The spectrum from 7.5 to 11 microns is compared to that of pure OPE to confirm a good separation. The absorp tion band a t 8 microns was chosen, as it is much narrower than the one a t 8.9 microns, thus minimizing any possible error due to changing background. If the sample of raw undiluted gasoline is put through the alumina column, OPE will be quantitatively separated. This is not recommended, because the raw gasoline causes pockets of vapor to
form in the column, which makes the thoroughness of the washing questionable. An occasional high result for OPE may have been caused by this. Very little time is saved, because a much larger quantity of liquid is put through the column. The main feature of this method is that it presents a means of separating the OPE from a complex mixture. The analysis of complex mixtures is often attempted with no thought to separation; this is an example where
Determination of Iron, Lead, and Arsenic in Antimony Sulfide GEORGE NORWITZ, JOSEPH COHEN, and MARTIN E. EVERETT Pifman-Dunn laborafories, Frankford Arsenal, Philadelphia, Pa.
b Improved procedures are proposed for the determination of iron, lead, and arsenic in antimony sulfide. Iron is determined colorimetrically with ophenanthroline after dissolving in hydrochloric acid, addition of tartaric acid, and treating with hydroxylamine hydrochloride, o-phenanthroline, and sodium acetate. Lead is extracted from an ammoniacal tartrate medium with a solution of dithizone in chloroform and is precipitated as lead sulfate. Up to a 3-gram sample can b e handled and there are no interferences. Arsenic is determined colorimetrically by the molybdenum blue method after distillation of the arsenic. The distillation requires only 9 to 1 1 minutes. The temperature during distillation must not rise above 95” c.; otherwise some antimony will distill and interfere with the molybdenum blue color.
A
(Sb& is used in ammunition, pyrotechnics, and paints. Because the gravimetric and volumetric methods previously proposed for the determination of iron (3-5), lead (8, 5 ) , and arsenic (5) in antimony sulfide are unreliable and time-consuming, the Ordnance Ammunition Command authorized this laboratory to investigate improved methods for these determinations. NTIMONY SULFIDE
DETERMINATION OF IRON
The iron was determined colorimetrically with o-phenanthroline after tartaric acid had been added to pre1 132
0
ANALYTICAL CHEMISTRY
vent hydrolysis of the antimony. The tartaric acid did not prevent reduction of the iron by the hydroxylamine hydrochloride. The presence of antimony had no effect on the color. Reagents. TION.
STAND.4RD I R O K S O L U -
No. 1 (I ml. = 1.00 mg. of
Fe). Dissolve 1.0000 gram of pure iron (Sational Bureau of Standards Sample 55d) in 75 ml. of hydrochloric acid by warming on the hot plate. Add 3 ml. of hydrogen peroxide (30%) and boil for 10 minutes to destroy the peroxide. Cool and dilute to 1 liter in a volumetric flask. So. 2 (1 ml. = 0.10 mg. of Fe) Pipet 50 ml. of standard iron solution No. 1 into a 500-ml. volumetric flask and dilute to the mark. Hydroxylamine hydrochloride solution, 5%. o-Phenanthroline solution, 0.27& Tartaric acid solution. 10%. Sodium Acetate Solution, 55%. Dissolve 250 grams of sodium acetate trihydrate in water and dilute t o 500 ml. Preparation of Calibration Curve. Measure accurately 1-, 2-, 3-, 5-, 6-, and 7-ml. portions of standard iron solution No. 2 into 200-ml. volumetric flasks and add 40 ml. of water, 4 ml. of hydrochloric acid, and 4 ml. of tartaric acid solution. Carry along a reagent blank. Add 10 ml. of hydroxylamine hydrochloride solution and allow t o stand for 15 minutes. A4dd 10 ml. of o-phenanthroline solution and 20 ml. of sodium acetate solution, and dilute t o the mark with water. Allow to stand for 30 minutes, and measure the transmittance a t 500 mp, setting the spectrophotometer or o with colorimeter a t 1 0 0 ~ transmittance the reagent blank. Plot milligrams of iron against per cent transmittance. Procedure. Transfer a 0.5-gram
a simple separation facilitates an otherwise almost impossible determination. LITERATURE CITED
(1) Rohm
& Haas Go., Washington Square, Philadelphia 5, Pa., “The NonIonic Octylphenoxyethanol (OPE) Series,” October 1955. (2) lbid., “Triton Surface-Active Agents,” 1951.
