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Aerosol Propellank Specifically Processed CHECK. Dow's John C. Moore checks chromatogram obtained by gel permeation chromatography, which separates a polymer's constituents by molecular weight
Gel Permeation Analyzes Polymers Chromatographic technique separates polymer constituents according to molecular weight Gel permeation chromatography may greatly simplify determining molecular weight distribution of polymers. The chromatographic technique, as developed by John C. Moore of Dow Chemical, uses columns packed with polystyrene gels which separate and pass the polymer's constituents in a solvent according to their molecular size. The column effluents are detected and recorded by a continuous differential refractometer. Solvent, flow rate, and temperature are held constant. The polymer being analyzed must be relatively nonpolar and soluble in the flowing solvent. And the solvent should be a good swelling agent for polystyrene gels, Mr. Moore told the ACS Southwest Regional Meeting, held in Dallas, Tex. The technique will separate narrowly dispersed polymers. It will also handle large molecules, Mr. Moore says. Although not enough data are available to know whether good resolution is possible with molecular weights in the multimillion range, the technique shows promise. Mr. Moore has used such diverse materials as polystyrenes and polypropylene glycols to calibrate his column; yet, these materials don't require a
PROPANE ISOBUTANE N-BUTANE Check these features
quality
change in conditions. As a result, the technique should readily sort out copolymers and other complex mixtures according to molecular size.
Cross-Linked Gels.
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low cost stability
Key to the
technique is hydrophobic polystyrene gels with enough cross-linking to give needed rigidity to a gel and satisfactory flow through the packed column. In addition, the permeability of the gel is regulated over a wide range by varying the amount and kind of diluent at the time of cross-linking (as is done in making highly permeable ion exchange resins). In effect, the gel has a rugged internal structurethicker internal walls and larger passages than gels cross-linked without the special diluents. Separation depends on the dissolved polymer molecules diffusing in and out of fine-mesh beads of solvent-swollen, cross-linked polystyrene gel. Molecules too large to do this bump from bead to bead and elute first. Successively smaller molecules find more volume to diffuse into, and are eluted later by the flowing solvent. The concentration curve from the refractometer as drawn by a recorder is, in effect, a molecular size distribution curve, Mr. Moore says.
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low odor pressure control Custom Blends Tailored to Meet Your N e e d s . . . Available in Cylinders and Tank Cars from Borger# Texas . . . Tank Trucks from Philadelphia, Pa. Inquiries Invited PHILLIPS PETROLEUM COMPANY Special Products Division Bartlesville, Oklahoma
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918-FE 6-6600 DEC.
17, 1962 C & E N
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Isatoic Anhydride 0 0 * Imaginative chemists are finding interesting new uses for this highly reactive chemical and its derivatives. For instance, in the manufacture of: Agricultural chemicals: Amides and esters of anthranilic acid, o-carboxyphenylcarbamates, substituted ureas, and nitrogen heterocyclics, such as the 4-ketobenztriazines. Dyestuffs and Pigments: 5-substituted anthranilic acids, including chloro, nitro and sulfo analogs which may be viewed as o-carboxy derivatives of the commercially important p-chloroaniline, p-nitroaniline and sulfanilic acid. Flavors and Fragrances: Near quantitative yields of high quality anthranilate esters from single kettle operation. Isatoic anhydride as deodorizing agent for mercaptans, amines and alcohols. Pharmaceuticals: Aromatic and heterocyclic compounds such as benzoyleneureas, quinazolines, quinolines, o-aminobenzophenones, anthranilic acid hydrazides, o-carboxyphenylcarbamates and o-carboxyphenyl ureas as intermediates and final products. Write for Bulletin 62-8 and samples. Maumee Chemical Company, 1310 Expressway Drive, Toledo 8, Ohio.
