1168
ANALYTICAL CHEMISTRY
The results found for the four samples of murexide, with two runs per sample, are presented in Table 11. Statistical tests showed that the results are not dependent on the weight of sample taken within the limits shown. The essentially pure murexide samples A and C did not differ significantly, whereas the impure samples B and D did differ significantly between themselves and from A and C. The estimated standard deviation of a single run was 0.45% murexide. The anhydrous calcium purpurate was found to be very hygroscopic and could not be conveniently used in this method. The slightly high water content found for the monohydrate (Table I ) could perhaps be ascribed to a slight amount of thermal decomposition of the calcium purpurate taking place during the water determination. Calcium purpurate monohydrate is slightly hygroscopic, but not sufficiently so to make the weighings difficult. For this reason, the monohydrate was selected as the more suitable form for the gravimetric method. The assay results presented in Table I1 were further verified in a relative manner by absorbance determinations on each sample. Sample A was arbitrarily taken as the standard, with an assigned purity of 100%. Using the Beer’s law constant obtained with this sample, the per cent purities of the remaining samples were determined spectrophotometrically.
Colorimetric Procedure. To each of nine 100-ml. volumetric flasks, 14.82 ml. of 0.200N sodium hydroxide and 25.00 ml. of 0.200N potassium phos hate, monobasic, were added (this buffer mixture results in a p 8 of 7.0 when diluted to the mark). Between 40 and 50 mg. of murexide from each of the four sources were weighed to the nearest 0.1 mg., transferred to 250-ml. volumetric flasks, dissolved, and diluted to the mark with distilled water. A 10.00-ml. aliquot of a murexide solution was added to each of two 100-ml. flasks, the solution diluted to volume, and the absorbances determined a t 525 mp (the absorption maximum of murexide under these conditions) in 1-cm. cells versus a blank prepared by diluting the solution in the ninth 100-ml. flask to the mark with distilled water.
Table 11. Murexide Found for Various Samples Sample Taken, Mg. 100-116 59-73 a
Murexide Found, % Sample B C D
A 100.3a 101.0
74.8 74.1
99.9 100.4
69.8 70.3
100.7 74.5 Mean Each number represents one run.
100.2
70.1
-
Mean 86.20 86.45
Table 111. Relative Purity of Murexide Samples by Absorbance Measurements Sample Purity,
a
Mean Arbitrary standard.
Aa
B
C
D
99.5 100.5
74.2 75.0
99.7 98.6
69.1 69.7
100.0
74.6
99.2
69.5
The results of the colorimetric procedure are shown in Table 111. These figures compare favorably with those reported in Table 11, within the experimental error. Thus the proposed gravimetric procedure for the assay of murexide provides an absolute method for the standardization of a colorimetric analytical curve for this compound. LITERATURE CITED
(1) Davidson, David, J . A m . Cheni. Soc., 58, 1 8 2 1 (1936). (2) Hartley, W. K.,J . ChenL. Soc. (London),87, 1 7 9 1 (1905). (3) Kuhn, R., and Lyman, J. C., B e r . , 69, 1547 (1936). (4) Williams, RI. B., and Jloser, J. H., ANAL. CHEM.,25, 1414 (1953). RECEIVEDfor review February 8, 1954.
Accepted April 16, 1954. P a r t of a thesis of James H. Moser presented to the Graduate School of Oregon State College in partial fulfillment of requirements for degree of doctor of philosophy. Approved for publication b y the Oregon State College Monograph Committee, Research Paper No. 243, Department of Chemistry, School of Science.
Determination of Traces of Antimony in Soils and Rocks F. N. WARD and H. W. LAKIN Geochemical Prospecting Research Laboratory, Denver Federal Center, Building 25, Denver, Colo.