RECEIVED for review February 4, 1960. Accepted hlap 19, 1960.
sample to a covered 4Oo-ml. beaker and add 20 ml. of hydrochloric acid. Boil 011 the hot plate for 5 minutes to dissolve the sample and drive off the hydrogen sulfide. Cool to room temperature and add 20 ml. of tartaric acid solution. Wash into a 100-ml. volumetric flask with water and dilute t o the mark. Pipet an aliquot into a 200-ml. volumetric flask. For iron up to 0.7Youse a 20-ml. aliquot; from 0.7 to 1,4% use a 10-ml. aliquot, Add 30 ml. of water and 10 ml. of hydroxylamine hydrochloride solution, and allow to stand for 15 minutes. Add 10 ml. of o-phenanthroline solution and 20 ml. of sodium acetate solution, and dilute to the mark with mater. Allow to stand for 30 minutes, and measure the transmittance a t 500 mp, setting the spectrophotometer or colorimeter a t 100% transmittance with the reagent blank. Convert the readings to milligrams of iron by consulting the calibration curve and calculate the per cent iron. DETERMINATION OF LEAD
The lead was extracted from an ammoniacal tartrate medium by a solution of dithizone in chloroform and then determined as lead sulfate. As much as a 3-gram sample could be handled and there m-ere no interferences. Antimony did not form a dithizonate (7) and was not extracted under these conditions. Small amounts of silica, tungsten, niobium, or tantalum that might be present were filtered off prior to the extraction. If any of these substances remained in solution, they were not extracted with dithizone. Barium and strontium did not interfere, because they did not form dithizonates and were not extracted. Previous investigators have apparently not extracted amounts of lead (to 6 mg.) in which the authors were interested. I t was necessary to extract with relatively large volumes of a solution of dithizone in chloroform, add chloroform after each extraction, and then drain off the chloroform to remove the droplets of dithizone solution dispersed in the aqueous solution. I t was also necessary to use a chloroform solution
of the dithizone rather than a carbon tetrachloride solution. With the latter solution a red precipitate formed, which seemed to be a mixture of precipitated dithizone and lead dithizonate. -4fter the extractions, the combined extracts were evaporated to dryness, nitric and sulfuric acids were added, and the solution was evaporated to fumes of sulfuric acid. Kater Tyas added, the solution allowed to stand overnight, and the lead sulfate filtered through a sintered porcelain crucible. The lead sulfate was dried by placing the sintered crucible in a porcelain crucible and heating over a Aleker burner for 5 minutes (8). Reagents. Tartaric acid, 20%. Dithizone Solution, 0.027,. Dissolve 0.1 gram of dithizone in 500 ml. of reagent grade chloroform. This solution will keep for about a ITeek. Procedure. Weigh the sample into a covered 250-ml. beaker: 0 to 0.2% lead, 3 grams; 0.2 to 0.3Y0, 2 grams; 0.3 to 0.6y0, 1 gram. Add 30 ml. of hydrochloric acid and boil for 8 t o 10 minutes to dissolve the sample and drive off the hydrogen sulfide. Add 20 nil. of wat'er and filter through a medium-texture filter paper previously washed with dilute hydrochloric acid (1 to 5). Collect the filtrate in a 500-ml. beaker. Wash with dilute hydrochloric acid (1 to 5) and discard the precipitate. Add 30 ml. of tartaric acid solution. Keutralize to litmus paper with ammonium hydroxide and add 5 drops in excess. Cool, dilute to about 200 ml. with water, and wash into a 500-nil. separatory funnel. Add 50 ml. of dithizone solution and shake for 2 minutes. Allow t o settle and drain off the chloroform layer into a clean 400-ml. beaker. Add 10 ml. of chloroform to the separatory funnel and, without shaking, drain into t'he 400-ml. beaker. Repeat this rinsing treatment with another 10 ml. of chloroform. Use this rinsing technique after every extraction. Extract with another 50-nil. portion of dit'hizone solution, and then extract with 25-ml. portions until the final extract is green or bluish green. Two to five extractions are usually required. Evaporate the combined extracts to dryness by heating on an electric hot plate under a hood. Add 5 nil. of nitric acid and 3 ml. of sulfuric acid,
1. 2. 3.
