ANALYTICAL CHEMISTRY
710
LITERATURE CITED
with very radioactive solutions. The “air lift” principle of circulating the solvent could be adapted to very small amounts of solutions. Hence the apparatus as presented here could be scaled down to handle smaller amounts of chelating agent,s. ;\loreover, it could be scaled u p t80allow the extraction of larger amounts of material per run. A va1,iety of chelating agents could be used, t’he only requiremcnt being that the solut,ion of thr chelating agent be lighter than the solution of the extractant anti that there he a minimum tcmdrncy toward forming emulnioii~ upon stirring. The system could be especially adapted to the sel)ai.ation of materials whose distribution coefficients betxec,n the chelating agent and the aqueous inetiium are rather small, where thc continuous extraction would result in a building ui) of the desired product.
Cnryell. C. D., and Sugarman. N., Satiorial Nuclear Energg. Serieb, Plutonium Project Record, 1-01. 9, “Radiochemical Studies: The Fi.+ioii Products,” X e w Tork, McGraw-Hill Book Co., 1951. Craig, L. C., =1xa~.CHEY.,21, 85 (1949); 22, G 1 (1950); 23, 41 (1951).
Hagemann, F., J . Am. Chem. Soc., 7 2 , 7 6 8 (1950). Meiiike. IF-. IT.. U.S. Atomic Enerev Commission Declassified Documents AECD-2738 and AECD-2750 (Auguit 1949) ; AECD-3C84 (March 1951). IbicZ., Procedure 88-1. Ibid., Procedure 89-1. hIillrr, D. R., Thompson, K.C., and Cunningham, B. B.. Phvs. Rei’., 74, 347 (1948).
Reid, J. C., and Calvin, M., U. S.Atomic Energy Commission De(-lassified Document MDDC-1405 (Aug. 13, 1947) ; J . I m . Chem. Soc.. 72, 2948 (1950). Seaborg, G. T., C‘hem. Eng. S e u v . 25, 2819 (194i). Veissberger, A . , “Techniques of Organic Chemistry,” 1-01. 111, Sen- T o r k , Interscience Publishers, 1950.
ACKNOWLEDG>IEST
The authors wish to thank the Michigan llemorial Phoeni\Project for its generous support of this rescarch and continuetl encouragement of work in the nuclear ficltl.
RI?ci:I\-ED
for review -4ugost 2-1, 1!151.
Accepted January 2 , 1952.
Determination of Sulfur and Halogens Improred Quartz Tube Combustion Apparatus E. 1). PETERS, G. C. ROUNDS,
AND
E. J. AGAZZI
Shell Development Co., Emeryrille, Calif. Of the \arious methods av:iilable for the determination of sulfur and halogens in organic materials, the horizontal quartz tube combustion method of Crote is particularl? iiseful because of its reliability and general applicabilit:. In appljing this method to numerous samples originating from research and from manufacture of petroleum products and cheniicals, an improied apparatus and procedure haie been developed which combine convenience and versatilitj. The apparatus is of dual unitized design, rugged, and efficient to operate. Satisfactor)
F
OR the determination of sulfur or halogens in organic materials, a number of accurate and reliable methods are avail-
able. Decomposition of the sample is achieved in any one of a variety of ways: by oxidation with an acid as in the well-known nirthod of Carius (6):b y fusion with sodium peroxide in a met,al bomb (5, l d ) , by reduction with metallic sodium in liquid ammonia solution (16, 19), by combust~ioiiin a metal bomb filled with oxygen under pressure ( I , 2 ) , by conibustion from a wick lamp ( 4 , 11, 18, 20),or by combustion in a vertical (8) or horizontal tube ( 7 ) in a stream of air or oxygen. , The applicability and convenience with which these methods can be applied vary widely. The choice of any one method over the others depends upon the characteristics of the material under test, accuracy desired, availability of equipment, and experience and training of the operator. h s a rule, methods involving combustion with air or oxygen are more generally applicable, more convenient, and more reliable when carried out on a routine basis than are t,hose involving chemical treatment of the sample. I n t,he authors’ laboratory, three combustion methods have been chosen to cover the wide variety of organic materials encountered. The lamp method is used when the sample is volatile and contains only a small concentration, generally less than I%, of sulfur or halogen, the osJ-gen bomb method is used when the sample contains metallic constituents, and.the horizontal combustion tube method is employed for all other types of samples.
