to be within a narrow range of weight a n d draft resistance (Table V). Because a n y variation in the physical properties of the cigarette sample would contribute greatly to the variations exhibited in Table V, determinations mere made on five aliquots of the same smoke concentrate, thus eliminating this variable. The results were 11.64, 11.68, 11.66, 11.63, and 11.64 mg., respectively, of nicotine recovered. DISCUSSION
Steam distillation of the acidic smoke concentrate prior to distillation of the nicotine eliminates a considerable portion of the interferences which contribute high and inconsistent backgrounds t o the ultraviolet spectra, and which cause inconsistent results. If freshly distilled nicotine is used in preparation of the caJibration curve, there will be no appreciable background in the ultraviolet spectrum. and the absorption at 259 mp will correspond directly to the nicotine concentration. However, there will be some background
if the nicotine has not been freshly distilled. The interfererdes which cause high and inconsistent backgrounds in the ultraviolet spectra of nicotine derived from tobacco smoke are not evident in nicotine, which is steam-distilled from tobacco itself. For this reason, the preliminary steam distillation of acidic solution found neceseary in the analysis of smoke is not a required step in the determination of nicotine in tobacco. Khen the smoke of ten or more cigarettes is contained in the solution t o be analyzed, or when the smoke has an abnormally high nicotine content, the dilution technique of Willets et al. will probably have to be employed. LITERATURE CITED
(1) Assoc. Offic. Agr., Ckernists, "Official Methods of -4nalysis, 8th ed., p. 66, 1955. (2) Bradford, J. A., Harlan, W. R., Hanmer, H. R., Ind. Eng. Chem. 28, 836-9 (1936). (3) Fabre, R., Truhaut, R., Boudene, C., Ann. pharm.franc. 10, 579-94 (1952).
(4) Filk, H., Sturmer, E., Loeser, A., drznezmztfel-Forsch. 4 (No. 6), 367-8 (1954). (5) Freeman, F. M., Analvst 80, 520-2 (19t5). (6) Giovanni, G., I1 Tabacco 57, 103-21 (1953). (7) Greenberg, L. A., Lester, D., Haggard, H. W.,J . Pharmacol. Exptl. Therap. 104, 162-7 (1952). (8) Houston, F. G., ANAL. CHEM. 24, 1831-2 (1952). (9) Jeffrey, R. Tu'., Eoff, W. H., Ibid., 27, 1903 (1956). (10) Jensen, C. O., Haley, D. E., J . Agr. Research 51,267-76 (1935). (11) Keith, C. H., Newsome, J. R., Tobacco Sei. 2, 14-19; Tobacco 146, Yo. 9,22-7 (Feb. 28,1958). (12) Leiserson, L., Walker, T. B., ANAL. CHEW ...~ . 27.1129-30 f 1955). (13) hlarkn-ood, L. N.,j. Assoc. O@c. Agr. Chemists 22, 427-36 (1939). (14) hforani, V., Giovannini, E., Chim. e ind. (Milan) 37, 109-12 (1955). (15) Willits, C. o., Swain, M. L.,Con~
nellv. J. A.. Brice. B. A.. ASAL. CHEM.
22, i30-3 (1950). ' (16) Wolff, W. A., Hawkins, 31. A., Giles, TI-. E., J . Biol. Chem. 175, 825-31 (1948).
RECEIVEDfor review March 22, 1958. Accepted July 2, 1958.
Determination of Chlorine and Bromine by the High-Temperature Combustion Method S. W. NICKSIC
and L. L. FARLEY
California Research Corp., Richmond, Calif.
b High-temperature combustion apparatus normally used for sulfur determination has been a d a p t e d to samples containing chlorine and bromine. The procedure for determining halogens i s similar to that used in determining sulfur in petroleum fractions. A weighed sample in a ceramic boat is slowly moved into the combustion zone while a stream of oxygen i s passed over it. The sample burns, and the exit gases are scrubbed with a solution of 5% aqueous sodium bisulfite. When the sample has burned completely, the absorbing solution i s drained out and titrated potentiometrically with silver nitrate. The method i s suitable for materials that are difficult to decompose by other methods, and it i s especially useful for determining the chloride content of refractory inorganic catalysts.