4. 5.
6. 7. 8. 9.
cover with a watch glass, and evaporate to fumes of sulfuric acid. Add a few drops of nitric acid with a medicine dropper to complete the elimination of organic matter. Fume for 5 minutes with the cover lid ajar, cool, and wash down the cover lid and sides of the beaker. Evaporate to fumes of sulfuric acid without the cover lid and fume for 5 minutes. Cool, add 50 ml. of water, cover with a watch glass, and boil for 1 minute. Xllow t o stand overnight a t room temperature. Filter through a tared 20-ml. sintered porcelain crucible (Coors No. 2001), and transfer, and wash the precipitate with dilute sulfuric acid (5 to 1000). Place the sintered crucible in a 30-ml. porcelain crucible and heat the outside crucible with a Meker burner for 5 minutes. Cool in a desiccator and weigh. The factor for converting PbS04 to Pb is 0.6833. DETERMINATION OF ARSENIC
It was not feasible t o determine arsenic directly in antimony sulfide. The Gutzeit method was valueless for materials containing large amounts of antimony. The molybdenum blue colorimetric method for arsenic was not directly applicable because of interference from antimony which hydrolyzed. Phosphorus and silicon interfered. It was decided, therefore, to separate the arsenic by distillation and then apply the molybdenum blue method. illany methods have been proposed for the determination of arsenic in alloys containing antimony by use of the molybdenum blue method after distillation of the arsenic (1, 6, 7 ) . However, the results m*ere low and erratic when these procedures were applied to antimony sulfide, because of the partial distillation of the antimony. This antimony repressed the development of the molybdenum blue color, apparently because hydrazine sulfate was consumed in reducing the antimony or because the precipitated antimonic acid occluded arsenic. The procedure of Bartlet, R700d, and Chapman ( d ) , who noted a somewhat similar interference from tin (metastannic acid) , was not applicable to the present problem. The interference from antimony
Distillation flask made from 250-ml. Erlenmeyer flask b y attaching inlet tube 7 mm. wide 24/40 ground-glass joint Connecting tube (Scientific Glass Apparatus Co., J-225, Catalog J-52) 1 0 / 3 0 ground-glass joint Thermometer, ' 0 to 110' C. (Scientific Glass Apparatus Co., J-2300, Catalog J-52) Condenser, 2 0 inches long Adapter. Vertical part is 4 inches long, made from tubing 7 mm. wide 3 0 4 . pharmaceutical graduate 10. Ice and water 400-ml. beaker 1 1. Bunsen burner
5
could be overcome by conducting the distillation a t a temperature not above 95" C. At 92" to 95" C. the distillation of arsenic was complete in 9 to 11 minutes when a fairly rapid flow of an inert gas was used. Previous investigators used a maximum temperature of 105' to 111" C. for the distillation of arsenic. A hydrochloric-hydrobromic acid medium was used for the distillation, as recommended by Rodden (6). The distillation apparatus employed in this laboratory is shown in Figure 1. All parts were made of borosilicate glass. After the distillation, the distillate was treated with nitric acid and evaporated to dryness (6, 7 ) . The conditions for the evaporation were not critical. There is little chance of volatilization of arsenic chloride, as the arsenic is in the quinquevalent state. It is recommended that the evaporation be accomplished by heating on the hot plate away from direct heat, SO that the solution is very hot but does not boil. On boiling d o m to dryness very rapidly, 95% of the arsenic was recovered. The color was stable overnight. Reagents. Standard Arsenic 801ution (1 ml. = 0.10 mg. of As). Add 0.2641 gram of As203 t o 5 ml. of sodium hydroxide solution (5555) contained in a 250-ml. beaker. Swirl for a fen- minutes, wash d o n n the sides of the beaker nith water, and heat a t 50" C. to dissolve. Dilute t o about 100 ml. and make acid to litmus paper with nitric acid. Cool and dilute to 2 liters in a volumetric flask. Hydrazine sulfate solution, 0.15%. Ammonium Molybdate Solution, 1%. Add 70 ml. of sulfuric acid t o about 300 ml. of water, cool, and dilute to 500 ml. with water. Add 5 grams of (NHd),h I 0 , 0 ~ ~ . 4 Hand ~ o stir to dissolve. Hydrazine Sulfate-Ammonium Molybdate Reagent ( 7 ) . Add 30 ml. of ammonium molybdate solution to about 200 ml. of water. Add 3 ml. of hydrazine sulfate solution and dilute to 300 ml. Prepare fresh daily. Preparation of Calibration Curve. By means of a microburet or micropipet transfer 0.5-, 1-, 1.5-, 2-, 2.5-, and 3-ml. aliquots of standard arsenic
-
Figure 1 .