A relatively simple, rapid, and moderately accurate method for the determination of traces of antimony in soils and roclrs is based on the reaction of pentavalent antimony with rhodamine B in isopropyl ether after extraction of the antimony from 1 to 2M hydrochloric acid. The suggested procedure is applicable to samples containing from 0.5 to 50 p.p.m. of antimony, and with modifications it can be used on samples containing larger amounts. Four determinations on two rocks containing less than 2 p.p.m. of antimony agree within 0.4 p.p.m., and four determinations on seven soils containing 2 to 10 p.p.m. of antimony agree within 1 p.p.m. of the mean. The conditions for oxidation of the antimony and the subsequent extraction of the pentavalent form with isopropyl ether have been established. Experiments show that the antimony-rhodamine B compound is stable in isopropyl ether for more than 3 hours. The suggested procedure permits the determination of 2 y of antimony in the presence of 30,000 y of iron, 250 y of arsenic, and 300 y of gold and/or thallium. Data are given to show the applicability of the method to routine laboratory and field use. Under field conditions the method has been used to determine traces of antimony in as many as 20 soil samples in an 8-hour day.
T
HE U. S. Geological Survey is currently engaged in a program designed to investigate the usefulness of geochemical prospecting in locating new ore bodies and extending older ones ( 1 , 8, 10). The chemical analysis of soils or rocks for various elements such as copper, lead, zinc, molybdenum, silver, or arsenic is a primary step in geochemical prospecting. Although antimony is not abundant, it is common in sulfide deposits; and the chemical analysis of soils or rocks for antimony is worth while, because the soil or rock sample containing an abnormal concentration of antimony may indicate a sulfide deposit. A search of the literature revealed that existing methods were inadequate for determining the traces of antimony in such soils or rocks. Therefore, it was necessary to develop a new procedure, which was sensitive enough to distinguish anomalous values from background values. In this paper the background value of antimony is defined as the amount found in representative soils from nonmineralized areas. Recent estimates of the abundance of antimony in the earth’s crust ( 1 4 ) are all in the range of 0.3 to 1 p.p.m Because very few determinations of antimony in soils and rocks have been made, three of the estimates were made only on igneous rocks. As igneous rocks constitute about 95% of the earth’s crust ( B ) , the antimony content of igneous rocks can serve as a background value in the establishment of the range over which a method of
1169
V O L U M E 2 6 , NO. 7, J U L Y 1 9 5 4 determining the element can be useful in applied geochemical prospecting. The reaction of antimony with iodide in acid solution is the basis of a method developed by McChesney (11) for the determination of 5 to 50 p.p.m. of antimony. In his method antimony(111) or (V) reacts with iodide to produce the strongly colored iodoantimonite ion. Clarke (3’) developed a method for the determination of small amounts of antimony based on the reaction of pyridine with antimony(II1) in the presence of iodide. The colored double iodide formed in this reaction tends to precipitate because of its slight solubility and some means of keeping it in suspension is required. Because of the decreased sensitivity the method based on the formation of the double iodide is less useful than the method developed by McChesney, and neither method is sensitive enough to determine directly the small quantities of antimony in soils and rocks. Recently West and Hamilton ( 1 7 ) reported that benzene extracts antimony(II1) from iodide solution and that the trivalent antimony reacts with rhodamine B, in the organic medium. Perhaps this reaction could be the basis of a quantitative method for determining traces of antimony, but n o procedure based on the reaction has been suggested. However, the reaction of antimony(V) with rhodamine B announced by Eegriwe (6) in 1927 is the basis of several colorimetric methods (6, I S , 16) recommended for determining traces of antimony. In hydrochloric acid or in sulfuric acid containing chloride, antimony(V) reacts with rhodamine B to form a redviolet compound or complex ion of unknown composition. The reaction is extremely sensitive and under the proper conditions as little as 0.1 y of antimony in the form of the rhodamine B compound produces a distinct color in 4 ml. of solution. Destruction or removal of the excess rhodamine B is a problem common to methods based on this reaction. Heretofore, the problem was solved in either one