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

0

20

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60

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120

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160

180

200

0 2 4 6 8 10

Time (min)

Sign

al (a

rb. u

nits

)

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100

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200

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300

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400

450

0 2 4 6 8 10

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

2

3

45 6

1

2

3

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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250

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750

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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300

0 100 200 300 400

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