Separation and Infrared Spectroscopic Determination of Nonionic Octylphenoxyethanol Additives in Gasoline R. M. SHERWOOD
and F. W. CHAPMAN, Jr.
Atlantic Refining Co., Philadelphia, Pa.
b The use of octylphenoxyethanoltype compounds in gasoline as carburetor anti-icing additives required a method of determination for control purposes. The residue from a sample of gasoline which has been evaporated on a steam bath is dissolved in carbon tetrachloride and passed through a small column of activated alumina, which adsorbs the octylphenoxyethanol (OPE). Washing with carbon tetrachloride and then with a 1 to 19 solution of pyridine and carbon tetrachloride removes interferences. Following elution with 1 to 4 isopropyl alcohol-carbon tetrachloride, the OPE is determined from its infrared absorption. In samples of gasoline containing 100 p.p.m. of OPE, the precision and accuracy are relative.
&3y0
S
~LIALLamounts
of octylphenoxyethanol (OPE) (1, 3 ) type compounds in gasoline act as carburetor anti-icing additives. Because these compounds are composed only of carbon, hydrogen, and oxygen, a method other than elemental analysis was necessary for their determination in a complex mixture such as gasoline. Numerous techniques including extraction with different agents under varied conditions, direct determination in the gasoline by infrared absorption, adsorption on conditioned cellulose, and determination by ultraviolet absorption measurement were unsatisfactory. The only completely satisfactory method for this type of sample was separation on activated alumina followed by infrared absorption as the final means of measurement. This simple procedure s e p arates the OPE from all other materials in gasolines which would interfere with its determination by infrared absorption. Commonly used interfering additives which are removed include: tetraethyllead fluid, phosphorus compounds used as surface-ignition additives, amines used as antioxidants, antilacquering agents, and dyes. REAGENTS
Pyridine-CC4 Solution, 1 ml. of pyridine and 19 ml. of carbon tetra: chloride made fresh. If this solution
is cloudy, the addition of 1 to 2 ml. of diethyl ether will clear it. Isopropyl Alcohol-CClr Solution, 5 ml. of isopropyl alcohol and 20 ml. of carbon tetrachloride. PROCEDURE
Place a small plug of glass wool in the bottom of the chromatographic column 15 em. in length and 1 em. in inside diameter and nearly fill the column with carbon tetrachloride. Add the activated alumina, Alcoa, Grade F-1, 48- to 100-mesh, to a depth of 7 em., and then drain off the carbon tetrachloride until its surface is just above that of the alumina. The column is now ready to use. Pipet 50 ml. of the gasoline sample into a 150-ml. beaker, place on a steam bath under a stream of nitrogen or air, and evaporate to about 5 ml. Quantitatively transfer this onto the column using carbon tetrachloride to wash out the beaker. Adjust the flow rate a t 2 or 3 drops per second, and when the level of the liquid reaches the alumina, wash the column with about 30 ml. of carbon tetrachloride. When the level of the last r a s h has reached the alumina surface, add 15 ml. of the 1 to 19 pyridine-carbon tetrachloride solution to the column and adjust the flow rate to about 1 drop per second. T h e n the level of this solution reaches the surface of the alumina, add 8 to 10 ml. of the 1 to 4 isopropyl alcoholcarbon tetrachloride solution to elute the OPE. Collect the eluate in a 20-ml. beaker. \Then the column has drained, place the beaker on a steam bath and evaporate the solvent in a stream of nitrogen or air. When all solvent is removed, let the beaker cool and quantitatively transfer the residue to a 2-ml. volumetric flask with carbon disulfide dispensed from a hypodermic syringe and needle. Dilute to the mark and mix. Dry the syringe and needle and withdraw about 1 ml. of the solution from the flask. Fill a 1-mm. sodium chloride absorption cell with this solution and obtain its absorption spectrum from 7.5 to 11 microns either against carbon disulfide in a 1-mm. reference cell or against air, because the slight absorption of carbon disulfide in this region is flat. The concentration of the OPE in this final solution can be calculated in several ways, but is done in this laboratory by base line measurement of the absorption at 8 microns. For the volumes specified our calculation becomes:
Yc OPE in gasoline (w./v.) =
Ck 2 A'XAkXjOO where
-I8= absorbance (base line) of the sample a t its %micron peak absorbance (base line) of a CS2 solution of OPE of known concentration a t its 8-micron peak C k = concentration of the known CS2 solution of OPE expressed as mg./ml. In Table I, column A shows the precision of the method on a plant sample of gasoline containing OPE. Column B shows the accuracy of the method on a sample of gasoline to which an exact amount of OPE was added in the laboratory. =
Table 1.
Analysis of Gasoline Samples
Sample Aa, Found 0.0094 0.0095 0.0095 0,0092 0.0095
Sample Bb Found Added 0,0091 0,0091 0.0093
0.0094 0.0094 0.0094
Regular plant gasoline. Plant gasoline containing known amount of OPE. DISCUSSION
The alumina should be discarded after one separation, as it does not quantitatively retain the OPE after being used several times. Drying the used column by vacuum permits the alumina to be easily poured out. A standard solution of the OPE can be made in carbon tetrachloride. An aliquot of this containing about 4 mg. of OPE is used to determine A k and should be run through the procedure before A k is measured. This eliminates any error in absorptivity due to traces of impurity that may be present in commercial grade OPE. The OPE used in most of this work is designated as Triton X-45. Triton X-100 (both Rohm & Haas Co.) could be determined as accurately by this method, with no modification other than using it to measure Ah. Others in this series might also be measured by this method. VOL. 32, NO. 9, AUGUST 1960
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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
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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.
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 colorimeter a t 1 0 0 ~ transmittance o with the reagent blank. Plot milligrams of iron against per cent transmittance. Procedure. Transfer a 0.5-gram TION.
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-ActiveAgents,” 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
