Determination of Oxygen in Organic Materials by Modified Schutze-Unterzaucher Method Applications to Petroleum Products hIOKRIS DUNDY AND ERVIN STEHR Beacon Research Laboratories, The Texas Go., Beacon, S. I-. The SchGtze-Unterzaucher method was investigated because high results were obtained when certain lots of iodine pentoxide were used in the determination of oxygen; analysis of hydrocarbon samples indicated oxygen contents as high as 2.5%. Data indicate that this anomaly is caused by liberation of extraneous iodine from the iodine pentoxide through the partial reaction of the oxidant and the hydrogen formed by the pyrolysis of the sample. A gravimetric procedure precludes interference due to extraneous iodine. The iodine is retained in an absorption tube containing crystals of sodium thiosulfate and suitable drying agents. The carbon dioxide is weighed by conven tional means in a Pregl micro absorption tube. Improvements in apparatus and e x periences with both methods are described.
formed from the hydrocarbon samples was gaseous hl-drogen and not hydrocarbons of low molecular weight. The sulfur compounds were largely converted t o hydrogen sulfide when sufficient hydrogen was present in the sample, but where a deficiency of hydrogen existed there was an increasing tendency for the formation of carbon disulfide. Carbonyl sulfide was produced in much smaller quantities. Nitrogen where present was converted to hydrogen cyanide. Small quantities of hydrogen cyanide were also obtained from the samples containing no nitrogen, an indication that the sweeping gas had probably reacted with the hot carbon to a limited extent. Organic chlorine compounds formed hydrogen chloride. $]though the data presented are not extensive enough to give a satisfactory indication of exactly what happens in the reaction tube, the results give a better understanding of why there were some interferences in the volumetric method of Unterzaucher, Graham and Winmill ( 5 ) , who determined carbon monoxide in ill mixtures of other gases, found that iodine pentoxide heated HE need for a reliable method of determining petroleum products has been apparent for many years. above 135" c. consumed hydrogen but that the reaction took Until recently no reliable direct methods TYereavailable and the place a t temperatures as low as 100" C. when carbon monoxide elemellt was usually estimated indirectly by ascertaining the perwas mixed with the hydrogen. This information led to the belief centages of all the other elements in the sample and then subthat hydrogen, which is formed in the reaction tube, might be reacting with the iodine pentoxide heated a t 119" C., thus libeltracting the sum of these values from 100. was introduced in 1939 by ating iodine and contributing to the high results obtained by -4new approach to the Schiitze (5),who pyrolyzed the sample and passed it over carbon Cnterzaucher's method. Therefore samples of known oxygen content were analyzed using Unterzaucher's method but employheated at 10000 C. to convert the oxygen to carbon monoxide, to carbon dioxide and detering lower temperatures for heating the oxidation tube, to ascer,&ich was subsequently tain if selective reduction of the iodine pentoxide with carbon mined gravimetrically. others modified the procedure and intraduced improvements, The modification proposed by I;nter- monoxide could be effected a t lower temperatures. The results zaucher ( r ) , R,hich determined the carbon monoxide iodometof thew analyses are sh0Tr.n in Table 11. The data obtained for rically by reacting it with iodine pentoxide and measuring the henzoic acid indicated that heating the oxidant between 90' and iodine liberated, has been accepted in the past fen, years for de100" C. might be satisfactory, but subsequent data obtained trrmining oxygen in various types of material (1, 2, 4 ) . for hydrocarbons showed that iodine was still liberated a t the for oxygen TTere obtained in these laboratories, lower temperatures, although some improvement wa8 indicated. High