US 3722181 A
A process for making a chromatographic packing having a polymeric stationary phase in which molecules having the formula WHEREIN R3' is a hydroxyl, or an aliphatic or aromatic hydrocarbon monovalent radical, and R4 is a monovalent aliphatic or aromatic hydrocarbon radical, ARE PARTIALLY PREPOLYMERIZED, CHEMICALLY BONDED TO A POLYVALENT METAL-CONTAINING SUBSTRATE, THE METAL HAVING A VALENCE OF 3-5, AND FURTHER POLYMERIZED.
Description (OCR text may contain errors)
United States Patent [191 Kirkland et al.
[ CHROMATOGRAPHIC PACKING WITH CHEIWICALLY BONDED ORGANICSTATIONARY  Inventors: Joseph J. Kirkland; Paul C. Yates,
both of Wilmington, Del.  Assignee: E. I'. du Pont de Nemours and Com- 4 pany, Wilmington, Del. 221 Filed: May 22,1970
21 Appl. No.: 39,6 65
Primary EraminerJohn Adee Attorneyl-lerbert M. Wolf son 571 ABSTRACT A process for making a chromatographic packing having'a polymeric stationary phase in which molecules having the formula Mar. 27, 1973 wherein R is a hydroxyl, or an aliphatic or aromatic hydrocarbon monovalent radical, and
R is a monovalent aliphatic or aromatic hydrocarbon radical,
are partially prepolymerized, chemically bonded to a polyvalent metal-containing substrate, the metal having a valence of 3-5, and further polymerized.
The polymeric stationary phase has a repeating unit of the formula wherein A is --O or a monovalent aliphatic or aromatic hydrocarbon radical, Y and is chemically bonded to the-surface of the substrate by an where silicon is part of a repeating unit.
- 18 Claims, -12 Drawing Figures 20 CHROMATOGRAPHIC POLIMEPIC STATIONARY PHASE SUBSTRATE '23 PORES 22 POLYMER PATENTEUMAR271975 I 3,722,1 1
' SHEETEUF 6 I 2O CHRQMATOGR INVENTORS JOSEPH J. KIRKLAND PAUL C. YATES I I mwzommmm F 558% 23PORES e TlME minutes & w #3:: 2:3: I
mm RA. EN UM T S PATENTEDHARZYIUYS SHEET 0F 6 2 W Y T" H a N l E N H ER V0 w n@@ W m 2 N 0 w M MW W m T? 2 N 2 l O S 2 7 O N mmzoammm mmomoowm I 6 I F TIME, MINUETS FIG-8 TIME, MINUTES mmzoammm mmomoumm 275 (HOLD) TEMP. "C
INVENTORS JOSEPH J KIRKLAND PAUL c, YATES PATEPITEDHARZYIHH SHEET 5 OF 6 O lllllllllllll M73202 M73895 i MZEMQE UZSMQEH R E m M58355 E D M c zmzm mozomm v W n B 5 M N O U 2 C M 2 X. o m M w m o 2 H B C R J zw5o2omm mmzolmmm 5968K -INVENTORS JOSEPH J. KIRKLAND PAUL C. YATES TIME minu fes ATTORNEY PATENIEDHARZYISH 3 722,1 1
SHEET 8 OF 6 F I G- 10 I% XE-6O SILICONE III 2 O 0 0) L11 c:
m 0.72% CHEMICALLY B ONDED g NITRILE a: O a I l l l I (I 300 260 220 I80 I40 I00 I I l I I6 I4 I2 IO 8 6 4 2 O TIME MINUTES I I I I IO0.0
WEIGHT, mg m :8 N L 03 l I l T., C( CORRECTED) INVENTORS JOSEPH J. KIRKLAND PAUL c. YATES BY f'd I ATTORNEY .prepolymerizing hydroxysilane presence of a strictly limited quantity of water. After CHROMATOGRAPHIC PACKING WITH CHEMICALLY BONDED ORGANIC STATIONARY PHASES BACKGROUND or THE INVENTION This invention relates to improved chromatographic packings in which organosilanes are chemically bonded to a substrate and polymerized to form a stationary organicphase.
A previous attempt tochemically bond a stationary phase to a substrate involved the esterification of siliceous chromatographic supports with alcohols. However, the resulting Si O C linkage was hydrolytically unstable and the product consisted of monomolecular films that only allow adsorptive, but not partition, interactions with the solute.
Further, polymolecular silicones have been reacted to chromatographic supports by employing two series of steps. In the first series, dimethyldichlorosilane or methyltrichlorosilane is bonded to the silica substrate. In the second series, organochlorosilanes are attached to the above methylchlorosilanes. Due to the 'use of highly reactive chlorosilanes in both series of steps, the extent of reaction in each series is difficult to control, which usually results in films of variable thickness. In addition, the first series of steps places methyl groups on the substrate surface which reduces the effective polarity of the packing. This clearly represents a detriment when polarity is desired. Additionally, the second series of steps does not permit the use :of volatile organochlorosiles, thus restricting the choice of resultant stationary phases. Further, the particular organochlorosilanes that would be required as starting reagents toplace certain functional (e.g., amino) groups on the. surface would be self-reactive and thus selfdestructive. Lastly, it was necessary,to deactivate the remaining active surface sites before chromatographic use. Deactivation leaves a silicate ester which has suffrcient thermal and hydrolytic unstability to cause bleed at the higher temperatures used in gas chromatography. I
Chemical bonding of silanes as coupling agents to silica-containing surfaces is known in the prior art where the surface is contacted with an aqueous solu tion of the coupling agent, and the water removed. The resulting bondedlayer lacks porosity, has uncontrollable thickness, and hence,'is unsuitable for chromatography, which must have both to allow for precise diffusion of the substances being chromatographed.
Thus it is an object of this invention to provide a chromatographic packing with an organic stationary phase chemically bonded directly to a silica-containing substrate with a bond that is hydrolytically and thermally stable. v
- It is a further object to provide a process for producing such a packing wherein the thickness and porosity of the resulting chemically-bonded stationary phase are controllable.
