Membrane techniques for analysis, sampling and speciation in environmental measurements
Jan Åke JönssonLennart Mathiasson
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Analytical Chemistry Lund University Sweden
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Approaches to membrane extraction
• SLM (Supported liquid membrane) extraction —3 phases
• PME (Polymer membrane extraction) — 3 phases• MMLLE (Microporous membrane liquid-liquid extraction)
— two phases
Main objective: replace classical Liquid-Liquid ExtractionThese techniques use a non-porous membrane, and involve partitioning of the analytes over a phase boundary: Not filtration, not dialysis.
Trends. Anal. Chem., 1999, 18, 318; J. Chromatogr. A, 2000, 902, 205; Adv. Chromatogr, 2001, 41, 53; J. Sep. Sci., 2001, 24, 495
Trends. Anal. Chem., 1999, 18, 318; J. Chromatogr. A, 2000, 902, 205; Adv. Chromatogr, 2001, 41, 53; J. Sep. Sci., 2001, 24, 495
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General concepts of SLM
Trapping in a stagnant acceptor: by means of a chemical reaction, the extracted
molecules are made non-extractable (usually charged)
Trapping in a stagnant acceptor: by means of a chemical reaction, the extracted
molecules are made non-extractable (usually charged)
Three phases: Aqueous donor, Organic membrane, Aqueous acceptor
Organicmembrane
Aqueous acceptor phase, stagnant
Aqueous donor phase, flowing
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SLM extraction of basic analytes
Basic sample WasteB N A-
BH+ N
Organicmembrane
Aqueous, stagnantacidic acceptor phase
Donor phase
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Mass transferIn SLM, mass transfer is driven by the concentration difference
of the uncharged species:
CD total conc of analyte in sample, CA total (measured) conc in acceptor, αD , αA uncharged fraction of total conc in donor and acceptordM membrane thickness
For a base:
Jönsson et al., Anal Chim Acta, 1993, 227, 9Jönsson et al., Anal Chim Acta, 1993, 227, 9
)(1011
][BH[B]]B[
pHpKa −+ +=
+=α
AADDM
CCCd
CDdxdCDJ αα −=∆
∆−=−=
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Enrichment factors- after long-time enrichment
Aniline compounds with different pKa-values
Compound pKa1 4.62 4.03 2.54 2.3
Aniline compounds with different pKa-values
Compound pKa1 4.62 4.03 2.54 2.3
Chimuka et. al. Anal. Chem. 1998, 70, 3906Chimuka et. al. Anal. Chem. 1998, 70, 3906
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The membrane liquid in SLM
• Low solubility in water and low volatility • Stable from one day to several months• Low viscosity• Efficient solvent for analytes• May contain additives and carriers• The SLM is prepared by soaking a porous
PTFE membrane in the selected liquid
Examples: n-undecane, di-n-hexyl ether, undecanone, kerosene
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Chemical principles in SLM extractionAnalytes Donor Membrane Acceptor Transported
speciesTrapping
Acids acidic org (+TOPO) basic neutral anionsBases basic org acidic neutral cationsMetal ions 8-hydroxy-
quinolineorg DTPA complexes charged
complexesMetal ions, Aminoacids, Amines
acidic,pH=3
DEHPA acidic,pH=0
complexes countertransportof H+
Amino acidsamino phosphonates
basic Trioctylmethyl-ammonium
Acidic,chloride
ion pairs cations
Amino acids basic Pd-complex acid complexes cationsSugars, diol-containgcompounds
neutral boronic acidcarrier
acid covalently boundcomplexes
protonation ofcarrier
Anionic surfactants acidic +amine
org basic ion pairs deprotonation ofamine carrier
Triazine herbicides neutral Org Atrazineantibodies
permeation immunologicalas antigen-antibodycomplex
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Improvement of extraction- of carboxylic acids with TOPO
Shen et. al. Anal. Chim Acta., 1994, 292, 31Shen et. al. Anal. Chim Acta., 1994, 292, 31
butanoic propanoic100
0102030405060708090
0 5 10 15 20TOPO (%) in di-n-hexyl ether
E(%)
lactic
formic
(tri-n-octylphosphine oxide)
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Scope of SLM extraction
Extraction principles:• Simple permeation (acids, bases)• Hydrogen bonding carrier (more
polar acids and bases)
• Complex formers (metal ions)• Ion pairing (surfactants, amino
acids)• Immunological trapping (any…?)