procedures have been de\eloped for the determination of sctlfur and halogens in samplev covering a wide range of volatilitj and concentration. The accuracy of the method in general service work is about 0.03Yo for either sulfur or halogens. Applicability of the method can be extended to lower concentration ranges by making appropriate changes in apparatus and procedure. A good example of this is in the recent application of the method to determination of chlorine-containing pesticidal residues on certain food and forage crops.
This paper describes the apparatus and procedure used in the horizontal quartz tube method. The quartz tube combustion method was described in 1925 by Heslinga (9). He volatilized and burned the sample with air in a uartz combustion tube and completed the combustion by passing Ehe gases through a hot zone of quartz particles. He removed the oxides of sulfur from the gas stream by scrubbing with dilute hydrogen peroxide solution and determined the resulting sulfuric acid by titration. Grote and Iirekeler ( 7 ) employed an unpacked pluartz tube fitted with two sintered plates and a perforated plate; t ey applied the method to the determination of both sulfur and chlorine. Subsequently, their procedure was modified by Wurzschmitt and Zimmermann ( d l ), who eliminated the possibility of explosion by using a tube in which the sample was vaporized in a stream of inert gas and the vapors were then mixed with oxygen in the hot zone of the tube. Sulfur, chlorine, carbon, selenium, and mercury were determined in this manner by these Ivorkers. I n recent years, interest in this combustion method has come chiefly from microcheniists, and a number of micro adaptations of the method of Grote and Rrekeler have been published ( I S , 1 7 ) . Although little has been published on the macroprocedure, it has come to be used extensively by the petroleum industry. The a i d e versatility, convenience, and reliability of the quartz tube combustion method have been found very useful by the authors. During the past 13 years, the method ( 1 5 ) has been used daily and applied to many thousands of samples with good suc-
V O L U M E 2 4 , NO. 4, A P R I L 1 9 5 2
711
cess. Recently, in response to interest expressed by the pet,roleum industry, detsjls of the present and proaedure were made available to the American Society for Testing Materials (5). I n the development of the present apparatus, departures from the design of ~ ~and ~Krekeler t eweIe made with one basic ohjec. tive in mind: to have a rugged, unitized apparatus that would be convenient and efficient to operate. The dual feature provides a good meamre of efficiency and such items as the air-scrubbing syst.em, the absorber system, the furnaces with eontro]s,the means for introducing oxygen, and the gas burner sPten1 help to make operation of the apparatus convenient. DESCRIPTION OF APPARX
A photograph of the unitized, dual quartz tube combustion apparatu8 (available from the Braun Carp., 2260 East 15th st., Loa Angeles, Calif.) is shoiirn in F i w e 1, and a diagrammatic sketch of the gas flow system is given in Figure 2. Sir for combustion is drawn through each unit a t a rate of 3 liters per minute by application of a controlled vacuum. The air
is purificd by passage through 10% sodium hydroxide solution and 1.5% hydrogen peroxide solution, contained in scrubbers of special design. The scrubbers are equipped with mame sinteredglass disks to disperse the air and Can be cleaned and recharged (this is done daily) conveniently by means of leveling bulbs. If this purification is inadequat.e-e.g., when organic sulfur or halogen compounds are in the Bir-the scruhhen can he preceded b y a heated combustion tube. To facilitate the rapid and complete combustian of oarbanaoeons residues left by sOme m t e r i a l s upon burning in air, oxygen is provided. In conducting this step of the procedure, proper flow of oxygen is obtained by adjusting t,he oxygen COntrOI valve until the flaa- of air through the purification scrubbers ceases. The combustion tube is made of clear, fused quartz and is detailed in Figure 3. The tube is siniilar to that descrihed by Grote and Krekeler (7), diffeeringmainly in t h a t uarta rods, retained between two perforated quartz disks, areuse&pleee of the sinteredquartz disks. The combustion tube is attached to the absorber by means of a borosilicate glass adapter. A spring clamp is used to make the spherical connection tight between the cornbustion tube and the adapter. Two ahsorhors serve to remove sulfur or halogen from the .comhustian products; the absorbers are mounted on supports that m e convenient to use and easy to sdjust. The lower or primarv ahsorher is tho same as t h a t used for the determination sulfui by the lamp method (4).The upper or absorber collects any sulfur trioxide which escapes the primary absorber. Suitable trap8 are provided in the gas flow system, one being located hefore the combustion tube inlet and another (not a h o m in Figure 2) after the vacuum control valve, to prevent scrubber liquids from entering either the combustion
^.I..,
"-At."
