Extension of the Gelatin Method for the Detection of Micron-Sized Particles JAMES P. LODGE, JR., and HANNY M. FANZOI Department of Meteorology, University of Chicago, Chicago,
Products, 3100 South ashland Ave., Chicago, Ill. h mixture of 2 grams of gelatin and 5 ml. of’ water was allowed to stand for I d minutes, then heated in an oven a t 85” until the gelatin had di*solved. Then 5 ml. of glycerol were added, and the mixture was heated for an additional 15 minutes. Finally 1 ml. of a saturated solution of barium chloride in 20% hydrochloric acid was st’irred in, and the gelatin was returned to t’he oven for 10 minutei longer. Slides were prepared as for detection of calcium.
Application of the gelatin technique has been extended to the detection of calcium, nitrate, and sulfate ions in air-borne fine particles.
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I.\IULTANEOUSLY with the work reported by Pidgeon ( 2 ) ,a limited amount of work was done using similar techniques to tirvc.lop tests for other ions in air-borne fine particles. The critrri:i of L: successful test ryere that every particle gave a reaction spot, and that other ions either gave no test or gave a spot readily distinguished from that of the test substance.
The sulfate reaction gives a rat,her grainy white circular spot which vanishes under crossed polaroids. The individual crystals are roughly the same size as the calcium ammonium ferrocyanide crystals in the preceding test. Several hours’ standing is necessary before all the particles in a sample react to give suctli spots. S o naturally occurring substance int,erferes.
EXPERIMENTAL PROCEDURES
Calcium Ion. -4 mixture of 2.5 grams of purified pigskin gelatin (Eastman Kodak Co., Rochester, S . Y.)>8 ml. of glycerol, and 5 ml. of 30% aqueous ammonium ferrocyanide ( 1 ) was heated in an oven a t 85” C. until the gelatin was dissolved. Slides were prepared as described by Pidgeon ( 2 ) .
Nitrate Ion. Purified pigskin gelatin was prepared in the s a i i i ~ manner as for sulfate detection. The “sensitizing agent” was 1 ml. of a 4070 solution of Sitron in 1Oyo acetic acid. The characteristic reaction gives circular groups of fine ratliates, the individual q - s t a l s of which are birefringent. Thrw appear to be no interferences.
The calcium reaction sp0t.s consist of circular areas filled with tiny discrete crystals. These spots differ from the chloride “halos” pictured by Pidgeon ( 2 ) in that the individual crystals are larger, and there is no center “embryo.” It is doubtful if other substances giving insoluble or highly colored ferrocyanides clsist in soluble form except as localized industrial dusts. However, several were checked and all were found to differ markedly from the calcium spots-for example, ferric ion gives transparent areas of Prussian blue, and silver, copper, and zinc form areas of 1:rrge crystals only after several days’ standing. Sulfate Ion. Because commercial purified pigskin gelatin reacted strong1 with sulfate reagents, i t was necessary to use gelatin in w h i c i the final pH adjustment had been made with Iiydrochloric, rather than sulfuric acid. A suitable gelatin is UCop-Co 12XPF, obtainable from United Chemical and Organic
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ACKNOWLEDGMENT
The authors wish to thank Anthony Trozzolo, who did some of the early portions of the work reported here. LITERATURE CITED
(1) Feigl, F., “Qualitative Analysis by Spot Tests,” 3rd English ed.. p. 169, New York, Elsevier Publishing Co., 1947. (2) Pidgeon, F. D., A x ~ L .CHEM.,26, 1832 (1954). RECEIVED for review March 12, 1954. Arcepted April 8, 1954. Research sponsored by t h e Geophysics Research Directorate of t h e A i r Force Cambridge Research Center, Air Research and Development Command, under Contracts fiF 33(038)-23017 and .A.F lR;GO4)-G18.
Analysis of Micron-Sized Particles JAMES P. LODGE Cloud Physics Project, University of Chicago, Chicago 37, 111.
The commercial filter material Jlillipore w-as utilized as a medium for sampling and analyzing particles in the micron-size range. Studies of ammonium, calcium, and magnesium ions, halides, sulfates, and nitrates indicate that the technique is suited f o r identification of atmospheric articulate matter.
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S MANY fields of research, attention is becoming centcretl
upon the identification of airborne particles in the micronsize range. The experimental met~eorologistis especially concerned with those soluble particles which may play a role in condensation and precipitation phenomena in the atmosphere. Rlicromanipulative methods have been developed to a high degree of perfection ( 2 ) but inevitably require much skill and patience in their use. A highly simplified method of spot-testing in this size range was developed by Seely (6), u-ho used the method of impaction on gelatin previously impregnated with the specific reagent for some one test.
The author has made use of the recently perfected Millipore filter material as the medium both for sampling and for carrying out the tests. Following the philosophy of Seely’s method, the entire filter is treated with one specific. reagent, and the typical reaction is observed wherever it occurs. Millipore (1) is a commercial product (available from the Love11 Chemical Co., FVatertown, Mass.) derived from the “membrane filters” of Sanarelli, Zsigmondy, and others (6). As available, it retains particles down to ca. 0.2 micron, quantitatively. I t provides a remarkably uniform surface for the reactions, and becomes transparent when treated with immersion oil, which permits ready microscopic examination of the reaction sites. The individual tests, as developed, have been checked to assure that a reaction site is obtained from every particle. In order to do this, individual filters, after sampling the test material, were cut in two; half was treated chemically and the other half n a s examined directly. In all cases the number of reaction sites 1829
