZ-POP NP SPE, FV= Time (min) 8

9 Recoveries of PAHs Using EZ-POP NP Olive oil spiked at 2 ng/g with PAHs from 2-6 rings, including those listed in the EU regulation. The sample set contained 3 spiked replicates and one unspiked olive oil blank. 5-Methylchrysene used as internal standard. Final extracts concentrated to 0.2 ml for analysis. Extracts analyzed by GC-MS/SIM and HPLC-FLD. Matrix-matched standards used for quantitation. 9

10 Example of GC-MS/SIM analysis of olive oil extract Time (min) 1. Naphthalene 2. Acenaphthylene (GC only) 3. Acenaphthene 4. Fluorene 5. Phenanthrene 6. Anthracene 7. Fluoranthene 8. Pyrene 9. Benzo[a]anthracene 10. Chrysene methyl Chrysene (IS) 12. Benzo[b]fluoranthene 13. Benzo[k]fluoranthene 14. Benzo[a]pyrene 15. Dibenzo[a,h]anthracene 16. Benzo[g,h,i]perylene 17. Indeno[1,2,3-cd]pyrene Single quadrupole MS GC-MS: Agilent 7890/5975, selected ion mode (SIM) column: SLB-5ms, 20 m x 0.18 mm I.D. x 0.18 µm oven: 60 C (1 min.), 15 C/min. to 250 C, 8 C/min. to 330 C (7 min.) inj. temp.: 300 C MS Temps: interface 330 C, source 250 C, quads. 200 C carrier gas: helium, 1 ml/min constant flow injection: 0.5 µl pulsed splitless (50 psi until 0.75 min, splitter open at 0.75 min.) liner: Focus Liner with taper and quartz wool Higher MS temps to minimize tailing of heavy PAHs Pulsed injection to increase response of heavy PAHs 10

11 Example of HPLC-FLD analysis of olive oil extract, 2 ng/g spike Time (min) Instrument: Agilent 1200 / 1260 FLD column: Supelcosil LC-PAH, 25 cm x 4.6 mm I.D., 5 µm mobile phase: (A) water (B) acetonitrile gradient: 40% B for 5 min, to 100% in 15 min; held at 100% B for 10 min flow rate: 1.4 ml/min column temp.: 30 C detector: fluorescence, programmed injection: 20 µl Naphthalene 2. Acenaphthylene (GC only) 3. Acenaphthene 4. Fluorene 5. Phenanthrene 6. Anthracene 7. Fluoranthene 8. Pyrene 9. Benzo[a]anthracene 10. Chrysene methyl Chrysene (IS) 12. Benzo[b]fluoranthene 13. Benzo[k]fluoranthene 14. Benzo[a]pyrene 15. Dibenzo[a,h]anthracene 16. Benzo[g,h,i]perylene 17. Indeno[1,2,3-cd]pyrene 11

12 PAH Recoveries; GC-MS/SIM analysis 2 ng/g spike level % RSD % Recovery (n=4) Naphthalene Acenaphthene 96 4 Acenaphthylene Fluorene Phenanthrene Anthracene 99 8 Fluoranthene Pyrene 99 6 Benzo[a]anthracene 98 7 Chrysene 98 9 Benzo[b]fluoranthene 94 5 Benzo[k]fluoranthene 95 2 Benzo[a]pyrene 86 3 Indeno[1,2,3-cd]pyrene 85 2 Dibenz[a,h]anthracene Benzo[g,h,i]perylene 82 4 Recoveries >80% for most PAHs RSD values <15% for most PAHs Method was acceptable for detection at 2 ng/g on single quadrupole MS instrument Regulated PAHs per EU 835/

13 Comparison of GC-MS to HPLC-FLD results 180% 160% 140% 120% 100% 80% 60% 40% 20% 0% GC-MS; matrix stds. HPLC-matrix stds Does not fluoresce Larger difference due to interference in HPLC analysis 13