Connection to:• LC (RP, NP, IC, IP)• CE• AAS, PSA
Matrix types:• Environmental (surface and waste water, soil liquids)• Biological (blood plasma, urine, manure)
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Extraction efficiency E:
E = nA / nI = CAVA/ CIVI
E → 1 when the donor flow rate FD → 0 and decreases with FD (Donor flow rate)
a - E is limited by diffusion in the donor phase (large K)
b - E is limited by diffusion in the membrane (small K)
FD
E
Flow dependence (I)
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Flow dependence (II)
Ea
FD
The enrichment factor Ea(total accumulated amount of analyte in acceptor) increases with donor flow rate as lower E is offset by higher input.
Thus: •For large samples (e.g lake water), use high FD to obtain best accumulation of analyte. •For small samples (e.g. blood plasma), use small FD to obtain highest E (see previous page)
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Comparison SLM - SPE
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180
200
0 2 4 6 8 10
Time (min)
Sign
al (a
rb. u
nits
)
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450
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Time (min)
Sig
nal
(arb
. un
its)SLM SPE
0.5 µg/l SLM-extracted 1.0 µg/l SPE-extracted
Methoxy-s-triazine herbicides in river water
Megersa et. al. J. Chromatogr. A, 1999, 830, 203Megersa et. al. J. Chromatogr. A, 1999, 830, 203
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Simple membrane extraction set-up for lab and field sampling use
Acid
Acceptor is manuallyharvested and taken to HPLC-analysis
Sample
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-2000
3000
8000
13000
18000
23000
28000
33000
0 10 20 30 40
54
3
21
Response/nA
time/min
50
0
Knutsson et. al. Chromatographia, 1996, 42, 165Knutsson et. al. Chromatographia, 1996, 42, 165
Spiked Kävlinge river water1. monochlorophenol 50 ng/L2. dichlorophenol 100 ng/L3. trichlorophenol 100 ng/L4. tetrachlorophenol 100 ng/L5. pentachlorophenol 100ng/L(electrochemical detection)
SLM-LC - chlorinated phenols in natural water
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Field sampling - Acids in waters
AcidAcceptor is manuallyharvested and taken to lab for HPLC-analysis
Sampling point
24 h samplings in Vemmen-högsån. LOD < 100 ng/L (ppt) or 0.5 nM.
Cl
OCH3
OOH
MCPA
0
20
40
60
80
0 10 20Dates in May
ppb MCPA
Knutsson et al, J. Agric. Food. Chem.,1992, 40, 2413
Jung et al, Anal. Chim. Acta 2002, 474, 49 (sampling of phenolics in soil-free greenhouse cultivations)
Knutsson et al, J. Agric. Food. Chem.,1992, 40, 2413
Jung et al, Anal. Chim. Acta 2002, 474, 49 (sampling of phenolics in soil-free greenhouse cultivations)
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Dodecylbenzenesulfonic acid (one isomer)
DBSA
Donor : RSO3- + HNR’3
+→ RSO3 - HNR3
+
Acceptor: RSO3 - HNR’3
+ + OH- → RSO3 -
+ NR’3
(NR’3 = tri-n-hexylamine)
EMembrane liquid
di-n-hexylether 0.71
1-chlorotetradecane 0.51
n-undecane 0.40
Miliotis et al, Intern. J. Environ. Anal.Chem., 1996, 64, 35
Miliotis et al, Intern. J. Environ. Anal.Chem., 1996, 64, 35
CH3
CH3
SO
OO-
Ion-pair extraction - Anionic surfactants
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Metal Extraction
Papantoni et al, Analyst 1995, 120,1471Papantoni et al, Analyst 1995, 120,1471
Extraction of Cu2+ using 8-Hydroxyquinoline added tothe donor phase and DTPA inthe acceptor.
Extraction of Cu2+ using 8-Hydroxyquinoline added tothe donor phase and DTPA inthe acceptor.