of two ways. Bromine (6) was used to destroy the excess rhodamine B, or benzene (16), in which the rhodamine B is insoluble, was used as an immiscible solvent t o extract the antimony-rhodamine B compound from the aqueous solution. Because rhodamine B reacts with other cations, such as iron, commonly present in the solution of a soil or rork sample to form colored compounds soluble in benzene, toluene, and similar aromatic hydrocarbons, methods using these solvents to separate antimony directly from the sample solution are not applicable. Obviously, the separation of antimony from interfering elements is necessary before using rhodamine B. Maren (13) used isopropyl ether to extract antimony(V) from 1.5M hydrochloric acid and thus separated the antimony from more than 90% of the iron present. He found that the antimony-rhodamine B compound could be formed as a fine dispersion in the ether phase by shaking the ether containing the antimony with an aqueous solution of rhodamine B. The dispersion can be treated as a solution. Later in the study of a procedure for separating antimony(V) from antimony(II1) Edwards and Voigt (4)reported that isopropyl ether extracts a t least 98% of antimony(V) from hydrochloric acid solutions varying in acid concentrations from 3 to 9M. Extrapolation of their data to a lower acid concentration indicates that isopropyl ether should extract approximately 90% of antimony(V) from 1 or 2-11 hydrochloric acid. As isopropyl ether extracts about 90% of the antimony(”) from 1 or 2M hydrochloric acid and a t this acid concentration fails to extract quantitatively some other elements, such as iron, which also react with rhodamine B, the isopropyl ether estraction should provide a means of concentrating and isolating antimony for quantitative estimation. EXPERIMENTAL
Formation of Antimony-Rhodamine B Compound in Isopropyl Ether. In the work reported here, antimony(V) is extracted
from hydrochloric acid by shaking 5 ml. of isopropyl ether with 70 ml. of 1.5M hydrochloric acid for 15 seconds. The ratio of ether to acid is considerably smaller than that employed by Edwards and Voigt (4)and the effect attributable to different ratios is not known. I t was not expedient to iirvestigate these ratios systematically. The isopropyl ether containing antimony(\‘) is shaken with an aqueous solution of rhodamine B to form the colored compound of antimony in the ether. Under certain conditions, the unreacted rhodamine B is evtracted by the isopropyl ether Therefore, it was necessary to investigate and establish the conditions under which the antimony-rhodamine B compound alone could be obtained in the ether layer. I t was found that: Isoprop3-1 ether shaken successively with 3, 4, 5 , or 6 J 1 hydrochloric arid and then with an aqueous solution of rhodamine B was colored red with the rhodamine B. Isopropvl ether shaken successively with 1 or 2M hydrochloric acid and then with an aqueous solution of rhodamine B remained colorless. Isopropyl ether shaken successively with 1, 2, 3, 4, 5 , or 6 M hvdrochloric acid and then with a 1-11hvdrochloric acid solution of rhodamine B remained colorless. These observations show that under certain conditions the rhodamine B partitions itself between the inorganic and the organic phase. As the antimony-rhodamine B compound and the rhodamine B are both colored red, either one may be mistaken for the other. Therefore, to make certain that any red color in the isopropyl ether is caused by the antimony-rhodamine B compound and not by the rhodamine B alone, the antimony compound is formed by shaking the isopropyl ether containing the antimony with a LIf hydrochloric acid solution of rhodamine B. Furthermore, the use of such a solution of rhodamine B, hereafter referred to as rhodamine B reagent, permits a greater range with respect to the acid concentration, and the greater range is especially important in field applications. Stability of Antimony-Rhodamine B Compound in Isopropyl Ether. Because the proposed procedure varies somewhat from published methods based on the rhodamine B reaction (11, I S , 15), an investigation of the stability of the antimony-rhodamine B compound in isopropyl ether is in order. Accordingly, absorbance measurements were made a t intervals during 3 hours on isopropyl ether solutions containing 1, 2, and 3 y of antimony as the rhodamine B compound. The results, which are given in Table I, show little change in the absorbance of each solution during 3 hours. In a similar experiment carried on for 6.5 hours, the absorbance of an isopropyl ether solution containing antimony as the rhodamine B compound decreased insignificantly from 0.222 to 0.218.
Table I.
Stability of Antimony-Rhodamine B in Isopropyl Ether
Time, Min.