jvhen Unterzaucher's method was applied to compounds of The favorable results with benzoic acid were therefore assumed to be coincidental and probably a result of compensating errors. kn0lr.n oxygen content. The anomaly was especially apparent when the method was used for analyzing material containing A more direct indication of the effect of hydrogen on the iodine little or no oxygen. Results for the oxygen content of hydropentoxide was obtained by passing hydrogen gas through the carbon samples, which contained no oxygen, ranged as high as oxidation tube and determining the iodine liberated. Data 2.570, although blank determinations run under the same rondiwere obtained bJ- passing the hydrogen through the oxidation tions gave satisfactory results. The reactions taking place in the reaction and oxidation tubes were therefore investigated to ascertain the source of Table I. Analysis of Gases Obtained by Pyrolyzing Organic the trouble. Organic compounds containing various combinaCompounds and Passing Products Formed over Carbon Heated at 1125' C. tions of carbon and other elements were pyrolyzed Analysis b y Mass Spectroiiieter of Gases from Reaction TubeY and the products of decomposition passed over Coinpound Hz C H I CO Cot HIS CSs COS HCN " 2 1 carbon heated a t 1125" C. The gaseous products ?;aphthaleneb , . .. .. .. 0.5 , . 98.7 0 . 8 .. resulting from these reactions were collected a t n-Hexadecaneb 99.3 0.6 0.1 .. 7 1 . 0 0 . 2 1 8 : 8 Trace 9:s 0.3 0.1 0.1 .. the exit end of the reaction tube by displacing ~ ~ ~ ~ $ ~ u l f o n e a 52.3 . . 37.2 .. 8.00.2 0.2 2.1 .. water or mercury from a gas-sampling pipet. To Thioureab 56.8 .. .. .. 27.0 5 . 5 . . 10.7 . . sum-Di-n-butylisothiourea prevent excessive dilution a minimum quantity of icrateb 3 9 . 8 0 . 2 5 3 . 0 Trace 1 . 6 Trace Trace 5.4 nitrogen was used to sweep the products through o-ehlorobenzoic wide 32.8 . ". 3 . .. .. 0 . 8 11:7
T
'
the reaction tube into the gas pipet. The data shown in Table I have been calculated on the nitrogen-free basis. The product predominantly
a
b C
On nitrogen-free basis. Collected over water. Collected over mercury.
1408
'
'
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1
Figure 1.
Apparatus f e r Determining Oxygen i n Organic Material
lube alone and through both the reaction and oxidation tubes. The gas was passed t,hrough the purification train to remow interiering substances before being used for the test. The results of these tests, shown in Table 111, indicate that an appreciable amount of iodine is liberated from the oxidation tube by passing hydrogen through it, probably by a partial reaction oi the hydrogen and oxidant a t the operating temperature of 1190 The use of a gravimetric method precludes the possibility of interference due to reduction of the iodine pentoxide by hydrogen because the oxygen is measured by weighing the carbon dioxide produced by the oxidation instead of determining the iodino liberated. The following method has been found satisfactory for detcrmining oxygen in many different types of material.
c.
APPARATUS
Purification Train. The apparatus, which is shown a t the right in Figure 1 and diagrammatically in Figure 2, consists of an oxygen-absorbing scrubber, A , a sulfuric acid scrubber, B, an absorption tube, C', a Hoivmeter, D,and a LT-tube absorber, E.
1409
ANALYTICAL CHEMISTRY
1410
Table 11. Effect of Temperature of Iodine Pentoxide on Results for Oxygen by Unterzaucher's Method Compound Benzoic acid
Tempersture of IzOa, c. 119 95-100 90-95 75-80
% Oxygen Found 26.69 26.55 26.12 26 03 26 17 25 95 25 67 25.47
Calculated 26.20
wire 0.014 inch in diameter. The end coils are placed closer together than are those in the center of the tube to compensate for the greater heat losses through the ends of the furnace. The heating unit is insulated with 85% magnesia and enclosed in a suitable metal shell. A continuously variable autotransformer is used to control the temperature. The use of a Mariotte bottle and preheater has been found unnecessary.