Apparatus for distillation of arsenic VOL. 32, NO. 9, AUGUST 1 9 6 0
1133
the hot plate and add 50 ml. of hydrazine sulfate-ammonium molybdate reagent. Place the 250-ml. beakers in 600-ml. beakers which contain about 525 ml. of vigorously boiling tap water. .411ow t o stand in the boiling water for
solution t o 250-ml. beakers, and add 10 ml. of water and 15 ml. of nitric acid. Carry along a blank. Place t h e beakers on t h e hot plate away from the direct heat and evaporate to complete dryness. Remove from
Table
I.
Iron, Lead, and Arsenic in Samples of Antimony Sulfide
Found. CT, Lead
Arsenic
0,004
0.226"
0.062O 0.004
0.0216 0,001
B, natural Sb2S3, tech. grade Std. dev.
0.290" 0.007
0 . 54a
0 . 032b
C, synthetic Sb& Std. dev.
0,052" 0.004
0 . 043b
0,021b 0,001
Sample
Iron
A, natural Sb&
Std. dev.
0.012
0.003
0.002
Av. of six determinations. Av. of five determinations.
Table
Synthetic Sample, G.
ca
0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
II.
Recovery of Metals Added to Synthetic Samples
Added
Total present
0 . 50b 1.OOb
0.76
2. OOb 3 . OOb 3 . 2Sb 4,O O C 5.OW
6. o o c 7 .o o c
Metal, Mg. Total found IRON
1.26 2.26 3.26 3.51 4.26 5.26 6.26 7.26
Recovered
0.75 1.30 2.28 3.19 3.49 4.21 5.30 6.39
0.49
7.20
1.04 2.02 2.93 3.23 3.95 5.04 6.13 6.94
2.32 3.00 3.28 4.03 4.92 5.80 6.42 5.71
0.46 1.14 1.42 2.17 3.06 3.94 5.18 5.09
0.131 0.151 0.206 0.260 0.252 0,135
0.026 0.046 0.101 0.155 0.147 0.093
0.245
0.203 0,253 0.515 0,979 1.004
LEAD Ad
3
0.50
1.00 1.50
3 3
3
2.00
3
4.00 5.00
3.00
3
2 1
5.00
2.36 2.86 3.36 3.86 4.86 5.86 6.24 5.62 ARSENIC
A m 0.5 0.5 0.5 0.5 0.5 0.2 0.2 0.2 0.1 0.1 0.1 0.1
0.02 0.05 0.10 0.15 0.15 0.10 0.15
0.125 0.155 0.205 0.255 0.255 0.142 0.192
0.20 0 251 0,501
0.242
1.OOQ 1 .o o g
~
~~
0.271 0.521 1.021 1.021
0.200
0.274
0.536
1.000
1,025
0.158
15 minutes. Cool to room teniperature, transfer to 50-mI. volumetric flasks, and dilute to the mark with water. Measure the transmittance a t 660 m,u, setting the spectrophotometer or colorimeter a t 100% transmittance with the reagent blank. Plot milligrams of arsenic against per cent transmittance. Procedure. Weigh the sample into a covered 250-ml. beaker: 0 to 0.05% arsenic, 0.5 gram; 0.05 t o 0.125%: 0.2 gram; 0.125 t o 170, 0.1 gram. Add 10 ml. of nitric acid and 5 ml. of sulfuric acid. Evaporate t o fumes of sulfuric acid and with the cover lid ajar fume strongly for 7 minutes. A4110wto cool and wash down the cover lid with exactly 5 ml. of water. Cool. Assemble the distillation apparatus as shom-n in Figure 1. Add 20 nil. of water to the graduate, and ice and m t e r to the 400-ml. beaker. Pour the solution of the sample into the distillation flask and retain the beaker. Add 0.3 gram of hydrazine sulfate and 2 ml. of hydrobromic acid (48'34 to the distillation flask. Add a total of 10 ml. of hydrochloric acid in two portions to the 250-ml. beaker and decant into the flask. Pour the last portion of the hydrochloric acid around the top of the flask to wash down any adhering material. Do