1 y Sb
0 25 60 90 120 180
0.137 0.136 0.136 0. I3rr 0.137
0.137
4hsorbance 2 y Sb 0.245 0,245
n . 246 n
246
0.246 0.244
3 y Sb
0.338 n.339 0.341 n 340 0.340
0.337
As the isopropvl ether solutions of the antimony-rhodamine B compound formed under the conditions described in the proposed procedure seem to be stable for as long as 6 hours, the analvst can measure the absorbance more or less a t his convenience. ABSORPTIONCURVE. Absorbance measurements were made on an isopropyl ether solution of 2 y of antimony in the form of the rhodamine B compound with a Beckman DU spectrophotometer a t wave lengths ranging from 460 to 600 mp and a t a slit width of 1.5 mm. The curve obtained bv “ Idottine absorbance against wave length is shown in Figure 1. Under the conditions Y
1170
ANALYTICAL CHEMISTRY
given in this paper, the maximum absorption occurs a t wave lengths between 545 and 555 mw. For comparison the absorption curve of an aqueous solution of rhodamine B is shown also in Figure 1. Because the maximum absorption for both the rhodamine B and the antimony-rhodamine B compound occurred a t similar wave lengths, extreme care was exercised in the development of the proposed method to make certain that the red color, whose absorption was measured, was caused by the antimony-rhodamine B compound and not by the rhodamine B.
from absorbance measurements of the isopropyl ether solutions of the antimony-rhodamine B compound. Data obtained in this work show that the concentration of the antimony-rhodamine B compound in the isopropyl ether can be as great as 2.5 y of antimony per ml. Diluting the isopropyl ether after the extraction to bring the antimony concentration within the desired range, 0 to 2.5 y per ml., proved to be practicable. In order to establish the feasibility of the dilution technique, standard solutions containing 20 and 100 y of antimony were analyzed by the proposed procedure. The absorbance of the 5-ml. isopropyl ether extracts of each standard solution was too great for reliable measurement with a Beckman DU spectrophotometer. The isopropyl ether solutions were diluted until the antimony concentrations were 2.0 and 2.5 y per ml. The absorbance of these solutions and of those obtained by successive dilution are shown in Table 11.
Table 11. Antimony Found by -4bsorbanceMeasurements on Successively Diluted Isopropyl Ether Solutions
0 2001
Sb,
Isopropyl Ether, Y
100
M1.
40 60 100
Concn. Sb in Ether, y per M1.
2.5 1.7 1. 0
Absorbance
0.855
0.608
0.380
Sb Recovered, y
97.2
103.0 105.0
L
WAVE
LENGTH,
mp
Figure 1. Absorption Curves A.
B.
Isopropyl ether solution of antimony-rhodamine B compound Aqueous solution of rhodamine B
If the absorbance measurements are made using a smaller slit and the ultraviolet-sensitive phototube in place of the redsensitive phototube, the absorption peak is somewhat narrower and slightly displaced toward the longer wave lengths. Practically, the absorbance measurements can be made with light varying in wave length from 540 to 560 mp. This is indeed fortunate, as many common filter photometers afford, under the best conditions, a band spread of as much as 50 mp. In the present work all of the remaining absorbance measurements were made a t 545 m p using a 1.5-mm. slit. Application of Beer’s Law to Antimony-Rhodamine B Isopropyl Ether System. From observations made on isopropyl ether solutions containing less than 1.5 p.p.m. of antimony, llaren (13) concludes that the system deviates slightly from Beer’s law. The present investigation of this system was made by measuring the absorbance of five separate isopropyl ether solutions of the antimony-rhodamine B compound varying in antimony concentration from 0.5 to 2.5 y per ml. Over this range, a straight line was obtained by plotting absorbance against concentration. However, a close inspection and additional measurements a t higher concentrations reveal that these points lie on a curve instead of a straight line. In other words, Beer’s law is not followed exactly. Because the curvature is slight, a straight line can be drawn through these points, and, in practice, satisfactory antimony determinations can be made
