be on the order of milligrams. It may be minimized by inserting a vial with a capillary outlet into the sample container as in Figure 2, vi. This arrangement has a twofold effect: It reduces the free space above the sample and thus the quantity of residual vapor; the expansion of the air in the vial with rising temperature causes a n air leak through the capillary, which assists in purging volatile products from the bulb. VOLUMETRIC ANALYSIS
OF VOLATILE MATTER
Evolution of Noncondensable Gases. T h e evolution of permanent
gases can be measured gravimetrically, as in experiment C (Figure 4), or volumetrically. The gravimetric measurements divided by t h e corresponding volumetric measurements give t h e average density of t h e gases a t a n y chosen temperature. For volumetric measurements the tube assembly in Figure 2, iii, was used, except that the top of the tube was not suspended from the thermobalance but connected to a soap filmtype of gas flowmeter of 5-mL capacity. Readings of gas flow were taken every minute. Rates of evolution of gas by weight and by volume (converted to N.T.P.) obtained in parallel experi-
ments are represented in Figure 11 by curves i and ii. The curve of the variation of gas density with temperature was drawn by dividing values on curve i by corresponding values on curve ii; the resulting curve, iii, is in satisfactory agreement with curve iv plotted from density values calculated from gas analyses of a 10-gram assay made under comparable carbonizing conditions. Evolution of Carbon in Volatile Form. The results of gravimetric experiments t o determine the rate of evolution of carbon in volatile form are shown in Figure 8, B. Besides being measured by weight, carbon dioxide can also be measured by volume using t h e floLTmeter. The values obtained by t h e two methods (converted to S.T.P.) for the same coal sample are plotted in Figure 12, i and ii. These curves show satisfactory agreement, apart from a slight temperature shift. To determine the amount of carbon present in noncondensable gases as carbon dioxide, carbon monoxide, and hydrocarbons, the gases (after the tar and liquor had been condensed from the volatile matter, as in experiment C) were passed through a section of tube containing copper oxide and Arneil catalyst a t 640" C. The gases were completely oxidized to carbon dioxide and
water. After the water had been trapped, the flow of carbon dioxide was measured. Curve iii, Figure 12, shows the variation in the rate of evolution of carbon dioxide, and hence of carbon, with carbonizing temperature. Figure 13 shows diagrammatically the tube assembly and indicates the successive stages of treatment of the volatile matter in this experiment. ACKNOWLEDGMENT
The author thanks H. R. Brown, Officer-in-Charge of the Coal Research Section, C.S.I.R.O., under whose direction the work was carried out, for help and encouragement. LITERATURE CITED
(1) Braude, E. A., "Determination of
0rg:Fic Structures by Physical hlethods, E. A. Braude and F. C. Nachod, eds., Chap. 4, p. 138, Academic Press, New York, 1955. (2) Waters, P. L., C. S.I. R . 0. Coal Research Section, Rept. Ref. T. C. 18 (1956). (3) Waters, P. L., J. Sci. Instr. 35, 41 (1958); Coke and Gas 20, 252, 289, 341 (1958). (4) Waters, P. L., Suture 178, 324 (1956). RECEIVED for review December 22, 1959. Accepted March 31, 1960. Work undertaken as part of the program of the Coal Research Section, Commonweath Scientific and Industrial Research Organination, Australia.
Visible and Infrared Spectroscopic Determination of Trace Amounts of Silicones in Foods and BioIogicaI Materials H. J. HORNER, J. E. WEILER, and N. C. ANGELOTTI Analytical and Spectroscopy laboratories,
,Since the introduction of silicones to the food and drug industry, numerous problems involving the determination of these materials in trace amounts have arisen. Because silicones give no color tests or distinctive reactions, it was necessary to develop special extraction and concentration techniques to obtain samples in a form suitable for analysis. The scope of this investigation has extended from the analysis of foods to the detection of silicones in human lung tissue, blood, and animal organs. A chemical silicon determination may b e applied, provided residual silica content does not interfere. A more definitive infrared technique has also been evolved for the detection and measurement of si I icones
.
858
ANALYTICAL CHEMISTRY
Dow
Corning Corp., Midland, Mich.
