Silver Chloride Disk Technique for Infrared Spectra of Aqueous Polymer Suspensions Richard K. Metzler, Research Division, Weyerhaeuser Co., Longview, Wash.
PPLICATION
of
aqueous
polymer
A suspensions to potassium bromide
pressed disks for preparation of qualitative infrared spectra is sometimes complicated by the water solubility of the disk. Water insoluble silver chloride or Trtran plates (Eastman Kodak Co.) are expensive and are time-consuming to maintain in perfect condition, especially when it is desirable to cure the polymer on the plate. The use of silver chloride windows is reported in the literature ( 1 , I, 6) and special techniques using silver chloride have been published (3-5, '7, 8 ) . Many of the inherent difficulties of using and maintaining silver chloride for infrared spectrometry can be eliminated by the preparation of low cost, disposable pressed disks from powdered silver chloride using the type of die commonly employed for preparation of potassium bromide pellets. A spectrum may be prepared directly from a wet film of an aqueous suspension applied to the disk, or from a film dried on the disk. The choice depends upon the speed required in obtaining the spectrum and the interpretation that is to be gained.
minutes in a vacuum oven, the spectrum was rerun. All spectral curves were prepared on a Perkin-Elmer Model 21 double-beam infrared spectrophotometer, with use of a grating type variable beam attenuator (Barnes Engineering
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EXPERIMENTAL
Reagent grade powdered silver chloride, screened through a 60-mesh Tyler sieve was dried in a vacuum oven for 48 hours a t 80" C. A paper retaining ring (Spex Industries, Inc.) was placed inside a 13-mm. die and about 300 mg. of powder was spread on top of the ring. The die was centered in a 20-ton hydraulic press and evacuated for one minute while under one-ton gauge pressure. The disk was then pressed a t 12.5 tons gauge pressure. At a somewhat higher cost suitable disks were also prepared from 10-mm. squares cut from a silver chloride pressed plate (Barnes Engineering Co., ATR-SP-1) normally used for preparing attenuated total reflectance spectra. The corners of the square were cut off to permit insertion into the die. A11 parts of the die that come in coiltact with silver chloride should be kept highly polished with crocus cloth. These parts must also be kept clean and d r y to avoid corrosion and to prevent the disk from sticking to the metal surfaces. The silver chloride must be protected from light a t all times to minimize discoloration. Transmittance spectra were first obtained on wet polymer films applied to a silver chloride disk, or in the case of less viscous resins, sandwiched between two disks. Then, after curing the sample on a disk a t 80' C. for 30 2378
ANALYTICAL CHEMISTRY
Co., BA-1) for reference beam compensation. A slit program of 927 was used with gain 5.6, response 1, suppression 2, and speed of 3 microns per minute with recorder chart scale of 2 em. per micron.
Figure 1
.
WAVELENGTH-
MICRONS
Spectra of phenol-resorcinol-formaldehyde resin
A. Dry.
6. 45% woter solution between two AgCl disks
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Figure 2. A. Dry.
B.
Spectra of polyamide resin
Wet film cart from 4970 water solution on single AgCl disk
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DISCUSSION
The silver chloride disks prepared by this technique were only slightly pink in color and completely transparent. Blank disks without reference beam compensation corild be adjusted to give a baseline a t greater than 90% transmittance between 3.5 and 15 microns with the aid of the 100yo transmittance adjustment. Full compensation was easily obtained by placing a similar silver chloride disk in the reference beam. Storage between layers of polyurethane foam protected from light lengthened the useful life of the disk. Sonie examples of the spectra obtained from polymer films on silver chloride disks are shown in Figures 1 and 2. They illustrate that even in the presence of some residual water good definition is obtained. The wet resorcinol reqin (Figure 1) was sandwiched between two silver chloride disks and retained practically all of its original 45% water throughout the 4-minute scan. h rescan of the same sample within 10 minutes gave inten$ities almost identical to the original. The
resin was still easily identified from the spect,ra of the wet film. Similar types of resins were easily distinguished from wet film spectra as long as the 0-H stretching vibration was not the only criterion of identification. Polyamide us. urea-formaldehyde and phenol-formaldehyde 1)s. phenolresorcinol-formaldehyde were good examides. The silver chloride disk technique also lends itself well to rapidly determining qualitative and semiquantitative changes taking place in resins as a result of curing. The qualitative change is well illustrated in the resorcinol resin spectra. In comparing the dry and wet sllectra! note the intensity decrea3e in the dry spectra at the 9.6- and 11.4micron bands. These hands originate from the methylol hydroxyl C--0 stretching vibration and the C-H out-of-plane bending vibration associated with the aromatic ring, respectively. The low cost and the ease of preparing silver chloride disks allow disposal after each use. However, if wet polymer films were washed off the disk, it could be
reused four to five times before scratching and darkening necessitated disposal. ACKNOWLEDGMENT
The suggestions of L. E. Dowd and the assistance of T. L. Robertson are gratefully acknowledged. The author t,hanks the Weyerhaeuser Co. Research Division for providing the facilities for this work and for permitting its publication. LITERATURE CITED
(1) Barnes, R. B., ANAL. CHEM.21, 7
(1949). ( 2 ) Fuoss, K.hI Rea. Scz. Instruments 16, 154 (1945). 13) LeSech. Chimae Anal. (Paris) 40. 425 (1958); 6.d. 53, 4900g (1059). ( 4 ) LeSech, Congr. groupe avance. methods anal. spectrog. met., Paris 10e, ~
'
195 (1957).