The data in the last column of Table I1 show that satisfactory estimations can be made by measuring the absorbance of the dilute solutions and prove the feasibility of the dilution technique. Varying the sample aliquot to control the amount of antimony being estimated is unnecessary. The proposed method is applicable to materials containing more than trace amounts of antimony. It has been used on materials containing as much as 0.5% antimony. The authors have observed occasional failures of the dilution step with some batches of isopropyl ether. Absorbance measurements on a given isopropyl ether solution of the antimonyrhodamine B compound before and after dilution did not show the calculated decrease in the concentration of antimony. The nature of the difficulty has not been determined but it can be corrected by shaking the diluted isopropyl ether solution of the complex with rhodamine B reagent before measuring the absorbance. To be on the safe side, this step has been incorporated in the procedure. Conditions for Oxidation and Extraction of Antimony. Isopropyl ether readily extracts antimony(V) but not antimony( 111) from hydrochloric acid (4). Therefore, the use of isopropyl ether to separate antimony from other elements requires that the antimony be present as antimony(V). Sandell (15) observed that cerium(1V) completely oxidized antimony(II1) to antimony(V) in 6 M hydrochloric acid but not in 1 or 2M acid. Therefore, during the oxidation of antimony(II1) with cerium(IV), the hydrochloric acid concentration must be near 6 M . The oxidation of antimony(II1) to antimony(V) with cerium(IV) has several interesting aspects. The intermediate valence state, antimony(IV), is apparently a stable state, for Hillehrand and Lundell (9) recommend the tetroxide as a weighing form in the gravimetric determination of antimony. Under certain conditions antimony(II1) is oxidized to antimony(IV), and even a strong oxidizing agent like cerium(1V) fails to oxidize the antimony(1V) to (V). On the other hand, a reducing agent like sulfite (13) readily reduces antimony(1V) to (111), although it has no effect on antimony(V). Therefore, in order to make certain that all antimony(1V) is reduced to antimony(II1) before
V O L U M E 2 6 , NO. 7, J U L Y 1 9 5 4
1171
the addition of cerium(IV), a small amount of sodium sulfite is added in accordance with Maren's suggestion in an earlier publication (11). When no deliberate attempts were made to control the temperature of the solution during the oxidation and subsequent extraction with isopropyl ether, only 50 to 80% was recovered from 2 y of antimony. Young (10)states that hot concentrated hydrochloric acid reduces cerium(1V) and Willard and Diehl (18) found that warm hydrochloric acid reacts with isopropyl ether. This reaction is presumably one of reduction. If one or both of these reactions take place appreciably in warm 6 M hydrochloric acid, it is possible that no oxidation of antimony(II1) will occur. As both of these side reactions are known to occur a t elevated temperatures, they can be prevented perhaps completely by allowing the desired oxidation of the antimony(II1) to take place a t a lower temperature. Accordingly, a series of experiments was made on standard solutions of antimony in order to observe the effect of temperature. In these experiments the temperature of the antimony solution was maintained a t 25" C. or less during the oxidation and extraction. The results showed that excellent recoveries of antimony could be made repeatedly. At 25" C. or less, little or no chlorine is produced during the oxidation and the precautions given by Sandell ( 1 5 ) with regard to the individual operations do not apply. Interfering Elements. In aqueous medium, iron(III), gold, thallium, and tungsten react with rhodamine B to give highly colored products (16). Arsenic, copper, and tin also react similarly (IS). The isopropyl ether extraction separates antimony from bismuth, chromium, cobalt, lead, and tungsten, because these elements do not extract appreciably (15). Conversely, the isopropyl ether extracts with antimony such elements as iron(111), arsenic, gold, tin, and thallium. The steps necessary to eliminate the interference caused by iron( 111) are interesting. In the procedure, antimony(111) is oxidized to antimony(V) with cerium(IV), and the excess of the latter is destroyed with hydroxylamine hydrochloride. This reagent also reduces much of the iron(II1) to (11) which isopropyl
Table 111. Effect of Other Elements on Determination of Antimony with Rhodamine B (Isopropyl Ether Extraction) Element
Au
Amt. of Element Added, y
100 100 300 300
1,000 1,000
Fe(1II)
1,000 1,000 30,000 30,000 1,000
Sb Added, y
None 2.0 None 2.0 None 2.0 None 2 0
Sb Found, y
0.0 1.8