Extraction of Co2+ using SCN-
in the donor, methyltrioctylammonium chloride in themembrane and DTPA in theacceptor. Also works (E>0.75)for Cu2+, Cd2+ and Zn2+
Extraction of Co2+ using SCN-
in the donor, methyltrioctylammonium chloride in themembrane and DTPA in theacceptor. Also works (E>0.75)for Cu2+, Cd2+ and Zn2+
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H+
M2+(DH)2
MD2
Donor Membrane Acceptor
M2+
H+
PO
RO
OH
OR
DEHPA (Diethylhexyl phosphoric acid)pKa ≈ 1.5
Donor : pH = 3Acceptor : pH = 0E > 80% for many metals (Cu, Pb, Cd, ...)
Djane et al, Fresenius J. Anal. Chem 1997, 358, 822Djane et al, Fresenius J. Anal. Chem 1997, 358, 822
Metal extraction with alkyl phosphoric acid
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H+
HA+ (DH)2
HAD(HD)3
Donor Membrane Acceptor
H+
HA+
Donor: HCl, pH = 3Acceptor: HCl, pH = 0E = 56% for Trp
PO
RO
OH
OR
DEHPA (Diethylhexyl phosphoric acid)pKa ≈ 1.5
Wieczorek et al, Anal. Chim. Acta 1997, 346, 191Drapala et al. Acta Biochim. Pol. 2001, 48, 1113Romero et al, J. Sep. Sci. 2002, 25, 584
Amino acid, peptide or amine extractionwith alkyl phosphoric acid
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Donor buffer
Acceptor buffer
LC-column
Waste
Pump
10 µl membrane channels
Detector
SLM-LC setup For biomedical samples; Autoinjector style
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Basic drug metabolites in urine
-10000
0
10000
20000
30000
40000
50000
0 2 4 6 8 10 12 14 16 18 20
Time (min)
Res
pons
e
-10000
0
10000
20000
30000
40000
50000
0 2 4 6 8 10 12 14 16 18 20
Time (min)
Res
pons
e
1
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3
45 6
1
2
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4 5 6
a
b
Polar metabolites of Ropivacaine (about 1 µM each) extracted by SLM from:
(a) water
(b) urine
Analysis by isocratic ion-pair LC.
Polar metabolites of Ropivacaine (about 1 µM each) extracted by SLM from:
(a) water
(b) urine
Analysis by isocratic ion-pair LC.
Jönsson et al., J. Chromatogr. A, 2000, 870, 151Jönsson et al., J. Chromatogr. A, 2000, 870, 151
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Basic drugs in blood plasmaSLM-LC-UV of Amperozide
Blood plasma Water
4µg/mL N
N
NH
CH3
O
F
F
I
Lindegård et al,Anal. Chem., 1994, 66, 4490
Lindegård et al,Anal. Chem., 1994, 66, 4490Protein binding calculated from SLM experiments:
99% Literature value: 97%
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SLM-CE setup
CZE
inletoutlet
UV
waste
2
3
4
5waste
1
1. Hollow-fiber SLM unit
2. Donor pump
3. Acceptor pump
4. Splitter
5. Switch
Pálmarsdóttir et al., Anal. Chem., 1997, 69, 1732
Pálmarsdóttir et al., Anal. Chem., 1997, 69, 1732
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Basic drugs in blood plasma (II)
Bambuterol by SLM-CE
O
N O
CH3
CH3
NH
CH3CH3
CH3
OH
O
N O
CH3
CH3
Time (min)
Abs.
205
nm
1µM physostigmin (A) and 4 nM Bambuterol (B) Pálmarsdóttir et al.,
Anal.Chem. 1997, 69, 1732Pálmarsdóttir et al., Anal.Chem. 1997, 69, 1732
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• Free dissolved concentrations of pollutants∝ fugacity (chemical activity of a gas - “escaping tendency”) - chemical potential
• Important quantity in environ-mental modeling
• Controls diffusional and other transports
• At equilibrium, fugacities are equal
After Ph. Mayer, Roskilde
Fugacity
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Sensing fugacity (activity) in three steps
• bring sampler into equilibrium with the medium (e.g. environmental water)
• measure concentration in sampler
• determine fugacity (or dissolved concentration)
This can be made by SPME for nonpolar compounds. For polar compounds we suggest a membrane
approach
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Sensing fugacity in three steps using Matrix-SPME
polymer coated fiber is equilibrated with sediment ≈ 1µL PDMS in 10 ml sediment
CPDMS is measured by gas chromatographyDesorption at 275oC and trapping at 50oC
Dissolved porewater concentrations: Cdissolved=Cpolymer/Kpolymer,water
Mayer et al. Environ. Sci. Technol. 2000, 34: 5177-5183Mayer P, Vaes WHJ, Tolls J, Hermens JLM and D Mackay. Environ.
