SOLID PHASE EXTRACTION: Fundamentals and Recent Developments

Transcription

1 SOLID PHASE EXTRACTION: Fundamentals and Recent Developments Olga I. Shimelis, Ph.D Principal R&D Scientist sigma-aldrich.com/analytical

2 Time Spent on the Analytical Process R.E. Majors, LC/GC Magazine, 1992, 1997,

3 Fit of Solid Phase Extraction in the Analytical or Chromatography Workflow SPE is a Sample Prep Technique Sample Collection/ Storage Sample Prep Separation Detection Analysis Fraction Collection It is used to extract analytes from a wide variety of matrices prior to HPLC or GC analysis. SPE is form of liquid chromatography used for sample prep of liquid samples, the particle size for SPE is larger then for HPLC SPE is selective and versatile: Many different sorbents and elution conditions are available for different analytes and matrices 3

4 Important Goals of an SPE Extraction The characteristics of a good SPE method are: High analyte recovery Recovery measured relative to an internal standard No interference from sample matrix components High analyte concentration Simple method, minimal steps Reproducible No waste Shortest extraction time that still gives good results Minimum wash and elution solvents 4

5 How Does SPE Work? There are 2 different elution strategies in SPE. Which one to choose depends on the goal of the extraction. Bind-Elute Strategy (shown on next slide) Most common Bind: Analytes bind to sorbent in the tube, unwanted matrix components are washed off Elute: Eluant changed to remove analytes from tube Different eluants can be used to fractionate the analytes Analytes are concentrated via evaporation prior to HPLC or GC analysis Interference Removal Bind all unwanted matrix components and allow analytes to pass through during the sample loading stage Like chemical filtration Bind-elute SPE strategy is the most common. 5

6 Bind-elute Strategy Diagram Shown is a step-by-step bind-elute SPE extraction, beginning with a filtered sample containing analytes and internal standard (IS) in a matrix and ending with purified and concentrated analytes and internal standard ready for HPLC or GC analysis. 1) Apply sample to SPE tube 2) Apply wash solvent 3) Apply elution solvent 4) Evaporate elution solvent, reconstitute Original sample (analytes & IS in a matrix) HPLC or GC analysis Must first condition & equilibrate SPE tube Matrix fraction = waste Analyte fraction A dilute solution of analytes & IS in the elution solvent Purified & concentrated analytes & IS 6

7 Interference Removal Strategy Chemical Filtration Sample with Internal Standard in Matrix Matrix adsorbed Analytes & IS pass 2) Apply elution solvent 3) Evaporate elution solvent, reconstitute Must first condition & equilibrate SPE tube

8 Understanding Retention Mechanisms

9 Reversed-Phase SPE Common Sorbents: C18-functionalized silica, polymeric (DVB), carbon

10 Normal-Phase SPE Common Sorbents: Bare Silica, NH2 or Diol-functionalized silica,florisil, Alumina,

11 Ion-Exchange SPE Advantage: Wash with 100% Organic possible very clean Extracts

12 Useful Ion Exchange SPE Tips Ion exchange kinetics slower than RP & NP => reduce flow rate Strong vs. weak ion-exchangers Strong = Weak = Counter-Ion Selectivity sorbent functional group always ionized regardless of ph sorbent functional group has controllable pka; commonly used for extracting strong analytes

13 The Critical Role of ph in SPE Neutral State (Blue) = promotes hydrophobic (RP) interaction Ionized State (Green) = promotes electrostatic (IOX) interaction Ionization of Acidic & Basic Molecules- Acids (e.g., carboxylic acids): (e.g., R-COOH R-COO - ) HA H + + A - (Un-ionized) (ionized) 50% 100% low ph 0% 0% high ph 100% Bases (e.g., amines): (e.g., R-NH 3 + R-NH 2 ) pka of most acids (e.g. COOH) is 3-5 Presence of halogen atom near a carboxy group strengthens acid effect (electron sink) e.g., acetic acid (pka 4.75), monochloro acetic acid (pka 2.85), dichloroacetic acid (pka 1.48) BH + + OH - (Ionized) B 50% 100% low ph 0% 0% high ph 100% (Un-ionized) pka of most amines is 8-11 Aromatic (electron sink) amines have a lower pka than aliphatic amines e.g., Aromatic amines- aniline (pka 4.6), pyridine (pka 5.2); Aliphatic amines- (pka 9.7), dimethylamine (pka 10.7)

