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“This is he pee e iewed e sion o he ollowing a icle: Roman-Hidalgo, C.,
San igosa-Mu illo, E., Ramos-Payán, M., Pe e sen, N.J., Ku e , J.P. and
Pede sen-Bje gaa d, S. (2019), On-chip elec omemb ane ex ac ion o acidic
d ugs. ELECTROPHORESIS, 40: 2514-2521, which has been published in inal
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1
On-chip elec omemb ane ex ac ion o acidic d ugs
C is ina Roman Hidalgoa, Elia San igosa Mu illob, Ma ía Ramos Payána,*, Nickolaj J.
Pe e senc, Jö g P. Ku e c, S ig Pede sen-Bje gaa dc,d,*
aDepa men o Analy ical Chemis y, Facul y o Chemis y, Uni e si y o Se ille, c/P o .
Ga cía González s/n, 41012, Se ille, Spain
bDepa men o Analy ical Chemis y, Uni e si a Au ónoma de Ba celona, 08193
Bella e a, Ba celona, Spain
cDepa men o Pha macy, Facul y o Heal h and Medical Sciences, Uni e si y o
Copenhagen, 2100 Copenhagen, Denma k
dSchool o Pha macy, Uni e si y o Oslo, P.O. Box 1068 Blinde n, 0316 Oslo, No way
Abs ac
In he p esen wo k, a new suppo ed liquid memb ane (SLM) has been de eloped o on-
chip elec omemb ane ex ac ion o acidic d ugs combined wi h HPLC o CE, p o iding
signi ican ly highe s abili y han hose epo ed up o da e. The a ge analy es a e i e
widely used non-s e oidal an i-in lamma o y d ugs (NSAIDs): ibup o en (IBU),
diclo enac (DIC), nap oxen (NAX), ke op o en (KTP) and salicylic acid (SAL). Two
di e en mic ochip de ices we e used, bo h consis ed basically o wo poly(me hyl
me hac yla e) (PMMA) pla es wi h indi idual channels o accep o and sample
solu ions, espec i ely, and a 25 m hick po ous polyp opylene memb ane imp egna ed
wi h he o ganic sol en in be ween. The SLM consis ing o a mix u e o 1-undecanol and
2-ni ophenyl oc yl e he (NPOE) in a a io 1:3 was ound o be he mos sui able liquid
memb ane o he ex ac ion o hese acidic d ugs unde dynamic condi ions. I showed a
long- e m s abili y o a leas 8 hou s, a low sys em cu en a ound 20 A, and eco e ies
o e 94% o he a ge analy es. NPOE was included in he SLM o signi ican ly dec ease
he ex ac ion cu en compa ed o pu e 1-undecanol, while he ex ac ion p ope ies was
2
almos una ec ed. Mo eo e , i has been success ully applied o he de e mina ion o he
a ge analy es in human u ine samples, p o iding high ex ac ion e iciency.
1. In oduc ion
Sample p epa a ion is a ime consuming s ep in many analy ical p ocedu es. Fo his
eason, subs an ial esea ch has been de o ed o he de elopmen o new sample
p epa a ion echniques in ecen yea s. In his esea ch, ocus has been on analysis ime,
analy e p e-concen a ion, sample clean-up, au oma ion, and minia u iza ion. The
in oduc ion o solid-phase mic oex ac ion (SPME) ini ia ed his de elopmen [1], and
was, among o he s, ollowed by single d op mic oex ac ion (SDME) [2], hollow- ibe
liquid-phase mic oex ac ion (HF-LPME) [3], and elec omemb ane ex ac ion (EME)
[4]. The la e echnique was in oduced in 2006 and p oposed he use o an ex e nal
elec ical ield o p omo e he ex ac ion o cha ged analy es om he sample o an
accep o solu ion ac oss a SLM.