0.0 1.7 4.2 >10 0.2 2.0
None 2.0 Sone
0.2
1,000
2.0
Kone
cu
1,000 1,000 1.000 1.000
2.0
1.5 0.0 1.8 0.0 1 .I)
Sn(I1)
1.000
None 2.0
0.3
1,000
100 300 300 1,000 1,000 1,000 10,000 10,000
None Pione 2.0 None None 2.0 None 2.0
0.0
co
Cr
TI(U
W
2.0
Sone
1.7 0.3
1.8
0.2 1.8 >10 0.0 1.8 0.1 1.9
ether does not extract. Moreover, isopropyl ether extracts no more than 10% of the remaining iron(II1) from 1.5M hydrochloric acid (13). After most of the aqueous solution is separated from the isopropyl ether, the latter is washed once with a few milliliters of a 1 M hydrochloric acid solution of hydroxylamine. This treatment of the isopropyl ether containing the antimony and detectable traces of iron(II1) with the liM hydrochloric acid solution of hydroxylamine decreases the concentration of iron(111) in the ether because of the reduction previously described. Moreover, the separation referred to decreases further the amount of iron(II1) in the isopropyl ether. At this point the quantity of iron(I1I) in the isopropyl ether is small indeed, but as an addition01 precaution the isopropyl ether is washed again with a few milliliters of 1M hydrochloric acid. In this manner 2 y of antimony can be determined satisfactorily in the presence of 30,000 y of iron(II1). The interferences caused by the elements which are extracted by isopropyl ether are not easily eliminated. A workable procedure requires the determination of the quantities of such elements that can be present and still permit a satisfactory determination of antimony. Accordingly, varying amounts of the interfering elements were added to 2 y of antimony and the mixtures were taken through the procedure. The results of these runs and other interference tests are shown in Table 111. With regard to the amounts that ran be tolerated arsenic(III), gold, and thallium(1) are serious interferences. The quantities of these elements that can be present during a satisfactory determination of 2 y of antimony are 250, 300, and 300 y , respectively. From these data it is obvious that the ratios of arsenic, gold, and thallium to antimony can be 125,150,and 150, respectively. The relative abundance of arsenic, gold, and thallium certainly does not indicate that any of these elements will be a serious interference in the proposed method, because the ratios calculated from the relative abundance of the elements in igneous rocks given by Goldschmidt ( 7 ) are 5.0, 0.005, and 0.3, respectively. Reagents and Apparatus Required for Field Determinations. Flux, fused sodium bisulfate. Prior to use, heat in a porcelain casserole and fuse gently for 5 minutes. Cool and crush cake. Hydrochloric acid, 6.W. Hydrochloric acid, 1M. Standard antimony solution, 0.170 antimony in 6.V hydrochloric acid. Dissolve 0.274 gram of antimony potassium tartrate in 100 ml. of 6M hydrochloric acid. Standard antimony solution, 0.002% antimony in 6 M hydrochloric acid. Dilute 2 ml. of 0.1% standard solution to 100 ml. with 6M hydrochloric acid. Ceric sulfate. Dissolve 3.3 grams of anhydrous ceric sulfate in 100 ml. of 0.5%' sulfuric acid. Hydroxylamine hydrochloride. Dissolve 1 gram of hydroxylamine hydrochloride in 100 ml. of water. Hydroxylamine hydrochloride. Dissolve 1 gram of hydroxylamine hydrochloride in 100 ml. of 1M hydrochloric acid. Isopropyl ether. Practical grade is suitable provided it is peroxide free. Saturate with 1M hydrochloric acid. Rhodamine B reagent. Dissolve 0.02 gram of rhodamine B (tetraethyl rhodamine) in 100 ml. of liM hydrochloric acid. Sodium sulfite. Dissolve 1 gram sodium sulfite in 100 ml. of water. 3Iullite mortar and pestle, outside diameter of mortar, 75 mm. One sieve, 80 mesh. The sieve consists of silk bolting cloth in an aluminum holder having an outside diameter of 100 mm. One aluminum receiver to fit the sieve holder. One small camel's hair brush. Borosilicate glass culture tubes, 18 X 150 mm. Tubes, flat bottom, 14 X 80 mm. outside dimensions. Separatory funnels, Squibb type 125-ml. capacity. One 100-ml. borosilicate glass voiumetric flask with stopper. One test-tube rack holding a t least 20 tubes. One separatory funnel rack holding 4 to 6 funnels. Balance, torsion with sensitivity of 0.002 gram Six 5-ml. pipets, calibrated in tenths of a milliliter. One 0.1-ml. pipet, calibrated in hundredths of a milliliter. One 50-ml. graduated cylinder. Filter paper, No. 42, Whatman, 7-cm. diameter. Funnels, small, diameter of top, 40 mm. Spatula, small porcelain.