7 SUMMARY OFTHE INVENTION These and other objects are accomplished by reagents in the prepolymerization, the silane reagent is reacted to the surface of the substrate, and further polymerized to form the chemically-bonded stationary phase. The
silane reagent molecules have thegeneral formula wherein R is a hydroxyl or a monovalent aliphatic or aromatic hydrocarbon radical, and
R is a monovalent aliphatic or aromatic hydrocarbon. R or K, may contain atoms other than carbon and hydrogen. The bonded polymolecular stationary phase has arepeating unit with the formula wherein A is a monovalent aliphatic or aromatic hydrocarbon radical. The stationary phase is bonded to the polyvalent metaLcontaining substrate surface through an linkage, where M is the metal and is part of a repeating unit.-
By choice of R and (when not a hydroxyl) R the chemically bonded stationary phase may be produced with a variety of functional groups, resulting in chromatographic packing with widely diverse selectivity. The resulting packings may vary from extremely polar to non-polar according to the needs of the particular separation to be performed.
The thickness of the resulting stationary phase is controlled by controlling the quantities of starting materials. Thus, bonded stationary phase may be deposited that is controllably monomolecularly or polymolecularly thick. In particular, a polymolecular layer of predetermined thickness, which will allow for precise diffusions, may be bonded to the substrate.
Mixtures of the above starting compounds may be reacted to the surface and copolymerized to give blends for particular purposes. The compositions of these blends are determined by controlling the concentrations of initial reactants. g Y
A particularly .useful type of blend is one by which the degree ,of cross-linking in the bonded and polymerized stationary phase can be controlled. Greater concentrations of starting reagents in which R 'is a hydroxyl result in higher degree of cross-linking, which is particularly useful for gas chromatography (hereinafterreferred to as G.C.). On the other hand, greater concentrations of compounds with R being non-hydroxyl result in less cross-linking which is desired for liquid chromatography (hereinafter referred to as L.C. The extreme degrees of cross-linking are obtained by using either one of these (hydroxyl or non-hydroxyl) alone. I
, tion with a nitrile The use in L.C. of packings with the chemically bonded stationary phase eliminates the necessity for precolumns or presaturating the carrier with the stationary phase. Further, high column efficiencies are maintained because of the homogeneous distribution of the stationary phaseon the surface of the supports. This bonded stationary phase provides greater column stability and eliminates many problems associated with the loss of partitioning liquid during the operation of conventional liquid liquid chromatographic columns. G.C. substrates with the chemically bound liquid stationary phase show very low vapor pressure. Thus column life is extended and the level of noise in the detection system due to stationary phase .bleed.is minimal. These packings also show very high thermal stability as preferred for G.C.
BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a diagrammatical representation of a crosssection of a preferred chromatographic support material.
FIG. 2 is a schematic cross-section of a polymeric stationary phase chemically bonded to a substrate.
FIG. 3 shows the chemical structure of the polymeric stationary phase.
FIG. 4 is a part of the liquid chromatographic separation of sulfonamides using the present invention.
FIG. 5 compares liquid chromatographic HETP v. Carrier Velocity Plots of the present invention with the prior art.
FIG. 6 is a plot of the'liquid chromatographic separation of thiolhydroxamates using the present invention.
FIG. 7 is a plot of the liquid chromatographic separabonded phase column of the present invention.
FIG. 8 is a plot showing a programmed temperature gas chromatographic separation in an ether bondedphase of the present invention.
FIG. 9 compares chromatograms showing the selectivity in gas chromatography of the ether bondedphase of the present invention.
FIG. 10 is a plot showing the relative bleed rate of a nitrile stationarybonded-phase of the present invention as against a column of the prior art.
FIG. 1 l is a plot of a thermograviometric curve for a vention.
FIG. 12 is a plot of. gas chromatographic separation of aromatic hydrocarbons with a nitrile bondedphase.
DETAILED DESCRIPTIGN OF THE INVENTION Chromatographic packings may be prepared having chemically bonded organic stationary phases with'a variety of functional groups, resulting in widely diverse chromatographic selectivity. Bonded-phase packings may be prepared for gas and liquid chromatography on a variety of substrates. The composition of the substrate is not critical, except that its surface must be capable of chemically reacting with silanols. Silicacontaining substrates are preferred, although any polyvalent metal-containing substrate may be used where the valence of the metal is from-three'through five. Examples of useful substrates include diatomaceous earths, silica gel, glasses, sand, alu- V chemically bonded nitrile packing of the present inminosilicates', quartz, porous silica beads, and clays. Additionally, non-alkaline metal oxides, alumina,
thoria, titania, zirconia, and non-alkaline metals with an oxide skin may be utilized.
When the substrate is in the form of a support (i.e., particulate), the shape of the particles is not critical. Examples of shapes include rings, polyhedra, saddles, platelets, fibers, hollow tubes, rods, or cylinders. Spherical supports are preferred because of their regular and reproducible packing characteristics and ease and con- .veniencein handling.
The controlled surface porosity, support of FIG. 1 (described in U.S. Pat. No. 3,505,785 and sold under the trade name Zipax by E. I. du Pont de Nemours and Company, Wilmington, Del.) is a preferred embodiment of a support structure. It has an impervious core 11, preferably of glass or other ceramic material and a porous coating 15 made up of sequentially adsorbed monolayers 13 of microparticles. It consists of discrete spherical particles having a large number of superficial shallow pores l2 and no deep pores. It has regular and reproducible packing characteristics,' ease and convenience in handling, and desirable characteristics for high-speed, high-efficiency gas and liquid chromatography.
'In discussing substrates, the terms surface, surface area available surface, etc. refer to all surfaces which are accessible from the exterior of the substrate. In FIG. 1, for example, the surfaces within the pores-12 would be included in these terms. 7 I
It is often desirable for the support or. substrate surface to have a high initial population of metal-hydroxy, or preferably -SiOI-I groups. This is best accomplished by treating the surface with acid or base. The preferred procedure is to heat the support with concentrated nitric or hydrochloric acid on a steam bath for several hours. Excess acid or base should be removed from the surface by thorough washing before the support is dried for reaction with the silane reagents.