gives you a lot
to think about
MAUMEE Quality Organics 44
C&EN
DEC. 17,
1962
A typical gel is made of styrene, divinylbenzene, and toluene (the diluent). If the composition ratio is 30:10:60, the molecular weight permeability limit is about 7000. As part of the toluene is replaced by n-dodecane—less polar and a precipitant for polystyrene-permeability increases up to a molecular weight limit of about 2 million for polystyrene, with dodecane and toluene (75:25) as the diluent. A more polar material (isoamyl alcohol), as it progressively replaces diethylbenzene as a diluent, gives little increase in permeability at first. This is probably due to the loss of some isoamyl alcohol to the aqueous continuous phase in which the beads are polymerized. With larger portions of isoamyl alcohol, permeability increases beyond the largest (molecular weight of 3.5 million) test polymer. Diffusion Process. The chromatographic separation is nearly an equilibrium process, Mr. Moore says. Solute molecules diffuse very rapidly into all parts of the gel network not barred mechanically to them. With small samples at slow flow rates, very sharp peaks can be obtained. With larger samples or with faster flow rates, the peaks are broader, but they do not come up earlier in the chromatogram as would be expected if separation depends on diffusion rates. Large molecules don't seem to affect the gel's permeability to small molecules. As a result, the elution pattern of a mixture matches the sum of elution patterns of its components, if column overloads are avoided. The mechanism is similar to that for the separation of small, nonionic hydrophilic molecules by water elution through beds of ion exchange resins, as worked out earlier by other Dow scientists. More recently, similar separations of large hydrophilic molecules in water solution have been described by others, and given names such as gel filtration, chromatography on cross-linked gels, and restricted diffusion chromatography. Mr. Moore proposes gel permeation chromatography as a general name. In the future, Mr. Moore hopes to adapt the gel permeation control technique to some hydrophilic resins. The result may be a strong, rigid columnpacking material which can make sharp separations between very large water-soluble molecules such as proteins and viruses and, in addition, separate these materials from ions and small molecules.
Radiometric Technique Determines Iron A radiometric technique for determining iron has been developed by Dr. George J. Rotariu and Elizabeth L. Hoskins of Booz-AUen Applied Research, Inc., Glenview, 111. Involved is the reaction of ferric ion with hydroquinone : Kr 85 clathrate in a nonaqueous liquid environment, Dr. Rotariu told the winter meeting of the American Nuclear Society, held in Washington, D.C. The two steps in the procedure are: extraction of aqueous ferric ion ( p H 3) with thenoyltrifluoroacetone (TTA) dissolved in trifluorotoluene, followed by the addition of hydrogen chloride and hydroquinone : Kr 85 clathrate to the ferric ion-TTA complex. The first step provides a selective way to separate iron from other metallic ions, and puts the ferric ion in a complex form. The second step releases ferric ion from the complex, allowing reaction with the solid clathrate. This releases Kr 85 in an amount proportional to the amount of ferric ion present. A linear dependence of concentration vs. amount of Kr 85 released is obtained for ferric ion concentrations of 2 to 20 p.p.m. BRIEFS A magnetic field may affect cell growth, studies at IIT Research Institute (formerly Armour Research Foundation) show. Dr. M. R. Purvis finds that when a photosynthetic protozoan (Euglena gracilis) is exposed to a strong magnetic field, there seems to be a slight increase in growth, compared with unexposed protozoan. The increase in cell growth suggests the possibility that magnetic fields can cause some changes in cellular metabolism. The findings may affect research in ion propulsion of space vehicles, since such systems use large magnets.
RUN A DAY'S SULFUR DETERMINATIONS BEFORE MORNING COFFEE BREAK WITH FISHER'S NEW INDUCTION SULFUR APPARATUS In less time than it takes to bring a conventional hot-tube furnace up to temperature, you can run 10 accurate sulfur determinations with the new Induction Sulfur Apparatus—and keep right on running them at the rate of 10 an hour. You'll finish a day's usual sulfur work by midmorning. The new apparatus warms up in 30 seconds, is simple to operate, can handle up to 2.5 grams of
Addition of cysteine to meat tenderizers gives better results than does tenderizer alone, according to Dr. John R. Whitaker of the University of California, Davis. The tenderizing action of ficin and bromelain is also enhanced when meat is close to its normal acidity, somewhat salty, and warm (above 70° C.). Adding more tenderizer isn't effective; 10 mg. of ficin works as well as 50 mg.
ferrous or nonferrous metals. Connect it to a Fisher Model 36 Titrimeter® and the entire analysis is automatic. Full facts in free Bulletin 10-466. Write for it and ask about acquiring the Induction Sulfur Apparatus through the Fisher Financing Plan. Fisher Scientific Company, 101 Fisher Building, Pittsburgh 19, Pa.
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