Table 111. Effect of Hydrogen on Results Obtained by Unterzaucher and Proposed Methods HY-
n-Eicosane
95-100
1.46
Sone
Method
0 54
heat the central portion of the furnace tube, while the other coil furnishes heat a t the ends of the furnace tube. Each unit is controlled by a separate continuously variable autotransformer, so that the temperatures a t the ends and center of the furnace can be equalized by adjusting the voltage input to each unit. The heating coils are wound on an 8-inch (20-cm.) piece of Alundum tubing 0.75 inch in outside diameter and are composed of wire 0.014 inch in diameter, made of an alloy containing 80% platinum and 20% rhodium. Winding of the end heaters is started 0.25 inch from the ends of the Alundum tube and extends for 1.125 inches toward the center. The coils near the ends of the tube are spaced close together to compensate for the greater heat losses through the ends of the furnace. Five feet (24 turns) of wire are required for each end coil. The center unit extends for 5 inches in the middle of the alundum tube and consists of 17.5 feet (84 turns) of wire. Thermocouples, made from No. 28 B. and S. gage platinum-platinum plus 13y0 rhodium wire, are placed a t points 0.75 and 4 inches from the entrance end of the tube furnace to ascertain the temperatures a t these points. The furnace is insulated with Sil-0-Cell Superbrick and 85% magnesia. The outer shell is made of stainless steel and the end plates are of Alsimag 202. A single pyrometer with a two-way contact switch is used to read the temperatures.
Proposed
CO2, Mg.
Route of Gases rhrough reaction
drogen, MI. 220
Through reaction tube
220
0.134
250
0.191
..
0.02 AThio- Oxygen, sulfate Parts Sohper tion, iM1. 100,000 2.59 110
.. ..
16 19
REAGENTS
Iodine Pentoxide. Baker's reagent grade iodine pentoxide is screened to exclude particles finer than 100-mesh. The screened iodine pentoxide is introduced into the oxidation tube and conditioned by heating a t 230" to 240" C. for 24 hours, followed by heating at 150" C. for 40 to 50 hours while a flow of pure, dry nitrogen is maintained. Carbon. Carbon black, pelletized (J. hi. Huber, Inc.), is conditioned by gradually heating it to 550' C. and maintaining it a t that temperature for several hours while dry nitrogen gas is passed over it. Nitrogen Gas, Matheson's prepurified nitrogen. Oxsorbent, available from Burrell Technical Supply Co. Ascarite, 8- to 20-mesh. Anhydrone, 20- to 50-mesh.
( 8 Mesh)
Figure 3.
Reaction Tube Filling
Constant Temperature Unit. A thermostatically controlled heating unit, used to heat the iodine pentoxide, consists of an aluminum cylinder, 8 inches in length, through which a suitable hole is bored to accommodate the conventional oxidation tube. At either side of the central portion of the tube hole, two well holes are drilled in a vertical position to accommodate a thermometer and mercury-type thermostat. The outer circumference of the cylinder is covered with mica and v-ound with h-0. 22 B. and S. gage Nichrome wire. Approximately 95 feet of wire are required and are wound on the cylinder in two sections of 60 turns each, leaving a space 0.5 inch wide in the center so that the thermometer and thermostat can be inserted. The heating block is insulated with 85% magnesia and enclosed in a stainless steel sleeve. A constant temperature of 119' C. is maintained by means of a fixed mercury thermostat and relay. Movable Heater. The sample heater consists of a sniall movable electric furnace. The furnace tube, which is fabricated from a 3-inch length of Alundum tubing 0.75 inch in outside diameter, is wound with 15 feet (72 turns) of 80% pIatinum-20% rhodium
Drierite, indicating, 10-to 20-mesh. Phosphorus Pentoxide, C.P. powder. Silica Gel, 14-to 20-mesh. Sulfuric Acid, C.P. (95 to 96%). Silica, 8-mesh ignited at 1000" C. for 1 hour. PREPARATION OF APPARATUS
The units of the purification train are filled and assembled as shown in Figure 2. The oxygen-absorbing scrubber, A , is charged with Oxsorbent, a commercial preparation supplied by the Burrell Technical Supply Co., 1942 Fifth Ave., Pittsburgh 19, Pa. The reagent is introduced into the scrubber through the top joint under a blanket of nitrogen gas which, during this operation, enters the upper bulb of the scrubber through a side tube and leaves through the top joint. T o scrub the nitrogen during the analysis, the gas is
V O L U M E 2 3 , NO. 10, O C T O B E R 1 9 5 1
1411
allowed to ent,er the lower portion of the scrubber, pass up through the lower bulb containing the beads and absorbing liquid, and leave through t8heupper section of the middle bulb. The sulfuric acid scrubber, B , which is used to remove water carried over from A , is filled with concentrated sulfuric acid to a point 1 em. above the tip of the inner tube. One half of absorber C is filled with Ascarite, the other half with 10- to 20-mesh Drierite, the layers of absorbent being held in place and separated by means of glass wool plugs. The G-tube, E , contains in its left arm 20- to 50-mesh Anhydrone and in its right arm equal lengths of Ascarite and silica gel, the reagents being held in place with glass wool plugs. All the. joints of the purification train are sealed t.ogether by means of Kronig's cement. The reaction tube is filled as indicated in Figure 3. The fine platinum wire plugs and granulat,ed silica effectively serve to hold the carbon in place. The reaction tube is attached to the purification train by means of a sleeve of impregnated rubber t'ubing with the ends of the glass tubing in contact x i t h each other.