The reagents employed to produce the chemically bonded organic stationary phase are silanols having the formula where R and R are given above. They are preferably prepared from silicate esters with the formula where R and R5 are alkoxy, R is alkoxy or R and R is given above. 1
A list of commercially available reagents is shown in Table I. Table II gives other reagents which are not presentlyv known to be commercially available. Their structures encompass a variety of configurations. These may be synthesized according to the general techniques contained in Chemistry of the Silicones, by R. G. Rochow, John Wiley & Sons, New York, 2nd Ed. l.
TABLE I Reagent Formula 'y-Glycidoxypropyltrimethoxysilane (a, b)
- Mercaptopropyltrimethpxysilane (a) H S H1), S i (O C H); -y-Am1nopropyltriethoxysilane (a, c) NH1( CH1): S i (O CiH4):
[N 13- (aminoethyl)-v-amino-(2-methyl) propyl]-methyldimethoxysilane (b) H N(CH1)1NH CH C H (C Hz) C H1 i C Hz)i -y Methaeryloxypropyltrimethpxysilane (a, b) CH\ C C H 0 O (C H1); S i 0 CH1):
Methyltriethoxysilane (a, c).. CH Si(O C1115);
Phenyltriethoxysilane (a, c) Col I5 S i (0 02115);
Vinyltriethoxysilane (a, c) C H; Si(0 C2H5)3 Amyltr ethoxysilane (a) C H 1Si(O CzH5 a Ethyltnethoxysilane (a) C H Si(OCzH5)3.
Methyltrimethoxysilane (b). CHJSI(O CH3);
Phenyltrimethoxysilane (b) l CH Si(0 CH3);
Diphenyldiethoxysilane (b) (Ca CH2=CHSI(OOCCH )3 3-chloropropyl-trimethoxysilane (b Cl (CH2); Si(O CH3): N-(N-methoxycarbonylmethyl-B-ethylan1ino)-'y-aminopr0pyltrimethoxysilane (b) CH O 0 C CH; C HzNH C HmNH C Hz)a- S i O C Ha); B-Cyanoethyl-triethoxysilane (c) CH (C Hz): S i (O C HzHsJa fl-Cyanoethyl-methyldiethoxysilane (c) CH(CH2)zSi-( C2H5):
(a) Available from Union Carbide Corporation, 270 Park Avenue, New York, N.Y. 10017. (b) Available from Dow-Corning Corporation. Midland, Michigan. (0) Available from General Electric, Silicone Products Department, Waterford, New York, 12188.
TABLE II Reagent Formula 'y-(aminocarbonyl)propyl-triethoxysilane HzNO C(CH2)a C2 s)a fl-nitroethyl-trieth0xysilane O NCH CH S1 (O C H 2 s); (a,v-dihydroxypropyl)-methyldimethoxysilane HO CH C Hz- CH (O H) Sl i( C a):
M ethylsulfinylmethyl-triethoxysilane C H3 S 0 CH: S i (O 0211:); Perfluoropropyl-trimethoxysilane F3C C F2C Fz-S 1 0 CH3): p-Sulfamoylphenyl-methyldimethoxysilane NHzSO1-CiH4- $1M) CH3 2 p-(Methoxycarbonyl) phenyl-trimethoxysilanc C H 0 CCsH4' i (0 CHa): L-(+)-D-[5-(methoxycarbonyl)-5-aminopent-l-yl-sulfamoyl]-phenyltrimeth oxysilane C H 0 0 C C H (NH (C HzhNHS O 2 C HiSi O C Ha); Methylsulionylmethyl-triethoxysilane CH3S0zCH2Sl (0 C2 5);
A silicate ester, when used as the reagent, must first more than about a lOO-fold equivalent excess. One
' be hydrolyzed to the silanol which then engages in equivalent to a -fold equivalent excess generally sufprepolymerization, reaction with the substrate surface, fices. A very large excess of water inhibits the suband subsequent polymerization. Factors which affect I sequent partial polymerization. The hydrolysis is northis hydrolysis include: mally run at elevated temperatures (preferably the 50 boiling point of the non-aqueous solvent) for a period 1. high or low pH (b or id of about 30 minutes to several hours.
2. presence of soluble salts of certain metals such as The Operation h e y Performed longer e" copper, lead, zinc, and iron, and required for hydrolysis, 1n order to effect partial 3. temperature. polymerization. If necessary for the partial polymeriza- In general, the silane ester (except for aminosilanes), mm, the Water Content and P 0f the Solution y be is hydrolyzed under acidic conditions preferably at adjustee, e latterto a value of fro 3 through 6 by elevated temperatures. For the subsequent h i acehe or some other catalyst: prepolymerization, the hydrolysis is preferably carried Pamal P y f P h sllahee before eafihon out by refluxingthe reagent in a non-aqueous solvent to the substrate 15 essemlal h produclng a m ly containing several molar excesses of water with an acid bonded Stational'y Phase haymg the requll'ed thlckness catalyst. The solvent in addition to having some soluand porosity. initiation of polymerization may be deterbility for water should be non-reactive with the reagent mmed y p e g a Small amount of the -e f water or the (acid or base) catalyst. It should boil in the ing luti n In Water. The appearance of cloudiness mrange of about 25 to 300C, preferably 50 to 200C. dicates that the prepolymerization, having progressed Ethers such as tetrahydrofuran and dioxane have to the point where at least part of the silane reagent is worked satisfactorily. insoluble in water, is sufficient. Contrariwise, this The amount of water added to the non-aqueous solprepolymerization should not progress so far as to apvent for the hydrolysis should be at least one-third of preciably increase the viscosity of the silane-containing the equivalent of the silane reagent and need not be solution.
The reaction of the prepolymerized silane to the substrate, followed by the final polymerization, is carried out at temperatures from about 50 to 350C, a range of lO-250C. being' preferred. Times required for this step vary from a few minutes to several hours, but usually l-3 hours is adequate for the preferred temperature range.