( 5 3 Schemer, W. C., LIurphy, J. E., \Tilliamson, L., ASAL. CHEM.29, 1113 (1957). (6) Sharp, D. W. A,, "Spectrovision," Unicam Instruments Ltd., Y o . 12 (1962). ( 7 ) Stevenson, H. J. R., Levine, S.,RPV. Sci. Instr. 24, 229 (1953). (8) Strong, J. ( t o the United States of America), U.S. Patent 2,700,002 (Jan. 18, 1955); C.A. 49, 5792e (1955).
Porous Glass as an Adsorbent for Thin layer Chromatography J. K. G. Kramer,
E. 0. Schiller, H. D.
Gesser, and A. D. Robinson, Parker Chemical Laboratory, University of Manitoba,
Winnipeg, Canada
has been used as a medium in gasliquid chromatography ( 2 , 8) and in liquid-solid chromatography (3) in the form of plates (1 inch X 4 inches x lj16 inch). To the latter, electrophoresis techniques have been applied ( 1 ) . I t was pointed out, that porous glass (Corning Glass Works, Code 7930) possesses desirable properties for chromatographic use, such as its extremely porous structure, uniformity of pore size, large surface area, inert inorganic nature, and optical transparency. The last property mentioned applies only when the porous glass is w e d in the form of plates. Porous glass plates gave well defined separations of water-soluble inks (3) using aqueous developers; however, when organic solvents were used as eluvnts! the resolution was much poorer, and 10 to 20 times longer development times were required. I t was necessary to Im'treat the porous glass plates with an acidic fluoride solution or heat them in absolute methanol before using organic liquids of Ion dielectric constant as elucmts. W e have found that porous glass can be usrd as an adsorbent for thin layer OROCS
GLASS
p chromatographic
chromatography (TLC) to circumvent these disadvantages. Porous glass was ground to a mesh size 200 to 250 and mixed with plaster of Paris of the same mesh size in a ratio of 87 to 13, porous glass to plaster of Paris. The new adsorbent was applied to the plates in the same manner as described by Stahl (7'). The thickness of the coating was 0.012
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Figure 1. The development of three waxes, beeswax, 1, 4, 7; bayberry wax, 2, 5, 8; and spermaceti, 3, 6, 9; is compared on three different thin layer adsorbents, porous glass, 1-3; silica gel G, 4-6; and aluminum oxide G, 7-9 The some eluent was used: petroleum ether (b.p. 38'-49')/ethyl ether = 9 5 / 5 (v./v.)
inch. The chromat,ograms were dried a t room temperature, followed by heating to 130" C. for 3 hours to activate them, and then stored in a desiccator. I n several cases a superior separation was achieved on thin layer chroniatograms with porous glass as adsorbent, compared to silica gel G and aluminum oxide G. Often more spots appeared and the corresponding R, values were greater, using the same developer (see Figure 1). These spots were equally or more distinct. Partition chromatography is operative even with nonpolar solvents suc,h as petroleum ether-ether. Since the pore and particle size of the adsorbent can be controlled, one is capable of changing the conditions of separation. It was furthermore observed that faint spots were darker on the porous glass chromatograms than on silica gel G after the plates were charred with chromic-sulfuric acid and then heated a t 150" C. Powdered glass (about 300 mesh) has previously been adapted to thin layer chromatography (4-6); however, it does not possess the desirable properties of porous glass, such as its large surface area, its uniform pore size, and the ability to be able to control the pore VOL. 36, NO. 12, NOVEMBER 1 9 6 4
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