1
Sepa a ion o sodium lac a e om Span 80 and SDS su ac an s
by ul a il a ion
La a Roque, Isabel Escude o*, José M. Beni o
Depa men o Bio echnology and Food Science, Uni e si y o Bu gos, Plaza Misael
Bañuelos s/n, 09001 Bu gos, Spain
E-mail add esses: l 0010@uni e sidaddebu gos.es (L. Roque), [email p o ec ed]
(J.M. Beni o)
*Co esponding au ho . Tel.: +34-947258809; ax: +34-947258831. E-mail add ess:
[email p o ec ed]
Abs ac
The ul a il a ion p ocess o sepa a ion o sodium lac a e om so bi an monoolea e
(Span 80) and sodium dodecyl sul a e (SDS) su ac an s using Z O2 la -disc
ul a il a ion memb anes was s udied in his wo k. The s udy is ocused on he
in luence o he nominal molecula weigh limi o he memb ane (NMWL), he
ansmemb ane p essu e (TMP), and ini ial lac ic acid concen a ion (CA) on he
pe mea e lux (Jp) and ejec ions obse ed o ion lac a e (RA) and SDS (RS) using a ull
cen al composi e expe imen al design and esponse su ace me hodology.
Expe imen s we e conduc ed in ou s ages: a i s s age o lac ic acid ex ac ion wi h
niosomes o mula ed wi h Span 80 (20 mol/m3) and SDS (4 mol/m3), a second back-
ex ac ion s age conduc ed by NaOH addi ion un il pH > 12 o niosomes b eaking and
sodium lac a e eleasing, and a hi d and ou h ul a il a ion s ages a 25 oC o
sepa a e he lac a e ions om he mixed su ac an s.
Memb ane NMWL, TMP and hei in e ac ions p esen ed s a is ically signi ican
in luence on he pe mea e lux. Rejec ions o lac a e ion and SDS we e lowe han
4.5% and highe han 86%, espec i ely, whe eas Span 80 ejec ion was 100% in all
ange o expe imen al condi ions es ed.
The op imal condi ions we e es ablished o maximum alues o pe mea e lux, and
hey we e ob ained o a 2 ba TMP and 15 kDa NMWL memb ane. Unde hese
condi ions, he ejec ions o SDS su ac an and lac a e ion we e 87.3% and 4.31%,
espec i ely, wi h a pe mea e lux o 42.63 L/m2h. The an agonis ic e ec be ween
pe mea e lux and SDS ejec ion is also p o ed.
Keywo ds
Lac ic acid; Span 80; SDS; Ul a il a ion; Expe imen al design me hodology
1. In oduc ion
Lac ic acid is o pa amoun impo ance in pha maceu ical and ood indus ies due
o i s p ope ies as a p ese a i e, acidulan , pH egula o , and la o ing. I s use has
conside ably inc eased in he las yea s because o he inc eased p oduc ion o
polylac ic acid (PLA) biodeg adable he moplas ic [1–4].
In lac ic acid biop oduc ion, unsus ainable and high ene gy consump ion
con en ional sepa a ion echniques, such as p ecipi a ion wi h calcium hyd oxide o
2
sol en ex ac ion, a e usually used o he lac ic acid sepa a ion om e men a ion
b o hs [5,6]. Memb ane-based sepa a ion echniques [7] ha e p o en o be e ec i e
because hey can a oid accumula ion o lac ic acid in he e men a ion b o hs,
p e en ing p oduc inhibi ion and inc easing p oduc i i y o he e men a ion p ocess. In
his way, hollow- ibe con ac o s using o ganic sol en s [8–10] and micella enhanced
ul a il a ion (MEUF) using su ac an s ha e been s udied [11–14]. Mo e ecen ly, he
use o niosomes as lac ic acid ex ac ion agen s has also been s udied [15].
Niosomes a e esicles o med by one o mo e bilaye s o non-ionic su ac an s
enclosing an aqueous inside ca i y. Niosomes a e widely used in medical and
pha macological applica ions o hei abili y o mic oencapsula e compounds o
di e en na u e [16–20]. Howe e , he use o niosomes as ex ac ion agen s o solu es
om e y low concen a ion aqueous solu ions is a new applica ion in he ield o
sus ainable p ocesses ha has ba ely been explo ed.