Other procedures in which silane ester reagents may be prepolymerized and reacted to the chromatographic substrates include:
1. Preparing an acidic (pH 3 to 5) aqueous solution of the reagent whereby it hydrolyzes to the corresponding silanol compound. A suitable chromatographic substrate is soaked in the solution and excess liquid filtered off. The mixture is first heated to a temperature below 100C. to initiate polymerization, and then further heated to carry out the reaction to the substrate surface and to complete polymerization to form the polymeric organic phase.
2. The silane ester reagent is deposited on the chromatographic substrate by evaporation from a suitable volatile solvent. The reagent is then hydrolyzed and prepolymerized by passing moist air or steam through the coated support. The reaction with the surface and polymerization is then carried out by heating.
3. The silicate ester reagent contained in a volatile unreactive solvent such as tetrahydrofuran is hydrolyzed and prepolymerized by adding aqueous hydrochloric acid and refluxing the mixture. The substrate is added to this solution. The volatile organic solvent is then removed by low temperature vacuum distillation. A large excess of toluene, xylene or other suita ble solvent is added to the wet powder and the watersolvent azeotrope is continuously removed until the reaction and polymerization is complete.
4. Chemical means may be used to remove the water which is the driving force in these reactions. The addition of reagents that readily react with water, such as dimethoxypropane, will effect the desired prepolymerization, the reaction to the substrate surface, and the subsequent polymerization.
A final extraction step may be used to remove any silane not bonded to the substrate. The solvents used in this step should have some solubility for the unbonded polymer which insures that the polymer left on the substrate is indeed chemically bonded thereto.
Mixtures of different types of silane molecules may also be used in the prepolymerization, reaction, and polymerization steps. In this manner, bonded stationary phases having blends of various properties suitable for particular separations may be developed.
A particularly useful type of blend" is the one controlling the extent of cross-linking in the polymerization process. Packings for gas chromatography generally require a highly cross-linked structure, in order for the polymer to have optimum stability at high temperatures. Conversely, packings for liquid chromatography should have a less cross-linked polymeric phase. This lower order of cross-linking permits better penetration of the carrier, with subsequent improved 1 accessibility of the solute into the solvated polymeric structure. The chemically bonded stationary phases also possess unique chemical and physical properties because of theirability to swell in certain solvents and to form gelatinous, ordered structures which function as selective stationary gel phases.
to the usual trialkoxysilicate, R Si (OR') reagents. The addition of dialkoxysilicates to the reaction significantly reduces the cross-linking, since the other group (R") attached to the silicon atom does not engage in the polymerization. The addition of the modifying functional group R also may impart desirable physical and chemical properties to the bonded phase.
As shown in the examples below, the reaction of the silicate reagents to the substrate surface proceeds very close to quantitatively. Thus, by controlling the initial amounts of reagents, it is possible to determined the thickness of the resulting film of chemically bonded stationary phase upon the substrate surface. A monolayer film may be produced, for example, where it is desired to effect selective adsorption. However,'in the usual partition chromatography, a substrate with a polymolecular layer is utilized.
In the latter case the polymeric stationary phase is basically a three-dimensional porous network of repetitive, functional groups of the silane structure, chemically bonded to the support surface by an A schematic cross-section representation of the porous polymer structure is shown in FIG. 2 where the substrate is indicated at 20, the chemically bonded stationary phase at 21, a portion of polymer at 22, and the pores at 23. FIG. 3 gives an exploded schematic representation of the claimed structure of a piece of polymer 22.
This chemically-bonded organic phase should have an average thickness of 30 A to 10,000 A, with 502,000 A being preferred. This preferred range encompasses sufficient thickness to ensure the desired chromatographic interactions without being so large (thick) so as to greatly affect column efficiency as a result of resistance to mass transfer of the solute within the polymeric phase. The bonded stationary phase should have about 20 to 95 percent of its volume consisting of pores, with a range of 35 to percent preferred. The polymer should be sufiiciently porous to allow penetration by the carrier phase and the sample components, while having sufficient cross-linking to ensure that the desired mechanical and chemical stability will be obtained.
Usually in chromatography, the substrate is a particulate support. These particles are coated with the stationary phase and packed into columns. In the present invention, this stationary phase is chemically bonded to the support particles, which are then packed into columns in the usual way. However, the present invention is also useful in other forms of chromatography. The stationary phase may be bonded to a substrate of silica gel. Also, where a capillary tube without p a particulate support is used for the column, a stationa- 'ry phase may be bonded directly onto the column wall diatomaceous earth with one of the bonded polymers. This chromatographically active material is coated in thin layers on plates in the usual manner. The plates are usually glass and flat, but other materials and shapes may be used. Mixtures of compounds are then spotted on these thin layer plates and developed, using the usual procedures for liquidfadsorption thin layer chromatography. This approach permits the thin layer chromatography of relatively insoluble compounds to be carried out with polar solvents in a liquid-liquid partitioning mode. The techniques of liquid-liquid thin layer chromatography are generally difficult, and chromatographic separations of sparingly soluble compounds by the liquid-liquid partition approach is generally impossible without the use of a chemically bound stationary phase. I v v In liquidchromatography, use of packings with bonded stationary phases provides additional operational advantages over columns 1 with conventional mechanically held liquid phases. Peaks may bej-collected and the constituent readily isolated for further characterization by simply evaporating the volatile carrier system. This is possible because the sample is not contaminated by a less volatile stationary phase which I is usually present in carrier-saturation amounts in a conventional liquid-liquid system.'Further, it is practical to recycle the effluent fromthe detector backinto the reservoir for further use, without any treatment, since the carrier need not be equilibrated with a stationary phase.
Packings with chemically-bound stationary phases column. Thus, it is possible to chromatograph a sample having components with widely varying partition ratios in a single chromatographic run in a manner that assures that all of the sample constituents are eluted;
' Regenerationof the bonded-phase packing after a gradient elution run is accomplished rapidly.