..""
I:--
Disks, Irnm.thick with I . 5mm.hole
lllci
Figure
q"z%."-pa."""" l r C U l U L l
"1
b11C C"ILI"U~III"II
b""6
18
I
13eittea M
950' t o 1000" C. with B 7.25-inch electrically heated furnace. The furnace temperatureisiLdjustpd by arheostat and ismeasured by a thermocouple that eoniiects to a pyrometer mounted on the front ane el. A blastAviw burner equipped with a wide grid is employed to vaporize the sample. The heat output of this type of burner is sufficient to heat the inner Inla, surfsee (lover portion) of the combustion tube t o a temperature of approximstely 840" C., while sir is SP'O" 8.00 flowing through the apparatus. Excessive heating of the furnace support.8 and front panel is avoided by perforations in the furnace shield, location of a sheet of insulating Transite below the furnaces, and mounting the front panel so t h a t
1. Dual Uniti Apparatus
COMBUSTION PROCEDURE:
X
I L,"*
The optimum weight of samples for analysis is t h a t containing 35 to 40 mg. of sulfur or 2 to 4 milliequivalents .Il.l.-.-
I
I
I
F i g u r e 2.
Gas Flow System
TT
~.. > C L L .... Ir. ....
halogen content is low, the sample size need he limited only hv the capacity of the porcelain- combustion boat, which is about 2 grams for the boat most generally used (Coors No. 61. Solids or heavv liauida are weighed directly into %he ;ombustion boat. Heavy liquids which tend to "creep" from the boat
712
ANALYTICAL CHEMISTRY
are weighed in sections of borosilicate glass tubing 7 to 8 mm. in outside diameter, sealed at one end. Hygroscopic or volatile liquids are conveniently delivered from a small weighing pipet into a boat placed partially inside the combustion tube while air is drawn through the unit at the required rate. Samples too volatile to handle in this manner are placed in tubes of borosilicate glass made by sealing one end of a section of tubing ( 7 to 8 mm. in outside diameter) and drawing the other to a fine capillary. Sample is drawn into these tubes by warming the sealed end in a small flame, inserting the tip of the capillary into the liquid being sampled, and cooling the sealed end with dry ice. The capillary is then bent so that it lies along the bulb. After reweighing, the tube is laid in a porcelain hoat, capillary side u p , with the sealed end elevated and t'oward the furnace. Heating t,he sample tube causes expansion of the gas bubble a t the sealed end, thus expelling the sample. Because of the difficulty in controlling the rate of vaporization of volatile materials, it is recommended that the sample size be restricted to 0.3 gram or less when this technique is used. Combustion of the sample is caarrietl out as f o l l o w : , Place 30 ml. of absorbent in the primary absorber and 10 nil. in the secondary absorber. -idjust the vacuum to draw air through the absorbers a t a rate of 3 k 0.5 lit,ers per minute. Insert the saniple boat into the vomhustion tube and slide it to a position 140 to 150 mm. from the tube entrance. Replace the inlet, connecation and vaporize the sample :tt B slow, uniform rate by gratiually nioving the burner to\vard thr hoat. The original position of the burner with respect to t h r hoat depends upon the volatility of the sample. For ext.remely volatile mples this distance should be as great as possihle. The h i r should