1 CHEMICALS AND BACKGROUND SOLUTION

93



Membranes



Further characterisation is reported in the organics characterisation section below. An overview over

some characteristics is also shown in Chapter 2. The organics were prepared as 100 mgL-l organic

carbon stock solutions by mixing the dry powder with MilliQ water without increasing the pH. The

solutions were stored at 4°C in the dark. The amount of powder required for 100 mL stock solution

was 18.4 mg, 18.6 mg and 200 mg for HA, FA and NOM respectively. This reflects the carbon content

of the organics.



Hematite was selected as a model colloid in this study due to its well understood aggregation behaviour,

the monodisperse, spherical nature of the colloids and the fact that the synthesis of colloids of various

primary particle sizes (40 to 500 nm) is possible. WGLlle silica and clays may be more abundant in

surface waters, hematite appears to be a good compromise between real systems and a simple model

compound.

The synthesis of monodispersed, spherical hematite colloids of four primary particle sizes is described

in detail in Appendix 3. The main properties of these colloids are also given in Appendx 3.



Commercially available flat sheet membranes were selected. The primary selection criterium was that

the membrane be made of a hydrophlic material, which adsorbs less organics than more hydrophobic

polymers. For comparison, the membranes used are listed in Table 4.2 with their pore size or molecular

weight cut-off (MYVCO) as specified by the manufacturer.



Table 4.2 Characteristics OfMF, UF and NF membranes used in experiments.

Process



Mdhpore



Type



GVWP

GVHP



UF



hblhpore



PLHK

PLTK

PLGC

PLCC

PLBC

PWC



Fluid



CA-UF



Systems



NF



TFC-SR

TFC-S

TFC-ULP



Copyright © 2001 by Andrea I. Schafer



Typical



Specifications



Pure Water



Surface Charge



Operating

Pressure

[bar1

MF



Supplier



Pore Size [pm]

Molecular Weight

cut-off p a l



Flux

Fm-2h-l]



at p H 8



94



MATERIALS AND METHODS



This characterisation is relatively vague, as different methods are used by each manufacturer (Readman

(1991), Thorsen e t al. (1997)). As a more comparable parameter, the pure water fluxes as determined in

the experiments are also given, as well as the membrane zeta potential at pH 8. A new membrane was

used for each experiment (except for fractionation experiments).

The results of surface charge measurements of the membranes as a function of pH, pure water fluxes

and electronmicrographs are shown in the MF, UF, and N F chapters, respectively.



4.4.1



Microfdtration Membranes



Two microfiltration membranes @hllipore, hydrophilic ( G W ) and hydrophobic (GVHP)) with

nominal pore sizes of 0.22 pm were used. The hydrophlic membrane is a modified hydrophobic

membrane. The hydrophilic membrane was chosen for most experiments because hydrophlic

membranes have a reduced adsorption capacity towards hydrophobic organics (Jucker and

Clark(1994)).The membrane material is a modified polyvinylidene fluoride (PVDF).

The hydrophobic membrane was soaked in a 50% ethanol solution for 10 minutes to wet the pores and

then rinsed with MilliQ water. All membranes were soaked in warm MdliQ water for 30 minutes prior

to use to remove any organic contamination.



4.4.2



Ultrafiltration Membranes



Ultrafiltration was used for fouling, rejection, and fractionation experiments. The fractionation

experiments require membranes with very low adsorption characteristics to reduce loss of organics on

the membranes. It was thus necessary to find low fouling membranes, whch are available in a range of

membrane molecular weight cut-offs QWXCO). The fillipore "PL series" fulfil the low adsorption

condtion and they are available in seven MWCOs in the range from 1 kDa to 300 kDa. The

fractionation membranes selected were the PLAC, PLBC, PLCC, PLGC, PLTIC, and PLHIC with

MWCOs of 1, 3, 5, 10, 30, and 100 kDa, respectively. Fouling and rejection experiments were carried

out with the 10 and 100 kDa membranes.

These regenerated cellulose membranes on a non-woven polypropylene substrate are described by the

manufacturer as low protein-binding and hydrophlic. The MWCO (as described in Table 4.2) is

determined by a range of Dextran markers. A MWCO of 10 kDa means that 90°/o of markers with a

molecular weight greater than 10 kDa were retained.

