HYPHENATED AND COMPREHENSIVE CHROMATOGRAPHIC TECHNIQUES FOR TRACE ANALYSIS IN EDIBLE OILS AND FATS

Transcription

1 HYPHENATED AND COMPREHENSIVE CHROMATOGRAPHIC TECHNIQUES FOR TRACE ANALYSIS IN EDIBLE OILS AND FATS Hans-Gerd Janssen Unilever Foods R&D Vlaardingen, Vlaardingen, the Netherlands University of Amsterdam, Amsterdam, the Netherlands

2 The importance of edible oils and fats Each year the human population uses approx. 100,000,000 tonnes of fats and oils from animal and vegetable sources. Edible products: - Cooking fat - Frying oils - Margarines, spreads - Dairy products, cheese, butter - Salad oils, mayonnaise - Snacks (ice cream, chocolate, crisps...) Non-edible products: - Soapy detergents - Cosmetics - Motor fuels - Intermediates for chemicals (paint..)

3 Edible fats and oils (minor constituents) Natural ingredients Contaminants Sterolesters Pesticides Glycolipids PAHs Sterolglucosides Dioxines Alcohols Solvents Natural antioxidants / vitamins Stabilisers (BHT, EDTA..) Carotenoids. Minerals / metals... Steradienes Alkanes Oxidized lipids Polymerised TAGs.. Monochloropropanediol esters (MCPD-esters) Dialkylketones Glycidyl fatty acid esters

4 Edible fats and oils (main components) O Main compounds - Triglycerides (approx. 90%) - Diglycerides (approx. 5%) - Monoglycerides (approx. 0-5%) - Free Fatty Acids (approx. 0-1%) O CH 2 O C R O CH O C R' O CH 2 O C R" R= CCCCCCCC.. R = CCCC=CCC.. R = CC=CCCC=CC.. CH 3 (CH 2 ) 14 C OH OH - Phospholipids (approx. 0-2%) - Sterols (approx. 0-2%) - Wax esters (approx mg/kg) OH O O O O OH O OR 1 CH 2 O C R O O O OR OH 2 CH O C R' O O O O OR 3 O OR 3 CH 2 O P O R" O O OR 3 CH 3 (CH 2 ) 14 C O (CH 2 ) 15 CH 3 OH

5 Target compound analysis Requirements for Chrom - MS: Fast Sensitive More detail / more selective Higher certainty Automated In-line Cheap Alternatives: Sensors. Selective isolation - sensors Immuno / Affinity methods NMR Sampling Sampe prep. Separation Detection

6 Target compound analysis: Definitions 1. Sample preparation procedures: - Homogenisation (grinding, mixing, vortexing, turraxing, etc.), - Extraction (shaking, soxhlett, ultrasonic, SFE, ASE, etc.) - Derivatisation (silylation, alkylation, trans-esterification, acetylation, etc.), - Clean up (SPE, GPC, LL partitioning, etc.), - Pre-concentration / LVI. AUTOMATION 2. Selectivity: - The ability to see differences (in sample prep., separation, detection). 3. Sensitivity: - The ability to detect low concentrations. MASS SPECTROMETRY MULTI-DIMENSIONAL CHROMATOGR. LARGE VOLUME INJECTION MASS SPECTROMETRY

7 Why do we need sample prep.? AIM WHAT Liberate the compounds from the matrix Remove dirt (damages LC/GC/MS etc.) Remove interfering analytes Pre-concentrate the analytes Extraction Clean-up Selective clean-up Preconcentration Study only part of the molecule (Enzyme)conversion Better chromatographic/ Derivatisation detection properties

8 Large volume sampling: environmental application Organochlorines extracted from waste water. 1 µl GC-AED Large volume sampling is a good alternative for evaporative preconcentration! 40 µl

9 Mass spectrometry: The power of selectivity Peak Name Unique mass 1 1-Nonene ethyl-1,4-79 cyclohexane Deconvolution: An additional means for selectivity (But not the starting point!) Time: Seconds

