Topics in..
.
Chemical Instrumentation
I
Edited by GALEN W. EWING, Seton Hall University, So. Orange, N. J. 07079
These articles are intended to serve the readers o f ~ ~JOURNAL l s by calling attention lo new developments in the theory, d e d n , or availability of chemical laborato~yinstrumentation, or by presenting useful insights and ezplanations of topics that are o j practical importance lo those who use, or teach the use of, modem instrumentation and instrumental techniques. The editor invites correspondence from prospective contributors.
LII. Current Trends in Gel Permeation Chromatography. Part One: Theory and Equipment JACK CAZES, Mobil Research and Development Corp., Poulsboro, N . J. 0 8 0 6 6
I. Introduction This report is presented as asupplement t o an earlier paper entitled, "Gel P m e a Lion Chromatography," which was published in 1966 as part of the "Topics in Chemical Instmmntation" series ( 1 ) . The past four years have seen many changes in the nature of gel permeation chromatography (GPC). Whereas it was slmost exclusively a polymer fractionation method, i t has now taken its place as a generally applicable separation technique along with other, more commonly known liquid-phase chromstographio techniques, e.g., liquid-solid adsorption, liquid-liquid partition, ion exchange, etc. I n fact, GPC is, for d l practical purposes, a special type of liquid-liquid partitioning in which the stationary phase is the solvent contained within the gel pores and the moving phase is the solvent outside of the column substrate particles. The development of new, more universally applicable column substrates that are capable of "sorting" molecules on the basis of molecular size and shape have extended the scope of GPC t o verv, hieh . sndverv low molecular weight sulwtiurw, t o use with n uiae vkrirty of s~,lvcr.t.~, horh aqutow 8l.d wynnir, and l o i n h - t r n l - i w l e wl,.tralions xnd pwlirations. There is no universally accepted name for t,he technique described in this paper. The name "gel permeation," which was coined by John C. Moore of the Dow Chemical Co., has persisted in the polymer literature, but is no longer wholly suitable, since there Itre now substrates that are capable of separating molecules on the basis of size, which are not gels, e.g.! porous glass, silica, etc. "Gel filtratlon," long used by the biochemists, is not completely acceptable either, because the pro-
cess is not really one involving filtration in its usual sense. Other expressions that have been used include "molecular sieve chromatography," "restricted diffusion chromatography,'' and others. All of these terms are the result of attempts t o choose a name based either on the suspected meohanism of the separation or on the type of column substrate being used. "Gel permeation" has been retained in the present report primarily t o avoid confusion. I t appears in much of the literature cited, and, for that matter, almost all of the non-biomedical literature dealing with this subject. Several excellent reviews (2-4) have been published on this versatile technique, including a book entitled "Gel Chromatography" (6). A short two-day course entitled "Fundamentals of Gel Permeation Chromatogmphy," is offered several times a year a t various locations in the United States under the sponsorship of the American Chemical Society. The course is aimed a t the individual who has had little or no exposure to GPC and who is interested in actually performing size separations. A series of International Seminars on GPC have been and are continuing to be held a t least once a year under the sponsorship of Waters Associates, Inc., Framingham, Mass. Those that have already been held or have been scheduled are summarized here: 1st-Jan., 196&Cleveland 2 n d S e p t . 1617,196.5-Boston 3rd-May 19-20,1966--Geneva 4th-May 22-24,1967-Miami 5th-Summer, 1968-London 6 t h - 4 e t . 7-9,196&Miami 7 t h - 4 c t . 12-15,1969--Monaco 8th-July 1-3,1970-Prague 9 t h 4 c t . 5-8,1970--Miami
Jack Cares currently holds the position Supervising Chemist in charge of the iepnrations llesenrch Group at Mobil tesenrch and Development Corp.. Pnuls,om. N. J. He had previously spent even years with Mobil Chemical Co.. vhere he was involved in many areas of esenreh, including organic chemical and dymer process research, design and np,lieation of andytionl instrumentation. :el permention ehromatogmphy, and omputeriaed data proees~ing. Other nterests have inoluded organic synthesis. cgnnio free-mdienl reaction mechanisms. .nd electronic circuitry for chemical intrumentntion. Dr. Cnees reoeived a B.S. in Chemistry 1955) at the City College of New York, .nd both MS. and Ph.D. degrees in srganio chemistry at New York Univeritu. Dr. Cams hns taught at Queens College New York) and a t l t u t g e r ~ t h eState lniversity (New Brunswlck). He eurently teaches :L Short Course on Gel 'ermeation Chromatography for the Lmerienn Chema:al Society. ~f
Preprints of the papers presented were published by Waters and some of the more recent ones are still available from them. They have also prepared an extensive bibliography on GPC containing references t o several hundred papers. The ASTM D-20 committee is currently involved in formulating a standardized terminology for GPC as well as an acceptable recommended practice. A "round robin" experiment will certainly follow acceptance of a suitable procedure. Liquid chromatography and, consequently, GPC are currently experiencing a renaissance similar t o that which gas chromatography underwent in the late 1950's. The development of suitable instrumentation and a desperate need for a iractionation technique applicable to non-volatile, (Continued a page A4891
Volume 47, Number 7, July 1970
/
A461
Chemical Instrumentation
DEGASSING
RESERVOIR
thermally labile substances have been largely responsible for this rebirth.