Prior to use, the membranes were soaked in 0.1 M NaOH for 30 minutes and flushed with 3.4 L of

MilliQ water in order to remove the glycerin preservative, whch can strongly interfere with UV and

DOC analysis. Alternatively, flushng the membrane with 1L fiUiQ also removed the glycerin

sufficiently.



4.4.3



Nanofdtration Membranes



Nanofiltration membranes were received from Fluid Systems in San Diego, USA (now Koch

Membrane Systems). T h n film composite membranes were chosen due to their low fouling

characteristics compared to polysulphone membranes used in other studes. The CA-UF membrane is,

as the name suggests, classed as a UF membrane and the material is cellulose acetate. However, it is

treated as a NF membrane here as it is often used for similar applications according to the

manufacturer, and also because it exhibits some salt rejection. Membrane characteristics as given from



Copyright © 2001 by Andrea I. Schafer



95



Membranes



the supplier are summarised in Table 4.3. The cut-off was specified to be about 5 kDa and the material

is non-ionogenic. The active layer of this membrane is about 150 nm. CA membranes have generally a

50% lower flux than TFC membranes, but are cheaper.

The TFC membranes are chemically modified to render the membranes more hydrophilic, but more

details were not available. All three membranes have different additives and post-treatments in the

manufacturing process. The manufacturer estimates the thckness of the active layer of the TFC

membranes to be 150 to 200 nm. For the TFC-SR membrane a dfferent monomer was used compared

to the other TFC membranes. \%le

the TFC-S and TFC-ULP membranes are made from

metaphenylene diarnine with acid chloride (a benzene ring with two to three carboxglic acid groups),

the TFC-SR membrane is fabricated from a mixture of cyclo-aliphatic amine with acid chloride. This

means that the TFC-S and TFC-ULP have both positive and negative functional groups, whereas the

TFC-SR membrane has negative functional groups only. Marker tests with 1% lactose (180 Da)

solutions at pH 6-7 showed a rejection of 94.4% and 90.6% for the TFC-SR and TFC-S membranes,

respectively. Rejection of the membrane is expected to be higher ('I'akigawa (1999)).



Table 4.3 Membrane Infornationfrom Flziid Systems Corporation (now Kocb Membrane Systems), San Diego.

TFC-S

Material



Test

Condttions



TFC-SR



TFC-ULP



CA-UF



TFC P-1 on PS base



Cellulose Diacetate



1 g/L NaCl



2 g/L NaC1



tap water 3.5 bar



25°C pH 7.5 7 bar



TFC Polyamide (PA\) TFC proprietary P-\ on PS

base, coated with PT';\

on Polpsulfone (PS)

base

(dye to check for damage)



1 g/L NaC1,



Flux



2.5 g/L AlgSO,



2.5 g/L AlgSO,



25OC pH 7.5 5.6 bar



25OC pH 7.5 5.6 bar



14.7 L/m'h



14.7 L/m2h



14.7 L/m2h



16.5 L/m2h



98.5% hardness,



98.5% C

1



Not specified



N F or softentng of

municipal water at

dtralow pressure; up

to 45°C



nanofiltration or softening

of municipal water at

ultralow pressure; up to

1 ppm C12; up to 45 "C



Industrial or municipal

water



Surface water at

moderate pressure if

chlorination desired

(up to 1 ppm C12)



5.6 bar



5.6 bar



3.5-12.25 bar



p H range



4-11



Rejection



95°/a hardness,



4-6



85% C1

Design

Application



Design

Pressure



(560 kPa)



Storage



0.5% sodmm meta

bisulfite, ALilliQ after



ultralow pressure



Medium



3.5 bar

(560 kPa)

unknown



ALilliQ after wash



SUiQ after wash



wash with warm AlilliQ to

remove PT',I coating



soak in XLdliQ



wash

Pretreatmen t



wash wlth SIdhQ



Copyright © 2001 by Andrea I. Schafer



wash with ALtUIQ



96



MATERIALS AND METHODS



All membranes were stored in a refrigerator (4 K ) in plastic bags in the medium in which they arrived,

and sealed. A few membranes of each type were cut out, pretreated and then placed in a Petri dish in

the refrigerator for use in experiments.



Stirred cell systems were selected for the experimental work for a number of reasons; (i) volumes are

small whch is required for the use of IHSS reference material, (ii) membrane samples are small which

allows the use of a new membrane for each experiment, (iii) the solution chemistry can be precisely

controlled, (iv) experiments are relatively short and thus the investigation of a great number of

parameters is possible, and (v) the concentration in the cell represents the concentration in a crossflow

module (recovery about 70%). A comparison of mass transfer values was demonstrated in the case of



NF in Chapter 7. Drawings of the filtration equipment are shown in Appendix 2. A hydrodynamic

analysis is also shown in Appendix 2.