never be placwl directly under the hoat at this stag?. TKOraliid vaporization vtill be evidenced by pulsations in the visible vapor hetween the boat and furnace. When this occurs, remove the burner until pulsations cease. Advance the burner along the tube until t,he furnace is reached. Place t,he hurner adjusted to full heat beneath the boat, set a Sichronie wire g:tuze tunnel over the tube above the burner, and turn on the osygrn until the flow of ail, through the scrubbers stops. Burn all rrsidu:il carbon by advanring the burner and gauze along the tube. Disconnect the quartz tube from the exit adapter and close the spherical opening of the adapter with a glass stopper. Allow vacuum to remain on for a fe\v seconds, rlose the vacuum control valve, and slowly admit a i l , into the system through the vent causing the liquid in the secondary absorber to be dran-n into the primary absorber. .b the pressure alo\vl~-equalizes, remove the spray t8rapand rinse it with distilled water. IVhen all liquid has drained from the secondary ahsorber, rinse immediately with about 20 nil. of distilled \\-atel,. Remove the secondary absorber, and wash both t,he ground joint and the bottom of the sintered plate. Rinse both stopper and adapter with a small quantity of water: collecting the washings in the primary absorher. DETEHMlN.\TION OF SULFUR
sorbed fioni the gas stream by use of an alkaline solution containing a reducing agent. Grote and Krekeler successfully employed dilute sodium hydroxide solution containing sodium sulfite. I n this work, an alkaline solution of hydrogen peroxide was found to be equally effective and someivhat more convenient.
Table I .
Sulfur in Materials of Known Sulfur Content (Acidiiiietric procedure) Sulfur,
.\laterial Sulfur. flowers
Calcd. 100.0
nipropyl sulfide
27.1
Methyl thiophene
32.7
Thioohene
38 1
XIethyl mercaptan
66.7
1;thyl disulfide
3 2 . ,i '
Thiophenol
29.1
ii-Anryl diiulfide plus white oil
1.4;
Phenol
0.00
Toluene
0.00
IYhite oil
0 00
Tahle IT.
5;
Found 9 9 . 8 , 100.0 99.9 27.2 2i.l 32.3 32.6 38.0 38.0 66.9 67.0 a?, 2 .i2 4 29.0 29.0 1.48. 1.50 1.49 0.00 0.00 0 00 0 00 0.00 0 00
Sulfur in Yarious IIaterials (hcidimetric procediire)
Material Sulfurized Cis Synthetic rubber 1,ubricating oil A 1,ubrirating oil B 1.ubricating oil C 1.nbricating oil D Crude tar acids
Sulfur, 52 7.56 7.34 0.11 0 11 0.40 0 42 0 02 0 02 .o. 59 0 60 1 13 1 13 0 01 0.02
llrtterial Sulfurized oleic acid Diesel fuel High-sulfur additive , Sulfur additive Yiscous cil
Gas oil
Sulfur, 5& 9.26 9.33 1.02, 1.02 1 00. 33.0. 33.0 9 . 9 7 , 9 92 9.99, 9.98 2.16, 2 . 1 6 2.19, 2.18 1.58 1 , b8
For the determination of halide ions, the convenient and accurate Volhard method was chosen. I n determining chlorine, the titration for chloride can be performed without destruction of the es(*essperoside. However. for hromine anti iodine, it is essential to deconipose the excess hydrogen peroside: otherwise, the elemrnt:il halogens are produced upon acidification. The dkaline solution containing the peroxide i p hoilrd for ahout 30 minutes. Then, to make rertain that thc last traces of peroxide are removed and to reduce any hypohalogenates or halogenates, a small quantit,y (approsimately 0.5 gram) of hydrazine sulfate is added just prior to the acidification step.