VALVE-LOOP
SAMPLE
11. Mechanism of the Separation An excellent review of the theory and mechanics of GPC separations was published by Altgelt (6). A t least lhree mechanisms have been proposed t o describe the GPC separation process, and all of them probably operate simultaneously with one or more dominating under a given set of operating parameters. GPC is a. liquid-liquid partition chromatagraphic process in which solute molecules distribute themselver between two liquid phases-the liquid contained in the gel pores and the liquid outside of the gel, i.e., in t,he interstit,ial volume. According t o the steric aclusion meehanism i t is assumed that 0 different fractions of the total pore volume are accessible t o different sise
pores into which they can enter, whereas small molecules can enter a relatively large number of pores. 0 there is diffusional equilibrium; the time required for solute molecules t o enter into and emerge from gel particles is much smaller than the residence time of the solute aone. The process would, therefore, be expected t o he flow-rate insunsit,ive (not diffusion controlled) over a relatively wide range of linear velocities, and this is indeed what is most often observed experimentally. A distribution coefficient is thus defined: Kd = Vi.
....
/Vi
and the retention volume of a given species becomes
V n = V.
+ KdVi
where Vi.
....
= accessible porevolume Vi = total pore volume V , = interstitidvolume
The cffects of steric exclusion should be most evidenl where s. major portion of the solute molecules is larger than many of the gel pores. In the rml7iclcd diffusion ?ncehanism the process is assumed Lo be, to a significant degree, 8, dinusion-controlled one, i.e., there is no diffusional equilibrium. Observed retention volumes should then be affected by changes in flow-rate; the shapes of broad chromatographic bands observed for polydispe~.scmixbulw should also be flow-ralc depende~~t.The absence of difiusiord equilibrium should he most pronounced s t very high linear velocities, and it is under such condiliona that the restricted dilfusion mechanism would be the dominant one. Several t h c m c l p a m i c lheories have been advanced for the separation. Marsden has distinguished between the enthnlpy and entropy contributions t o Kc,
AUTOMATIC SAMPLING SYSTEM
FRACT IONACOLUMN
I
I
DETECTOR
k-------------4
-. .
RECYCLE SYSTEM
---Figure 1.
ELECrRKAL CONNEC~/ONS
I 1
FRACTION COLLECTOR
I
COMPUTER
I
I !
I
I-----
r
Liquid chromatography system.