EXAMPLE 1 Preparation of Ether/Zipax" Packing for Liquid Chromatography Twenty-five grams of 40 microns Zipax and 150 ml. of concentrated nitric acid are placed in a 250 ml. beaker and heated on a steam bath for 2hours with occasional stirring. The resulting support is. washed free of acid by repeatedly slurrying with distilled water. The
material is then air-dried on a Buchner sintered glass vacuum filter and heated for l hour at 125C. in a circulating air oven.
To a 100 ml. round bottom flask is added 25 ml. of I fresh reagent grade tetrahydrofuran (Fisher Scientific Co.), 6.65 ml. of a 50 mg./ml. tetrahydrofuran solution of Dow Corning Z-6040 ('y-glycidoxypropyltrimethoxysilane) and 0.75 ml. of 0.01N hydrochloric acid. This mixture is refluxed gently under a condenser for 30 minutes. This hydrolysis mixture is then added to the 25 grams of acid-treated Zipax from above, contained in a shallow evaporating dish. The volatile solvent is removed while stirring the mixture under a slow stream of nitrogen. The resulting dry powder is then heated for 1 hour at 125C. in a circulating air oven. When cooled, the mixture is then transferred to a 500 ml. round bottom flask containing 150 ml. of dioxane.
1 This mixture is reflux ed with gentle stirring for 30 solvent is then decanted, and another 150 ml. of absolute methanol added and again the mixture refluxed for 10 minutes. The solvent is decanted and the resulting support air dried on a sintered glass Buchner funnel. The support is. then dried in a circulating air oven for 30 minutes at C.
Elemental analysis of the resulting ether bondedphase carried out on an F & M Scientific Co. Model C, H & N analyzer showed 0.35, 0.33 percent carbon, and 0.062, 0,63 percent'hydrogen. Assuming the reaction depicted below, elemental data show that 0.77
percent polymer was present on the Zipaxf representing 88 percent of theoretical.
' g 0 (onno si-(o11, ,o cmen-4 m unomm on A s1-on Ho s1 s1 cm o uincno1n -rno I n Si-0H i O 1 I -SiO-Si(CH2)a-OCHz-+CHQCHQ k 1 -mo i, l
-S|1OH The porosity of the polymeric stationaryphase itself is evidenced by surface area measurementsmade on Zipax coated. with the following amounts of the ether" bonded-phase.
Material Surf. Area, mlg. Uncoated Zipax" i 1.0 I 0.38 ether" 0. l. I 6% ether" 0.19 1.65% ether 0.42
The rapid decrease in surface area when Zipax is coated with a small amount of polymer indicates that initially, the polymer reacts in the pores between the microparticles. The surface area then rises as the amount of polymer bonded to the support increases clearly showing that the bonded stationary phase is indeed porous. Also, the stationary phase is not extractedby boiling organic'solvents which would normally have significant'solubility for the polymer indicating that the polymer has actually reacted with the Zipax" surface.
An illustrative chromatographic separation using this -ether/BZipax boned-phase packing is shown in Fl( 4. This mixture of aromatic sulfonamides was separated in-about 6.5 minutes with a 1 meter X 2.1 mm i.d., column, using a carrier of 5 percent chloroform in hexane at 27C., a flow of 2.66 cc./min., a column input pressure of .860 psi, and an ultraviolet detector sensitivity of 0.05 absorbance, full-scale. The-apparatus employed wasdescribed in an article :by Joseph J. Kirkland in Journal of Chromatograph Science 7, '7 (1969).
The ether bonded-phase column used to separate these sulfonamides is unafi'ected'by thechloroform in the carrier. Had this separation been carried out with a conventional system, the polar solvent would have had appreciable solubility for the stationary liquid, necessitating presaturation of the carrier by'the stationary phase and a pre-equilibrating column containing packing with the stationary phase. None of these precautions were required with a bonded-phase column.
' The efficiency of the dry-packed ether bondedphase column is nearly equivalent to that of comparable liquid-liquid chromatographicv columns made with -mechanically held stationary phases. FIG. 5 shows I comparative HETP (height equivalent to a theoretical plate), versus linear carrier velocity plots for. two
I columns made from the same original 325-400 mes Zipax supports. One column embodies mechanicallyheld I percent Bfi-oxydipropionitrile as the stationary phase, while the other consists of a' 0.94 percent ether bonded-phase. HETP data .for the bonded I phase column is slightly higher than that for the conventional liquid-liquid column for two solutes of which acetophenone is essentially unretarded and benzyl alcohol is moderately retained.
After obtaining the original HETP data, the ether bonded-phase column was operated at input pressures up to5,000 psi and carrier linear velocities up to 40 cm./sec. Even under these very drastic conditions, the column showed little degradation, as evidenced by the especially'marked points 25 in the FIG. 5 plot. Operation of conventional liquid-liquid chromatographic columns at carriervelocities of 40 cm./sec. is very difficult, because of the loss of mechanically held stationary phase.
The uniqueness of the etherfbonded-phase for liquid chromatographic separations is further illustrated in FIG. 6. This synthetic mixture of the thiolhydroxamates shown was separated in a 1 meter X 2:1 mm. i.d., column of the 325-400 mesh Zipax containing 0.94 percent ether bonded-phase, the column being operated at 27C., with a carrier of 1.0 percent chloroform in hexane. These compounds are difficult to separate with conventional liquid-liquid chromatographic systems because of their polyfunc tionality and their, high polarity. They are strongly retained on most conventional stationary phases, and
require a polar carrier to elute them in a reasonable time. The solubility vof the stationary phase in this rapidly moving polar carrier causes extreme difficulty in maintaining a column of constant performance. No
such difficulties are experienced with the ether bonded-phase packing, and carriers havingany desired polarity can be used to chromatograph highly polar compounds.
