Sample Decomposition via Flowthrough Oxygen Flask Combustion Jon Belisle, C. D. Green, and L. D. Winter 3M Co., 3M Center, St. Paul, Minn. 55101 THESCHONIGER FLASK combustion method is well known as a method for the decomposition of organic materials. Experience in this laboratory has shown the method to be limited in terms of sample size. Lisk (I) has partially overcome this by increasing the size of the flask and attaching a balloon for the sake of safety. His work in pesticide residue analysis has employed both a 1- and 5-liter flask. We have found that the practical upper limit for sample size in a Niter flask is about 1 gram (dry weight). If the sample size is increased beyond this, carbon formation and incomplete combustion result. It has been our experience that a 5-liter flask is as large as is conveniently practical. To work with the larger samples that are necessitated by low concentration of the element under analysis and yet avoid combining successive 1-gram burns, we have designed a flowthrough system whereby oxygen is added during the time of combustion. By the same token the displaced combustion gases are absorbed in the continuous technique. EXPERIMENTAL
A single-neck 5-liter round-bottomed flask was modified by the addition of inlet and exit tubes, The inlet tube is connected to an oxygen tank by way of glass tubing, ball joints, (1) D. J. Lisk in “Residue Review,” F. A. Gunther, Ed., Vol. 1, Academic Press, New York, 1962, p. 152.
and a safety bottle. The exit tube leads to the absorber solution. The ball joints are held together with spring clips and the standard taper joints by coil springs. The flow is controlled by a valve on the tank regulator. The sample is compacted and placed in a platinum basket fashioned from a 2- x 5-inch perforated sheet (obtained from Englehard Industries, Newark, N. J., perforated platinum sheet, No. C) (see Figure 1). A 4- X ‘/*-inch fuse, constructed from black filter paper, is inserted in the sample with one end free to be used for sample ignition. The sample holder is inserted in the combustion flask and the flask is flushed with oxygen. Just prior to ignition the oxygen is turned off, since with ignition the rapidly expanding gases cause sufficient positive pressure through the absorber solution. The fuse is ignited with the use of the ignitor shown in Figure 2. The ignitor is turned on and positioned so the focal point of the light hits the fuse. After the initial ignition of the fuse, the ignitor is removed and sample ignition allowed to proceed. At the completion of the initial combustion, the oxygen flow rate is maintained at about 6 to 8 liters/min to sustain the decomposition. The rate may vary depending on the burning rate of the sample and efficiency of the absorbed solution with respect to the element of interest. Combustion gases are passed through an appropriate absorber solution whose composition depends upon the particular element under analysis. After the completion of the combustion and the flask has cooled, the flask and sample holder are rinsed several times. The rinsings are combined with the absorber solution and the appropriate analysis is performed.
IS SUPPORT A
Figure 2. Ignitor 1. 2. 3. 4. 5.
Figure 1. Combustion apparatus 1006
ANALYTICAL CHEMISTRY
Sylvania DFC, DFN projector lamp Amphenol 7854-type standard socket Plastic tubing, lI/&ch i.d., 7 inches in length Normally open type push-button switch No. 6 rubber stopper drilled to accommodate electrical wiring 6. Electrical wiring
DISCUSSION
A variety of organic materials have been decomposed using this technique. Samples, approximately 10 grams (dry weight) in size, of bread, potato chips, clover, rhubarb leaves, strawberry leaves, etc. have been burned with little or no carbon formation. The combustion proceeds smoothly and controllably. Because of the quantity of heat liberated, it is advisable to set the flask in several inches of ice water with a fan directed toward the flask. Also, depending on the analysis, it may be necessary to cool the absorber solution. The combustion should be carried out behind a shield. However, combustions using this size sample have been performed numerous times with no indication of hazard. It has been found in this laboratory that the life expectancy of the ignitor bulb can be prolonged if one uses a Variac to increase the voltage gradually rather than apply the full 110 V with an on-off switch. We have used the described system for fluorine analysis whereby a sample was “spiked” with a known amount of organically bound fluorine. A recovery of 90 & 10% at the 1-ppm level was found. This takes into account the workup of the sample leading to the final analysis. Lisk (I) found a recovery of 80 to 109% at the 1- to 14-ppm level for chlorinated pesticides. However, he first concentrated the chlo-
rinated component in a large sample via a solvent extraction. The chlorinated component was then decomposed. The absorber solution for the above analysis was 30 ml of water placed in a 100-ml graduate. The exit tube from the flask led to the bottom of the absorber solution. Baffles were placed on the portion of the tube immersed in the absorber solution. The purpose of the baffles was to break up the gas bubbles and thus aid in the absorption of the hydrofluoric acid. After the combustion was complete, the oxygen was allowed to flow for another 5 min. The flask and sample holder were rinsed with 0.01N sodium hydroxide to remove any absorbed fluoride. Analysis of the absorber solution for fluoride ion was accomplished via one of the various published colorimetric techniques (2). It is felt that this decomposition technique can be applied to numerous elements, both volatile and nonvolatile. The major limiting factors being the degree of difficulty in converting the element involved to the proper valence state and the choice of the proper absorbing solution required to retain that element. RECEIVEDfor review November 13, 1967. Accepted February 8,1968. (2) R. Belcher and T. S. West, Talanta, 8,853 (1961).