14 Comparison of GC and HPLC Data- Summary Analysis of 2 ng/g olive oils spikes GC-MS/SIM HPLC-FLD Recovery Reproducibility >80% for all except naphthalene < 20% for all except phenanthrene >80% for all except naphthalene < 20% for 12 of 16 compounds Background No interference in SIM Interference with fluorene 14

15 GC Method Ruggedness Test Loss of response in GC can occur as a result of residue buildup in the inlet liner residue buildup in the column contamination of the detector Tested cleanliness of the olive oil extract Made 110 injections of an olive oil extract into GC-MS system Spiked with 28 different PAHs (2-6 rings) Monitored absolute response of PAHs Contaminated GC inlet liner 15

16 GC Method Ruggedness Test- Results Area counts start 110 inj Decrease in absolute response after 110 injections 12 Some loss of response was expected. 17 of 28 PAHs decreased in response by <20%. # Compounds < 10% 10-20% 21-30% 31-40% 41-50% 16

17 The cleanliness of the extract was acceptable for GC-MS analysis Inlet liner after 110 injections of olive oil extract Pattern left by autosampler in vial caps after 110 injections 17

18 How does EZ-POP NP compare to other SPE methods? 1. Silica gel SPE 2. MIP SPE Experiment Olive oil samples spiked at 20 ng/g with 28 PAHs Samples extracted using EZ-POP NP, silica gel SPE, and MIP SPE; 3 replicates with each method plus a blank 0.5 gm sample size per SPE cartridge for each method Internal standards used (deuterated PAHs) GC-MS/SIM Analysis Methods Silica Gel SPE Condition: 20 ml hexane Load: 1 ml of 5 gm oil diluted to FV10 ml in hexane. Add internal standard directly to cartridge. Wash: 8 ml hexane:methylene chloride (70:30) Elute: 8 ml hexane:methylene chloride (70:30) Concentrate: FV=1 ml under nitrogen at 40 C MIP SPE Condition: 1 ml cyclohexane Load: 0.5 gm oil diluted to 1 ml in cyclohexane Wash: 1 ml cyclohexane Elute: 3 x 1 ml ethyl acetate Concentrate: < 1 ml (not dryness) under nitrogen at 40 C. Adjust final volume to 1 ml with ethyl acetate. 18

19 Results- PAH Recoveries, 2-3 rings 120% EZ-POP NP Silica Gel MIP 100% 80% 60% 40% 20% 0% For Silica gel and MIP, matrix interference prevented accurate quantitation for most of these PAHs. Low recovery of naphthalene and biphenyl using MIP. 19

20 Results- PAH Recoveries, 4 rings EZ-POP NP Silica Gel MIP 120% 100% 80% 60% 40% 20% 0% Low recoveries using silica gel Matrix interference with chrysene & triphenylene using MIP 20

21 Results- PAH Recoveries, 5-6 rings EZ-POP NP Silica Gel MIP 120% 100% 80% 60% 40% 20% 0% Lower recoveries using silica gel MIP recoveries very good MIP SPE suitable for heavier PAHs (>4 rings) 21

22 How does GC-MS background compare? abundance 0.00E E E+07 Silica gel SPE Time (min) 0.00E E E+07 EZ-POP NP SPE Time (min) 0.00E E E+07 MIP SPE glycerides Time (min) 22

23 In Conclusion EZ-POP NP is suitable for Extraction of full range of PAHs from 2-6 rings from olive oil. Detection of PAHs at levels specified in EU Regulation 835/2011. Producing an extract that can be analyzed by GC-MS/SIM or HPLC-FLD without the need for a solvent exchange. Very rugged GC-MS method on a single quadrupole instrument Very clean extract; will not prematurely foul GC-MS system 23

24 In Conclusion Compared to other SPE methods EZ-POP NP will give better recoveries for PAHs of 2-4 rings than MIP SPE and overall better recoveries than silica gel SPE. EZ-POP NP produces a cleaner extract than silica gel and MIP SPE. The EZ-POP method is easier and more versatile than silica gel or MIP SPE. Less steps in SPE method Less solvent usage than silica gel Produces an extract in acetonitrile; which can be run by GC or LC. 24