EXAMPLE 2 Preparation of B-Cyanoethyl/Zypax Bonded-Phase Twenty-five milliliters of reagent grade dioxane (Special Services, Du Pont Experimental Station), 5.5 ml. of mg./ml. General Electric XC-37l 1 (B- cyanoethyltriethoxysilane) in dioxane, and 2 ml. of 0.1N hydrochloric acid are combined in a 250 ml. round bottom flask and refluxed for 1 hour under a condenser: The resulting hydrolyzed mixture is poured onto 25 grams of 400 mesh Zipax (acid-washed as described above), and the solvent removed while continuously stirring under warm air from a heat gun. The resulting dry powder is heated for 1 hour at 1509C. in a circulating air oven. The treated material is transferred to'a'500 ml. roundbottom flask and refluxed with 200 ml. of absolute methanol for 15 minutes. The slightly cloudy solvent is decanted ancl the support again refluxed with 200 ml. of fresh absolute methanol for 15 minutes. The clear solvent is decanted and the support again refluxed for 15 minutes with a fresh 200 ml. portion of absolute methanol. The clear solvent is decanted, the treated support air dried on a sintered glass Buchner filter funnel, and then heated in a circulating air oven for 30 minutes at C.
'inconventional By elemental analysis, the resulting bonded-phase showed 0.23, 0.232 percent carbon, 0.032, 0.034 percent hydrogen, and 0.087, 0.089 percent nitrogen. These data indicate that the packing material contained 0.83 percent silicone polymer (calculated on the structure proposed below), or 90 percent of theoretiabsolute methanol. After the third extraction, the material is filtered off on a sintered glass Buchner filter funnel and air-dried. The treated support is then dried to 150C. for 30 minutes in a circulating air oven.
cal. Nitrogen absorption (flow method) showed that the surface area of this material was 0.44 m /g.
' ---S:iO- Si-CHaCHzCN compounds which can readily hydrogen-bond. Compounds with acidic -'NH, groups areparticularly retarded, and certain substituted phenolics, such as 4- acetamidophenol, are also highly retained.
.The a-cyanoacetanilide peak in FIG. 7 has a HETP of 1.89 mm. at a flowrate of 4.35 cc./min., which corresponds to 8.0 theoretical plates/sec. (4.8 effective plates/sec). When operated at a carrier linear velocity of 1 cm./sec. or less, this column demonstrates HETP of less than 1 mm. for similar solutes. v
The efficiency of the bonded-phase liquid chromatographic columns depends on the type and polarity of the carrier used. Columns with nitrile bonded-phase packing show poor efficiency with hexane as carrier. However, as' the polarity of the carrieris increased, so does the efficiency of the column .(equal solute partition ratios). s
EXAMPLE 3 v Preparation of Ester/ZipaxBonded-Phase To a 100 ml. round-bottom flask is added ml. of reagent grade dioxane, 2 ml. ofO. l N'hydrochloric acid, and 4 ml. of a 70 mg ./ml. solution of Union Carbide Silane A474 ('y methacryloxy-propyltrimethoxysilane) in dioxane. The resulting mixture is refluxed gently for 1 hour under a condenser. This hydrolysis mixture is then added to 20 grams of 400 mesh- Zipax contained in a shallow evaporating dish, and the solvent removed while gently stirring the mixture under warm air from a heat gun. The resulting mixture is then heatedfor 1 hour at 150C. in a circulating air oven. The treated support is then transferred to a 500 ml. round-bottom flask which contains 200 ml. of absolute methanol. The mixture is refluxed for l5 minutes, the
repeated two more times with fresh 200ml. portions of Elemental analysis of the ester bonded-phase showed carbon 0.443 percent, hydrogen 0.077 percent, indicating that l.07 percent (96 percent of theory by carbon. analysis) of the polymer phase below was present on the support. The surface'area of this product by nitrogen adsorption (flow method) was 0.52 m /g.
S iO- Si-(CHzh-O 0 c 011;):0112
H i v I g n EXAMPLE4 Preparation of Ether Bonded-Phase I v for Gas Chromatography Fifty grams of 100-140 mesh Zipax" (nitrogen surface area 0.46 r n lg.) is heated in a muffle furnace at 725C. for 1 hour, then cooled in a desiccator. Thev resulting material is then treated with nitric acid in the manner described in Example l, above.
, To a 100 ml. round-bottom flask is added 20 ml. of reagent grade dioxane, 10 ml. of I00 mg./ml. Dow Corning Z6040 (y-glycidoxypropyltrimethoxysilane) and 5 ml. of 0.1N hydrochloric acid. The mixture is refluxed under a condenser for 1 hour and then added to the 100440 mesh acid-treated-Zipax described above. The volatile solvent is removed from the soluclear solvent decanted, andthis'extractive technique tion while stirring the mixture under warm air from a heat gun. The resulting material is heated at 150C. for
one hour. in a circulating air oven. The support is then placed in a 500 ml. round-bottom flask with 200 ml; of
absolute-methanol and refluxed with gentle agitation for 15 minutes. The solvent isfdecanted and the extraction carried out twice more with fresh 200 ml. portions of absolute methanol. The thrice-extracted.material is filtered off onto a sintered glass Buchner filter funnel,
air-dried and then heated in a circulating air oven at 150C. for 30 minutes. Elemental analysis of the sam ple showed 0.50 percent carbon, corresponding to 1.1
percent polymer on the Zipax" surface, or 82 percent of theoretical.
Use of the -ether bonded-phase packing for a gas chromatographic separation is shown in FIG. 8. This separation was carried out on a 1 meter X A inch o.d., inch i.d. glass column, using helium carrier gas flowrate of 50 cc./min. andla flame ionization detector sensitivity of l X 10* amp. full-scale, with a Beckman GC-4 gas chromatograph. 0.2 Microliters of the test mixture was injected at an initial column temperature of C., and the temperature of the column was continuously increased at 133C. per minute. The versatility of this column permits the separation of both low boiling compounds (hexane) and very high boiling 1 compounds (di-normal butyl-phthalate). The bleed of 'thisfether bonded-phase column at high temperatures is minimal, as evidenced by the slight increase in baseline of the chromatogram approaching 300C. for
this uncompensated single column system.