ANALYTICAL CHEMISTRY
1172 One portable gasoline stove. Water, purified by passing tap water through one of the several types of resin demineralizers now commercially available. PROCEDURE
Solution of Sample. Place 0.2 gram of soil or rock ground to pass the 80-mesh sieve and 1.5 grams of flux in a culture tube. Mix the contents by alternately rotating the tube and tapping gently against a hard surface. Heat the tube to effect a fusion of the contents. Continue the fusion until practically all of the organic matter is destroyed and the tube is full of white fumes. Remove tube from heat and while cooling rotate to form a thin cake around the inner wall. When the tube and contents are cool, add 6 ml. of 6M hydrochloric acid; heat the tube gently and stir the contents until the salts resulting from the fusion are in solution. Do not allow the solution to boil. Add 1 ml. of sodium sulfite reagent and 3 ml. of 6 M hydrochloric acid. Shake tube gently to mix contents. Transfer the contents of the tube to a funnel fitted with a dry No. 42 fluted filter paper and collect filtrate in a 125-mI. separatory funnel. Rinse the tube and the residue on the filter paper twice with 3-ml. portions of hot 6 M hydrochloric acid and once with 2 ml. of hot water. Isopropyl Ether Extraction of Antimony. Cool filtrate in the separatory funnel to 25' C. or less, add 3 ml. of ceric sulfate solution, and shake. Add 10 drops of aqueous hydroxylamine hydrochloride, shake, and allow the funnel contents to stand 1 minute or until the excess ceric sulfate is destroyed. Add 45 ml. of water and cool the solution to 25' C. or less. Add 5 ml. of isopropyl ether to the funnel and shake the funnel with moderate vigor for 30 seconds. Allow the solution to stand 5 minutes and drain off all but about 0.5 ml. of the aqueous phase. Add 2 ml. of a 1M hydrochloric acid solution of hydroxylamine and shake the funnel for 1 or 2 seconds. Allow phases to separate and drain off all but about 0.5 ml. of the aqueous phase. Add 2 ml. of l M hydrochloric acid and shake for 1 or 2 seconds. Allow phases to separate as before and drain aqueous phase. Estimation. Add 2 ml. of rhodamine B reagent to the funnel and shake the contents for 10 seconds. When the phases have separated, pour the isopropyl ether into a cuvet and measure the absorbance a t 545 to 555 mp. Determine the number of micrograms of antimony from a previously established standard curve. I n the field determine the antimony content of the sample solution by comparing visually small flat-bottomed Nessler tubes containing a 3-ml. portion of the isopropyl ether solution of the antimony-rhodamine B compound obtained from the sample and tubes containing isopropyl ether solutions of the antimonyrhodamine B compound prepared similarly from 0.5, l, 2, 3, and 4 y of antimony. If the color intensity of the isopropyl ether solution obtained from a sample is greater than that of the standard solution prepared from 4 y of antimony, dilute the isopropyl ether sample solution with isopropyl ether and shake with 2 ml. of rhodamine B reagent. Repeat until the color intensity of the isopropyl ether solution obtained from a sample is similar to one of the isopropyl ether solutions obtained from a standard. Multiply the number of micrograms of antimony present in the similar standard by a factor obtained by dividing the final volume of isopropyl ether by 4, instead of 5, because about 1 ml. of isopropyl ether is not recovered from the first extraction. Multiply the results obtained by either method of estimation by 5 to convert to parts per million or divide by 2000 to convert to per cent.