W
of silicones t o the food and drug industries, a need arose for the development of techniques for the determination and identification of these materials in trace amounts. Food and Drug Administration regulations require that when silicones are used in the processing of foods or pharmaceuticals, the residual silicone content in the finished product be known or be able t o be determined analytically. This residual content generally falls in the part per million range. Because of their chemical inertness silicones cannot be detected by simple chemical tests. Several methods of detection are applicable t o the determination of silicones in this range: radioactive tracer techniques in which the silicone in a tagged ITH THE INTRODUCTION
form is used in the processing step; a n internal standard technique where a known amount of a more easily analyzed element or compound is added to the silicone with subsequent analysis for this material in the sample; spectrophotometric silica determination; and extraction and concentration of the silicone followed by a n infrared examination of the extract. The radioactive tracer technique was not thought feasible because of the expense and the equipment needed for this type of analysis. The internal standard technique, although satisfactory, is not considered generally applicable because the additive may respond differently to treatment for analysis than the silicone. Because of the obvious shortcomings of the first
metric flask. Add Solution A to Solution B and dilute to 250 ml. Table 1. Silica Recovery Study on Oxalic Acid. Dissolve 20 grams of Ground Beef the acid in 180 ml. of water. ReStandard Silicon Solution. AccuVISIBLE SPECTROPHOTOMETRY Sample Sios, P.P.M. covery, rately weigh 0.0321 gram of feldspar, No. Added Found % National Bureau of Standards sample Chemical silicon determination by KO. 70. Place in a Parr bomb and 1 Blank 0.0 ... colorimetric methods can be applied 2 2.4 86 2.8 treat as described under calibration. !There the residual silica content in the 96 3 5.2 5.4 After bombing and dilution to 1000 ml., 4 10.6 10.8 98 material being examined is low or can the concentration will be 0.01 me. of 91 15.4 5 16.9 be adequately compensated for by a silicon per ml. 6 98 21.9 22.3 Preparation of Silica Calibration blank. Curve. Mix 2 t o 3 grams of sodium I n many cases chemical silicon deperoxide with 50 to 160 mg. of sucrose termination is not applicable. The in a Parr peroxide bomb. Accurately extraction and infrared technique is sulfuric acid (15%) t o the residue in the weigh 0.0321 gram of feldspar and more desirable because it is quantitative platinum dishes until only a charred add it t o the mixture in the bomb. and qualitative. These conditions are mass remains. Then add fuming nitric Fill the bomb with sodium peroxide preferred by Food and Drug Adminisacid dropwise until the charred residue and t a p on the desk so the cover will is covered completely. Place the dishes tration regulations. seat properly. Secure the locking again under infrared lamps until white Colorimetric silica procedures have nuts and place the bomb in a shielded sulfur trioxide fumes appear. Repeat firing rack. Heat the bomb t o a been discussed by several authors the fuming nitric acid treatment and dull red gloTv with a blast burner (6-7) and a variation of the standard evarorate the samples again under the using gas and oxygen. Quench immethod ( I ) that has a much higher lamp. Continue this process until mediately in cold water. The time degree of sensitivity was developed most of the carbon has been oxidized. required from the application of the specifically for food samples with low Complete the oxidation by heating the flame until bombing is complete should silicon content. I t s lower limit of dried residue in a muffle furnace a t be 30 to 40 seconds. detection is about 0.1 y of silica per 800' C. After cooling to room temperature, 1 ml. of solution. Phosphorus and To prepare the residue for coloriopen the bomb and rinse the cover into a metric silicon analysis, solubilize the fluoride interferences are effectively 400-ml. nickel or RIonel beaker. Dilute residue by fusion with sodium carbonto 100 to 125 ml. Place the bomb on masked through the use of oxalic acid ate. Combine approximately a 5 to 1 its side in the beaker and cover the when the concentration of the interferratio of sodium carbonate to residue beaker with a nickel or None1 cover. ing ions in the final solution used for and heat over a Rleker burner until a A vigorous reaction occurs! \Then analysis is of the