F aile e al. [21] obse ed ha he addi ion o sui able amoun s o he anionic
su ac an sodium dodecyl sul a e (SDS) o non-ionic su ac an Span 80 (so bi an
monoolea e) o mula ions yields a s abilizing e ec on he niosome bilaye , imp o ing
lac ic acid en apmen e iciency. Howe e , he addi ion o ionic su ac an s o he
niosome dispe sions can lead o he comple e solubiliza ion o esicles. The
solubiliza ion p ocess o Span 80 niosomes by addi ion o SDS has been ecen ly
s udied [22]. I was iden i ied as a h ee-s age micelliza ion p ocess: SDS adso p ion
un il sa u a ion, in ensi ica ion o he bilaye solubiliza ion by mixed micelles o ma ion,
and comple e bilaye solubiliza ion by micelliza ion. The c i ical poin s co esponding o
SDS concen a ion o niosome sa u a ion and o al solubiliza ion we e iden i ied o
se e al Span 80 niosome concen a ions, being 12 and 16 mol/m3 o SDS,
espec i ely, o he 20 mol/m3 Span 80 o mula ion.
The memb ane hyb id p ocess o lac ic acid ex ac ion by niosomes o mula ed
wi h Span 80 and SDS in p e-sa u a ion concen a ions, using a 0.20 µm po e size la -
disc TiO2 mic o il a ion memb ane and 0.3 ba o ansmemb ane p essu e, has been
s udied in a p e ious wo k [15]. Bes esul s showed a 33% lac ic acid ex ac ion
deg ee a e 30 min equilib ium ime, using niosomes o Span 80 (20 mol/m3) and SDS
(4 mol/m3) as ex ac ion agen s, pH < pKa o lac ic acid (pKa = 3.4), and a SDS/lac ic
acid mola a io o 0.01. Back-ex ac ion o lac a e ion was conduc ed by addi ion o
NaOH un il pH > 12 whe e b eaking o niosomes was obse ed. Howe e , a signi ican
pe mea e lux decline wi h espec o wa e lux (Jp/Jw = 0.38) was ob ained du ing he
sepa a ion o componen s due o ouling by mixed micelles and SDS monome s in he
pola iza ion laye and wi hin he la ge po es o he mic o il a ion memb ane. These
esul s ha e led o he p esen wo k ocused on he use o ul a il a ion (UF)
memb anes in o de o educe ouling and o imp o e he pe mea e lux du ing he
back-ex ac ion s age a pH > 12.
This wo k is a con inua ion o he p e ious one [15] and aims o model and op imize
he emo al o lac a e ion om back-ex ac ion aqueous solu ions a pH > 12 con aining
Span 80 and SDS su ac an s in he s a ed concen a ions, using ul a il a ion
memb anes. A Cen al Composi e Design (CCD) and Response Su ace Me hodology
(RSM) we e used o s udy he e ec o he ac o s (lac a e ion concen a ion,
ansmemb ane p essu e, and memb ane nominal molecula weigh limi ), on he
pe mea e lux and ejec ion o componen s. RSM app oach was also used o gain an
unde s anding o he concen a ion pola iza ion phenomenon. The op imiza ion o he
p ocess condi ions was conduc ed in o de o achie e maximum pe mea e lux and
su ac an s ejec ion, and minimum lac a e ion ejec ion.