4.5.1



Microfiltration Equipment



All experiments were carried out in a magnetically stirred batch cell (volume of 110 mL, membrane area

15.2 . 10-4m" at a pressure of 100 kPa (if not otherwise indcated), pressurised with nitrogen gas. A

reservoir of 1.5 L volume was connected to the stirred cell. A photo of a Perspex stirred cell with

reservoir, manufactured in the university workshop, is shown in Figure 4.1.



Figure 4.1 Perqex stirred cell w t reservoir.

ih



All stirred experiments were stirred at 270 rpm (measured with a Philips PR 9115/00 stroboscope). A

balance and stop watch were used to measure permeate volume. Experiments were conducted at a

temperature of 25



+ 1 OC.



Copyright © 2001 by Andrea I. Schafer



Filtration Equipment



4.5.2



Ultrafiltration Equipment



The same system as described in the MF section and shown in Figure 4.1 was used for all rejection,

fouling, and fractionation ultrafiltration experiments. The balance was connected to a PC for flux data

collection.



4.5.3



Nanofiltration Equipment



Nanofiltration experiments were carried out in a stainless steel stirred cell with an Amicon magnetic

stirrer on a magnetic heater plate (Industrial Equipment & Control, Australia). The calibration is

shown in Figure 4.2.

The volume of the cell was 189 mL, the inner dameter 56.6 mm (resulting in a membrane surface area

of 21.2 10-"%



The stirrer speed could be varied from about 200 to 2000 rpm, with a setting of 400



rpm used routinely. The stirrer speed was measured using a Phlips PR 9115/00 stroboscope. One

side of the stirrer bar was labelled to avoid measuring of half rotations.



Figure 4.2 Calibration of magnetic stirrer table.



Figure 4.3 Stainless steel stirred cell set-zp.



Copyright © 2001 by Andrea I. Schafer



98



MATERIALS AND METHODS



The stirred cell was pressurised with instrument grade air. An- was used (rather than N 2), to provide

C02 for the carbonate buffer. pH changes due to the high pressure air were estimated to be less

significant than with N2 (see Appendix 5 for details). A photo of the set-up is shown in

Figure 4.3

and a schematic in Figure 4.4.

The cell was equipped with a pressure gauge mounted in the stainless steel line after the air cylinder, a

stainless steel reservoir with a volume of 2 L, a pressure release valve, a fluid inlet and outlet

connection, a pressure safety valve, and a refill opening on top of the reservoir. O n top of the stirred

cell, a fluid inlet connection, a pressure release valve and a temperature probe fitting were mounted.

The temperature was measured with a PT 100 probe, connected to a Kane-May ISM 330 indicator.

To control the temperature inside the cell, it was placed in a 2 L plastic beaker, through whch tap

water was circulated continuouslp. The temperature was kept constant (unless otherwise indicated) at

20 "C k 1 ()C. Permeate flux was measured by weight with a Mettler-Toledo PR 2002 (0.1 to 2100g)



balance, whch was connected to a PC equipped with Mettler-Toledo BalanceLink software.



Figure 4.4 Stainless steel stirred cell set-up. A : stirred

cell: z~olme185 mL; B: magnetic stirrer (Amicon, dtiven

bJy magnetic stirrer table); C: membrane; D: stainless steel

porons support; E: reseruoir uolnme 2000 mL, F:

pressurired instrtlment air inlet, G: feed inlet, presswe

release and safe9 valves; H: permeate outlet (to balance

and PC).



4.6.1



p H Value



A Beckrnan glass electrode (Ag/AgCl) was used for solution preparations and no contamination was

observed. The electrode was only used in samples after DOC analysis and was cleaned prior to use for

pH adjustment.



4.6.2



Conductivity



Conductivity was measured using a Lutron CD-4303 portable instrument.



4.6.3



Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES)



A Perkin Elmer Optima 3000 Spectrometer was used to determine the cation content of solutions.

Samples and multielement standards (0, 1, 10 and 100 mgL-l) were diluted with 5% nitric acid. All vials

used were cleaned with 1 M sulphuric acid. Detection limits are 3, 5,0.1, 5, and 70 pgL-' for Fe, Al, Ca,

Na, and I<, respectively.