=t 10" C. This tenipei:ituit' is maintained throughout the analysis. The flow of nitrogen is also adjusted a t this time, so that the gas passes through the train and out the safety tube a t a rate of 10 ml. per minute. If the furnace has been operating a t lower temperatures during shut-down, the above conditions must be maintained for 1 hour before the first analysis is started. hTonvolatile liquids or solids are weighed in micro platinum boats and volatile liquids in quartz capillary weighin tubes sealed with parafin wax. The flow of nitrogen is firected through the reaction tube in a reverse direction, by means of the three-way stopcocks and bypass tube and the sample is placed in the reaction tube a t a point approximately 12 em. in front of the stationary furnace. The reverse flow of gas is continued for 10 minutes to flush the tube and sample free of air. During this time, the micro absorption tube, which was weighed previously by the conventional technique used in the microdetermination of carbon and hydrogen, is attached to the end of the iodine scrubber hy means of a sleeve of impregnated rubber tubing, and the
e 0 0 mrn.
114/36 I
LPz05-Sillca
Mixture
I
Joint
Sodium Thiosulfate C r y st ole.
L l n d l s o t i n g Drlerite ( IO-eOMeeh 1
F igure 1.
I
Iodine Absorption Tube
The acid gas scrubber, s h i c h is placed betaeen the reaction tube and oxidation tube, is filled for one third of its length with hnhydrone, and then Ascarite is added t o fill the other two thirds of the tube; glass wool plugs a t the ends and between the fillings hold the reagents in place. I t is attached to the reaction tube through a three-way stopcock by meam of glass joints sealed with Kronig's cement. The by-pass tube is placed between the three-way stopcock at this point and a similar stopcock attached to the end of the purification train; ball and socket joints, which are also sealed with cement, make the connections. The oxidation tube is filled with iodine pentoxide held in place with glass wool plu s. I t is placed in the constant temperature device, and attache% to the outlet of the acid gas scrubber by a sealed ball and socket joint. The iodine absorption tube, shown in Figure 4, is filled in the following manner beginning at the constricted end: First a plug of glass wool 5 nim. in length followed by a 50mm. layer of silica-phosphorus pentoxide mixture is placed in the tube, next a glass wool plug 5 mm. long followed by a layer of indicating Drierite 90 mm. long is added, then a plug of glass wool 5 mm. long folloned by sodium thiosulfate crystals for a distance of 35 mm., and finally a glass wool plug 10 mm. in length is placed in the tube to complete the filling. I t is connected to the oxidation tube through a -$- 14/38 joint sealed with Kronig's cement. The micro absorption tube is filled in the same manner as the carbon dioxide absorption tube used for the microdetermination of carbon and hydrogen. This filling consists of a glass wool plug, a 2.5- to 3-cm. layer of Anhydrone, another glass wool plug, a layer of Ascarite extending to within 5 mm. of the ground joint, and finally a glass wool plug. The ground joint of the absorption tube is sealed together with Kronig's cement after completing the filling. A safety tube, which is attached to the end of the train to prevent contamination by u-ater or acid gases from the air, contains Ascarite and Anhydrone.