The unique selectivity of the chemically bonded polymeric ether packing for gas chromatographic separations is illustrated in FIG. 9. The upper curve shows the separation of a mixture of aliphatic hydrocarbons and 4-bromobiphenyl on a column of 1.1 percent bonded ether on Zipax" support operated at 275C. The lower curve is the same mixture chromatographed under identical conditions on a 1.0 percent Carboxwax M (aliphatic polyether) column, except that the temperature was 200C. The separation factors were very high for these compounds on the ether bonded-phase column operated at- 275C., compared to those on Carbowax 20M at 200C. A similar pattern is apparent for the aromatic compound, 4-bromobiphenyl; its retention time on the ether" column at 275C. is 1.4 minutes, as compared to 0.25
min. for the Carbowax 20M column at the same temperature.
EXAMPLE 5 Preparation of BCyanoethyl/Zipax Bonded-phase for Gas Chromatography XE-60 packing cannot be used to this temperature thermogravimetric plot shown in FIG. 11. These data were obtained on a Du Pont- Model 950 Thermogravimetric Analyzer (E. I. du Pont de Nemours &
To a 100 ml. round-bottom flask is added 25 ml of reagentgrade dioxane, 2 ml. of 0.1N hydrochloric acid, and 5.0 ml. of a 70-mg./ml. solution of General Electric XC-37l l (B-cyanoethyltriethoxysilane) in dioxane; This mixture is refluxed under a condenser for .1 hour and is then added to a shallow evaporating dish containing 25 g. of l00-l20 mesh acid-treated Zipax. The solvent is removed from the mixture by stirring under a stream of warm air from a heat gun. The mixture is then heatedat 150C. for one hour in a circulating air oven. The resulting material is then extracted three times by refluxing in 300 ml. volumes of absolute methanol as described in earlier examples. Elemental analysis of the final'material showed 0.205, 0,205 percent' carbon, 0.025, 0.020 percent hydrogen, and 0.076, 0.071 percent nitrogen, indicating 0.72 percent polymer on the surface of the Zipax, or 86 percent of v theory.
The very high temperature stability of the B- cyanoethyl bonded-phase packing is illustrated in FIG. 10. This figure shows thebackground current of a flame ionization detector operated at l X 10 amp., full-scale, when a V4 inch o.d. Vs inch i.d. glass column of fl-cyanoethyl bonded-phase was programmed from 100 to'. 300C. On the same plot is the background current obtained under the same conditions (slightly displaced upward on the scale to show differences) for a similar column of 1 percent General Electric XE-60 (25 percent cyanoethyl, methyl silicon polymer), mechanically dispersed on 100-120 mesh Zipax support.- vBoth of these columns were conditioned at 250C. for 16 hours before this test. While the bonded nitrile packing shows essentially no fbleed at 275C.', the conventional XE-60 column starts to show significant background at about 225C. The nitrile column is stable to at least 300C., while the Co., Inc., Wilmington, Del.) operated at a heating rate of 10C. per minute, using a flow of 85 cc'./min. of air. The curve shows the weight loss on a 100 mg. sample of the nitrile material as a function of temperature; This study indicates that the organic polymeric phase is essentially stable to about 325C, then begins to degrade slowly at higher temperatures.
The level of column bleed at 300C. for the ether and nitrile bonded-phase materials is compared in Table III with conventional mechanically-held liquid phases. Zipax was used as the support in all measurements, and all columns were conditioned at 250C. for 16 hours prior to taking themeasurements,
except Carbowax 20M, which was conditioned at 200C. The selectivity. of the ether bonded-phase packing can' be roughly compared to the aliphatic polyether, Carbowax 20M. The data in Table III demonstrate the superior thermal stability of both Carbowax 20M and the ether bonded-phase on Zipax support. A similar comparison is made between the bonded nitrilelmaterial and silicone XE-60, a polymer containing 25 percent nitrile grouping s. The superior thermal stability of the bonded polymer is apparent. An even lower. level of column bleed occurs at a 'lower polymer concentration, as indicated by the data for the 0. l 2 percent nitrile polymer column.
TABLE in BLEED RATES OF GAS CHROMATOGRAPHIC COLUMNS Support lOO-l40 mesh Zipax Weight Percent "Bleed" Rate at Stationary Phase Loading (Amperes, full-scale) Carbowax" 20M 1.0 5 X l0- Ether" Bonded-phase 1.1 7 X 10" XE- 60 Silicone 1.0 2 X 10" Nitrile" Bonded-phase 0.72 l X 10" Niti-ile Bonded-phase 0.12 l X 10' matography are large. This characteristic is a function of the high polarity of the polymeric phase, and may be advantageous for carrying out certain selective separations. FIG. 12 shows the separation of a mixture of aromatic hydrocarbons carried out on a column containing only 0.12 percent nitrile bonded phase on Zipax. After sample injection, the column was held at 25C. for 1 minute, then programmed at 15C./min. to C.
17 The stability of the bonded-phase packings at high temperatures makes it possible for chromatographic separations to be carried out over wide'ranges in temperature without changes occurring to the column.
. With the use of the present invention, it is possible to prepare chromatographic phases of very high polarity whichat high temperatures demonstrate a stability previously obtained only, with nonpolar silicone stationary 1 phases (polydimethylsiloxane,
EXAMPLE 6 Ion Exchange Bonded-Phase for Liquid Chromatography by passing concentrated nitric acid through the tubing while heating over a steam bath. The capillary is then thoroughly washed with distilled water to-eliminate all acid, rinsed with reagent grade acetone and dried with dry nitrogen. About 50 ml. of a 5 percent (by weight) solution of Union Carbide Silane A-16 (amyltriethox ysilane) is passed through the capillary, dry nitrogen I connected to the tubing, and the excess solution removed by the pressure of the gas. The flow of dry nitrogen is continued through the capillary .until all of the excess solvent has been evaporated, leaving a thin I film of A-16 onthe interior surface of the glass. A
acetic acid. A vacuum (water purnp)' is repeatedly 1 pulled on the solution to degas the support thoroughly and allow the solution to completely wet the support surface. The mixture is transferred to a sintered glass I Buchnerfilter funnel and the excess'solution filtered off. The moist bed is transferred to 'an evaporating dish and heated at 125C. forl hour'in a circulating air oven. The resulting sample is refluxed three times with .fresh 200 ml. portionsof absolute methanol, each time decanting the. solvent after the treatment. The ex;
tract ed beads are filtered off on a sintered glass stream of moist air (relative humidity of about 85 percent) is then passed through the capillary until the silane ester is completely hydrolyzed, as evidenced by no more ethanol being evolved from the tubing. The capillary is then placed in a 110C. oven and a stream of dry nitrogen slowly passed through the tubing for several hours.
capillary bondedephase column is particularly useful for separating complex mixtures of aliphatic and substituted aromatic hydrocarbons.