14 Keys to Successful SPE methods

15 Consider the analyte(s) of interest What functional groups may influence the analytes solubility, polarity, ionization state (pka), etc.? Hydrophilic Groups: Hydroxyl -OH Amino -NH 2 Carboxyl -COOH Amido -CONH 2 Guanidino -NH(C=NH)NH Amine -NR + 3 Sulfate -SO - 3 Hydrophobic Groups: Carbon-Carbon Carbon-Hydrogen Carbon-Halogen Olefin Aromatic Neutral Groups: Carbonyl -C=O Ether -O-R Nitrile -C=N -C-C -C-H -C-Cl -C=C

16 SPE Phase selection YOUR Sample matrix is: Aqueous (Biological Fluids, water, aqueous extracts) Organic (organic extracts in hexane, dichloromethane) Recommended Retention Mechanisms: Reversed-Phase Ion-Exchange Normal-Phase Analyte Characteristic: Moderately polar to non-polar compounds Weak cations/anions Strong cations/anions Polar to moderately polar compounds Recommended SPE phases: C18, C8, Ph, CN, DPA-6S, Carbon, SupelSelect HLB SAX, SCX, MCAX WCX, NH2, PSA Si, -CN, Diol, -NH2, Florisil, Alumina

17 Key to Successful SPE Methods Choose the appropriate SPE phase by understanding the sample matrix and identifying analyte(s) functional groups that influence its solubility, polarity, etc.. Understand how the analyte(s) behaves on the sorbent in response to changing extraction conditions. Manipulate these conditions to meet the defined sample prep objectives Supel Sphere dual-layer Multiple sorbents beds can be combined in one cartridge to improve the selectivity of the cleanup method

18 On the Outside: SPE Formats Different SPE formats are available. They all have the following in common: sorbent particles held securely in place to withstand the force of the liquid flow. 96-well plates Sorbent particles are contained inside the wells, held in place by frits Tubes Tubes (plastic or glass) are the most common SPE format. Also called cartridges. Disks Loose sorbent Sorbent particles are held in an inert, permeable filter disk. Allows faster flow rates and larger samples A modern format, called dispersive SPE where sorbent is loose in a tube 18

19 Using the Appropriate Bed Weight for Sample Size 96-well plates often comes with different bed weights Sorbent Bed weight Loading volume Retained by sorbent 15 mg µl up to 30 µl 25 mg µl 75 µl 50 mg µl 120 µl 100 mg µl 250 µl

20 Peak Area (mau*s) Peak Area (mau*s) Peak Area (mau*s) SPE Method Development: Tricyclic Antidepressants from Serum on C18 SPE Wash/Elute Profile Evaluation- Low ph Wash/Elute Profile Neutral ph Wash/Elute Profile Amitriptyline pka 9.76 High ph Wash/Elute Profile % Methanol % Methanol % Methanol At low ph, complete elution occurs at 60% MeOH. At low ph, retention limit is 10% MeOH. At neutral ph, complete elution occurs at 80% MeOH. At neutral ph, retention limit is 20% MeOH. Under basic ph, complete elution occurs at 80% MeOH. Under high ph, retention limit is 40% MeOH.