3
2. Ma e ials and me hods
2.1. Chemicals
DL-Lac ic acid (>90% pu i y, Fluka) was used as solu e. The non-ionic su ac an
so bi an monoolea e (Span 80, >95% pu i y, Sigma-Ald ich) and he anionic su ac an
sodium dodecyl sul a e (SDS, 99%, Sigma-Ald ich) we e used in he o mula ion o
niosomes. O he chemicals such as me hanol (HPLC g ade, HiPe Sol Ch omano m),
maleic acid (>99%, Fluka), phospho ic acid (>85%, Sigma-Ald ich), disodium hyd ogen
phospha e dodecahyd a e (>98%, Pan eac), po assium dihyd ogen phospha e
(>99.5%, Me ck), sodium hyd oxide (analysis g ade, Scha lau), and phenolph halein
(99%, Pan eac) we e used h oughou he expe imen s. Fo he de e mina ion o SDS
concen a ion he ollowing chemicals we e used: e hyl iole (99%, Sigma-Ald ich),
glacial ace ic acid o analysis quali y (Pan eac), sodium ace a e o analysis (Me ck),
anhyd ous sodium sul a e o analysis (Scha lau), oluene (>99.5%, Anala No mapu
VWR Chemicals) and e hylenediamine e aace ic acid (EDTA, >99%, Sigma-Ald ich).
Ul apu e deionized Milli-Q wa e (Millipo e, USA), wi h a conduc i i y o 0.1 μS/cm,
was used o he p epa a ion o all solu ions.
2.2. Niosome o ma ion
Niosomes we e p epa ed by ul asonica ion o 10 cm3 aqueous solu ions o Span
80 (20 mol/m3) and SDS (4 mol/m3). These concen a ions we e chosen on he basis o
p e ious wo ks [15,21]. The applica ion o ul asounds was ca ied ou o e a 5-min
e ec i e ime, by pulses e e y 5 s (5 s on and 5 s o , 60 cycles; 30% ampli ude, 500
W), o a oid o e hea ing o he sample, using a high-in ensi y ul asonic p ocesso
(Vib a-Cell VCX 500, Sonics & Ma e ials Inc., USA) equipped wi h a 3 mm-diame e
i anium alloy bicylind ical p obe. Following, samples we e cen i uged (Eppendo 5804
cen i uge) o 15 min a 9000 pm, in o de o emo e any ace o me al de ached om
he p obe.
2.3. Expe imen al p ocedu e
UF expe imen s we e ca ied ou using a Spi lab il a ion cell (TAMI Indus ies,
F ance) wi h 90 mm diame e la -disc ce amic memb anes (INSIDE DisRAM, TAMI
Indus ies, F ance), made o a Z O2 ac i e laye suppo ed on TiO2, wi h 56.3 cm2 o
e ec i e a ea. The nominal molecula weigh limi s (NMWL) o he memb anes we e 3,
8 and 15 kDa.
All expe imen s we e conduc ed using he ollowing ou -s age p o ocol:
1. Ex ac ion s age: i was ca ied ou by mixing 400 cm3 o aqueous solu ion
con aining lac ic acid (CA = 5, 10 and 15 mol/m3), named as Fo, and 10 cm3 o
dispe sed phase con aining niosomes, named as Fd. The mix u e was
con inuously s i ed a 375 pm and 20 oC o 30 min o each equilib ium.
2. Back-ex ac ion s age: his s age was pe o med by addi ion o a equi ed
olume o NaOH (1 N) aqueous solu ion o he abo e men ioned dispe sion
un il pH abou 12.2 ± 0.2. I was allowed 45-50 min o each equilib ium and
hen a 60 cm3 sample was wi hd awn o analysis. The sample and emaining
dispe sion we e iden i ied as Fbis.
3. UF s age in cons an concen a ion mode. The eed solu ion (Fbis) was ed o he
ul a il a ion cell by a pe is al ic pump (Mas e lex l/s economy d i e Cole
Pa me , CRS o o EW-07518-00) a a p e ixed low a e and p essu e.
Pe mea e and e en a e s eams we e eci cula ed o he 1 L jacke ed eed ank,
4
whe e he eed solu ion was kep a cons an empe a u e (20 ºC) and s i ed a
375 pm. Adjus men o ansmemb ane p essu e (TMP) was achie ed by a
needle al e loca ed in he e en a e s eam. The sys em is also equipped wi h
a lowme e and a p essu e gauge, bo h placed a he inle o he il a ion cell.
Expe imen s we e un o 30 min unde speci ic TMP (1, 1.5 o 2 ba ) in o de o
achie e s able condi ions in he pola iza ion laye and memb ane.