(7). deVries relates Vn t o the molar volume of the salute and the pore sise distribution of the gel (8). Casassa (9) proposes a theory which accounts far the separation on the basis of the existence of different chain conformations within either spherical, eylindriesl, or deb-shaped pores. He concludes that distribut,ion of solute between the two phases is governed entirely by the loss of conformational entropy upon entering t,he pares. Carmichael (10) relates the behavior of random-coil molecules in uniform pores t o the probability that t,he root-mean-square end-to-end distance of the molecules will be less than the average pore radius. A secondary czclusion effect has recently been ~ r o ~ o s e( 1d1 ) to account for the exceptidnaily good separalions observed with columns operated under apparently overloaded conditions, i.e., with as much as ten times the normally used sample loading. Briefly, if a mixture of large and small molecules is placed onto R. gel, the smnll molecules will diffuse most rapidly into the gel pares. The larger molecules will, eansoquent,ly, find relatively few unoccupied pores and the probability of their dilfusing into an occupied pare will be reduced. The larger molecules will most probably move further down the column until they find unoecupiod pares. The net result is enhancement of the separation. '
Ill. Resolution Classiedly, resolution of two chromatographicponkfi has been defined as
Baseline resolution is observed when Rw = 15. This equation, however, does not tell us anything about the factors that affect resolution. An equation can be derived
in which the first factor represents seleetivity, t,he second, capacity, and the third, random dispersion. The srleelivily term is concerned with the distribution eoeffieient,s of the two solute species and with how different they are. The greater t,he differenceb e h e e n K, and K2, the greater will be t,he difference between VR, and VE,. Thus, resolution of a given solute pair could be increased by choosing a gel such t,hat the difforenee bet,weenK, and R2is increased. The capacity term is related t o the capacit,y ratio, K', which includes terms involving both dislribution coefficient and amount of stationery phase in tho column. The magnitude of K' actually determines how long a fiolute will remain on the column. Small values of K ' result in small retention volumes. The random dispersion term is a funetion of the number of theoretical plates, N, in the column. Separation, per se, is not achieved by a large N; a hlgh plate count will only assure a minimum of sprendiug of an olhereise narrow, well shaped chromai.ographic band. llandom dispersion includes the effects of flow inequalities within the column due t o inhomogeneities in the packing density in the column, nonequilihrium of the iolute between the two phases, and longitudinal diffusion, primarily in the moving phase.
IV. Equipment
where
Rw = n o . of peak widthsresolution; Vnl and Vn,
= retention volumes, at the peak maxima, for the two species; WI and W 1 = extrapolated base widths for the two species.
Since GPC is a specific l,ype of liquid chromatography, much of the equipment t h a t is customarily used for the more classical liquid-phase column chromatographio techniques can be employed for this fractionation method. I t is of value here t o outline briefly some of the various (Conlinued on page A4fi4)
Chemical Instrumentotion kinds of apparatus that are applicable, but no attempt will be made to provide a complete listing of all available paraphernalia; first we shall look at component types that can be used in "do-it-yourself" approaches and then we'll see what is available commercially in the way of complete liquid chromatographs. Figure 1is a flow-sheet that outlines the various components that can be included in a. complete liquid chromatographic system. The only part that is absolutely essential, of course, is the fractionation column, for it is in the column that the actual separation of a. mixture into its components takes place; furthermore, it is merely the nature of the column suhstrate that classifies a chromatograph as a GPC instrument, i.e., when a substrate is used that separates molecules on the basis of molecular size one refers to the instrument as s. gel permeation chromatograph. Otherwise, it is simply a liquid chromatograph. All of the components, with the exception of the column, are chosen either t o improve reproducibility and/or reliability or to render operation more convenient. GPC can be performed, in its simplest form, with an open glass chromatographic column packed with a suitable aubstrat,e. Solvent is generally supplied from a reservoir at the top of the column via gravity feed. Fraction collection can involve no more than periodically changing a container situated under the bottom of the column with the detection method being either visuitl observation (in the case of colored substances), or removal of solvent from the collected fractions followed by ohservation and/or weighing of the sample residue contained in each vessel. At the other extreme one might include in his instrument such "trimmings" as automatic sample injection and fraction collection, multiple liquid chromatographic detectors, provision for recycling all or part of the sample through the same column for improved resolution, and a digital computer for automatic control of various functions and operating parameters (temperature, pressure, flow-rate, cycle control, etc.) as well as automatic data processing. At least one manufacturer (Problematits, Inc., Waltham, Mass.) bas described such an integrated system designed around a. small dedicated computer. Of course, increased com~ l e x i t vgenerally results in increased cost, often beyond the limits that can be justified on the basis of the utility of the technique itself (better known as "payout" in the jmgonaf the accountant). Table 1 lists manufacturers of liquid chromatography components.
A. Pumps Three basic pump designs probably account for most of the commercially avdable liquid metering pumps: (1) Peristallic pumps are useful, primarily, for low pressure applicetions for flow-rates at or near those at grwity-feed conditions. They are not positive displacement systems and feed rate for a given motor speed generally is not reproduciblefrom day to day.
A464
/
Journal o f Chemicol Education
Toble 1.