C
methods of analysis have distinct advantages. They consume less time than other methods because of the rapid sample decomposition which is peculiar to these procedures and they are not usually restricted to OMBUSTION
1802
ANALYTICAL CHEMISTRY
any one type of sample or concentration range. Such methods for the determination of halogens date back to the days of Pregl (6). Considerable interest in them has been reawakened intermittently (1-3, 6, 7, 8) and today combustion methods are common in petroleum laboratories. The high-temperature combustion apparatus has long been used in the steel industry for the determination of sulfur and carbon in ferrous metals. I t s usefulness has been extended to petroleum products and related materials, and it is being studied by ASTM Committee D-2 on Petroleum Products and Lubricants (6)as a possible ASThI standard for sulfur determination. This paper describes the adaptation of the high-temperature combustion apparatus to compounds containing chlorine and bromine. Sodium bisulfite solution is used in the absorbers to absorb chlorine and bromine and t o convert them quantitatively to the ionic form for subsequent titration. Iodine compositions were not studied. B y using the high-temperature combustion apparatus where it is available, not only is a separate furnace for halogens eliminated,
but also the scope of analysis is extended to samples that cannot otherwise be easily handled. APPARATUS A N D REAGENTS
The apparatus has been described (2). The furnace used is a dual, resistance-type unit operating at 2400" to 2600" F. The combustion tubes are ceramic. The absorbers consist of extra coarse gas dispersion tubes assembled in a glass container with a glass stopcock for draining out the absorbing solution. The quartz wool plug in the hot part of the combustion zone is essential, and the position of this plug, as well as the position of the combustion tube in the furnace, is an operating variable. Brief experiments were made with an induction furnace, but the first results were not as good as those obtained with the resistance unit. The halogen-containing solutions were titrated on a Precision-Dow Recordomatic Titrator. This versatile instrument shortened the analysis time. However, the halogens may be titrated potentiometrically by any standard method. The reagents required are a 5% aqueous solution of sodium bisulfite and
standardized O.1N silver nitrate. A small amount of 1 to 1 nitric acid is added prior to the titration. PROCEDURE
The procedure for determining halogens begins with a combustion step ( 2 ) . The furnace temperature is adjusted to 2500" i 100" F., and the oxygen flow rate is set at 0.5 liter per minute. The absorber contains 70 =t 5 ml. of 5% sodium bisulfite solution. The sample is weighed into a conibustion boat. The proper size depends on the nature of the sample, which should not exceed 0.4 gram for flammable materials. One or 2 grams may be used for refractory or high-boiling solids. The latter must be burned a t a carefully controlled rate to avoid flashes. The sample boat is inserted into the inlet end of the combustion tube, which is then closed with the inserter assembly. The boat is pushed into the hot zone at a rate of about 1 inch in 5 minutes. This operation is one that can be learned only by experience with various types of samples. The objective is to achieve a reasonable combustion rate without causing the sample to flash to the extent of blowing out the sample inserter assembly, or cracking the tube. After the sample boat has reached the hottest part of the furnace, the combustion is continued for a t least 15 minutes. The solution is drained from the absorber into a 250-ml. beaker, and the absorber and lines are washed thoroughly with distilled water. Kashings are added to the beaker. Five ml. of 1 to 1 nitric acid are added, and the solution is titrated potentiometrically with silver nitrate. A silver indicating electrode and a glass reference electrode are used. The curve is plotted and the end point obtained in the usual way. Occasional check runs with a standard sample are desirable to determine if the apparatus is functioning properly. RESULTS
Absorber Solution. Because of t h e complex nature of t h e combustion products, i t was necessary t o find a reagent which mould rapidly reduce t h e gases t o halides. I n single scrubbers, hydrogen peroxide solutions u p to 30% in strength, with and without added acid, were inadequate, a: was a 5% aqueous solution of hydrazine. d 5% aqueous solution of sodium bisulfite gave quantitative recovery on known samples. T o test the decay rate of the sodium bisulfite solution, small aliquots mere withdrawn from the absorber from time to time and titrated with standard iodine solution (Table I). After 2 hours' bubbling Kith oxygen, there was still 6.9 of the original 69.3 meq. available. The addition of 5 ml. of 0.1-V hydrochloric acid to 70 ml. of 5% sodium bisulfite solution consistently required the stoichiometric
-
amount of 0.1S silver nitrate a t the equivalence point. Sample Pyrolysis. Hexachlorobenzene as used in much of t h e early developmental work. This compound was found to be difficult to pyrolyze completely because its molecule contains only carbon and chlorine. The addition of a few drops of white oil aided the pyrolysis, and this is recommended for samples that do not contain hydrogen. The quartz wool plug was
Table I. Rate of Oxidation of 5% Sodium Bisulfite Solution. (Oxygen Bubbling Rate of 0.5 Liter per Minute)
Bubbling Time, Hr. Original solution '/2
1 I'/Z
2
bleq./'70 111. 69.3 42.9 12.1 7.6 6.9
Table II.
pH 5.10
.. ..