A picture of the assembled units is shown in Figure 1. Before the apparatus is placed in service, it must be conditioned for several hours by passing nitrogen through the train while the heating units are maintained a t operating temperatures. PROCEDURE
At the beginning of the analysis, the stationary furnace ia adjusted by means of the two voltage control units, 80 that the temperature a t the center and ends of the heating unit is 1125'
two units are placed together with glass to glass contact. The safety tube is also attached to t.he exit end of the absorption tube in t,he same manner. The direction of the flow of nitrogen in the react,ion tube is then reversed, allowing the gas to pass through the acid gas scrubber, oxidation tube, iodine absorption tube, micro absorption tube, and safety tube to the atmosphere. The movable heater, which is placed 4 cm. in back of the sample, is turned on and the pyrolysis is started. If the sample has been weighed in a combustion boat, the temperature of the movable heat,er is immediat.ely raised to 1000" to 1100" C., but for a volatile sample the heater is kept a t a relatively low temperature until the sample has volatilized. I n the latter case, the reaction tube is heated with a micro burner in the vicinity of the sealed tip of the capillary until the paraffin melts and the capillary is opened. Heat is applied to the sample by either moving the heater forward in the case of the nonvolatile samples, or gently heating the capillary sample tube with a low flame when volatile material is analyzed. The rat,e of heating is controlled so that the flow of nitrogen, measured by the flowmeter, does not drop below 7 ml. per minute. When the sample haR been completely pyrolyzed and the movable heater has contact,ed the stationary heater and remained a t that point for approximately 5 minutes, the react'ion tube is heated rapidly at 1000" to 1100" C. by means of the movable heater. The latter is then shut off and allowed to cool. The nitrogen flow is continued for another 20 t o 30 minut'es t o sweep t,he products of pyrolysis through the apparatus. The micro absorption tube is then removed, wiped in the usual manner, and weighed. The number of determinations that can be made in a day by this method, using two absorption tubes alternately, is comparable to t,hat of the iodometric method. During periods when the apparatus is not in use, the temperature of the furnace is maintained a t approximately 600" C. CA LCULATlON S
Over a period of one year, the magnitude of the blank ranged between 0.02 and 0.10 mg. of carbon dioxide for the 600 ml. of nitrogen normally used in each analysis; the reproducibility from day to day was within rt0.01 mg. The per cent oxygen is calculated as follows: %oxygen
=
(TV1 - W,) X 0.3636
WS
x
100
1412
ANALYTICAL CHEMISTRY
Table IV. Results Obtained by Proposed Method on Saniples of Known Composition, Using Ascarite Scrubber Cornpound
Sample, BIg.
Benzoic acida
15.624 10.612 13.689 12.806 12.553 9.571 13.312 8,533 Sucroseb 8.112 11.182 10.982 3-I'entanol 58.931 46.950 17.70i 1:tliyI acetate 28.771 36,036 2-Ethylhexanol 48.772 Dioxane (EKCo. 33.920 39,720 2144) 12.119 o-Chlorobenzoic 9 ,563 Acidb 16.771 d-Bromocaniphor 26.635 (EKCo. 44) 13.893 o-Iodobenzoic acidb 13,269 8.89.: m-Sitrophenol 9.562 (EKCo. 1340) l-Bsonio-3-n1troben- 12.058 aene (CBCo. 650) 16.033 a
6
Carbon Per Dioxideu, Alg. Found 11.325 26,35 26.41 7.707 26.07 9,813 26.10 9,194 26.01 8,980 26.08 6,866 26.14 9,570 12.096 51.53 11.550 51.77 15,767 51.27 51.30 15.493 18.35 29.748 18.54 23.941 17,547 36.03 28.959 36,60 12.347 12,46 12.40 16.629 3 6 , 50 34,054 36.55 39.927 20.35 6.780 5.353 20.35 3 220 6.98 ;7,047 6.89 12.8i 4.919 12.97 4.732 34.57 8.45i 9.011 34.38 5,332 16.08 6,620 15 99
Cent Oxygen Calcd. Difference 26.20 +o 15 +0.21 -0.13 -0.10 -0.lH -0.12 -0.06 51.42 f0.11 +0.35 -0,l5 -0.12 18.l a +0.50 +0.39
36.32
-0.29 f0.28
36.32
+o. 17 +o. 1 1 +o 18
20.44
-0.09
6.92
+0.06
12.90
-0.03 -0.03 +0.07
34,51
+0.06
15.84
+0.24 +O. 15
12.29
f0.23
-0.09
-0.13