EME is in e es ing because mass ans e is apid due o he elec ical ield, and because
p e-concen a ion and sample clean-up is achie ed. In addi ion, EME p o ides high
selec i i y based on he di ec ion and he magni ude o he elec ical ield, and based on
he chemical composi ion o he SLM. Because he accep o solu ion is aqueous, i can
be injec ed and analyzed di ec ly by high pe o mance liquid ch oma og aphy (HPLC),
liquid ch oma og aphy–mass spec ome y (LC–MS), o capilla y elec opho esis (CE).
The SLM is a mic oli e olume (3-15 µL) o an o ganic sol en immobilized in he po es
o a polyme ic memb ane suppo , and he amoun o o ganic sol en used pe sample is
educed o a minimum compa ed o he la ge olumes used in adi ional echniques.
Thus, EME can be conside ed as a g een chemis y app oach o analy ical sample
p epa a ion [5-7].
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EME has been de eloped in o he 96-well o ma o high- h oughpu sample p epa a ion,
bu can also be pe o med in mic o luidic de ices. Thus, in 2010, Pe e sen e al.
demons a ed o he i s ime down-scaling o EME o a chip sys em, which was e med
on-chip EME [8]. This sys em was ope a ed wi h a s agnan accep o solu ion and a
dynamic (i.e., lowing) sample, and new sample was con inuously deli e ed o he
memb ane. Due o he la e , he sys em p o ided high ex ac ion e iciency. La e , a
double- low sys em was de eloped, whe e bo h accep o solu ion and sample we e
pumped cons an ly in o he chip de ice [9]. This u he imp o ed e iciency, and on-chip
EME shows po en ial as a u u e sample p epa a ion echnique.
The composi ion o he SLM plays an impo an ole in he ex ac ion e iciency, and
selec ion o a p ope sol en is c i ical [10]. Based on cu en unde s anding, he ideal
o ganic sol en has o be wa e -immiscible and wi h a ce ain hyd ophobici y.
Immiscibili y wi h wa e is impo an o a oid leakage o he SLM du ing ex ac ion
(samples and accep o solu ions a e bo h aqueous), and hyd ophobici y is impo an in
o de o imp egna e comple ely he memb ane suppo . In addi ion, hyd ophobici y is also
impo an o a oid excessi e lux o ma ix ions ac oss he SLM. This educes cu en
(and conduc i i y) in he sys em and ensu es sys em s abili y. The o ganic sol en should
p e e ably be o low iscosi y o acili a e as mass ans e o he analy es, and o low
ola ili y o a oid e apo a ion. Finally, he o ganic sol en should acili a e s ong
hyd ogen binding and dipole-dipole in e ac ions wi h he analy es, o acili a e hei
ans e as ionic species in o he SLM. The la e can o some ex en be p edic ed by he
Kamle and Ta sol a och omic pa ame e s ,  and π* [11, 12]. Thus, acco ding o
li e a u e, EME o acidic analy es equi es sol en s as SLM wi h high hyd ogen bonding
acidi y (α) and dipola i y–pola izabili y (π*), and low hyd ogen bonding basici y ().
The e o e long-chain alcohols seem o be he mos sui able o ganic sol en s o acidic
4
analy es. Fo EME o basic analy es, high hyd ogen bonding basici y () is equi ed, and
2-ni ophenyl oc yl e he (NPOE), ei he as pu e sol en o mixed wi h addi i es such as
di-(2-e hylhexyl) phospha e (DEHP) o is-(2-e hylhexyl) phospha e (TEHP) is a highly
sui able sol en [13, 14].
In mos pape s ela ed o EME o acidic subs ances, 1-hep anol o 1-oc anol we e ound
o be he mos e icien SLMs [10, 14-19]. To ou knowledge, only one single pape is
a ailable in he li e a u e desc ibing on-chip EME o acidic d ugs [20], whe e
simul aneous ex ac ion o acidic and basic d ugs was p oposed, achie ing he bes
ex ac ion e iciency wi h 1-oc anol as SLM o he acidic analy es. 1-Oc anol is op imal
in e ms o hyd ogen bonding acidi y (α), hyd ogen bonding basici y (), and dipola i y–
pola izabili y (π*) [21]. Howe e , due o sligh wa e solubili y (1.2 g/L) i may no be
s able unde low condi ions and, in ou expe ience, i s use as o ganic sol en in
mic o luidic chip de ices should be, he e o e, a oided. Al hough a conside able numbe
o esea ch pape s ha e been published on EME o acidic analy es, s ill no highly s able
SLMs ha e been iden i ied.