21 SPE Products from Supelco Supel -Select (basic method provided) Hydrophilic modified styrene based polymers Great generic SPE HybridSPE -Phospholipid (method & guidelines provided) Simultaneous removal of phospholipids and proteins Enhances MS detection by reducing ion suppression SupelMIP (method provided) Molecularly imprinted polymers Highly selective for analytes in difficult matrices Supel Sphere Carbon/NH2 (for Japanese positive system) Dual layer tubes for pesticide residue analysis Supel QuE (standardized methods) QuEChERS tubes and supplies Z-Sep family of sorbents for more challenging matrices cleanup 21

22 Triclosan in creek water Triclosan It is commonly known as antibacterial agent in personal care products Triclosan was first registered as a pesticide with the US EPA in Currently, triclosan also has 20 antimicrobial registrations. A more comprehensive review of triclosan by EPA started in Triclosan was previously found to be persistently present in the environment, it should be labelled as toxic to fish and other aquatic animals Triclosan was analyzed in a small stream and in a waste-treatment plant eluent Supel-Select HLB A generic hydrophilic-lipophilic polymer SPE sorbent Functions under reversed-phase conditions Compatible with aqueous loading samples 22

23 Supel-Select HLB: triclosan extraction/concentration Sample collection Sample Preparation Per EPA method 1692 Amber glass container should be used Sample analyzed within 7 days Acidify 50 ml or 100 ml sample to ph 2 Add 25 mg or 50 mg of EDTA-Na 4, mix for 60 min 500 ml per EPA method Condition SPE tube Load Wash Elution 3 ml methanol Supel-Select HLB, 60 mg/3 ml (54182-U) 3 ml distilled water 3 ml 0.01 M HCl Load prepared sample ( ml) 10 ml DI water Dry for 10 minutes under vacuum 3 ml acetonitrile: methanol (1:1) Evaporate to dryness under vacuum Reconstitute into mobile phase solvent 7 ml wash was tested 6 ml elution was tested 88% recovery from spiked water samples at 3500 ng/l 23

24 MRM 286.8/35.0 MRM 286.8/35.0 Supel-Select HLB SPE and LC-MS/MS: Triclosan in creek water 800 In waste-water plant effluent 60 In creek water, 1 mile downstream from discharge Triclosan found at 1100 ng/l 50 Triclosan found at 63 ng/l Time (min) time (min) Instrument: Agilent 1100/1200 HPLC and AB Sciex Qtrap 3200 HPLC Column: Ascentis Express C µm 15 x 2.1 mm Mobile phase: 40% Methanol, 40% Acetonitrile, 20% aqueous 0.1% formic acid Flow rate: ml/min Temperature: 30 Injector volume: 10.0 µl Detection: Q1/Q /35.0 ESI negative 24

25 Supel-Select HLB SPE: Triclosan in creek water SPE method was developed using Supel-Select HLB to clean and preconcentrate triclosan from water samples using reversed phase interactions The method was successfully applied to creek water and to waste-water using LC-MS/MS detection The creek level of triclosan was found to be 1/20 that in waste-water due to the dilution of the waste-water plant effluent in the creek. For more information, please visit sigma-aldrich.com/supel-select 25

26 Supel-Select SCX: Isolation and LC-MS Characterization of Illicit Bath Salts in Urine Phenethylamine and cathinone compounds were being marketed as bath salts, affects similar to heroin and methamphetamine there are three sets of isobaric compounds that require chromatographic resolution for positive confirmation: LC-MS method required for testing Supel-Select SCX: is a polymerically based cation exchange absorbent, containing a strong anion exchange sulfonic acid functionality. Analytes selectively retained via ion exchange High organic wash solvents displace endogenous matrix Bath salts eluted with basic organic solvent Result: Highly clean sample! 26

27 Supel-Select SCX: SPE method for bath salts Loading sample Supel-Select SCX, 30mg/1mL (54240-U) 1 ml water/urine spiked with 100 ng/ml bath salt mixture Conditioning 1 ml 1% formic acid in acetonitrile 1 ml water Loading and wash Load 1 ml spiked urine 1 ml water 1 ml 1% formic acid in acetonitrile 1 ml water Elution 2 ml 10% ammonium hydroxide in acetonitrile Evaporate to dryness, reconstitute into 100 μl water:methanol Inject into LC-MS, HILIC HPLC column 76-90% recoveries from spiked water samples 27