gen gas through iodine pentoxide treated as described above. The results show that an appreciable quantity of iodine is liberated from the oxidant by this treatment. As this table also indicates that the carbon dioxide produced is much less than the amount equivalent to the iodine liberated, a reaction between part of the hydrogen and some iodine-containing constituent of the oxidant is indicated. The difference between the oxygen content calculated from the iodine liberated by passing the gas through both the reaction and oxidation tubes, and the oxygen content calculated from the iodine liberated by passing the gas only through the oxidation tube, is equivalent to the oxygen content of the gas found by the gravimetric procedure. Table VI shows data obtained by the Unterzaucher and proposed method6 on oxygen-free samples after the iodine pentoside had been in service for various periods of time a t a temperature of 119" C The proposed gravimetric method gave satisfactory results with unaged oxidant, but unreasonably long periods of conditioning were required to give comparable results by the volumetric method. I\. hether this anomaly is due to impurities in the paiticular stock of iodine pentoxide tested has not been ascertained By using the gravimetrir procrtlure, hon cvei , the possibility ot
Table V. Results Obtained by Proposed Method on Petroleum Products
Corrected for blanh. Sational Bureau of Standards sainple. Material Topped crude oil
where Wl = weight of carbon dioxide collected for sample, WI = weight of carbon dioxide collected for blank, and TV3 = weight of sample.
Ileavy illel oil A
ACCUR4CY AYD PRECISIOh
Furnace fuel oil
IIeary fuel oil B
Sample, hlg.
49.8 47.3 53.8 61.5 45.5 74.0 45.9
Table IV shows data obtained for samples of known coinposition and indicates the precision and accuracy obtainable with the above procedure. The results shown have not bern selerted, but represent all values obtained with these samples. Table V shows oxygen results obtained on typical petroleum products.
Kerosene Clarified used oil Oxidized mineral oil Petroleum sediment A
DISCUSSION
Selection of Iodine-Absorbing Material. The use of potassium iodide-impregnated cotton as suggested by Schiitze ( 5 ) for absorbing the iodine liberated in the oxidation tube was found unsatisfactory when iodine pentoxide was used as the oxidant. Crystals of potassium iodicle were also found inadequate. The filling of the iodine scrubber, shown in Figure 4, is very satisfactory for removing iodine and moisture from the gmes before they enter the micro absorption tube. Enough thiosulfate is present in the scrubber so that it does not become ineffective before the Drierite. Therefore, indicating Drierite can be used to tell when to replace the filling-when almost the entire length of the Drierite layer has changed from blue to pink. As phosphorus pentoside is a very efficient drying agent and the bulk of the moisture is removed by the Drierite, the phosphorus pentoxide-silica filling is replaced only after many changes of the thiosulfate and Drierite lagers. Conditioning of Iodine Pentoxide. Iodine pentoxide conditioned as described above is adequate for use in the above gravimetric procedure. Although such treatment has also been considered satisfactory by other authors (1, 4 ) for the volumetric method proposed by Unterzaucher, stocks of iodine pentoxide available a t the authors' laboratories gave high results for oxygen when the oxidant, treated in this manner, was used for the volumetric procedure. Table I11 shows the effect of passing hydro-
Petroleum sediment B Gasoline .I Gasoline B a
55.5 64.8 71.9 57.0 63.4 47.1 37.1
77.7 63.9 12.581 10.281 11,850 12,656 44.7 101.7 58.0 65.0 48.0
COP.
Mg. 1.325 1.251 1.482 1,000 0.706 0.484 0.251 0.097
0.061 0 133 0,047 1.061 0.812 0.600 3.550 2.972 5,354 4.146 4.653 5.040 0.444 0.789 0.419 0.143 0 062
Per Cent Oxygen BY difference BY from proposed ultimate method analysis 0.97 .. 0.96 .. 1.00 , . 0.59 0.57 0.56 0.57 0.24 0.35 0.20 0.35 0.06 -0.10 0.04 -0.10 0.07 -0.15 0 03 -0.15 0.61 0.62 0.63 0.62 0.59 0.62 1.66 1.55 1.69 1.55 15.43 16.67 14.31 14.48 0.36 .. 0.28 .. 0.26 0.08 0.05
Corrected for blank.