order of 10 p.p.m. or uniform melt is obtained. After coolsolution is complete, remove the bomb less. ing, take up the fusionate in hydroand rinse into the beaker with distilled The foods are decomposed by ashing chloric acid and transfer the resultant n-ater. Dilute to 200 to 275 ml. Fill with fuming sulfuric and nitric acids. solution to a 100-ml. volumetric flask. the bomb with concentrated hydroThe carbon is finally oxidized by heatRepeat the ammonium molybdatechloric acid and let it stand for 1 oxalic acid procedure. ing in a muffle furnace a t 800" C. minute. Transfer the acid to the mixFrom the calibration curve, the To prepare the residue for coloriture in the beaker and add an addiweight of silica can be determined tional 35 ml. of hydrochloric acid. metric silicon determination, fusion is and the per cent silicon calculated. Then transfer the solution to a 1000-ml. effected with sodium carbonate. The volumetric flask, dilute to volume with fusionate is taken up in hydrochloric ion-free water, and let it stand for a t DISCUSSION acid. Subsequent reaction of the silileast 2 hours. con with ammonium molybdate forms Transfer suitable aliquots of the The following materials have been a yelloR silicon-molybdate complex stock solution containing 0.005 to 0.06 analyzed using this colorimetric prowhich can be reduced to the heteropoly mg. of silicon to 100-ml. volumetric cedure: catsup, precooked meatloaf, blue with l-amino-2-naphthol-4-sulfonic flasks. Dilute to 50 to 60 ml. with canned ham, precooked frozen sausages, acid. After development of the color ion exchange filtered water. Add 2 ml. wine, whiskey, lard, solutions of sucrose, of ammonium molybdate solution and let the per cent transmittance can be read sodium bicarbonate, sodium chloride, stand for 30 minutes. Add 2 ml. of oxalic a t 800 mp on a Eeckman Model B or acetic and lactic acids, and postage acid and shake well for 15 to 20 seconds. DG spectrophotometer. From a calistamp paper. These materials were Add 1 ml. of the reducing agent, dilute bration curve milligrams of silica can either processed or treated in some to volume, and let stand for 20 minutes. be ascertained and this is then backA final p H of 1.2 to 1.7 is necessary. manner with silicones and it was decalculated as per cent silicone in the Use a 50-mm. light path cell and read sired to know how much, if any, silicone food. per cent transmittance of the sample was picked up by the material in Mineral-free a ater was obtained by a t 800 mp. Plot a calibration curve question. The exact conditions of passing ordinary distilled water through of per cent transmittance us. milligrams sample preparation varied with the of silica per milliliter of solution on an ion exchange filter (a Deeminac particular material under examination. semilogarithm paper. filter was used in this work). Analysis of Food. PREPARATIONHowever, the final colorimetric analysis is the same for all. Reagents. Bmmonium Molybdate. FOR ASHING. Weigh the samples into Table I shows a recovery study perDissolve 18.8 grams of reagent grade 150-mm. diameter platinum dishes. Use enough sample to provide approxiformed on ground beef. The samples molybdate in 75 ml. of water. Add 23 ml. of concentrated reagent grade mately 1 X to 1.4 X 10-3 mg. of were wet-ashed, fused, and taken into sulfuric acid. Cool and dilute t o silica per milliliter of solution. solution in the prescribed manner. The 250 ml. ASHING. Place the platinum dishes reduced silicomolybdate blue color was Reductant Solution A. Dissolve 2 containing the foods being tested under developed and the silica concentration grams of anhydrous reagent grade infrared heat lamps until the sample is determined from the standard curve. sodium sulfite in 25 ml. of distilled dried, as indicated by some charring of Sample weights were approximately water and add 0.5 gram of l-amino-2the residue. I n the case of solutions, 10 grams and the silica was added in naphthol-4-sulfonic acid. evaporate the solvent and take the the form of dimethylpolysiloxane. As Reductant Solution B. Dissolve 25 residue to dryness under the heat lamp. grams of reagent grade sodium bisulfite is evident from Table I, this method At this point remove the samples in 200 ml. of water in a 250-ml. volufrom under the lamp and add fuming can be applied with a high degree of
two methods, studies %-eremade of the last two approaches.
-
VOL. 32,
NO. 7, JUNE 1960
859
5000
4w(L
3000
2500
2000
I500
1400
WAVE NUMBERS IN 1200 1100
I1M
CM' 700
loo0
1 -
* - -
p.
::
4
6
0
IO
(25
12
I
14
16
WAVE LENGTH IN MICRONS
Figure 1 .