not use any n-ater. Regulate the flow of inert gas (helium, argon, nitrogen, or carbon dioxide) to 5 bubbles per second at the exit tube. Adjust the Bunsen flame to about 3/4 inch and heat until the temperature rises to 93" C. (about 4 minutes). Remove the flame momentarily. S o w brush the flame back and forth across the bottom of the flask so that the temperature remains a t 92" to 95" C. for 5 minutes (7 minutes if the arsenic content is greater than 0.12501,). Detach the adapter and rinse it with a little water. For less than 0.125% arsenic wash the solution into a clean 250-ml. beaker; for more than 0.125'3T0 arsenic wash the solution into a 50-ml. volumetric flask, dilute to the mark, and pipet an aliquot containing about 0.15 to 0.25 mg. of arsenic into a clean 250-ml. beaker. Add 15 ml. of nitric acid to the solution in the 250-ml. beaker, place on the hot plate away from direct heat, and evaporate to complete dryness. Carry along a blank. Add 50 ml. of hydrazine sulfateammonium molybdate reagent and detach the precipitate (IT hich will later dissolve) from the bottom of the beaker by rubbing with a policeman. Rinse down and remove the policeman. Develop the color as described above. Convert the readings to milligrams of arsenic by consulting the calibration curve and calculate the per cent arsenic. RESULTS FOR IRON, LEAD, AND ARSENIC
Contains 0.05270 iron (Table I). b 20-ml. aliquot taken. c 10-ml. aliquot taken. d Contains 0.062% lead (Table I). e Contains 0.0217, arsenic (Table I). Distillate diluted to 50 ml. and 25-m1. aliquot taken. Distillate diluted to 50 ml. and 10-ml. aliquot taken.
1134
0
ANALYTICAL CHEMISTRY
The results obtained for iron, lead, and arsenic in three typical samples of antimony sulfide, analyzed several times each by the proposed methods, are shown in Table I. Precision is satisfactory. To establish the accuracy of
work on the colorimetric method for iron.
the procedures, aliquots of standard iron, lead, and arsenic solutions were added to one of the samples previously analyzed and the synthetic mixtures carried through the procedures. Recoveries were good (Table 11).
LITERATURE CITED
(1) Am. SOC. Testing Materials, Philadelphia, Pa., “1956 Book of ASTM Methods for Chemical Analysis of Metals,” p. 486. (2) Bartlet, J. C., Wood, X., Chapman, R. A., ANAL. CHEM.24, 1821 (1952). (3) \ , Cushman. A. S.. J . I n d . Eno. C h a . 10, 376 (19i8). ’ (4)McNabb, W. hl., Wagner, E. C.,
ACKNOWLEDGMENT
The authors thank Samuel Sitelman for his suggestions, and Leonard Markowitz for his preliminary experimental
ESG.CHEM., A N A L . ED. 2, 261 (1930). (5) Mjlitary Specification NILA-l59B, Antimony Sulfide. (6) Rodden, C. J., J. Research Natl. Bur. Standards 24, 7 (19:O). (7) Sandell, E. B., Colorimetric Determination of Traces of Metals,” pp. 141, 282, 555, Interscience, Sew York, 1959, (8) Scott, W.W., “Standard Methods ot Chemical Analysis,” Vol. 1, p. 505, Van Nostrand, New York, 1939. RECEIVEDfor review February 2, 1960. Accepted May 23, 1960. IND.