Subsequen ly, a 60 cm3 sample was wi hd awn o analysis and he sample and
emaining dispe sion we e iden i ied as F.
4. UF s age in concen a ion mode. Once he equilib ium wi h he memb ane was
eached, he eed solu ion F was ul a il a ed in concen a ion mode, emo ing
con inuously he pe mea e s eam and eci cula ing he e en a e o he eed
ank up o a olume concen a ion a io (VCR, he quo ien be ween ini ial eed
olume and e en a e olume) a ound 2. The pe mea e lux was calcula ed by
measu ing he ime needed o collec ing 10 cm3 pe mea e samples. Finally,
pe mea e and e en a e we e sepa a ed o analysis and named as P and R,
espec i ely.
Fig. 1 shows a scheme o he ou -s age p ocedu e and he se -up o he UF
expe imen al equipmen . Table 1 summa izes he analy ical measu emen s made o
di e en samples h ough he expe imen al p ocess.
EXTRACTION STAGE BACK-EXTRACTION STAGE
F
0
F
d
F
bis
(pH > 12)
NaOH
(1)
(2)
(3)
(4)
F
(5)
(2)
(3)
(4)
(5)
R
P
(1)
CONSTANT CONCENTRATION MODE UF STAGECONCENTRATION MODE UF STAGE
Figu e 1. Schema ic diag am o he ou -s age expe imen al p ocedu e. Fd: dispe sed phase,
Fo: con inuous phase, Fbis: dispe sion a pH > 12 wi hou memb ane con ac , F: eed dispe sion
a pH > 12 in con ac wi h he memb ane unde UF condi ions a cons an concen a ion, P and
R: pe mea e and e en a e a e UF in concen a ion mode, 1: eed ank, 2: pe is al ic pump, 3:
p essu e gauge, 4: memb ane module, 5: needle al e.
Memb ane cleaning was accomplished a e wa ds by insing wi h deionized wa e
o emo e he oam, ollowed by washing wi h 0.1 N sodium hyd oxide solu ion o 30
min, and hen wi h 0.17 w .% phospho ic acid solu ion o 30 min. A inal insing s ep
wi h deionized wa e un il neu ali y was su icien o es o e he ini ial wa e lux o he
memb ane.
5
Table 1. Summa y o analy ical measu emen s made o samples h ough he expe imen al
p ocedu e.
Sample
Desc ip ion
Analy ical measu emen s
Fo
Lac ic acid aqueous solu ion (ini ial
con inuous phase)
Lac ic acid concen a ion and pH
Fd
Aqueous dispe sion o niosomes (ini ial
dispe sed phase)
Size, PDI, ze a po en ial, and pH
Fbis Equilib ium dispe sion a pH > 12 (wi hou
memb ane)
Lac a e ion concen a ion, SDS
monome s concen a ion, size, PDI,
ze a po en ial, and pH
F
Bulk dispe sion a pH > 12 unde s eady-
s a e UF condi ions in cons an
concen a ion mode
Lac a e ion concen a ion, SDS
monome s concen a ion, size, PDI,
ze a po en ial, and pH
P Final pe mea e a e UF in concen a ion
mode (VCR = 2)
Lac a e ion concen a ion, SDS
monome s concen a ion, size, PDI,
ze a po en ial, and pH
R Final e en a e a e UF in concen a ion
mode (VCR = 2)
Lac a e ion concen a ion, SDS
monome s concen a ion, size, PDI,
ze a po en ial, and pH
2.4. Analy ical me hods
Lac a e ion concen a ion was de e mined by high pe o mance liquid
ch oma og aphy using a HPLC Shimadzu. A e e se phase column ACE 5C18 (ACE
HPLC columns) and a UV- is de ec o a 216 nm we e used. De ailed condi ions o he
analy ical me hod can be ound elsewhe e [15]. Samples we e measu ed in iplica e
and he analy ical e o was lowe han ± 0.001 mol/m3.
SDS monome concen a ion was de e mined by spec opho ome y a 615 nm
wi h a Hi achi U-2000 equipmen , using he e hyl iole me hod [23]. Samples we e
measu ed in iplica e and he analy ical e o was lowe han ± 0.002 mol/m3.