Some Manufacturers of Liquid Chromatogrophic Equipment
Manufacturer
Complete svstem Pumm
(2) Syringe pumps are available in volume capacities from a few milliliters to several liters (without refilling) for operation up to several thousand pounds pressure. They are pulseless and therefore ean be used with flow- and pressurebensitive detectors without pulsation damping systems. Their chief drawbacks are the need for periodic refilling and their large internd volume; in cases where recycle operation is desired, syringe pumps cannot be used, became fractionated sample components would be remixed when directed
Columns
Deteotors
Fraction collectors Valves
hack to the large solvent reservoir in the Pump. (3) Reciprocating piston pumps, available for operation up to several thousand pounds pressure can be readily used for conventiond as well as recycling chrome tography.
0. Columns Many column designs are available, of both metal and glass, of fixed length and adjustable length. Variable length col(Continued a page A466)
Chemical instrumentation umns often include a plunger that passes through the end-fitting of the column, which can be moved in or out t o obtain a given packing length inside the column. A "column kit" is available from Lahoratory Data. Control, Inc., which includes small-volume end-fittings together with precision bore tubing for assembling a variety of columns. Packed columns can he purchased from some of the manufaeturers of complete instmments. Extremely high resolution is reportedly attainable through the use of very narrow columns (1-2 mm diam) packed with very fine materials (200 mesh and smaller). The high pressures often required t o achieve practical flow-rates with narrow columns of course makes instrument design considerations more stringent (high pressure pumps, low volume "plumbing" and detectors, safety, etc.) and this must he kept in mind when considering their use. C. Detectors
Many kinds of liquid chromatographic detectors have been used and/or are available commercially. These are based on a variety of physical properties of molecules in 8dution. Some rely a n the presence of a specific chemical functionality. Others do not, and are more universal in their scope of applicability. Often, multiple detectors are used, one, non-specific (e.g., a differential refractometer) t o indicate the elution of all sample components, another, a specific one (e.g., a U.V. photometer), t o det,eet the presence of a specific chemical type in the eluate. With suitably selected dual detector systems one can, thus, obtain information concerning bath the molecular weight distribution and the relationship between MWD and chemical
ential refractometer and an ultraviolet spectrophotometer, to monitor the GPC fractionation of styrene-hutadiene copolymers; the former responds t o all polymer components, regardless of chemical type, while the latter is sensitive only t o the aromatic styrene blocks in the copolymer. A description of some liquid chromatographic detectors follows: (1) Differentiel rejraetomete7-extremely sensitive, with some commercial units capable of detecting a difference in refractive index of 1 0 ' or even 10-8 R.I. units. Detectors based on refractive index are almost universally applicable, since they do not rely on the presence of specific functional groups. Also, since many polymeric systems exhibit a constant refractive index over a wide molecular weight range, i t is often possible t o relate detector response t o quantity of sample eluting from the chramatogra,phic column. I t is far this reason that the differentialrefreetometer has found wide acceptranee in GPC frclctionations where molecular weight averages and distributions are t o he computed. These detectors are extremely flow- and temperaturesensitive (many organic solvents exhibit a, temperature coefficient of R.I. unitsIoC).
A466 / Journal o f Chemical Education
(2) Ultraviolet and visible photometers are tial t o a static electrode pair; a supporting available as both single and double beam electrolyte would be inbroduced into the systems. Use of these detectors is limited flowing liquid stream just ahead of the t o those applications where the solutes of deketor. A recording of both half-wave interest absorb radiation of the wavelength potential and diffusion current would proemployed and the solvent does not. For vide both qualitative and quantitative inspecific solutes that have high extinction formation concerning the species present. coefficients, U.V. and visible photometers (8) Grauimetric detectors involving direct offer extreme sensitivity with good tem- automatic continuous weighing of the perature and flow stability. chromatographic effluent (to yield den(3) Flame ionization-column effluent is sity), or automatic evaporation of solvent allowed to fall on and wet a moving and weighing of the resultant residue from met~llicwire, chain, or band which then discrete micro-fractions would seem t o offer a most valuable detector for liquid er ters an oven maintained a t a temper* t. re h'qh emugh t o completely evaporate chromatography. I t might well represent solvent f r a n the moving element, but not