Ashing Apparatus for Samples Containing Traces of Iodine GEORGEM. KARNS,Mellon Institute of Industrial Research, University of Pittsburgh, Pittsburgh, Pa.
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N THE preparation of large samples of organic material in position in the bulb and, with the collecting train in place, for the determination of traces of iodine, recognition the desired adjustment of the slight vacuum under which of the advantages of ashing samples in systems in which the system is to operate is made, with the oxygen speed iodine may be recovered from the vaporized combustion regulated to its proper rate. For convenience, the oxygenproducts as well as from the ash has led to the development inlet tube from a convenient flowmeter is attached a t 0. of closed systems for ashing in an atmosphere of oxygen. Carbon dioxide is admitted a t C, the speed of admission Most of the devices used for this purpose are based upon the being the minimum of continuous flow through a needle valve. appliance proposed by McClendon (1) and subsequently When the system is so arranged, the inner tube is removed developed by him and his co-workers. from the apparatus, the fuse material is ignited, and the tube Although valuable data have been accumulated by the use is quickly replaced, being held there by rubber bands about of apparatus of this well-known type, the operation is often the appropriate lugs. As the sample burns, the brass rod is attended with difficulty. With such apparatus it is usually used to push fresh portions of it gently into the flame area, necessary for oxygen to be swept through at a comparatively where it is consumed as oxygen becomes available. The high rate in order that no loss of products from the sample globular design of the combustion chamber causes circulating occurs by expansion during combustion. The rapid rate of gases to direct the incoming oxygen toward the sample. this gas stream, from which, of course, the iodine must be The rate of burning is adjusted by the oxygen speed. The recovered, necessitates in turn the employment of a high- apparatus illustrated will hold samples of from 35 to 60 capacity washing train involving the use of large amounts of grams, depending upon the type of material under considerawater and reagents which must be eliminated before the final tion. Such sizes of samples are adequate for determinations determination is made. Then, too, in apparatus of this type on most materials, but, if it is desired to analyze large samples, some part of it is subjected to intense heat, either from the additional cylinders of material may be ashed without interburning sample or from external application, and hence its rupting the oxygen flow. When the tube is to be removed to life is short, The apparatus described in this paper has been enable the addition of a second portion of sample, the ash designed to ash samdes slowly if desired. During such slow may be shaken down into the CUD about the central tube, rtshiig the oxygen ktilizaGhich is provided for that tion is quite efficient, makpurpose. ing it unnecessary to handle As the top portion of the sample burns, radiated heat a large excess of o x y g e n distils off some of the volaand therefore enabling the use of a c o m p a r a t i v e l y tile constituents from lower portions of the sample bes i m p l e c o 11e c ti n g train. PLhTINUM The apparatus is also cafore it reaches the burning pable of giving a good ash chamber. This distillate is rJjOLLAR without the aid of outside gently swept by the carbon heat, and during its operadioxide stream out of the tion no destructible part of central tube past the platiit becomes so excessively num collar, which is heated heated as to cause damage. by the burning sample, and Figure 1 shows the essent h r o u g h the flame area, tial parts of t h e new apwhere ignition takes place, paratus. In carrying out a The carbon dioxide stream combustion, the sample is also serves to prevent the either molded into cylindrimigration of the flame down cal form in a manner similar into the glass portion of the t o t h a t suggested by apparatus, thereby precludMcClendon and Remington ing the early destruction of (9), or placed in a paper the l a t t e r . The combusc y l i n d e r fitting the Pyrex tion products pass into the g l a s s i n n e r t u b e T. A collecting train through the small amount of s u i t a b l e outlet tube D. fuse material, such as The apparatus as illuscotton, is put on top of the trated has been used with s a m p l e . With the brass several sizes of inner tube, ramrod retired, the sample but the size shown has been BRA55 ROO is placed in position, being found to be more convenient properly held protruding in g e n e r a l than those of slightly above the platinum s m a l l e r diameter. Little collar, by the stopper and difference in operating the rod. The tube is then set apparatus has been found FIGURE 1. ASIIINGBULB 299
300
ANALYTICAL EDITION