The pa icle size dis ibu ion, he mean hyd odynamic diame e and he
polydispe si y index (PDI) o he samples we e ca ied ou by dynamic ligh sca e ing
(DLS) using a Ze asize Nano ZS appa a us (Mal e n Ins umen s L d., UK). The PDI is
a dimensionless measu e o he wid h o he size dis ibu ion anging om 0 o 1, a
highe alue being indica i e o a b oade dis ibu ion o pa icle size. The a e age
alue and he ela i e e o o he 3 eplica es, each o 5 measu emen s a 20 oC, was
conside ed o each sample.
Ze a po en ial measu emen s we e conduc ed wi h he a o emen ioned Ze asize
Nano ZS appa a us, using he Lase Dopple Velocime y echnique. They we e
pe o med on he same sample p e iously p epa ed o measu e he pa icle size, bu
using he app op ia e DTS1061 disposable olded capilla y cell equipped wi h
elec odes o allow he passage o elec ic cu en and he mo emen o he pa icles
acco ding o hei cha ge [24]. Six eplica es o 11 measu emen s we e pe o med o
each sample a 20 oC.
The pH measu emen was pe o med a 20 oC using a C ison GLP 22 pH-me e
i ed wi h a C ison 52-02 glass pH elec ode (C ison, Spain), wi h an e o o ± 0.01 pH
uni s.

6
Mo phological analysis o niosomes was pe o med by nega i e s aining
ansmission elec on mic oscopy (NS-TEM), using a JEOL-2000 EX-II TEM ope a ing
a 160–180 kV, wi h an image esolu ion o 1 nm, loca ed a he Uni e si y o O iedo
(Spain). A d ople o he selec ed sample was placed on a ca bon-coa ed coppe g id,
and he sample excess was emo ed using a piece o il e pape . Then, a d op o
phospho ungs ic acid solu ion (2% w/ ) was applied o he ca bon g id and le o 2
min. Once he excess o s aining agen was emo ed by abso bing wi h he il e pape ,
he sample was ai -d ied and he hin ilm o s ained niosomes was obse ed by TEM.
2.5. Expe imen al design and s a is ical analysis
Response Su ace Me hodology (RSM) and Cen al Composi e Design (CCD) wi h
h ee le els o each independen a iable we e used o s udy he e ec o NMWL (X1:
3–15 kDa), TMP (X2: 1–2 ba ) and lac ic acid ini ial concen a ion (X3: 5–15 mol/m3) on
he pe mea e lux (Jp), lac a e ion obse able ejec ion (RA), and SDS obse able
ejec ion (Rs). The ac o s and le els s udied a e summa ized in Table 2. Based on he
selec ed high and low le els, he NMWL ideal cen al poin should be 9 kDa. Howe e ,
a 8 kDa memb ane was used a he cen al poin s in his s udy, assuming ha his
change does no signi ican ly in luence he expe imen al design.
Table 2. Fac o s and le els s udied.
Fac o s
Le els
Low (-1) Cen e (0) High (+1)
X1: NMWL (kDa) 3 8 15
X2: TMP (ba ) 1 1.5 2
X3: CA (mol/m
3
) 5 10 15
The esponse a iables we e calcula ed using he ollowing equa ions:
A V
J
p
×
=
(1)
( )
( )
Fbis
i
pi
iC
C
1R −
=
(2)
whe e V is he olume o he pe mea e sample collec ed, is he ime needed o
collec ing he pe mea e sample, A is he memb ane e ec i e a ea (56.3 cm2), and Ci(p)
and Ci(Fbis) a e he o al concen a ion o lac a e ion o SDS in he inal pe mea e and
dispe sion a pH > 12 (Fbis dispe sion), espec i ely.