The e o e, he aim o his wo k was o de elop a s able SLM unde low condi ions in a
mic ochip de ice o EME o acidic d ugs. Fo his pu pose, se e al o ganic sol en s ha e
been es ed in wo di e en expe imen al se -ups o on-chip EME, wi h p ima y ocus
on ex ac ion e iciency, s abili y, and ex ac ion cu en . Fi e non-s e oidal an i-
in lamma o y d ugs (NSAIDs) we e used as a ge analy es (ibup o en, nap oxen,
ke op o en, salicylic acid, and diclo enac), and op imiza ion o he expe imen al
condi ions has been ca ied ou . Mo eo e , on-chip EME has been also e alua ed wi h
human u ine samples.
2. Expe imen al
2.1. Chemicals and sample solu ions

5
All chemicals we e o analy ical- eagen g ade. Salicylic acid (SAL), ke op o en (KTP),
nap oxen (NAX), diclo enac (DIC) and ibup o en (IBU) we e pu chased om Fluka–
Sigma–Ald ich. 1-oc anol, 1-nonanol, 1-decanol, 1-undecanol, 1-dodecanol, 1,1,2,2-
luo ooc anol, 2-ni ophenyl oc yl e he (NPOE), Aliqua ®336, sodium hyd oxide,
hyd ochlo ic acid, ammonia and me hanol we e pu chased om Fluka (Buchs,
Swi ze land). Isobu anol, bu anol, 1-pen anol and 1-hep anol we e pu chased om Fluka-
Sigma-Ald ich (Mad id, Spain).
Aqueous wo king solu ions o NSAIDs we e daily p epa ed by adequa e dilu ions om
me hanolic (IBU, KTP, NAX) and aqueous (SAL, DIC) 400 mg L-1 s ock solu ions s o ed
a 4°C.
2.2. Capilla y elec opho esis
Capilla y elec opho esis (CE) was pe o med wi h an Agilen Technologies HP3D CE
ins umen (Agilen Technologies, Waldb onn, Ge many) equipped wi h a UV-DAD
de ec o . The wa eleng hs used we e 220 nm o IBU, 225 nm o NAX and 253 o KTP.
The unning bu e was 30 mM NaAc:ACN (75:25, / ) pH 5 (adjus ed wi h HAc).
Sepa a ions we e pe o med a 25 kV in a 50 μm i.d. used-silica capilla y (TSP050375,
Polymic o Technologies, Phoenix, AZ) wi h an e ec i e leng h o 56 cm. The
empe a u e o he capilla y was se o 20ºC. Hyd odynamic injec ions we e pe o med
by applying 45 mba o 8 seconds. Daily, be o e use, he capilla y was successi ely
insed wi h 0.1 M NaOH, wa e , and he unning bu e o 5 min each. Be ween uns, i
was also condi ioned wi h 0.1 M NaOH (2 min), wa e (3 min), and he unning bu e (5
min).
The accep o solu ion was spiked wi h 30 µg mL-1 benzoic acid se ing as an in e nal
s anda d (IS) o co ec o possible e apo a i e loss o he accep o solu ion.
2.3. Liquid ch oma og aphy
6
The Agilen 1100 se ies HPLC sys em consis ed o a G1312A bina y pump. The injec o
was an G1313A au osample allowing an injec ion olume o 5 µL. Sepa a ions we e
ca ied ou a 25°C using a Pu osphe ® STAR RP-18e LiCh oCART® 3 m (75 mm x
4.0 mm i.d.) (VWR, Ba celona, Spain) HPLC column p oceeded by a gua d column
K omasil 100 Å, C18, 5 m (20 mm x 4.6 mm i.d.) (Scha lab S.L., Ba celona, Spain).