in working with samples of leafy vegetables, dried milk, mixed cattle foods, tankage, fish scrap, and commercial ground meat. Ground beef containing some fat has been successfully ashed without being previously dried. Using an oxygen speed of 1 liter per minute, a good iodine recovery was made by a simplified collecting train consisting of one condensing tube containing glass wool moistened with sodium bisulfite solution immersed in an ice bath, a Cottrell precipitator 30 cm. in length, and a single Milligan wash bottle containing caustic solution. Operating a t the low rate, the average sample is consumed at approximately 25 grams per hour. Although designed to make possible the ashing of samples with a simplified collecting train, the ashing bulb will operate equally well with trains capable of handling the products from a more rapid combustion. I n comparing the apparatus with others previously described, its chief advantage is in its smooth and governable operation. The burning of the sample being complete and controllable, little difficulty is encountered from the development of back pressure from the ignition of accumulated combustibles. It is therefore unnecessary to handle the rapid stream of gas that is usually recommended. It is possible to obtain satisfactory combustion without the usual application of heat from supplementary burners or coils outside or inside the apparatus. Heat-flow direction, distribution, and dissipation make special cooling devices, such as water-circulating coils, unnecessary either in the apparatus or about the feed mechanism. The behavior of the apparatus in this respect also makes it capable of prolonged use when constructed almost entirely of glass. The above-mentioned features, whose simplicity is readily recognizable by the experienced operator, are difficult to evaluate quantitatively in a procedure which is laborious a t
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best. However, analysts have developed satisfactory technic using the ashing bulb in four or five trial runs. Since the ashing device is used in the preparation of the sample, recovery is important only as the total procedure is influenced by the device in question. It suffices to say that using the ashing bulb with collecting trains described by McClendon and Remington, the recovery of iodine is equivalent to that obtained by them. When compared with the McClendon and Remington ashing tubes, it is more convenient to clean on account of its size, shape, and lack of internal coils, and on account of the fact that no ash can fuse into the bulb as it sometimes does with glass or silica tubes. The bulbs have been used for approximately one hundred runs without becoming noticeably affected in their hotter portions, a considerably longer life than that of the ashing tube made of Pyrex, which must be used at temperatures approaching its softening point. 'These, in the hands of operators of some experience, are often in bad condition after five or six runs. The bulb is better in this respect than the more expensive silica tubes, which often crack after alkaline ash fuses into them, even when special precautions are taken. Experience has demonstrated that the smooth operation of the ashing process in this apparatus makes available dependable types of collection hitherto unutilized in analyzing commodities for iodine. LITERATURE CITED (1) McClendon, J . Biol. Chem., 60, 289 (1924). (2) McClendon and Remington, J . Am. Chem. Soc., 51, 394-9 (1928).
RECEIVED December 30, 1931. Presented before the Division of Agricultural and Food Chemistry at the 82nd Meeting of the American Chemical Society, Buffalo, N. Y.,August 31 t o September 4, 1931.
Determination of Reducing Sugars in Food Products Proposed Colorimetric Method University of Colorado, Boulder, Colo, CHARLESF. POEAND FRANK G. EDSON, INCE Lewis and Benedict (4) first announced their colorimetric method for the determination of reducing sugars, several methods have been proposed for the estimation of these sugars in blood and urine. In the field of food chemistry these colorimetric methods have been applied but little. The authors ( 7 ) , in testing the effect of some reducing sugars on certain organic nitro compounds, found several compounds which might form a basis for a reagent for the quantitative estimation of reducing sugars in food products. Among these sodium 2,4-dinitrophenolate appeared to be very satisfactory. The purpose of the investigation reported in this paper was to develop a reagent using this compound for the estimation of reducing sugars in food products. While experimenting with sodium 2,4-dinitrophenolate: many different combinations of this substance with alkalies and alkali carbonates were tried. To the above combinations were added Rochelle salt, phenol, and sodium bisulfite separately and then in various combinations. All of these reagents were tested for the development of color with dextrose. As a result, two different reagents have been sug-
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gested, the first to be used when small amounts (1 to 10 per cent) of reducing sugars are present, and the second for larger amounts. Two reagents are suggested in order that the dilution factor may be eliminated as far as possible with the foods containing a large percentage of reducing sugars: 1.
2.
Sodium 2,44initrophenolate 8 grams Sodium hydroxide] 5 per cent 200 cc. 100 Phenol 2.5 grams Rochelle salt Distilled water, q. s. 1000 cc. Sodium 2,4dinitrophenolate 8 grams Sodium hydroxide] 5 per cent 200 cc. 100 grams Rochelle salt Distilled water, q. a. 1000 cc.
I n the above formulas the sodium 2,4-dinitrophenolate and phenol are dissolved in the sodium hydroxide solution. The Rochelle salt is dissolved in about 700 cc. of water. The solutions are mixed and diluted to 1 liter. The procedure used for the estimation of the reducing sugars may be stated as follows: A given amount of the food product containing the reducing sugars is weighed and the necessary dilution made. One cubic centimeter of this dilution