accuracy if the residual silica is nil or negligible in the material taken for analysis. The same degree of accuracy, in most instances, can be expected in the cases of other foodstuffs examined by this method. However, this colorimetric silica procedure is not applicable to all types of foodstuffs. There is no universal method for determining silica in these various samples. Preliminary studies on each type of material to be analyzed should be undertaken first before deciding which particular set of conditions should be used. INFRARED SPECTROSCOPY
I n cases where i t is desirable to know not only how much silicone is present in a particular sample but also the particular type of silicone, the extraction and infrared technique is used. This method is not applicable in all instances; however, with slight modifications it can be applied to numerous foodstuffs. The procedure utilizes the unique infrared absorption spectra of silicones to measure the amount of silicone fluid present in the sample (9). Figure 1 is a typical spectrum of dimethylpolysiloxane. If the fluid Concentration is low or if the matrix material has interfering spectral bands, the silicone is quantitatively extracted using a solvent which is then scanned in the infrared spectrometer, and the amount of silicone is determined ( 8 ) . The method can be used for concentrations ranging from 100% down to fractional part per million of silicone ( 3 ) . Some examples of typical determinations are given. Reagents. Carbon disulfide, specCarbon trophotometric grade. SOTE. disulfide vapors are extremely poisonous and flammable, and t h e material should be used in a hood only. Apparatus. Infrared spectrometer and sodium chloride cells of various thicknesses.
860
ANALYTICAL CHEMISTRY
Infrared spectrum of typical dimethylpolysiloxane
Standard Preparation. Keighed amounts of t h e proper silicone fluid are added t o a silicone-free matrix similar tto t'hat of t h e sample and thoroughly mixed by agitation, heating, or other processing as required. The standards arc t'hen analyzed as described below and t h e recovered silicone is compared to the amount added. It is important to carry through a t least one blank which is treated like the synthetic samples except for the addition of silicone. The blank is used to detect and correct for the presence of possible interfering bands and to help establish the base line points (Figure 2). Silicone stopcock grease should not be applied to apparatus used in this analysis because it might be extracted and contribute t o the subsequent determination of silicone. Separation of Silicone in Sample. Preliminary separation of t h e silicone may or may not be necessary, depending on its concentration and on the degree of interference from other substances in t h e sample. Direct determinat'ion of the silicone is preferred wherever i t is possible, in which case the material may be run as is (if liquid), or dissolved in carbon disulfide and analyzed. If separation of the silicone is required, direct extraction with carbon disulfide is usually the most' convenient method. Three or four extractions of the material and its container are usually sufficient. If the use of carbon disulfide is not feasible, a solvent such as benzene or chloroform may often be used. The silicone can then be determined in the solvent by infrared spectroscopy or i t may be necessary to evaporate the extract t o virtual dryness and then take up the residue in carbon disulfide for infrared analysis. I n some cases, aaeotropic distillation of the water in the sample followed by solvent extraction of the residue may be necessary (8). The volume of solvent used should be such t h a t the final concentration of silicone is a t least 0.05 mg. per ml.
An example of the extraction-in-
FREQUENCY, CM 1400
-1
1e00 I
co
I
1000
I
I -
-__
1
7
8 9 WAVE LENGTH, MICRONS
10
Figure 2. Infrared spectra of extracts from pineapple juice with and without silicone
frared method of analysis is a procedure for the determination of silicone antifoamer added to pineapple juice during processing. The water in the juice was azeotroped with benzene in a Dean Stark apparatus. Azeotroping of the water is accompanied b! the extraction of the silicone into the benzene. The majority of the pulp and sugars are insoluble in the benzene if, during the water removal, the residue is converted to a taffy-like consistency. This state is accomplished by applying enough heat during the azeotrope step to caramelize the residue partially but not char it. If the process is not carried to the caramelization stage, enough natural oils are extracted to interfere seriously with the analysis. If charring and carbonization
occur the residue acts as a n absorbent for silicone, causing lo^ results. After all the n-ater is removed and a taffy-like stage is reached, the benzene containing the silicone portion of the antifoam emulsion is decanted from the residue to a n evaporating dish with filtering to remove solid materials if necessary. The flask and filter are washed three times with fresh benzene and the total benzene extract and n-ashings are combined. The benzene is removed by heating in a hood on a n electric hot plate or steam bath. The residue is dried a t 100' C. for 1 hour and then dissolved with carbon disulfide and diluted to final volume. The snml:le in this stat'e is then submitted for a n infrared analysis. Infrared Determination of Dimethylpslysiloxane. -4portion of t h e carbon disulfide extract of thc residue is transfcrred to a cell of 0.6-mnt. path h g t h . Thc instrument is d l o w ed t o scan t 11P n-a ve-le ng t h interval from 7 . 5 to 9 iiiicrons a t t h e normal spcetl setting of approximately 1 micron per mii!utt.. The ;\IezSi hand a t 7.95 microns is used for qiinnt,itativemeasurement of t'he silicone content. The base line (-i) technique is used for the determination of the absorbance of the band.
Table
1 2 3 4
5
6
II.