Table VI.
Results Obtained on Oxygen-Free Samples by Unterzaucher and Proposed Bfethods
(After various periods of service of iodine pentoxide) Per Cent Oxygen Found Material Period of Time Unterzancher Proposed Analyzed 1 2 0 6 Used, Months method method Naphthalene 4 0.86 0.04 4 0.05 1.05 4 1.67 0.05 4 0.97 .. 4 0.85 .. 12 0.13 .. 12 0.10 .. 2 n-Eicosane 0.96 0.03 4 0.02 2.52 12 0.10 .. 12 0.11 .. IIexadecane 1 day 0.81 0 04 1 day 0 92 0.04 12 0.06 .. 12 0.05 ..
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1 Table VII.
Results Obtained for Sulfur Compounds hg Proposed Method
Per Cent Oxygen Liquid Ascarite nitrogen Compound scrubber trap Calculated Thioacetamide 4.86 0.00 None 0.06 None 8.42 Thiourea 5.79 0.05 Xone 0.02 Sone 8.92 0.06 Xone ,. 0.35 Xone 1-Methyl mercapto7.65 0.56 None ... benzothiazole Cystinea 27.10 26,92 26.65 2 6 . 6 2 26.65 26.85 27.51 27.72 Siilfanilic acid 27 72 27.96 27.31 27.72 a S a t i o n a l Bureau of Standards sample.
interferences due to extraneous liberation of iodine from the oaidant is precluded. Analysis of Samples Containing Sulfur. Although samples containing sulfur are usually converted, predominantly, to hydrogen sulfide in the reaction tube and removed by the acid gas scrubber, quantities of carbon disulfide and carbonyl sulfide are also formed which are not absorbed by the Ascarite. When these products pass through the oxidation and iodine absorption tubes, carbon dioxide and sulfur dioxide are produced n hich are subsequently retained in the micro absorption tube, giving high results for oxygen. By using a liquid nitrogen trap in place of the acid gas scrubber, the carbon disulfide and carbonyl sulfide are prevented from entering the oxidation tube. By thus eliniinating the carbon disulfide, inteifeience from that source is prevented, but because the carbonyl sulfide includes oxygen originat-
1413 ing from the sample, its removal causes low results. The data given in Table I, although not extensive, indicate that the amount of carbonyl sulfide formed is relatively small. For this reason appreciable errors as a result of the removal of carbonyl sulfide are not likely to occur when a liquid nitrogen trap is used. Table JrII shows data for several sulfur compounds, using the acid gas scrubber and liquid nitrogen trap for removing the interfering sulfur compounds. A decided advantage was indicated when a liquid nitrogen trap was employed in the analysis of these Yamples. Maylott and Lewis ( 4 ) have carried out a similar investigation on the interference of sulfui. compounds using the volunietric procedure. &Ch\OW LEDG-VENT
The authors sinceiely appiccidte the valued suggestions and advice of Harry Levin in the development of this project. Thanks are also extended to hidre\!' Ferrence, Leo F. Moore, Clayton L. Earl, and Allen Tomlins for their help in working out the details for construrting the special heating unitq. LITERATURE CITED
(1) Aluise, V. d.,Hall, R. T., Staats, F. C., and Becker, ]I-. \I-. ANAL.CHEM.,19, 347 (1947). (2) Dinerstein, R. 4.,and Klipp, R. IT.,Ibid.,21, 545 (1949). (3) Graham, J. I., and Winmill, T. F..-1.Chem. Soc. (London), 105, 1996 (1914). (4) Maylott, A. O., and Lewis, J. E., ANAL.CHEM.,22, 1051 (1950). (5) Schutse, hf., Z.a n d . Cheni., 118,245 (1939). (6) Steyermark, A., Alber, H. K., Aluise. J-. A,, Huffman, E. W.D.. Kuck, J. A,, hloran, ,J.