The mobile phase consis ed o 0.1% o mic acid (pH 2.6) (componen A) and me hanol
(componen B) a a low a e o 0.5 mL min-1. An ini ial elu ion g adien was p og ammed
om 35% o 25% A o 2 min, hen an isoc a ic mode o 5 min and inally a g adien
mode om 25% A o 0% A. The inal condi ion was kep o 1.5 min, ollowed by 4 min
e-equilib a ion. The wa eleng hs used o DAD we e 235, 255, 230, 280 and 225 nm o
SAL, KTP, NAX, DIC and IBU, espec i ely. Wa eleng hs we e sligh ly di e en in CE
and HPLC, due o ins umen al di e ences and because he chemical condi ions in CE
bu e and he HPLC mobile phase we e di e en , which a ec ed he UV abso p ion
maxima. The ch oma og am was comple ed in 9 min and he e en ion ime was 3.2, 4.7,
5.45, 8.05 and 8.5 min o SAL, KTP, NAX, DIC and IBU, espec i ely.
2.4. Calcula ion o eco e y and en ichmen ac o
Reco e y was de ined as he ac ion o analy e i in he sample solu ion ha was
ans e ed o he accep o phase, and was calcula ed, o he indi idual analy es i,
acco ding o he ollowing equa ion (Eq. 1):
Ri (%) = 𝑛𝑎𝑖𝑜𝑢𝑡𝑙𝑒𝑡
𝑛𝑠𝑖𝑖𝑛𝑡𝑙𝑒𝑡 · 100% = 𝑉
𝑎 · 𝐶𝑎𝑖𝑜𝑢𝑡𝑙𝑒𝑡
𝑉
𝑠 · 𝐶𝑠𝑖𝑖𝑛𝑡𝑙𝑒𝑡 · 100% (Eq. 1)
whe e 𝑛𝑎𝑖𝑜𝑢𝑡𝑙𝑒𝑡 is he amoun o analy e, i, ans e ed o he accep o phase and 𝑛𝑠𝑖𝑖𝑛𝑡𝑙𝑒𝑡
is he amoun o analy e, i, o iginally p esen in he olume, Vs , o sample p ocessed
h ough he chip. Va is he olume o he accep o ha ing he concen a ion o he analy e
i, 𝐶𝑎𝑖𝑜𝑢𝑡𝑙𝑒𝑡, a he ou le o he accep o channel, whe eas 𝐶𝑠𝑖𝑖𝑛𝑡𝑙𝑒𝑡 is he ini ial sample
concen a ion o he analy e i a he sample inle ese oi .
7
En ichmen ac o (EFi) o he analy e i was calcula ed acco ding o he ollowing
equa ion (Eq. 2):
EFi = 𝐶𝑎𝑖𝑜𝑢𝑡𝑙𝑒𝑡
𝐶𝑠𝑖𝑖𝑛𝑡𝑙𝑒𝑡 = Ri · 𝑉
𝑠
𝑉
𝑎 (Eq. 2)
The concen a ion, 𝐶𝑎𝑖𝑜𝑢𝑡𝑙𝑒𝑡, o analy e in he accep o solu ion was es ima ed by CE o
HPLC wi h UV-de ec ion using ex e nal calib a ion.
2.5. On-chip EME
Two se -ups ha e been used in his s udy. The wo on-chip EME de ices a e shown in
Figu e 1.
One o he chip de ices used (Figu e 1A) was composed o wo poly(me hyl
me hac yla e) (PMMA) (53 × 53 × 2.1 mm3) pla es, con aining i e indi idual channels
o ex ac ion. In bo h pla es, he 6 mm long sample and accep o channels wi h a dep h
o 50 μm and a wid h o 2.00 mm we e milled on a CNC mic o-milling machine (Folken
M3400 E CNC mini mill, Folken Indus ies, Glendale, CA).