Silicone Recovery Study on Pineapple Juice
0.0 3.G 5.4
0.0 3.2
6.3 24.3
4.4 5.5 20.2
5.6
4.4
..
89 82 i9 87 83
Bread. waffles, hydrolyzed vegetable protein. and canned and frozen vegetables nere all examined. I n the biological field. the same general method was used to examine liver, spleen, and kidney of rabbits, animal blood, blood anticoagulant, human blood, human lung. and rabbit feed. I n all cases recovery data equaled or exceeded those obtained in the pineapple juice studies (Table 11). LITERATURE CITED
(1) D ~ K Corning Corp., DOT Corning Annlvtical Method S o . 1.1.6 11956). ( 2 ) Ibib.: So. 4.1.2 (1958). ( 3 ) Ibid., No. 4.3.4 (1959). ( 4 ) Heigl, J. J., Bell, h l . F., IVhite, J. V., :%KAL. CHEM. 19,293 (194i). ( 5i Kahler, H. L.. 1x0. ENG. CHEU., XKAL.ED.13,536 (1941). ( 6 ) NrHard. J . A , . Servais. P . C.. Clark. H. rl.,As 4~ CHEX 20, 325 (1948). ( 7 ) Pettj-. G I T , I h d , 28, 250 (1956). (8I Pozcfsky, A , Grenoble, 11 E., Diwu k. Cosmetzc Inrl 80, 752 (1957). 4 ' 9 Smith, A L RIcHnrd J. il , A N ~ L C"EM3 1 , l l i - f (1959) ~I
DISCUSSION
From the absorbance, per cent concentration of silicone in the solution can be calculated and this figure is related to the amount of silicone in the original sample. Many vegetable materials that had been processed with silicone antifoaming agents have been examined by this procedure or various modifications of it as the specific sample required. The follou ing materials have been examined by the extraction and infrared technique.
~
RECEIVEDfor revien February 8. 1960. Accepted April 11. 1960. 11th Annual Pittsburgh Conference on hnalytical Chemittry and Applied Spectroscopy, IIarch 3, 1960.
Detection of Diphenylamine and Its Derivatives in Spot Test An a lysis FRITZ FEIGL and DAVID GOLDSTEIN laboraforio da Produck Mineral, Ministerio da Agriculfura, Rio de Janeiro, Brazil Translated by RALPH
E. OESPER,
University o f Cincinnafi
,The blue color produced by fusion with hydrated oxalic acid can b e used as a specific and sensitive test for diphenylamine and its derivatives. Carbazole derivatives also respond positively. Limits of identification have been determined for 15 compounds of these classes. Spot test analysis amounts are adequate.
A
and sensitive test for oxalic acid ( 4 ) is based on the formation of diphenylamine blue (Aniline Blue) n hen osalic acid is heated to 200" C. m-ith diphenylamine (melting point 83 " C.) : SPECIFIC
This reaction may also be employed for detecting diphenylamine in a sensitive manner. Furthermore, trials mith 25 compounds of this class shon-ed that, with the exception of dipicrylamine and nitrocarbazole derivatives of diphenylamine, they all, including carbazole, behave like the parent compound. Two groups should be distinguished among the derivatives of diphenylamine, according to M hether there is suhstitution in the benzene ring or in the imide group. illembers of the first group n i t h a n unoccupied para position may be expected to give a reaction analogous to that of diphenylamine. This is not to be excluded in the second group, but a preliminary splitting off of diphenylamine through pyrohydrolysis may also be taken into account. A cleavage of this kind can be accomplished by heating with hydrated oxalic acid, as in the region of 110" to 180" C. the water of hydration lost by the oxalic
acid acts as quasi-superheat>ed wat'er, which then brings about the requisite preliminary splitting off of diphenylamine. This is the reaction picture of a so-called pyrohydrolysis (Z), a type of reaction which has brought about analytically usable cleavages, including some n-hich cannot be accomplished by the wet method ( 5 ) . The assumption that a pyrohydrolytic splitting off of diphenylamine may precede the formation of dipheiiylamine blue, when X-substituted diphenylamine derivatives are fused with oxalic acid, is supported by the findings that fusion of 14''-acebyldiphenylamine or A--nitrosodiphenylamine with osalic acid a t 120' to 150" C. results in the splitting off of acetic or nitrous acids, respectively. These products are readily detected in the gas phase by acid-base indicator paper or with filter paper moistened with Griess reagent. The pyrohydrolyees underlying these cleavages, VOL. 32, NO. 7, JUNE 1960
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