The CCD model gene a ed 17 expe imen al uns wi h h ee eplica es a he
cen al poin which highligh he ep oducibili y o he expe imen s. A second-o de
deg ee polynomial equa ion was used o exp ess each p edic ed esponse (Y) as a
unc ion o he independen a iables unde s udy (X1, X2 and X3). The model equa ion
is as ollows:
322331132112
2
333
2
222
2
1113322110 XXaXXaXXaXaXaXaXaXaXaaY +++++++++=
(3)
7
whe e Y ep esen s he esponse a iable (Jp, RA, and RS, in his case), a0 is a
cons an , and ai, aii, aij a e he linea , quad a ic, and in e ac i e coe icien s,
espec i ely. Analysis o a iance (ANOVA) and leas signi ican di e ence (LSD) es
we e applied o de ec he e ec o he ac o s and s a is ically signi ican di e ences
among alues, espec i ely. The model was i ed by mul iple linea eg essions (MLR).
The alidi y o he empi ical model was es ed wi h ANOVA. The signi icance o each
es ima ed eg ession coe icien was assessed h ough alues o he s a is ic
pa ame e s F and p (p obabili y) wi h a 95% con idence le el. The expe imen al design
and da a analysis we e pe o med using STATGRAPHICS Cen u ion XVI (S a poin
Technologies, Inc., Wa en on, VA, USA).
Op imal condi ions we e de e mined wi h he help o he STATGRAPHICS
Cen u ion XVI so wa e, in o de o each he maximum pe mea e lux and SDS
ejec ion, and he minimum lac a e ion ejec ion, acco ding wi h he wo k objec i es.
3. Resul s and discussion
3.1. E ec o NaOH addi ion on he b eakup o niosomes
Pa icle size measu emen in he dispe sed phase (Fd) e eals niosomes o 200
nm a e age diame e and a PDI alue o 0.27, which indica es a homogeneous
popula ion (Fig. 2a). O he wise, de ailed analysis o DLS in ensi y da a o dispe sions
a pH > 12 e ealed ha he main peak obse ed in Fd, which is a ibu ed o niosomes,
disappea s in hese samples indica ing niosome des uc ion by he addi ion o NaOH
un il pH > 12. Howe e , peaks associa ed wi h mixed micelles o 78–80 nm in size and
Span 80 agg ega es la ge han 1000 nm we e obse ed in any o he Fbis, F and R
dispe sions. Resul s co esponding o a R dispe sion a e also depic ed in Fig. 2a. They
a e acco ding wi h p e ious wo ks [15,21]. As expec ed, ze a po en ial alues be ween
–45 and –38.5 mV we e ob ained in he Fd samples used in di e en expe imen s (–
40.8 mV o Fd sample shown in Fig. 2b), which indica e he p esence o nega i ely
cha ged niosomes due o he SDS adso bed in hei su ace. Besides, as shown in Fig.
2b, wo pa icle popula ions a e obse ed in he R dispe sion, wi h ze a po en ial alues
o –8 and –20 mV, indica ing weakly nega i ely cha ged pa icles. Simila esul s we e
ob ained o any o Fbis and F dispe sions (no shown), which co obo a e he b eakup
o he niosomes a pH > 12. No pa icles we e ound in pe mea es, ega dless o he
memb ane NMWL.
The p esence and mo phology o niosomes in he dispe sed phase (Fd) ha e been
con i med by TEM measu emen s. Fig. 3 shows wo pho omic og aphs o o mula ions
o 20 mol/m3 o Span 80 and 4 mol/m3 o SDS, whe e he whi e a eas co espond o he
g id. Fig. 3a shows he p esence o sphe ical niosomes o abou 200 nm in Fd, whose
sizes ag ee wi h hose measu ed by DLS. Fig. 3b shows absence o niosomes in he
dispe sion a pH > 12 (Fbis). Fig. 3b could co espond o la ge s uc u es o Span 80, as
i s concen a ion (20 mol/m3) is well abo e i s CMC (≈ 0.1 mol/m3 in wa e [25]), and
hey would be in acco dance wi h he la ge pa icles shown in Fig. 2a.
8
(a) (b)
Figu e 2. (a) Pa icle size dis ibu ions co esponding o dispe sed phase, Fd, and e en a e, R,
and (b) Ze a po en ial o Fd and R dispe sions, as desc ibed in Table 1.