10 Eliminating selective clean-up and derivatisation using exact mass time-of-flight MS after SPE Excellent selectivity and sensitivity is obtained. I:\Online\R207059\207414\ PRO\Data\, St. 100, test autosampler (9.094) Cm (608: :576) TOF MS EI+ 2.97e I:\Online\R207059\207414\ PRO\Data\, St. 100, test autosampler TOF MS EI TIC TOF MS EI Da 3.90e Acrylamide from 534 potatoe chips 9.43 % % Time TOF MS EI Da 3.43e TIC 71 amu,1 Da mass resolution % % I:\Online\R207059\207414\ PRO\Data\, St. 100, test autosampler (9.094) Cm (607:620-(563: :642)) TOF MS EI % m/z Zoom at m/z 71 Acrylamide Alkane fragment m/z e I:\Online\R207059\207414\ PRO\Data\, St. 100, test autosampler TOF MS EI TOF MS EI Da TIC e amu, 0.01 Da mass resolution % 9.43 % TOF MS Time EI Da 3.43e3

11 Comprehensive 2D Chromatography Normal Chromatography Heart-cut 2D Chromatography Comprehensive 2D Chromatography

12 Instrumentation for 2D GCxGC Schematic diagram of a GC GC system Schematic diagram of a GCxGC system Conventional capillary injection system Focusing to pulses of 10 ms and re-injection Fast Detector Sampling rate 100 Hz Conventional capillary column times faster than 1 st column Courtesy Jan Beens

13 Principle of GC GC

14 GC GC hardware Modulator 2 nd oven

15 Advantages of GC GC Improved chromatographic resolution Increased peak capacity Enhanced signal-to-noise ratios More effective automated qualitative and quantitative data processing More information per sample Minimizes dynamic range problems

16 GC GC ToF MS D: 2 m, 100 m, 0.1 m VF23-MS 2 D: 2 m, 100 m, 0.1 m VF23-MS POLAR Comprehensive GC GC in (trans) fatty acid analysis C 18 s Isothermal at 175 C C 16 POLAR 1 D: 30 m, 250 m, 0.25 m CP-WAX

17 Comprehensive GC GC in (trans) fatty acid analysis position 2 D: 2 m, 100 m, 0.1 m VF23-MS C18:0 C18:1 cis trans C18:

18 Comprehensive GC GC of non-saponifiables

19 Why do we need sample prep.? AIM MS Selec. Large volume Chrom injection helpful? Liberate the compounds from the matrix Remove dirt (damages LC/GC/MS etc.) Remove interfering analytes Pre-concentrate the analytes Better chromatographic/ detection properties Possibly No Possibly Yes Possibly

20 Off-line LC - large volume GC Collect a fraction and inject into the GC Injection valve Column UV Detector Alternative for: off-line TLC - GC Waste Results Mobile phase delivery FID to GC for analysis. Use large volume injection

21 GC retention time LC GC composition map of Olive oil GC-FID chromatogram OH-TAG's? 15 Sterol esters O-TAG's? Squalene Alkanes Wax esters TAG's Desmethyl sterols FFA's DAG's Fraction number NPLC-UV chromatogram

22 On-line GPC-GC for pesticides in oil PUMP SVE FPD-1 FPD-2 V1 GPC GC oven N 2 UV He V2 waste V3 waste Retention gap CP Sil 8CB CP Sil 13CB

23 Automated: On-line GPC-GC of organophosphorus pesticides Olive Oil Standard mixture ppb Pesticide fraction 600 LC-UV GC-FPD LC (GPC) transfer from LC to GC min GC Crude Sunflower, soy bean and rape seed oil. Global survey (17 countries): Many crude oils contained OPPs. Removal during refining close to 100% (Mihyahara and Saito, J. Agric. Food Chem., 41 (1993) 731).