Sci. Technol. Feature 2003, 37, 184A-191A
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Sensing fugacity in three steps using membrane extraction -
(equilibrium Sampling Through Membranes - ESTM)
• bring sampler (SLM device) into equilibrium with the medium (e.g. environmental water)
• measure concentration in the acceptor solution
• determine fugacity (or dissolved concentration) using the relevant enrichment factor
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What do we not measure?
• Total concentrations – Mass balances – Accounting of molecules
• “Recovery”– extraction efficiency: < 1 %– analytical recovery: > 99 %
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What do we measure?
CA proportional to fugacity (activity, dissolved concentration)– direction and extent of diffusion in multi-media
systems(as chemical potential related to fugacity and activity
Dissolved concentrations can be determined with appropriate factor (enrichment factor)– effective concentration for ….– availability of ...– link to aquatic toxicity data
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ESTM theory - Determination of free fraction by SLM
Remember: mass transfer is driven by the concentration difference of the uncharged species:
∆C = αD CD - αA CAor:
∆C = CF - αA CA
CF free fraction of the analyte in sample, ”fugacity” CA total (measured) conc. in acceptor, αA uncharged fraction of total conc. in acceptor, and
αA is not very near zero
Chimuka et al Anal Chem. 1998, 70, 3906Chimuka et al Anal Chem. 1998, 70, 3906
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At equilibrium, ∆C = 0 and the free fraction is:
CF = CA αA
As αA is known and possible to control, the free fraction can be calculated.
For simple bases:
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Ee
VS
ESTM theory II- Determination of free fraction by SLM
)( pHpKa −+=
1011
Aα
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(pHA - pKa) = 1.0 ==> αA = 1/9a: 100 ppb in water (Ee = 9.1)b: 10 ppm humic acid (83%)c: 20 ppm humic acid (65%)fitting of first order one-compartment model
unpublished student work (Christian Magnusson)
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1000
volume (ml)
c acc
epto
r (pp
b)
Water, Enrichment: 9.1
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1000
volume (ml)
c acc
epto
r (pp
b)
10 ppm humic acid: 83 % of water
0 50 100 150 2000
250
500
750
20 ppm humic acid: 65% of water
volume (ml)
c acc
epto
r (pp
b)
a b
c
ESTM of 2,4-dichlorophenol
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• As far as tested, ESTM works according to theory for sensing free concentrations.
• It is expected to work for acids, bases and other polar compounds, thus being a complement to the analogous technique of matrix-SPME
• By changing pH (or other parameters) it is possible to select the equilibrium enrichment factor at will, also to high values to measure very low free concentrations.
• To work with high factors, the volume ratio must be large, which calls for miniaturized membrane units
• The time needed to attain equilibrium might be long, studies in improvement of mass transfer kinetics are important.
Conclusions (on ESTM) and perspectives
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Speciation (kinetic approach)complexation to humus, etc.