28 Bath salts: HILIC chromatography Column: Ascentis Express HILIC (Si), 10 cm x 2.1 mm, 2.7 μm (53939-U) Mobile phase: (A) 5 mm ammonium formate in acetonitrile, (B) 5mM ammonium formate water (98:2) Flow rate: 0.6 ml/min; inj. 1 μl; standard at 200 ng/ml; Detection: TOF/ESI m/z 28

29 Recoveries of bath salts using Supel-Select SCX SPE cleanup and HILIC-MS detection Sample (100 ng/ml) Spiked water Spiked Urine MDVP Buphedrone Fluoromethcathinone Butylone Ethylone Fluoromethcathinone Mephedrone Methylone Methedrone

30 Supel-Select SCX: Isolation and LC-MS Characterization of Illicit Bath Salts in Urine The Supel-Select SCX sample prep method allows for efficient urine matrix removal while maintaining high analyte recovery. The combination of the ion-exchange SPE with the HILIC separation provides a novel approach for the testing of problematic bath salt compounds. By utilizing ion-exchange mechanisms for sample cleanup, and taking advantage of the unique selectivity of chromatographic modes such as HILIC, analytical chemists can greatly improve the selectivity and sensitivity of their difficult bioanalytical applications. For more information, please visit sigma-aldrich.com/supel-select 30

31 HybridSPE-Phospholipid (HybridSPE-PL) 96-well SPE plates and cartridges Zirconia-coated silica particles Features: Selective removal of phospholipid interferences and precipitated proteins Simple 2-3 step procedure Benefits Improved LC-MS sensitivity (reduced matrix effect) Enhanced column lifetime Gradients not needed to clean column 31

32 Monitoring Phospholipid Contamination PLs major component of cell membranes Polar head group, non-polar tail Largest subclass (phosphatidylcholine) monitored using m/z 184 or m/z 104 fragment ions Used as a marker for ion-suppression risk assessment during LC-MS/MS Determine selectivity effectiveness of sample prep technique polar head group non-polar tail J.L. Little et al. / J. Chromatogr. B 833 (2006)

33 Problem: Protein and Phospholipid Accumulation on HPLC Column Standard protein ppt technique Reduces performance Increases backpressure Unpredictable carry-over & elution in future injections Gradients needed to clean column Monitoring PLs at 184 m/z Inj. #20, 2150 psi Inj. #10 Inj. #5 Inj. #1, 2020 psi Time (min) Increasing backpressure from protein precipitation, and baseline from phospholipid build up HPLC column: Sub-2um C18, 5 cm x 2.1 mm I.D. 33

34 Solution: Phospholipids Selectively Removed using HybridSPE-PL Technology Proprietary HybridSPE zirconia-coated silica Phospholipids The Zr atom on the particle acts as a Lewis acid The phosphate groups on the phospholipids are strong Lewis bases and complex with the zirconium atoms Analytes are eluted free of phospholipids 34

35 HybridSPE-PL Method (96-Well Format) Precipitate proteins in well 100 µl plasma/serum 300 µl 1% formic acid in acetonitrile Add I.S. as necessary Mix Apply vacuum Resulting filtrate/eluate is free of proteins and phospholipids, ready for LC-MS 35

36 Improved Situation: No Protein or Phospholipid Accumulation Using HybridSPE-PL Consistent column performance No increase in backpressure Eliminates carry-over & elution in future injections Extends column lifetime Gradients are not needed to clean column 184 m/z Monitoring PLs at 184 m/z Inj. #20, 1925 psi Time (min) Inj. #1, 1920 psi Time (min) No change in back-pressure and baseline 36

37 Injs./day/instrument Improved Through-put with HybridSPE-PL Elimination of need for post-gradient HPLC column clean-up improves sample throughput HybridSPE-PL Std. PPT Gradient, 20 min. ~ 70 inj./day Isocratic, 2 min. ~ 700 inj./day 20 min min Time (min) 37

38 Overlay of HybridSPE-Small Volume and Protein Precipitation Samples Methadone and metabolites from plasma Sample was extracted using HybridSPE-PL small volume (20 ul of plasma was used) or standard PPT (100 ul of plasma was used) High concentration (1200 ng/ml), still shows suppression with standard ppt method EDDP HybridSPE-Small Volume Methadone EMDP Protein Precipitation Method Column: Ascentis Express RP-Amide 10 cm X 2.1, mm I.D., 2.7um; ESI+ detection 38