Cpon combustion, prnerally most of the sulfur appears as sulfur dioxide; only a m a l l part is converted to sulfur trioxide. Dilute hydrogcn peroxide solution (c.P., l,5yo)is an excellent ahsorhent for sulfur dioxide and with the aid of the sintered-glass plates it also serves \vel1 for sulfur trioxide. I n the absence of elements other than sulfur n.1iic.h also produce acids or bases upon combustion (halogens, nitrogen, phosphorus), sulfur may he determined by titration of the sulfuric acid formed in the absorher. The titration is perfomied directly in the absorber hy adding standard caustic solution to the small bulb of the absorber while the content? are agitated hy applying suction to the large bulb. I n the presence of other acid- or base-forming element$, sulfate ion in the absorber liquid is determined gravimetrically b y precipitation with barium chloride in t h r usual manner. Data illustrating the acruracy and precision obtainable are given in Tables I and TI. The sulfuric acid was determined acidiniet,rically in all cases. The values obtained for the sulfurfree materials (phenol, toluene, and white oil) by the acidimetric procedure show that no significant amounts of nitric acid are produced upon the combustion of these materials in air.
The sbsorlient used in the determination of halogens is prepared by placing 25 ml. of 2.57, sodium carbonate solution and 10 nil. of 6% hydrogen peroxide solution in the primary absorber and iiiisirig bj- drawing air through the mixture for a few seconds. Ten milliliters of this mixture are then transferred to the secondary absoi,ber. Sodium carbonate is preferred to the equally effective sodium hydroside, because it is Ivss corrosive to the sinteredglass plate. Although peroxide decomposition occurs at an appreciable rate in alkaline solution at room temperature, the amount of peroside present, is sufficient to assure an ample excess throughout the period of combustion. After ronibustion, the solut,ion is transferred from the absorber to a glass-stoppered Erlenmeyer flask and the halide ion is cleternlined l)y 1-olhard litration. Typiral results are shown in Tahle 111.
DETERJIIhATIOY O F HALOGENS
SIMULTANEOUS DETER3IINATION OF SULFUR AND CHLORINE
.\lthough organohalogen compounds generally yield hydrohalogen acids upon combustion, elemental halogens may also be produced. These halogen compounds can he quantitativelr ab-
It is possible to determine sulfur and chlorine simultaneously by using neutral hydrogen peroxide as absorhent and measuring the chloride ion content in addition to total acidity. The total
713
V O L U M E 2 4 , NO. 4, A P R I L 1 9 5 2 acidity is determined as i n the method for sulfur. The solution is then made alkaline and the methyl red indicator is destroyed by boiling. Chloride ion is determined by Volhard titration and the rwult thus obtained is assumed to he a measure of the hydroc*hloiic.acid present. The rcsitfual nc.idity is regarded as sulfuric acid. Results ohtainetl b y this procedure are shoa-xi in Table I\-. From thew valurp it appe:trs that neutrnl or acidic hydrogen peroxide is a good absorbent for chlorine. However,' tests b y this com1)ustion method have shoi\-n that with some materials-e.g., epichlorohydrin, dichlorohydrin, arid carbon tetrachloride-1 to 2oj, of the chlorine is lost when neutral or acidic hydrogen peroxide is used. Therefore! n-hrn the highest accuracy is desired for chlorine or other halogens, alkaline hydrogen peroxide should ) ) e c~inployed8.s tiesc.i,ihcd in the procedurr for halogens. I~ISCUSSION
The mcthods tlrecrihetl are intendetl primarily for organic. materials containing iiioi'e than 0.03yo .sulfur or halogen: houevpr, they have been applied to inorganic. materials, interest being centered upon the determination of sulfur. Kurzschmitt and Zimmermann (21 ) iletermined the sulfur content of iron pyrites. Serif and Schoherl ( 1 4 ) iinnlyztd materials containing the sulfatei: or sulfides of iron, ropprr, ant1 zinc. I n the authors' lahoratory, t h r sulfates of tin, bilver, chromium, a n d nirkel Tvere decomposed 1)y heating the samplr in the quartz tube to a temperature of 950" to 10011" C. by means of an electric furnace. I n general, the method should be applicwblc t o ally inorganic material n-hich releases i t 3 sulfur or htilogc,n upon heating in an oxidizing atmosphere. The analysis of organic8 materials csontaining metals, such as the alkalies or alkaline earths, which form sulfates or chlorides st,nl)le at the maximum temperature attained by the sample n-ould 1)e expected t o give low results. I n many rases recovery has heen found to be complete, hut the exact reason for this has not I)een esta1)lishecl. On the othcr hand. it n-ould seem that com-
'I'ahle 111.