EXAMPLES 8-12 C iiven in Table IV are a number of bonded-phase I chromatographic packings prepared bythe techniques and from the reagents shown. Also given" are the applications for which these systems'may' be used.
i Percent polymer I by Application of permaphasc Example Support Reagent weight packing I 8 Chromosorb" W, 100-200 mesh (Johns- Plienyltricthoxysilane 5.0 High temperature gas chromatography. V
Mansville Corp, diatomaceous earth). 9 Silicagel,b;744 (Davidson Chemical 00., fl-(3f4-epoxycyclohexyl)-ethyldirnethoxy-.. 10.0 Adsorption-partition liquid chromatog- Type 62 si ane. rap y. 10 staiinless steel capillary 1/16 o.d., 0.010 Dimethyldiethoxysilane Capillary gas chromatography. 11 Textured" glass beads 44-63u (Corning 3-chloropropyltrimethoxysilane 0.75 Partition liquid chromatography.
Glass 12 "Zipax (E. I. du Pont de Nemours'& L-(+)-p-[5-(methoxycarbonyD-fi-amino- 1.0 Liquid chromatographic separation of 00.). pent-l-yl-sullamoyll-phenyloptically active isomers. i trimethoxysllane. 13 Silica gel, 15-10;; (Camag") Gnfinma-glycydoxypropyltrlmethoxy- 10.0 Llqlllfil. partition thin layer chromatogsiane. I rap y.
' Approximately 0.5;. film.
Buchner funnel, air-dried, and then heated ina circulating air oven at 125C. for 30 minutes.
This weak anion exchange packing can be used to separate a wide variety of acidic compounds, or other materials which are retained on this basic chromatographic medium. The amino functionality can'also be quaternized to a strongly basic tetraalkylammonium derivation by well-known organic reactions. The quaternized form is a useful strong anion exchanger.
EXAMPLE 7 Bonded-Phase for Capillary Gas Chromatography I I A 100 meter 0.01 inch i.'cl. glass capillary is cleaned wherein A is O or amonovalent aliphatic or aromatic hydrocarbon radical and R is a monovalent aliphatic or aromatic hydrocarbon radical,
said metal of said substrate having a valence of 3 ,5, said stationary phase being chemically'bonded to the surface of said substrate by an linkage, wherein M is said polyvalent metal and wherein A is O- or a monovalent aliphatic or aromatic hydrocarbon radical and R is a monovalent or aliphaticor aromatic hydrocarbon radical,
said metal of said substrate having a valence of 35, said stationary phase being chemically bonded to the surface of said substrate by an linkage, wherein M is said polyvalent metal and is part of one of said repeating units of said stationary phase.
3. An apparatus for use in chromatographic separations comprising a resolving zone through which,
materials to be separated are passed, said resolving zone comprising a packing having a polyvalent metalcontaining substrate and a stationary phasehaving an average thickness of about 3.0 A to 10,000 A, said stationary phase comprising a'porous polymer having the repeating unit of the formula 4 7 wherein A is -O or a monovalent aliphatic or aromatic hydrocarbon radical and R is a monovalent aliphatic or aromatic hydrocarbon radical, I
said metal of said substrate having a valence. of 3-5, said stationary phase being chemically bonded to the surface of said substrate by an linkage, wherein M is said polyvalent metal and is part of one of said repeating units of said stationary phase, and said polymer comprising 5 to 80 percent of the volume of said stationary phase.
4. The apparatus of claim 3 wherein said metal is silicon.
5. The apparatus of claim 3 wherein A is O-.
6. The apparatus of claim 3 wherein said A is a monovalent aliphatic or aromatic hydrocarbon radical.
7. The apparatus of claim 3 wherein said stationary phase comprises at least two copolymerized portions, A
in the first of said portions being O-, and said A in the second of said portions being an aliphatic or aromatic hydrocarbon.
8. The apparatus of claim 3 wherein said packing is.
different in different parts of said resolving zone.
9. The apparatus of claim 3 wherein said resolving zone is disposed within a column.
' l0. The apparatus of claim 3wherein said resolving zone comprises a thin layer upon a surface.
11. An improved process for performing chromato graphic separations comprising:
a. placing the material to be separated in a carrier fluid;
b. contacting said material and said carrier fluid wit a packing having a polyvalent metal-containing substrate and a stationary phase having an average thickness of about from 30 A to 10,000 A, said stationary phase comprising a porous polymer having the repeating unit of the formula wherein A is --O- or a monovalent aliphatic or aromatic hydrocarbon radical and R is a monovalent or aliphatic or aromatic hydrocarbon radical,
said metal of said substrate having a valence of 3.5,
- said stationary phase being chemically bonded to the surface of said substrate by an M 0s iv linkage, wherein, M is said polyvalent metal and is part of one of said repeating units of said stationary phase, and said polymer Comprising about to 80 per cent of the volume of said stationary phase.
12. The process of claim 11 wherein said metal is silicon. v
13. The process of claim 11 wherein A is -O-.
14. The process of claim 11 wherein A is a. monovalent aliphatic or aromatic hydrocarbon radical. v
15. The process of claimflll wherein. said packing comprises at least two copolyrneriied portions, A inthe first of said portions being O, and A in the second of said portions being a monovalent aliphatic or aro- 17. The process of claim 11 wherein said resolving zone is disposed within a column.
18. The process of claim 11 wherein packing comprises a thin layer upon a surface.