4:60
also found to be necessary. Low and variable results are sometimes caused b y improper positioning of this plug. It should be fitted in a hot enough portion of the tube so that it does not build up a carbon deposit. Occasionally, a surge of pressure in the combustion zone will force the quartz wool plug out of the hot zone. Some compounds distill before they are pyrolyzed, and the plug catches the distillation product, and allows the pyrolysis to go to completion. Samples having a high sulfur content sometimes give thiosulfate as part of the pyrolysis products. The presence of thiosulfate is shown by abnormally high initial millivolt readings and tm-o shallow breaks in the titration curve. K h e n this occurs, the sample must be rerun and the thiosulfate decomposed before titration. The thiosulfate decomposition is easily accomplished by the addition of 5 ml. of 1 to 1nitric acid and heating t o 170" to 180" F. After cooling, the titration
Halogen Content by High-Temperature Combustion
Theoretical Halogen, 74.8
Hexachlorobenzene p-Chloroacetophenone
22.;
o-Xitrochlorobenzene
22 5
o-Chlorotoluene
28.0
Pentamethylene dibromide
69.6
p-Nitrobenxvl chloride
20.7
2,5-Dichloro-3,6-dihydrosy-p-quinone
34.0
n-Butyl bromide
58.3
Ethylene dichloride
71.1
Phenyl isothiocyanate Sodium chloride
60.8
FeC13.6H20
39.4
1
Unknown Organic bromide, % Br Organic chloride, % Cl Organic chloride containing 20y0 sulfur, % C1
21.6 27.5 27.6 71,5 69.6 21.1 21.3 32.5 31.8 60.0 59,7 71 .0 70.4 0.1
100 99
...
58.7 60.2 39.1
97 99 99
Comparative Results
Combustion method
Inorganic Catalyst, % C1 2 3 4 5 6
Recovery, % 96 97 99 99 96 96 98 99 102 100 102 103 96 94 103 102
21 3
0
Table 111.
Type of Sample
Halogen Found, % 71 8 72 2 22 5 22 6
0.22 0.19 0.26 0.20 0.075 0.05;
0.34 6.01,6.03 0.82 1.22
2.34
Halogen Content Comparative method Acid Digestion Extraction Procedure 0.22 0.16 0.16 0.15 0.058 0.038 Sodium Biphenyl Procedure 0.35 6.23 0.81 1.07 2.46 ~~~~
VOL. 30, NO. 1 1 , NOVEMBER 1958
-
1803
proceeds normally, and stoichiometric values of chloride are obtained. Table I1 lists results obtained on known compounds. The best available commercial material was used. There should be no difficulty in applying the method to any organic material that is not too volatile to weigh. Except for the formation of thiosulfate noted above, no interference was found. Alternate use of the equipment for sulfur and halogen analysis has caused no problems. After running catalyst samples, the exit end of the combustion tube in the hot zone was heated briefly before returning to sulfur analysis to remove condensed volatile portions of the catalysts which would interfere with sulfur analyses. Both chlorine and bromine can be estimated in the same material. Each has its own equivalence point, and by noting the volume of titrant a t the characteristic point, quantitative fi,vures for each can be obtained. Some work was done with inorganic materials, but this aspect was not fully explored. Nearly quantitative results were obtained with ferric chloride and sodium chloride. Samples containing barium, calcium, and zinc chlorides were also analyzed with good results. The outstanding application to inorganic material is the analysis of refractory material, such as re-forming catalysts. Table I11 compares results with those obtained by an acid extraction pro-
cedure. The high-temperature results are always higher and probably better in view of known uncertainties in the extraction steps, and the method is much faster. Grinding is not required, and relatively large samples (up to 5 grams) can be used when lorn concentrations are being determined. Certain residues containing complex cyanides were easily analyzed for chloride content when other methods gave unreliable answers. Table I11 shows agreement with results obtained on unknown organic samples by another method.
dual combustion furnace, together with an automatic titrimeter for the potentiometric titration of the chloride and bromide, two determinations can be made in 1hour. I n this laboratory, the sodium biphenyl (4) procedure for halogen has proved satisfactory for simple organic material. However, for analyzing insoluble materials, acidic compounds, residues, emulsifying systems, and inorganic catalysts, the high-temperature equipment, where already available for sulfur analysis, provides an extension of the scope of chlorine and bromine determinations.