Copyright © 2001 by Andrea I. Schafer



Organics Characterisation



99



The particle sol and filtration samples were diluted 1:l with HC1 (36'Yo) and heated (in a closed sample

vial) to dissolve the colloidal hematite. These samples were then analysed directly.



4.6.4



Ion Chromatography (IC)



IC was used for chloride determination for N F rejection experiments. Anions could not be analysed

as

using ICY humic substances interfere with the analysis (Hoffmann et al. (1986)). A Millipore Waters

Model 590 instrument was used with a Model 430 Conductivity detector. The eluent used was 0.68 gL -1

boric acid (H;BO3), 0.235 gL-' gluconic acid anhydride (C6H1006) and 0.3 gL-1 lithum hydroxide

@OH - 6 HzO).



4.7.1



Dissolved Organic Carbon (DOC)



Dissolved organic carbon was analysed using a Skalar 12 instrument. The method is based on UVpersulphate oxidation and described in detail in Appendix 4. The DOC of every sample was measured

as a routine analysis.

For samples containing colloids, aggregates or flocs the measured value is total organic carbon (TOC).

None of the samples were filtered as this would lead to loss of organics.



4.7.2



UV/VIS Spectroscopy



A Varian Cary 1E UV/VIS Spectrophotometer was used to evaluate the method and for further

standard analysis. Spectra of UV/VIS in the range from 190 to 500nm were obtained and correlations

established with DOC analysis. The method is further described and evaluated in Appenchx 4. UV/VIS

was also a routine analysis and the wavelength was used in rejection calculations.

At low wavelength (190 nm region), absorption by inorganics is observed. This is strong in the case of

unpurified Mooney Mooney NOM and absent in the purified IHSS samples. The ion content of all

samples is shown in section 4.7.6.

The W / V I S spectrum of NOM is attributed mainly to absorption of light energy by aromatic

compounds and can be broken into a series of transition bands, similar to those published for benzene

(Korshin et al. (1997b)). Three transition bands can be distinguished for each aromatic chromophore in

NOM - the local excitation (LE) band, the benzenoid ( ' 2 ) band, and the electron-transfer (ET) band.

The peaks vary in their height, width, and centre location depenchng on the composition of the NOM

(Kaecbng (1998)). The presence of these various peaks can be recognised in the shoulders on the

spectra as shown in Figure 4.5, however detailed analysis was not considered warranted.

From Figure 4.5, it can be seen that the (probably) soil-derived fidrich HA (purified with a lOOkDa UF

membrane) has the largest UV/VIS absorbance, followed by IHSS and the NOM HA fraction whch

are surprisingly similar. The FA fraction of Mooney Mooney NOM has a higher absorbance than the

unpurified NOM, which can be explained given the NOMs relatively high content of hydrophlic acids

of a very low absorbance. The IHSS FA also has a slightly lower absorbance over the complete

wavelength range.



Copyright © 2001 by Andrea I. Schafer



100



MATERIALS AND METHODS



5 0.15



Figure 4.5 C V Spectra of the organics zmd.

all wavelengths linear with concentration

IHSS FA



NOM

IHSS HA

Aldrich HA (c100 kDa)

NOM Hydrophilic Fraction

NOM HA Fraction



2

4.7.3



200



250



300



350



400



450



500



UVIVIS Wavelength [nm]



Titration



The NOhl sample, which was concentrated as described in Appendix 1, was titrated using a Metrohm

automatic titrator. .The titrator was operated in dynamic titration mode. The samples were acidified

from ambient pH to pH 2.8 with 0.1 M HNO3 and subsequently alkalised with 0.1 M NaOH to pH 10.

It was assumed that at pH 2.8 all acidic functional groups will be saturated, whereas at pH 10 all

carboxylic and half of the phenolic groups were dissociated. The limitations of these assumptions were

discussed in Chapter 2.

The titration vessel was purged with nitrogen to eliminate C 0 2. From the volume and molarity of

added base and the mass of titrated DOC, the content of acidic functional groups can be calculated.

Carboxylic acid content was calculated from the amount of base added until the end-point was reached.

Phenolic acid content was calculated as twice the difference in titrant required to change the pH of the

titrate from 8 to 10, since it was assumed that at pH 10 only half the phenolic groups were Issociated.

A solution of a concentration of 20 mgL-I as DOC NOM were titrated. The error due to the salt

content of NOM is likely to be high.