Halogen in \Iaterials of Known Halogen Content Halogen. % Found
filed.
Material I:pichlorohydrin
38.3
Glycerol dirhlorohydriii
4;.
6-Chlorallyl alcohol 2-Bromo-octane
38 4 41.4
4.4-Dibroinodiphenyl ether
48 7
3"
Trichloroacetophenone
47 6
p-Iodoacetanilide
48 6
2-Iodobenzoic acid, S B S Chlorinated Sample .4
;, 1
2
38.2 38 3 54.3 R4 2 88.3 41,4
41.6 48.8,48.4 48.4 47.3 47.2 48.2, 48.J 48.6 31 1 30.8
in white oil
0 13
0 13 0.16 0 12
Sample H
0.68
Saiiiple C
2.10
Sainple 11
6.05
0.61 0.38 0.66
0.63 2.02 2 02 2.02 6.03
6.05 5.98 6 06 Dichlorobenzene nirhlorobensene in oil Painple A
48 2
48.0
48.6 0 10
Saniple R
1 00
Saiiiple C
.iS i
0 11 0.11 1.01,1.00 0 99 p 95, 6.01 ; ,9 3 . ..
Value b y Carius niethrid: calculated value for p u r e inaterial is 55.0%. Chlorine content of roncentrate ( 1 7 . 2 5 . ) determined by quartz tube method. 0
plete recovery could be obtained by simply washing the residue in the combustion boat and combining the washings with the absorber liquid, provided the residual sulfate or chloride is watersoluble. Tests with materials containing metals and chlorine have shown that washing with normal amounts (approximately 50 ml.) of water does not alaays result in complete recovery of cahlorine, even though the metal present forms a water-soluble chloride. When the combustion of a chlorine-free material follows one containing chlorine and certain metals, high chlorine values are often obtained, indicsating that chlorine is bouvd by t'he quartz combustion tube and then sloa-ly released upon heating. The bound chlorine can usually he removed hy washing the tube with a large volume of water. ,ipplicability of the method to organic materials containing metals should therefore be established by comparison with a method which is known to be free of interference from most met,&. The oxygen bomb methods ( 1 , 2) are suitable for this purpose.
Table I V .
Simultaneous Determination of Sulfur and Chlorine
3Iaterial 2-3Iethyl-8,4-dichlorojuifoialle
Sulfur, % Present Found
lj.8
3.B-Dichloro~ulfolane
10.9
l.i..i 1.5.6 16 8
2,3-Dichloro- 1-propyl-3-sulfolaiiyl ether Mixture of benzyl sulfide and chlorinated wax Mixture of dichlorohydrin a n d benzyl sulfide 3Iixture of dichlorohydrin, amyl disulfide, and white oil
12.6
16.8 13.0
Chlorine, % Present Found ~
34.9 37.4
34.8 34.9 38.0
28.7
28.5
9.28
13.0 9.2,;
3.00
2.86
43.2
43 3
0.8i
0.8,;
22.1
22.1
6.59
28.5 6.57
The :illsorption of sulfur from the combustion gases is complicated by the presence of sulfur trioxide in the gas stream. Although sulfur dioxide constitutes the bulk of the sulfur in the gas stream and is quantitatively absorbed by the hydrogen peroxide solution, some sulfur trioside escapes as a visible mist. Grote and I