39 HybridSPE-PL Technology Fast and convenient SPE method uses Interference Removal strategy Complete removal of precipitated proteins and phospholipids for analysis of pharmaceutical compounds Reduces matrix effects, improves HPLC column lifetime and method throughput Can be used to extract and concentrate phospholipids in lipidomics application For more information, please visit sigma-aldrich.com/hybridspe-pl. 39

40 QuEChERS Method: Pesticides in Food Quick Easy Pesticides in fruit vegetable further food & feed Cheap Effective Rugged Safe 40

41 HOW DOES QUECHERS METHOD WORK? Weigh 10 g homogenized sample Add 10 ml acetonitrile, Add I.S. SHAKE Add 4 g MgSO4, 1 g NaCl, adjust to ph 5.5 with citrate buffer Add MgSO4 and PSA (C18) to aliquot Acidify extract to ph 5 SHAKE AND CENTRIFUGE SHAKE AND CENTRIFUGE OPTION: Acidic pesticides LC-MSMS OPTION: Acid-labile pesticides LC-MSMS GS-MS/ LC-MS/MS 41

42 QuEChERS Method: the choice of sorbents interference PSA C18 C18/PSA ENVI- Carb ENVI- Carb/PSA PSA/C18/ ENVI-Carb Z-Sep Z-Sep+ Z-Sep/C18 Fats X X X Pigments X X X X X X X X X X Sugars X X X X Acids X X X X New choice of cleanup sorbents for Fat-containing and pigmented samples: Supel Que Z-Sep for hydrophobic analytes Supel QuE Z-Sep/C18 (Discovery DSC-18 + Z-Sep) for samples containing <15% fat Supel QuE Z-Sep+ (C18 and zirconia dual bonded to silica) for samples containing >15% fat 42

43 QuEChERS: Pesticides in avocado by GC-MS using Z-Sep+ as a cleanup sorbent Pesticide mix included hydrophobic compounds (e.g.organochlorines, hexachlorbenzene) and some other more polar classes all GC-MS amenable QuEChERS extraction was performed Ratio 3 g sample to 25 ml acetonitrile extraction solvent improved recoveries Tested cleanup used Z-Sep+ with and without PSA and C18 The analysis performed using GC equipped with single quadrupole MS detector

44 Analysis of avocado extracts Scan mode Z-Sep+ cleanup Time (min) C18/PSA cleanup Time (min) 44

45 QuEChERS: Pesticides in avocado by GC-MS Results: Pesticide Recovery Z-Sep+ showed better recovery overall. PSA/C18: matrix interference prevented analysis of cyfluthrin, cypermethrin and deltametrin. Z-Sep+ showed better reproducibility than PSA/C18

46 Z-Sep and Z-Sep+ as cleanup sorbents for QuEChERS QuEChERS method is a multiresidue method for analysis of pesticides New family of Z-Sep sorbents can provide cleanup advantages Provide better removal of fatty and colored matrix components Provide better recovery of hydrophobic analytes in comparison to C18 cleanup No change in the QuEChERS procedure is required to try Z-Sep sorbents For more information, please visit sigma-aldrich.com/quechers or sigma-aldrich.com/zsep 46

47 SUMMARY 1. Choose the sorbent and SPE hardware according to you analysis needs 2. Pay attention to the ph of the loading, washing and elution solvents as it affects the recovery of the ionizable analytes 3. Stay informed of the new SPE developments that make sample prep easier, faster and more convenient 47

48 Resources To view the complete SPE product line from Supelco, instructional product videos/webinars, and technical literature, Visit sigma-aldrich.com/spe To request SPE samples for method development, Visit sigma-aldrich.com/spe-samples To learn more about HybridSPE-PL Visit sigma-aldrich.com/hybridspe-pl To learn more about ZSep Visit sigma-aldrich.com/zsep If you have additional questions related to this presentation, Contact 48