Table 4.4 describes the a c i d q and size of the three organics used and the average molecular weight as

found in the literature (for IHSS organics and purified Aldrich HA) or as measured (for NOW. The

reported rvlW will be verified later (see section 4.7.7) by analysis.



Table 4.4 Acid$ and average molecdar weight ofthe organics ( y ~ c k e r Clark (1984),'Beckett et al. (1987),

and

y

'Elering and Morel(1988),'ana&red b titration (lee above), 'Clark andhcker (1993), 'Children and Elimelecb

(1996)).

Type of Organic



Acidq [meq.gl]

Carboxylic



liverage Molecular Weight p a l



Phenolic



IHSS FA



3.41 5.45 6.1



1.512.05



IHSS HA



4.01 4.16



2.9' 2.16



Purified Aldnch L A



3.3(j



2.56



> 50 0006



Mooney Mooney NOM



5.14



1.34



< 10004



Copyright © 2001 by Andrea I. Schafer



7502

1100"



15002



12004



101



Organics Characterisation



4.7.4



Elemental Analysis



Elemental analysis of the IHSS reference material was provided by IHSS with purchase of the organic

material. The elemental analysis was performed for IHSS by Huffman Laboratories (Wheat Ridge, CO,

USA). Results are summarised in Table 4.5.



Table 4.5 Elemental analy,is resztlts ofthe organics used.

C



Sample [9/0]



H



0



N



S



P



Total



1-120



Ash



p

..

-



Stream HA Reference



52.89



4.1



43.40



1.17



0.58



<0.01



102.2



9.8



3.46



Stream F,i Reference



53.04



4.36



43.91



0.75



0.46



cO.01



102.5



8.9



0.98



Mooney Mooney NOM



6.3



The Mooney Mooney Dam NOM was also to be analysed by IHSS. However, the wet digestion

method whlch is used for HA and FA cannot be applied directly to NOM and is currently being

revised. The method to be developed will also analyse the ash composition.



4.7.5



XAD Fractionation



The XAD fractionation method is the classic concentration method for humic substances (see also

Chapter 2). The IHSS HA and FA samples were isolated using this method. This procedure was

therefore used to obtain humic substances from the Mooney Mooney NOM. The fractions were used

for NOM concentration and for experimental work.



A stock solution of about 4 g NOM in 500 mL water was prepared, resulting in a solution

concentration of 291. mgL-1 as DOC or a total mass of 145.5 mg organic carbon. The solution was

then desalted using an Amicon YC05 membrane (molecular weight cut-off 500 Da). According to

Amicon, this UF membrane does retain large salts such as phosphates and sulphates, but does not

retain a sipficant amount of smaller-sized salts. 310 mL of permeate were collected and discarded,

resulting in a loss of 5.0 mg organics (as DOC). Thus, 2.5% of organics, could be considered smaller

than the membrane pores.

The remaining solution volume of 190 mL was fractionated using the method of Leenheer (1981,

1996). Results are presented for the NOM sample in Figure 4.6.



Figure 4.6 Composition of

Moony Moony Dam NOM in

percent.



Copyright © 2001 by Andrea I. Schafer



102



MATERIALS AND METHODS



The sample has a high proportion of HA (47%) compared to fulvic and hydrophilic fractions (19%

each). T h s could account for the high microbiological activity in the Mooney Mooney Dam, w h c h

would result in a consumption of the more accessible fulvic and hydrophilic compounds. The relatively

high loss of organics in the XAD procedure is probably due to the presence of particulate organic

matter.



4.7.6



Cation Content of Organics



The cation content of the organic samples was determined using ICP-AES (see section 4.6.3 for

analytical details). Results are shown in Table 4.6.

The values per 100 mg DOC show the high salt content of NOM and its fractions. Whde the IHSS

samples and the XAD extracted HA and FA fractions of NOM are very low in cation content, the

NOM, the hydrophlic fraction of NOM, and the purified Aldrich HA have all very high cation

contents. The hydrophilc fraction has accumulated the entire salt content of the NOM sample. This

does not mean that all ions are associated with the hgdrophilic fraction, but due to the purification

method all ions remain in the hydrophilic sample. This needs to be considered when treatment data of

this sample are interpreted.



Table 4.6 Cation content of organics used The salt content ir per amount of DOC due to the stock rohtion

'

concentration. Vaher in bracketr are per l00 m g ~ .DOC, thus mg cationrper 100 mg DOC.