A bo h ends o he channels, 1.6 mm i.d. holes we e d illed h ough he pla e o se e as
inle and ou le o he sample and accep o solu ion. Abo e he sample channels, a po ous
polyp opylene memb ane (suppo ) was loca ed (co e ing he whole PMMA pla e), wi h
25 μm hickness, 55% po osi y, and 0.21 x 0.05 μm po es (Celga d 2500 mic opo ous
memb ane; Celga d, Cha lo e, NC). The second PMMA pla e was placed abo e he
polyp opylene memb ane and aligned o ma ch he posi ions o he sample and accep o
channels, and he whole assembly was ixed by sol en -assis ed bonding wi h e hanol and
cu ed in a 70°C o en ollowing he speci ic ins uc ions desc ibed p e iously by Pe e sen
e al. [22]. Small pla inum wi es (0.076 mm i.d.; Sigma-Ald ich) we e inse ed in o he
ou le o he sample and he inle o he accep o channels, espec i ely, and connec ed o
an EL302T T iple powe supply (DC) (Thu lby-Thanda Ins umen s LTD, Cambs, UK).
8
The second poly(me hyl me hac yla e (PMMA) de ice used (Figu e 1B) consis ed o wo
symme ical pla es wi h six holes o 6 mm o assembling and ou holes o 1.4 mm
diame e o in/ou le s Te lon ubes. The mic o luidic de ice con ained wo channels (one
o accep o solu ion and ano he o sample solu ion). The geome y o each channel was
23×3×0.12 mm and he channels we e sepa a ed by he same polyp opylene memb ane
as discussed abo e. Finally, wo elec odes (100 µm i.d.) we e loca ed in each channel.
The main di e ence o bo h chips is ela ed wi h he assembly mode as desc ibed abo e
and he possibili y o eplacing he la memb ane in he same channel (chip B). Fo chip
A, 5 channels we e buil simul aneously in he same de ice o be able o es di e en
SLMs wi hou he need o manu ac u e a new one, since he assembly equi es a longe
ime. Bo h de ices we e connec ed o sy inge pumps o deli e bo h he sample and
accep o solu ion in o he channels o he chip, and hey we e used in pa allel o s udy he
s abili y o he SLM in he EME o acidic d ugs. Once he ex ac ion was comple ed, he
accep o solu ion was collec ed using a mic opipe e and ans e ed o a ial o analysis
by capilla y elec opho esis in case o se -up A o by liquid ch oma og aphy o se -up B.
3. Resul s and discussion
3.1. Selec ion o he suppo liquid memb ane (SLM)
Selec i i y and e iciency o he EME sys em a e highly dependen on he chemical
p ope ies o he SLM [10]. As indica ed abo e, long-chain alcohols a e he mos sui able
o ganic sol en s o EME o acidic analy es due o hei high hyd ogen bonding acidi y
(). This allows dep o ona ed acidic d ugs, wi h hyd ogen bonding basici y and high
dipole momen , o be ans e ed in o he SLM as a esul o molecula in e ac ions [14].
The composi ion o he SLM also de e mines he elec ic cu en le el in he sys em,
o igina ing om ans e o analy e ions, back-g ound elec oly e ions, and sample ma ix
ions. Gene ally, high and uns able cu en s usually p o ide highe s anda d de ia ion and
15
compa ibili y wi h e y small olumes o biological luids, (d) po en ial o dynamic
ex ac ion, and (e) he g een na u e o he concep . F om au ho poin o iew, examples
o highly specialized applica ions may be ela ed o mic o-physiological sys ems o
o gan-on-chip echnologies. 1-Oc anol (C8 alcohol) p o ided high ex ac ion e iciency,
bu su e ed om poo long e m s abili y and high cu en . C9-C11 alcohols we e mo e
s able, p o ided less cu en , and p o ided simila eco e ies as 1-oc anol. C12 alcohol
was also es ed, bu his was less e icien in e ms o ex ac ion e iciency. Thus, as pu e
liquid, 1-undecanol (C11) u ned ou o be he op imal selec ion o acidic d ug subs ances.