(a) (b)
Figu e 3. TEM mic og aphs. (a) Niosomes o Span 80 (20 mol/m3) and SDS (4 mol/m3) in he
dispe sed phase (Fd). (b) Fo mula ion o Span 80 (20 mol/m3) and SDS (4 mol/m3) in aqueous
solu ion a pH > 12 (Fbis). Scale ba s: 0.2 µm.
I is well documen ed ha addi ion o low concen a ion o ca ions o anionic
su ac an (SDS) solu ions dec eases he epulsi e o ces be ween head g oups o
SDS monome s due o he elec os a ic shielding e ec , esul ing in he o ma ion o
micelles a lowe concen a ion han i s CMC (8.1 mol/m3 in wa e [11,26–32]).
Howe e , beyond a c i ical concen a ion, he sodium ions s a dis up ing he micella
packing, esul ing in less s able micelles [29,30].
In ligh o he esul s, i can be assumed ha he p esence o Span 80 monome s
is highly imp obable in dispe sions a pH > 12 due o i s hyd ophobic cha ac e (HLB =
4.3 [20]), whe eas he coexis ence o la ge Span 80 agg ega es wi h mixed micelles
and SDS su ac an monome s is highly p obably.
9
3.2. Expe imen al design
The ma ix o he CCD and expe imen al alues o he esponse a iables a e
gi en in Table 3.
Table 3. Ma ix o he cen al composi e design (CCD) and expe imen al alues o he esponse
a iables: pe mea e lux (Jp), lac a e ion obse able ejec ion (RA), and SDS obse able
ejec ion (RS).
Expe imen Fac o s Responses
NMWL
(kDa)
TMP
(ba )
C
A
(mol/m
3
)
J
p
(L/m
2
h)
RA RS
1 15 1 5 15,99
abc
0.0191
a
0,897
a
2 8 1,5 10 24,51
cd
0.0182
a
0,864
a
3
3
1
15
8,53a
0.0115a
0,888a
4 8 1,5 5 26,64
cd
0.0160
a
0,865
a
5 3 1,5 10 12,79
ab
0.0056
a
0,881
a
6 15 1,5 10 34,10
de
0.0315
a
0,880
a
7
8
1,5
15
19,18cd
0.0171a
0,891a
8 8 1 10 14,92
abc
0.0117
a
0,881
a
9 8 1,5 10 22,38
cd
0.0208
a
0,866
a
10 15 1 15 17,05
abcd
0.0193
a
0,887
a
11
3
1
5
9,06a
0.0025a
0,902a
12 3 2 5 20,25
bcd
0.0313
a
0,889
a
13 15 2 5 42,63
0.0431
a
0,873
a
14 15 2 15 40,50
0.0448
a
0,870
a
15
8
1,5
10
23,45cd
0.0077a
0,871a
16 8 2 10 27,71
de
0.0055
a
0,869
a
17 3 2 15 17,05
abcd
0.0313
a
0,890
a
Values wi h di e en le e s in each column a e signi ican ly di e en (LSD es , p < 0.05)
Table 3 shows ha Jp alues p esen la ge a ia ion, be ween 8 and 43 L/m2h.
Howe e , RA and RS alues we e lowe han 4.5% and highe han 86%, espec i ely,
wi h e y simila alues among hem o all expe imen s. LSD es was applied o each
esponse a iable, e ealing ha RA and RS alues we e no signi ican ly di e en (p >
0.05). Howe e , Jp alues iden i ied in Table 3 ha do no sha e a same le e we e
conside ed s a is ically di e en among hem (p < 0.05).
ANOVA o he i ed model o he Jp esponse shows ha he model was
s a is ically signi ican (p- alue = 0.001). Table 4 shows ha NMWL, TMP and hei
in e ac ion a e s a is ically signi ican (p < 0.05) on Jp. F alues indica e ha , o he
ange o ac o s s udied, NMWL and TMP ac o s ha e he s onge in luence on Jp,
and also ha in e ac ion be ween NMWL and TMP has syne gis ic e ec on Jp.
O he wise, CA ac o was no signi ican on Jp, indica ing ha i does no con ibu e on
he Jp esponse, in he ange o concen a ions es ed.