AX ⇔ X + Ak1
k-1A+
AX ⇔ X + Ak1
k-1A+
Donor Mem Acceptor
Extraction will depend on:• Transport of A through donor bulk (known from extraction when [X]=0• Transport of A through membrane (known from extraction when [X]=0• Transport of AX through donor bulk (maybe possible to neglect)• Complexation kinetics (sought)Applies to drug-protein binding, and environmental studies
Trtić-Petrović and Jönsson. Desalination., 2002, 148, 247Trtić-Petrović and Jönsson. Desalination., 2002, 148, 247
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General concepts of MMLLE
Extraction relies on high partition coefficients Permits easier on-line automation than
conventional LLE
Extraction relies on high partition coefficients Permits easier on-line automation than
conventional LLE
Two phases: Aqueous donor, Organic acceptor
OrganicmembraneOrganic acceptor
phase, flowing
Aqueous donor phase, flowing
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Lidocaine
0
50
100
0 5 10 15Fa (µl/min)
E%
Moving acceptor
Scope of MMLLE
Extraction principles:• Liquid-liquid distribution
(hydophobic compounds)• Complex formers (metal ions)• Ion pairing (surfactants)• Stagnant or moving acceptor
Matrix types• Environmental (surface
water, waste water)• Biological (blood plasma,
urine)
Connection to:• GC• LC (NPLC)
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mL
Ee
Cationicsurfactants
Enrichment
Stagnant acceptor
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donorphase
wastemembran
e unit
N2
solvent
Samples
wasteGC
carrier gas
Plasma sample
III
12
3
4
5
6
7
Time (min)12 14 16 18 20
Shen et. al. Anal. Chem., 1998, 70, 946Shen et. al. Anal. Chem., 1998, 70, 946
on-line connection to capillary gas chromatography
MMLLE - GC-local anaesthetics in blood plasma
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ESy -extraction syringe
Gas Chromatograph
Extraction unit
Piston
Needle
Miniaturized MMLLEwith direct and automatic GC-connection
Applied to PCB, PAH, Phthalates, chlorinated pesticides, etc.
Norberg and Thordarson, Analyst, 2000, 125, 673Norberg and Thordarson, Analyst, 2000, 125, 673
Hollow fiber
Sample in
ESyTech AB, LundPersonal Chemistry AB, Uppsala
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ESy -extraction syringe II
(Present prototype)
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ESy-GC-ECD Chromatogram of PCB congeners extracted from 1 mL of: a) 100ppt spiked reagent water, b) 100ppt spiked river water, c) blank river water, d) blank reagent water (T. Barri et al, unpublished)
a
b
c
d
ESy-GC-ECD of PCB
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General concepts of PME
A family of techniques: can utilize trapping as SLM, but also many other
possibilities. On-line or off-line, flow systems or static.
A family of techniques: can utilize trapping as SLM, but also many other
possibilities. On-line or off-line, flow systems or static.
Three phases: Aq/org/gas donor, Polymeric membrane, Aq/org/gas acceptorPolymeric
membrane (silicone rubber)
Acceptor phase, flowing or stagnant
Donor phase, flowing or stagnant
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Comparison PME vs. SLM
+ More stable membrane - insoluble
+ Any combination of phases
– Less possibilities for chemical tuning -Limited composition and no additives
– Slower extraction - Lower diffusion coefficients in polymers than in liquids
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Examples of PME-approaches
LDPE-Membrane
Liquid Sample
Organic Solvent
Analyte
Off-line aq/org extraction of polluted water (Hauser and Popp, J. Sep. Sci. 2001, 24, 551)
Extraction of phenols from process waste water, connected to HPLC(Melcher and Bouyoucos, Process Contr. Qual. 1990, 1, 63)
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MESI - Membrane extraction with a sorbent interface
Liquid/polymer/gas (or gas/polymer/gas) systems for direct connection to gas chromatographyPawliszyn et al., Anal. Chem. 1994, 66, 1339
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Membrane extraction in analytical chemistry
• Provides selective enrichment• Useful for sample pretreatment and
sampling• Applicable to environmental and biomedical
samples• Can be automated and connected on-line to
analytical instruments in a flow system• Essentially solvent-free — environmentally
friendly• Can provide speciation information
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• Negussie Megersa• Claes Melander• Kuria Ndung’u• Göran Nilvé• Jan Norberg• Sveinbjörg Palmarsdottir• Margareta Papantoni Sandahl• Roberto Romero• Yin Shen• Eddie Thordarsson• Piotr Wieczorek
• Gudjon Audunsson• Thaer Barri• Luke Chimuka• Nii-Kotey Djane• Anna Drapala• Pawel Dzygiel• Lena Grönberg• Magnus Knutsson• Boel Lindegård• Philipp Mayer• Tasso Miliotis
Not to forget: NFR, VR, SJFR, RALF, SNV, SIDA, SI, EU DG XII, Astra Draco, Astra Pain Control
Not to forget: NFR, VR, SJFR, RALF, SNV, SIDA, SI, EU DG XII, Astra Draco, Astra Pain Control
Thanks for contributions