Separation of Water-Soluble Vitamins on Starch Thin Layers S. E. Petrovie, B. E. Belia, and D. B. VukajloviC Department of Chemistry, Unicersity of Novi Sad, Novi Sad, Yugoslavia WATER-SOLUBLE VITAMINS are chemically and physiologically heterogeneous compounds, and most of them are distinguished by high instability. Thin-layer chromatography is a suitable method for analysis of these vitamins, but this method has rarely been used, and few publications have appeared to date (1-6). In published works, the separation of single vitamins from the substances which accompany them in natural materials, as well as the separation of related vitamins and their derivatives is mainly described. Ganshirt and Malzacher (2) separated the group of water-soluble vitamins on silica gel layers containing the fluorescent indicator ZS super using ultraviolet light (254 and 365 mp), sodium iodoplatinate, dichloroquinonchlorimide, and ninhydrin (only for pantothenic acid) for detection. We describe the separation of a group of water-soluble vitamins on thin layers of rice starch using ninhydrin (for all examined vitamins which are not visible in daylight) for detection. EXPERIMENTAL
Procedure. For preparation of the thin layers, which has rice starch (Carlo Erba, Milan, already been described (3, Italy) with addition of gypsum was used. Eight watersoluble vitamins (Pliva, Zagreb, Yugoslavia) (Table I) were examined individually and in the mixtures. Vitamins were dissolved in distilled water and the concentration of each vitamin was examined individually and in the mixture (Table I). Spots of 1 p1 of vitamin solutions were applied by micropipet on the thin layer and chromatoplates were developed by the ascending technique in a glass chamber which contained 50 ml of solvent mixture. The chromatograms
were run in the dark at room temperature without previous saturation of the chamber with solvent. The solvent system was n-butanol-acetic acid-water-pyridine (40 :10 :50: 2), and the upper layer was used for development. The developing time of chromatograms was about 5 hours for a solvent front of about 15 cm. Detection. The ninhydrin reagent, 0.5 gram of ninhydrin dissolved in 100 ml of methanol, was used for detection. The developed and dried chromatograms were heated in an oven for 30 minutes at 160” C. After heating, the cooled chromatograms were sprayed with ninhydrin reagent and heated again for about 10 minutes at 80” C. Colored spots of the vitamins appeared (Figure 1). Ultraviolet light at 254 and 365 mp was used for control. RESULTS AND DISCUSSION
All examined vitamins except Ca-pantothenate and p-aminobenzoic acid were separated by using rice starch as support. When vitamins were chromatographed individually, considerable differences of Rf values of Ca-pantothenate and paminobenzoic acid were obtained (Table I), but when the mixture of vitamins was separated, then Ca-pantothenate and p-aminobenzoic acid moved together. As is evident from (1) S . David and H. Hirshfeld, Bull. Soc. Chim. France, 1963, p.
1011. (2) H. Ganshirt and A. Malzacher, Naturwiss., 47, 279 (1960). (3) E. Niirnberg, Deut. Apotheker-Ztg., 101, 142 (1961). (4) E. Niirnberg, Ibid., p. 268. ( 5 ) K. Randerath, A)?gew. Chem., 73,436 (1961). (6) T. Sasaki, J. Chromatog., 24, 452 (1966). (7) S . M. Petrovib and S . E. Petrovif, ibid., 21,313 (1966). VOL 40, NO. 6 , MAY 1968
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