Howe e , mixing 1-undecanol wi h 2-ni ophenyl oc yl e he (NPOE) was ound o
imp o e pe o mance u he . Thus, he addi ion o NPOE educed cu en , while
ex ac ion e iciencies emained una ec ed as long as he 1-undecanol/NPOE a io was
no mo e han 1:3. The 1-undecanol:NPOE SLM was highly s able o long- e m
ope a ion, and ini ial e alua ion o on-chip EME combined wi h capilla y elec opho esis
o high-pe o mance liquid ch oma og aphy indica ed ha acidic d ug subs ances can be
ex ac ed and measu ed eliably om biological luids by such a concep in he u u e.
Acknowledgemen s
CRH is g a e ul o Uni e si y o Se illa o pe sonal unding h ough he V Plan P opio
de In es igación de la Uni e sidad de Se illa. MRP is g a e ul o he p og am “Juan de
la Cie a-Inco po ación” (G an numbe JCI-2015-26647) and he P ojec TEC2006-
79367-C2-1-R om he “Di ección Gene al de In es igación y Ges ión del PlanNacional
de I + D + I”.
The au ho s would also like o acknowledge F ede ik And é Hansen om he Depa men
o Pha macy, Uni e si y o Copenhagen, o ab ica ing he chips design A used in his
wo k.
Con lic o in e es

16
The au ho s decla e no con lic o in e es s.
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[27] Mille , J.N., Mille , J.C., S a is ics and Chemome ics o Analy ical Chemis y, 4 h
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18
Table 1
Table 1. Ob ained eco e ies (%) o each NSAID and achie ed cu en wi h di e en
suppo ed liquid memb anes (SLM) in bo h chip de ices (%RSD).
Chip A
IBU
DIC
NAX
KTP
SAL
Cu en
(A)
1-oc anol long-
e m s abili y (8h,
n=15)a
61
(19)
*
56 (19)
57
(20)
*
30-60
Undecanol:NPOE
1:3 ( / ) long-
e m s abili y (8h,
n=23)a
51 (9)
*
45 (9)
47 (9)
*
11-24
Undecanol:NPOE
1:3 ( / ) (n=3)b
105
(1)
*
98 (4)
104
(1)
*
14-23
Chip B
1-oc anol long-
e m s abili y
(1.5h, n=8)
93 (3)
76 (4)
95 (5)
92 (4)
33 (6)
12-100
Decanol long-
e m s abili y (4h,
n=34)
98 (1)
94 (1)
100 (2)
99 (2)
18 (2)
10-58
aSample low a e = accep o low a e: 3 L min-1.
bSample low a e: 0.5 L min-1; accep o low a e: 3 L min-1.
*DIC and SAL we e no s udied wi h he se -up A.
19
Table 2
Table 2. Calib a ion da a, Limi o De ec ion (LOD), Limi o Quan i a ion (LOQ) and
eco e ies o he a ge analy es in he op imal condi ions wi h bo h chip de ices (A and
B).
Se -up
IBU
DIC
NAX
KTP
SAL
Linea ange
(g mL-1)
A
16-60
*
18-60
18-60
*
B
1-10
0.23-10
0.26-10
0.3-10
0.26-10
Linea i y (R2)
A
0.9963
*
0.9956
0.9957
*
B
0.9986
0.9990
0.9993
0.9991
0.9984
LOD (g mL-
1)
A
5
*
5
5
*
B
0.3
0.07
0.08
0.1
0.08
LOQ (g mL-
1)
A
16
*
18
18
*
B
1.0
0.23
0.26
0.3
0.26
Reco e y (%)
(%RSD, n=3)
Aa
105 (1)
*
98 (4)
104 (1)
*
Bb
98 (1)
94 (1)
100 (2)
99 (2)
18 (2)
Cu en (A)
A
14-23 (SLM: undecanol:NPOE 1:3 / )
B
10-58 (SLM: decanol)
S abili y
A
8h a leas (n=23)
B
4h a leas (n=34)
aEx ac ion condi ions: 10V, 5 min, sample low a e= 0.5 L min-1, accep o low a e=
3 L min-1, sample and accep o composi ion a pH 10 (100 mM NH4Cl/NH3 bu e ).
bEx ac ion condi ions: 20V, 7 min, sample low a e= accep o low a e= 1 L min-1,
sample pH= 10.5, accep o pH= 11.5.