16
Figu e 10. Rela ionships be ween he pe mea e lux and TMP o di e en medium
composi ions. Symbols: expe imen al da a. Lines: beha io ends.
4. Conclusions
Z O2 ce amic ul a il a ion memb anes can be success ully used o he sepa a ion
o ion lac a e om he su ac an s Span 80 and SDS in aqueous solu ions a pH > 12.
P ocess op imiza ion by RSM showed ha , in he ange o condi ions s udied (TMP: 1–
2 ba , NMWL: 3–15 kDa, and CA: 5–15 mol/m3), bes esul s we e ob ained o he 15
kDa memb ane and a ansmemb ane p essu e o 2 ba . Unde hese condi ions he
pe mea e lux (Jp) was 42.63 L/m2h and SDS ejec ion (Rs) was 87.3%. Ion lac a e
concen a ion e ec was no s a is ically signi ican on Jp and i s ejec ion was lowe
han 4.5%. Span 80 ejec ion was 100% in all ange o expe imen al condi ions es ed,
as i o ms la ge agg ega es ha a e e ained by memb anes.
Al hough he di e ences be ween Rs alues we e no s a is ically signi ican wi h
95% signi icance le el, an an agonis ic beha io be ween Rs and Jp has been
expe imen ally es ed. I was obse ed ha UF p ocess was mainly con olled by
con ec ion and Jp inc eased as TMP inc eases, being his e ec mo e app eciable o
memb anes wi h highe NMWL. Besides, as Jp inc eases pa o SDS molecules
adso bed on he memb ane o accumula ed in he pola iza ion laye pass h ough he
memb ane dec easing he SDS monome s ejec ion. The e en ion o su ac an s a pH
> 12 a e in luenced by h ee p edominan e ec s: he memb ane sie ing ha yields
e en ion o mixed micelles and la ge agg ega es o Span 80, he de-compac ion o he
pola iza ion laye due o he micelles des abiliza ion caused by he excess o Na+ ions,
and he shielding o he nega i ely cha ged memb ane su ace by Na+ ions which
imp o es he pe mea ion o SDS monome s as Jp inc eases.
This s udy complemen s a p e iously one pe o med wi h a 0.20 µm TiO2
mic o il a ion memb ane and 0.3 ba TMP [15] whe e a signi ican pe mea e lux
decline was ob ained du ing he sepa a ion o componen s due o SDS monome s
0
10
20
30
40
50
60
0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1
Jp (L/m2 h)
TMP (ba )
Span 80, pH = 12.4
Span 80 + SDS, pH = 7
Span 80 + SDS, pH = 12.5
SDS, pH = 6.9
SDS, pH = 12.6

17
accumula ed in he pola iza ion laye and adso bed wi hin he la ge po es o he
mic o il a ion memb ane. A compa ison be ween bo h s udies shows ha Jp ob ained
wi h he 15 kDa ul a il a ion memb ane (Jp = 42.63 L/m2h a TMP = 2 ba ) was highe
han he ob ained wi h he 0.20 µm mic o il a ion memb ane (Jp = 19.19 L/m2h a TMP
= 0.3 ba ). Besides, smalle dec ease o Jp wi h ela ion o pu e wa e lux (Jw) was
ob ained wi h he UF memb ane (Jp/Jw = 0.61) han wi h he mic o il a ion one (Jp/Jw =
0.38). These esul s indica e an imp o emen in he ex ac ion-backex ac ion p ocess
o lac ic acid wi h Span 80 and SDS niosomes using ul a il a ion memb anes.
Acknowledgmen s
Financial suppo om he Minis e io de Economía y Compe i i idad (MINECO,
Spain) h ough p ojec CTQ2011-25239, and om Jun a de Cas illa y León h ough
p ojec BU055U16 co inanced by he Eu opean Regional De elopmen Fund (ERDF-
FEDER) is g a e ully acknowledged. The au ho s would like o hank D . Ca los Ál a ez
(Scien i ic Technical Se ices, Uni e si y o O iedo, Spain) o his aluable help and
assis ance wi h TEM measu emen s.
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