DISCUSSION
No limit was found to the upper range of the high-temperature method. The lower range is limited by the volatility of the material and the permissible sample sizes that can be handled. The resistance combustion apparatus has an upper sample limit of 0.4 gram for many materials. Thus, t o extend the range below a few tenths of 1%, more sensitive methods, such as colorimetric procedures, must be used to determine halogen content, or multiple burns must be made. Larger samples can be used on high-melting solids and refractory materials. The use of gelatin capsules is recommended for weighing volatile samples. The method is rapid for analyzing unknown materials and by using the
LITERATURE CITED
(1) Agazzi, E. J., Peters, E. D., Brooks, F. R., h A L . CHEX.25, 237 (1953). 1~, 2 ) ASTM Standards on Petroleum Prod-
ucts and Lubricants, Appendix 11. November 1956. (3) Belcher, R., Ingram, G., Anal. Chirn. Acta 7,319 (1952). (4) Liggett, L. M., ANAL.CHEY.26, 748 (1954). (5) Siederl, J. B., Siederl, V., “Micromethods of Quantitative Oreanic Analysis,” p. 16O;Riley, New York, 1942. (6) Pregl, F., Grant, J., “Quantitative Organic Microanalysis,” p. 85, Blakiston, Philadelphia, 1946. ( 7 ) Safford, H. W., Stragand, G. L., ANAL.CHEM.23, 520 (1961). (8) Sundberg, 0. R., Royer, G. L., Ibid., 18, 719 (1956). RECEIVED for review February 14, 1958. ilccepted June 6, 1958. Division of Petroleum Chemistry, 133rd Meeting, b C S , San Francisco, Calif., ilpril 1958.
Determination of Oxide Films on Tin Plate A. R. WILLEY and D.
F.
KELSEY
Research Division, American Can Co., Barringfon, 111.
A rapid coulometric procedure for the determination of oxide films on tin plate is described. Its validity was established by an independent analytical procedure based on a chemical solution principle. This coulometric method or close modifications thereof have been universally adopted by laboratories associated with the tin plate industry. Although designed primarily to study commercial problems posed by oxide films on electrolytic tin plate, the procedure is also useful in related research investigations.
T
IN OXIDE films
on tin plate formed during production at the mill, or developed during warehousing, have long been associated with adhesion failures of organic coatings, yellow surface discoloration, and soldering dif1804
ANALYTICAL CHEMISTRY
ficulties. Although a visual method for classifying the extent of surface oxidation on tin plate was early established, substantial progress in oxide film control required the development of a convenient and accurate analytical method. Among different investigators there is still a difference of opinion as to the exact chemical composition of the oxide, but data obtained in this study indicate that it is essentially stannous oxide. Kerr ( 7 ) and MacKaughton (8)used weight loss during cathodic reduction t o determine film thickness on very heavily oxided tin surfaces. The apparent ease of reduction of surface oxide by cathodic treatment suggested a method based on Faraday’s law for evaluation, and Miley (9) and llIiley and Evans (11) used such a method for
studying oxide films on iron. Later Miley(l0) demonstrated that the method was applicable to measurement of oxide films on copper. Similar studies were made by Price and Thomas (12) on silver, copper, and silver-copper alloy. Salt and Thomas ( I S ) and Katz (6) reported quantitative procedures for measurement of oxide on pure tin. The first application of the electrical reduction procedure for estimation of oxide films on tin plate appears to have been made by Donelson (3). Recently Frankenthal, Butler, and Davis (4) described a coulometric method for tin plate, as did Britton and Bright (1) who also studied the nature of the films. The technique described is based on the earlier methods used, but is improved by better circuitry and the use of a recording potentiometer to eliminate manual plotting of data. It rvas