*DIC and SAL we e no s udied wi h he se -up A.
20
Table 3
Table 3. Reco e ies o he a ge NSAIDs using EME+CE/HPLC om non-dilu ed spiked
u ine samples (%RSD, n=3).
Spiked
le el (g
mL-1)
IBU
DIC
NAX
KTP
SAL
U ine 1a
40
97 (6)
*
95 (5)
94 (6)
*
U ine 2b
0.75
93 (1)
87 (1)
92 (2)
93 (2)
14 (2)
U ine 3b
0.75β
92 (1)
89 (1)
100 (1)
94 (2)
17 (2)
aSe -up A; SLM: undecanol:NPOE 1:3 ( / ); Sample = spiked emale u ine in 100 mM
NH4Cl/NH3 bu e pH 10; sample low a e = 0.5 L min-1; Accep o phase = 100 mM
NH4Cl/NH3 bu e pH 10; accep o low a e = 3 L min-1; Ex ac ion ime = 5 min;
Vol age = 10 V.
bSe -up B; SLM: decanol; Sample = spiked emale (2) and male (3) u ine in NaOH a pH
10.5; sample low a e = 1 L min-1; Accep o phase = NaOH pH 11.5; accep o low a e
= 1 L min-1; Ex ac ion ime = 7 min; Vol age = 20 V.
*DIC and SAL we e no s udied wi h he se -up A.
βSpiked le el o IBU was 1.75 (µg mL-1).
Figu e 1
Figu e 1 Schema ic illus a ion o he wo on-chip EME sys ems used.

21
Figu e 2
22
Figu e 2. Reco e y (Ri) e sus sample low a e. SLM: undecanol:NPOE 1:3 ( / );
Sample = 40 g mL-1 o ibup o en (IBU), nap oxen (NAX) and ke op o en (KTP) in 100
mM NH4Cl/NH3 bu e pH 10; accep o low a e = 3 L min-1 (ammonium
chlo ide/ammonia bu e pH 10); Ex ac ion ime = 5 min; Vol age = 10 V. The e o
ba s e lec he o e all s anda d de ia ion, SD (n = 3).
Figu e 3
0
20
40
60
80
100
120
140
160
00,5 1 1,5 2 2,5 3 3,5 4
Reco e y (%)
Sample low (L min-1)
IBU
NAX
KTP
23
Figu e 3. En ichmen ac o (EFi) and eco e y (R, %) e sus accep o low a e. SLM:
undecanol:NPOE 1:3 ( / ); Sample = 40 g ml-1 o ibup o en (IBU), nap oxen (NAX)
and ke op o en (KTP) in 100 mM NH4Cl/NH3 bu e pH 10; sample low a e = 3 L
min-1; Accep o phase = 100 mM NH4Cl/NH3 bu e pH 10; Ex ac ion ime = 5 min;
Vol age = 10 V. The e o ba s e lec he o e all s anda d de ia ion, SD (n = 3).
0
10
20
30
40
50
60
70
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
0,7 1,2 1,7 2,2 2,7
Reco e y (%)
En ichmen ac o (EF)
Accep o low (µL min-1)
EF IBU
EF NAX
EF KTP
%R IBU
%R NAX
%R KTP
24
Figu e 4
Figu e 4. Reco e y (Ri) e sus ol age. SLM: undecanol:NPOE 1:3 ( / ); Sample = 40
g ml-1 o ibup o en (IBU), nap oxen (NAX) and ke op o en (KTP) in 100 mM
NH4Cl/NH3 bu e pH 10; Sample/accep o low a es = 3L min-1; Accep o phase = 100
mM NH4Cl/NH3 bu e pH 10; Ex ac ion ime = 5 min; Vol age = 10 V. The e o ba s
e lec he o e all s anda d de ia ion, SD (n = 3).
0
10
20
30
40
50
60
70
80
90
0 5 10 15 20 25 30
Reco e y (%)
Vol age (V)
IBU
NAX
KTP