as important an advance in liquid chrom* disturb the residual sample. This resid- tography as the katharometer (thermal ual material is then either passed directly conductivity detector) did in gas chrornathrough a flame ionization detector where tography. Both approaches mentioned i t is pyrolyzed snd ionized or it is first above have been shown t o he feasible in pyrolyaed in a high temperature furnace studies based on the use of an Electrobaland then the pyrolyzate is "blown" into ance as the sensor, and reported by Radthe flame ionization detector. I n both awski and Williams, but i t does not appear ceses, the flame ionization cell is similar t o that a commercial instrument will he that which is used with gas chromato- forthcoming in the foreseeable future (16). "Necessity is the mother of inventionngraphic instruments and the measured ionization current shoukl be related t o the as the need dictates, there is no doubt that amount of sample on the moving element specific detection systems will be forthand the relative proportion of carbon con- coming that are based on other molecular such as oolarizahilitv idielect.rir . tained in the sample molecules. I n actual ~1onerties practice, secondary ionization effects com- co!.iluul , pie,oelrctriv eITe(.t, viwhily, plicate the situation, and the observed Krlviu "elertric pvl" effwi ( ~ ~ ~ a . - u r e n ~ e r ~ t signal t o noise ratio leaves much t o he de- o f deflecrmn of ihnrgnl liquid Jroplet:. iu a sired. Consequently, the currently avail- field), and.. ?? able flame ionization detectors have not gained wide acceptance by liquid chromaD. Complete Systems tographers. Also, these detectors are Commercially available instruments for limited t o those applications where solvent e m be removed from the moving element performing liquid-phase molecular size without removing any of the solute (sam- separations can be classified, for our purposes as ple components). (4) Kcat of adsorption detectors gener1. gel permeation chromatographs ally consist of s. "micro-column" contain2. general-purpose liquid chromatoing a small amount of an adsorbent in graphs which a temperature sensing element (e.g., Although sepuralionr Imicd on molerulhr thermistor) is imbedded. The heat of ads i x difirrence> ( n u 1w performed will, d l sorption and desorption is detected and liquid chromatographs equipped with a measured as a change in temperature of the adsorbent column. Thin detector is suitable column substrate, some are better suited from the standpoint of convenience often very sensitive and useful for qualit* and separation efficiency attainable. tive detection; i t is not well suited for quantitative work, requiring frequent celi- Generally, maximum efficiency can be hration. realized with systems containing a minimum of dead volume with narrow bore (5) Electrical conductivity detectors gencolumns containing finely divided packing erally consist of a pair of metallic elec(substrate) with a narrow particle size di8trodes cmtained in a microcell together with a Wheetstane bridge measuring tribution. Some of the newer instruments circuit. Applications are limited t o those have been designed with this capability. systems that conduct electricity. Future Some are modular, others are not; some developments in the direction of high- have several detectors, automatic injecfrequency eleotrodeless conductivity tion, fraction collection, high pressure bridges might extend their usefulness t o pumping systems, etc. as options. Table 2 i s s s u r n m a q of some of the commercially poor conductors. available liquid chromatographs. The (6) Infrared detection has, thus far, specialized bio-medical analyzers have been limited t o homemade modifications been omitted primarily because they would of conventional recording infrared spectro- have t o be extensively modified t o make photometers (14, 16). Applications are them conveniently applicable t o GPC limited t o samples containing functional separations. groups that exhibit strong absorption bands within the wavelength range of the instrument. Sensitivity is relatively poor V. Column Substrates except in cases where an extremely strong Many new column substrates have heabsorption hand can be monitored (e.g., come commercially available since the carbonyl, C-H, etc.) earlier report (1). They can be classified (7) Polarographic detectors are not yet as being rigid, semi-rigid, or soft. The commercially wailable. A practical de- rigid substrates, char.racterized by their sign, however, might involve the applica- fixed, rather uniform, pore volume, high tion of a fixed or rapidly varying (in the (Continued on page A468) case of oscillographic instruments) poten-
. ~.
.
.
~
~
?
Table 2.
Commercial Liquid Chromatographic Systems
01 0
, 2
z
Manufacturer
%
Model
Basic prm
(8)
GPC eolumns
.
Auto. mnRefr. ject. index
Detectors Flame U.V. ionis'n.
.
Auto fract. Other collect.
Largest diam. column
Pump type
5 mm i.d.
S
Max. Dieicolti& Max. u r n Sample &/or p r ~ s . temp. reReeom(pslg) ("C) cycle carder pttter
Remarks
0,
n
3'
m
s. 5
A . Gel Permeation Chromatog~aphs Problematics, Inc. 223 Crescent St., Waltham, Mass. 02154
-%.