Sensitive Spot Test for Nitrogen Compounds in Petroleum Fractions PAUL V. PEURIFOY and MAXWELL NAGER Houston Research Laboratory, Shell
Oil Co., P. 0.Box 2527, Houston I ,
The nitrogen content of petroleum fractions may b e rapidly estimated by visual comparison of colored spots produced by the reaction of nitrogencontaining compounds and tetracyanoethylene on filter paper.
Tex.
Two pounds air pressure. Filter paper, Whatman No. 120, drop reaction paper. Weisz ring oven, National Appliance Co., H. Reeve Angel &- Co., Inc., agent. EXPERIMENTAL PROCEDURES
T
USE of tetracyanoethylene (TCNE) as a spot test reagent for aromatic hydrocarbons on filter paper has been described (3, 4). This reagent can also be used for the detection of other substances. Hydrocarbon-TCNE colors which persist a t room temperature are unstable upon heating. In contrast, however, many organic compounds containing hetero atoms, especially nitrogen compounds, leave a color on the paper after heating. Two semiquantitative techniques for the determination of total nitrogen in petroleum fractions have been developed. One method employs simple spraying and the other involves the Weisz ring oven (5). HE
REAGENTS A N D APPARATUS
TCNE was prepared in this laboratory by the dibromomalononitrilepotassium bromide complex method (1) or obtained from Eastman Organic Chemicals on special order. The compound is best purified by sublimation, but may be recrystallized from chlorobenzene (10 to 1). Because TCNE s l o d y evolves hydrogen cyanide on exposure to moist air, the reagent should be stored in a dark bottle under a blanket of inert gas. Pipets, 0.1 ml., Kahn-type. Spray bottle, 50-ml. glass reagent spray, Type R (Microchemical Specialties Co.. Berkeley, Calif.).
Detection of Nitrogen Compounds in Presence of Aromatic Hydrocarbons. Apply 0.05 ml. of sample to a square of filter paper ( = 23/4 inches square) supported on a 100-ml. beaker. When the sample has completely soaked into the paper, place in a vertical position and spray with a saturated solution of T C S E in benzene for 2 seconds from about 31/2inches. Place test paper in an oven a t 110’ C. for 5 minutes. Observe color and compare with colors of knolms. Ring Oven-Acetic Acid Method for Detection of Nitrogen Compounds in Presence of Aromatic Hydrocarbons. Place three pencil dots 11 mm. apart in line on a square of filter paper. Apply 0.05 ml. of sample to paper at the center dot. Center the sample paper on ring oven and with a capillary pipet, wash the sample spot with 60% acetic a d until the acid-wet area reaches the outer pencil dots. Place the test paper in an oven a t 110’ C. for 5 minutes. Remove the paper from the oven and allow to cool to room temperature. Spray as above with TCNE solution for 4 seconds. Heat the paper a t 110” C. for 5 minutes and compare colors. Color comparisons can be made with a series of samples of known nitrogen content treated by the same procedure or with a series prepared by dilution of a single known with nitrogen-free solvents-e.g., benzene, paraffin oil, iso-
octane-of about the same viscosity as the sample. Solvents used for dilution should have about the same viscosity, so that the spots will have the same area. An unknown sample may be diluted to obtain comparison with a known. Petroleum oils from different sources with the same nitrogen content may have slightly different colors, but a t low concentrations most samples appear to have about the same color. This is true below 100 p.p.m. for the simple spray method and below 10 p.p.m. for the ring oven method. I t is preferable to make estimates using knowns similar in composition to the unknowns; however, if knowns of different types must be used, comparisons are best made by dilution to the ranges specified above. Spots produced using the ring oven method have a narrow outer ring and a lighter inner spot. Comparisons should be made using the inner spot. RESULTS AND DISCUSSION
The nitrogen compounds tested include pyrroles, pyridines, indoles, pyrazoles, imidazoles, acridines, carbazoles, quinolines, and aliphatic and aromatic amines. The limit of detection appears to be in the range of lo-’ gram. Among the other hetero compounds tested, only the hydroxyl compounds and aromatic thiols seem to give colors sufficiently intense to interfere. Thiophenes leave no color; other sulfur compounds leave colors of very low intensity. Peroxides and hydroperoxides give only light or no colors. The colors produced by the VOL. 32, NO. 9, AUGUST 1960
1135