IHSS H A



IHSS FA



N O M HA



NOh.1 FA



A1 [mgL-l]



100



100



100



250.3



NOM



Aldrich 100



Hydrophhc



D O C [mgL-l]



NOM



kDa



22.1



12



114.5



0.10 (0.10)



0.02 (0.02)



0.58 (0.58)



0.24 (0.10)



0.07 (0.06)



0.47 (2.13)



0.28 (2.33)



Ca [mgL-l]



0.22 (0.22)



0 (0)



62.6 (62.6)



0.61 (0.24)



0.24 (0.21)



48.6 (219.9)



0.94 (7.83)



Fe [m&']



0.11 (0.11)



0 (0)



1.41 (1.41)



0.46 (0.18)



0.36 (0.31)



1.2 (5.43)



0.15 (1.25)



Na [mgL-'1



1.52 (1.52)



0.23 (0.23)



296 (296)



3.16 (1.26)



3.54 (3.09)



244 (1104.1)



12.3 (102.5)



I< [mgL-l]



0.55 (0.55) 0.41 (0.41)



52.4 (52.4)



2.16 (0.86)



1.19 (1.04)



1.43 (6.47)



0.47 (3.92)



4.7.7



High Performance Size Exclusion Chromatography (HPLC-SEC)



Size exclusion chromatography (SEC) enables the determination of the molecular size of organic

molecules. Samples were filtered through a 0.45 pm filter (Gelman Sciences Acrodiscs) prior to analysis.

The membrane filter material was Supor (Polyether-sulphone).

SEC was performed according to the method of Chin et al. (1994). A Shodex KW802.5 SEC column

PVaters Corp., Milford, MA., USA) was used and a Waters liquid chromatography system consisting of

the following components was used for the analysis: Waters 501 high pressure pump, Waters 717

autosampler, InterAction column temperature control oven, Waters 484 UV/VIS detector, and LVaters

Millenium 2.0 computer software package.

The mobile phase consisted of 200 mM phosphate at pH 6.8, adjusted to an ionic strength of 0.1 M

with high purity NaC1. The eluent was filtered through a preconditioned 0.22 pm membrane filter to

prevent interference from particulates. The system was operated at 1.0 mL/min and 30 ('C, with 200 pL



Copyright © 2001 by Andrea I. Schafer



103



Organics Characterisation



injections and detection at 260 nm. The mobile phase was degased for 30.minutes in an ultrasonic bath

prior to use.

The system was calibrated using polystyrene sulphonates (PSS) (Polysciences, NJ, USA). 1 gL-l

standards were prepared (35, 18, 8, 4.6 kDa). Blue Dextran, a high molecular weight polysaccharide

(approx. 2 000 kDa) and an acetone solution (1%) were used to determine the column's void volume

and total permeation volumes, respectively. The PSS's were detected at 224 nm (see Figure 4.7), the

acetone at 280 nm and the Blue Dextran at 260 nm. All samples were detected well inside the 15

min/sample run time.



Molecular Weight = 10



(Slope of L ~ n e RetentionTime)



+ Intercept of the Line.



(4.1)



The log of the molecular weight versus peak retention time for the PSS standards were plotted and

consistently yielded a straight line. By using the calibration equation:

The raw detector response versus retention time were converted to graphs of detector response versus

apparent molecular weight. The molecular weight determined for the organics used in this work is

shown in Figure 4.8. A number of observations can be made.

Surface water is the water from Mooney Mooney Dam prior to concentration and freeze drying,

whereas NOM is the redissolved powder of the same water. A. small, but nevertheless clear, increase in

molecular weight can be seen. It is thus obvious that the organic is being modified even using this

comparably "soft" concentration method.



Figure 4.7 HPLC-SEC PSS sta~zdardsin

single solzitions and as a mixttire.



100



1000



10000



Apparent Molecular Weight [Da]



The Aldrich HA has the largest size. Once this organic is purified by filtration through a 100 kDa

hIIVCO UF membrane, the size becomes comparable to the other organics. O f the purified

compounds, IHSS HA is the largest organic, and surface water the smallest. All organics have a size

distribution. The narrow peak at 300 Da is the salt peak. IHSS FA has a broader size distribution than

lHSS HA. Table 4.7 shows a summary of the peak molecular weight values. The values are the peak

height MW as determined from Figure 4.8.



Copyright © 2001 by Andrea I. Schafer