1000
Waters Associates, Inc. GPC-200 61 Fountain St. GPC/ALC-301 Frarningham, Mass. 01701 GPC/ALCdOl GPC/ALC-100 GPC/ALC-101 Ana-Prep
-20,000 16,500 9,900 4,980 8,400 12,825 29,500
X*
X
X
X
N
N
N
X X X X X X (X)
A N N N N
X X X A X X (XI
N A N A A N (N)
N N N
N N N N N N (N)
A A N X X X (A)
X
(A)
N
N N (N)
R 1" 0.d. 1'o.d. R a/8" a d . R ZL/,' a d . R 21/~X~.d. R 2'/2 0.d. R (1"o.d.) (R)
10,000
200
N
X
A
300 1,000 1,000 1,000 1,000 250 (250)
150 R.T. R.T. R.T. R.T. 150 (150)
N X N A X N (A)
X A A A X X (XI
N N N N N N (N)
On-line still for solvent recovery See Noteb See Notee SeeNote See Noted
B. General Purpose Lipllid Chromatographs 1)uPont Instrument TJiv. Wilmil~grou,Del. 19\98 Nester-Faust, Ine. 2401 Ogletown Rd. Newark, Del. 19711
620 1200-H 1240
Varian Aerograpb 4000-1 4000-2 2700 Mitchell Dr. Walnut Creek, Calif. 94598 400C-O 4120-5 Waters Associates, Inc. ALC-100 61 Fountain St. ALC-201 Framingham, Mass. 01701
,-. a
X
=
16,500
A
N
X(A)
X(A)
N
N
N
8 mm i.d.
S
3,000
200
A
X
N
See Notes*,'
7,025 4,600
A A
N N
A A
A X
A A
A A
A N
25 mm i.d. 8mmi.d.
S R
2,500 1,000
R.T. 125
N
N
A A
A A
See Notes'.'
1,700A 2,600 A 2,000A 12,550 A
N N N N
A X A X
X A A X
N N N N
A A X A
N N N N
/
G
0..
a/8"
o.d. 0.d.
G
G S
750 750 750 5,000
R.T. R.T. R.T. 90
N N N N
A A A A
A A A A
7,850 A 3,900A
N N
X X
A N
N N
N N
A N
a/8"
1" 0.d. o.d.
R R
1,000 1,000
R.T. R.T.
X N
A A
N N
See Note' See Not@ See Notes6.G Micro beat of sdsorpt. detector available See Noteb See Notec
0.d.
included in basic price; A = avdable as option at additional cost; N = notavdsble; R = reciprocating pump; S = syringe pump; G = gas pressurized solvent reservoir; R T =
j! room temperature (ambient).
2'
An accessory will be wailable late in 1970 to convert to ooeration UD to 3000 mie and 200'C. An accessory will be available late in 1970 t o convert to operation ub to 3000 bsii. *The Ana-prep instrument incorporates both an analytical and a preparative instrument in a single cabinet. Both sections can operate simultaneously, but only one can be monitored a t any given time with the refrectometer, via a refractameter selector velve. Deta in parentheses refer t o the analytical section of the instrument. ' Recycle accessory will be available late in 1970. J The DuPont 820 is available with either the refraotametric or U,V. detector for the basic mice shown. ; 'Art awrssuty oven for operation up to L O O T is available as a n option. (:oIumt.s rre jacketed; n tmqwraturr-vorrrrolld circulatmg bath may he uued for operation at higher ramp a ' TIM mstr!rrue!rt inrludes a r~ricrohenr-of-ndsorprion detector.
$
-
'
Table 3.
Commercially Available Column Substrates Pore diameter.
Designation
A.
B.
Distributor
Porous glass Bio-Glas 200 Bio-Glas 500 Rio-Gisr 1000 Bio-Glas 1500 Bio-Glas 2500 CPG-10-75 CPG-10-125 CPG-10-175 CPG-10-240 CPG-10-370 CPG-10-700 CPG-10-1250 cPG-10-*000 Porous Szizco Porasil-60 Porasil-250 Porasil-400 Poraail-1000 Porasil-1500 Poreail-2000 Merek-0-gel Si-150 Merok-o-gel SI-500 Merok-o-gel Si-1000
I A.
Moleculhr weight exoluaion limit
1
Polystyrene Gels Styragel 39720 Stvrad39721
Semi-Rigid Gala
...
00 A'
~