24 NPLC as sample preparation for GC (off-line or on-line) Aim: isolate specific compound classes for futher separation and quantification by GC-MS Target compound groups: - Sterol - Sterolesters - Waxesters - Partial glycerides - Glycidyl fatty acid esters

25 Experimental conditions: Glycidylesters by GC Standards GE-C12:0, GE-C14:0, GE-C16:0-d31, GE- C16:0, GE-C18:0, GE-C18:1, GE-C18:2, GE-C18:3. Columns On-column: 15 m x 0.25 mm x 0.10 µm DB-5ms (pre-column 1 m x 0.53 mm apolar deactivated). Splitless: 5 m x 0.10 mm x 0.2 µm Carbowax or 15 meter x 0.25 mm x 0.50 µm Carbowax. MS SIM ions Equipment Agilent 7890A GC with cold-on-column and split/splitless injector. Agilent 5975C inert XL mass selective detector. Target ion Qualifier 1 Qualifier 2 GE-C16:0-d X GE-C12: GE-C14: GE-C16: X GE-C18: GE-C18: GE-C18: GE-C18: Operating conditions Helium at 150 kpa (splitless injection) or 2 ml/min (on-column) Injection volume 1 µl. Temperature from 60 C (on-column) or 110 C (splitless) to 260 C at 10 C/min.

26 Detector signal (UV) Method development sample preparation II: NPLC method Normal phase TLC, SPE and LC are widely used for isolating specific compound-classes from edible oils and fats. Glycidyl ester are slightly less polar than triacylglycerides. GE-C18:1 Saturated GEs GE-C18:2 GE-C18:3 GE reference solution TAG DAG MAG.. Spiked palm oil min = 8 ml Time [min.] The NPLC step provides efficient isolation of the glycidyl-esters, but unfortunately only at low injected amounts. Enrichment prior to NPLC isolation is needed.

27 GE C12:0 GE C14:0 GE C18:0 GE C16:0-d31 GE C16:0 GE C18:1 GE C18:2 GC-MS analysis: the final method(doi: /j.chroma ) mg of oil (containing GE-C16:0-d 31) is dispersed in 4 ml of acetonitrile. 2. The oil is slightly warmed and vigorously mixed for 20 second. 3. The acetonitrile phase is washed with 2 ml of heptane. 4. Coextracted glycidyl-esters are recovered from the heptane by acetonitrile extraction. 5. The solvent is evaporated under nitrogen at 35 C. 6. The residue is redissolved in 1 ml hexane/isopropanol (85/15 v/v) µl of the extract are separated by gradient NPLC. 8. The glycidyl ester fraction is collected and evaporated (under nitrogen, at 35 C). 9. The residue is redissolved in 40 µl chloroform µl of the final sample is injected in GC-MS using splitless injection. MS detection is by SIM. Palm oil sample. Levels range from 0.02 mg/kg (GE-C12:0) to 14.9 m/kg (GE-C18:1) Time [min.]

28 Conclusions glycidyl esters by GC-MS GC-MS can be reliably used to quantify intact glycidyl esters in edible oils. NPLC isolation after ACN extraction gives very clean fractions. The final method is rather similar to other methods used in edible oil analysis (e.g. sterol analysis, waxesters, partial acylglycerides etc.) Detection limits are better than 0.05 mg/kg glycidol. Quantitative data from our new method agree very well with data from the AOCS ringtrial. The method proofed to be robust: so far over 500 samples were analysed without problems.

29 Instrumentation for Comprehensive (off-line) LC GC ( GC)(-MS) Injection valve Mobile phase delivery Column 1 st dimension Sequential GC GC analysis 2 nd dimension FID 3 rd dimension (ToF)-MS 4 th dimension

30 General conclusions Oil and fat samples are very complex. Lipids are disturbing both GC and LC analysis. Sample preparation is often needed, despite modern developments like selective MS, large volume injection etc. NPLC is a good sample preparation tool (non-polar analytes). Hyphenated systems are attractive. Comprehensive couplings are the ultimate hyphenated systems. Mass spectrometry and comprehensive techniques like GCxGC are the key tools, after suitable sample preparation by extraction, liquid/liquid partitioning and/or NPLC.