An acid digestion effects a partial solution of a soil or rock sample. As the valence of antimony in a given soil or rock sample may not be known and antimony(II1) is somewhat volatile under certain conditions, an acid attack, digestion, or fusion should oxidize the antimony to a less volatile state or providp conditions under which antimony(II1) is not easily lost by volatilization. An oxidizing acid such as nitric acid is not suitable because the last traces of nitrate are relatively difficult to remove and nitrate interferes in the reaction of antimony with rhodamine 13. Digestion of a soil or rock sample with hot concentrated sulfuric acid effects a partial solution, but this is slow.. Fusion of the sample with an acidic flux such as potassium or sodium pyrosulfate provides a rapid and convenient method of sample solution preparation. The sodium pyrosulfate, suggested as a suitable flux in the procedure, melts a t a relatively low temperature and decomposes in part rather quickly to provide a sulfuric acid solution from which antimony(II1) is not easily volatile (18). The suggested flux also oxidizes sulfides and the usual amounts of organic matter found in a soil or rock sample. The analysis of samples of known antimony content by the proposed procedure would provide data on the effectiveness of sample solution preparation, but, unfortunately, standard samples with antimony contents in the desired concentration range were unavailable. Until the effectiveness of the sample solution preparation can be determined, the authors believe that the ease and convenience of the p y r o d f a t e fusion deserves consideration. RESULTS
Recovery of Antimony Added. To test the proposed method, varying amounts of antimony(II1) in 6M hydrochloric acid were added to 0.2-gram portions of different soils A hose antimony content had been reasonably well established by repeated analysis and the mixtures were fused with sodium pyrosulfate. Each mixture R as carried through the proposed procedure and the antimony was determined by measuring the absorbance of the isopropyl ether extract a t 545 mp and referring to a standard curve. The results are shown in Table IV. Almost without evception 90% or more of the antimony initially present in the soil and the antimony added was recovered
Table I\'. Sample S o .
Recovery of Antimony Added to Soils
Sb Present,
y
Sb Added.
y
Sb Found, y
Recovery (if rldded Sh. y
2
DISCUSSION OF PROCEDURE
Solution Preparation. Silica is one of the major constituents of soils and rocks and the complete solution of a sample requires the solution of silicate minerals. Silica can be eliminated by volatilization as the tetrafluoride, but antimony may be volatilized a t the temperature necessary to remove the last traces of fluoride. Complete solution of the sample can be effected without volatilizing antimony by an alkaline fusion with hydroxide or peroxide. However, the acidification of aqueous extracts of alkaline fusions produces large quantities of silica and salts that cannot be kept in solution in 6 M hydrochloric acid under ordinary conditions. Their precipitation removes traces of antimony from solution by absorption or occlusion. Thus, solution of the sample by an alkaline fusion is hardly feasible. The original aim was the development of a rapid method for the determination of traces of antimony in soils and rocks under routine laboratory and field conditions, and so the complete solution of the sample may be unnecessary.
4
1.6
5
1. O
4.0 5.0 1.2
5.2 6.0 2.0
3.6 4.4 1
.o
Table V. Precision of Method Applied to Soils and Roche
Material Granite Diabase Soil Soil Soil Soil Soil SO!l
so11
Location Rhode Island Virginia North Carolina Idaho North Carolina North Carolina North Carolina Idaho Idaho
Sb Found, P P A I , Four Determinations Std. High Low hlean dev 0.4 0.6 0.2 0.9 1.2 0.1 1.3 1.1 1.5 0.8 2.3 3.5 4.0 4.5 4.5
5.5
9.0
10.0
3.0
3.5 3.5 4.0 6.5 8.5
3.6 3.9 4.1 4.9 7.9 9.5
0.5
0.5 0.5 0.6 1.1 0.7
V O L U M E 26, NO. 7, J U L Y 1 9 5 4
1173
Precision of Method W h e n Applied to Soils and Rocks. To demonstrate the precision of the method when applied to soils and rocks, four determinations of antimony were made a t different times on seven soil samples and two rock samples. The absorbancy of blanks in each run was zero. I n fact, identical readings were obtained on the samples when either the pure solvent or the blank was used in the null cell. For each sample the highest, lowest, and mean value as well as the standard deviations are shown in Table V.
Table VI.
satisfactory. The results obtained under field conditions or in temporary quarters are sufficiently accurate to indicate and define areas of antimony mineralization. hloreover, the method is short and simple enough to permit relatively unskilled workers to determine trace amounts of antimony in 20 or more samples of soils during an 8-hour day. ACKNOWLEDGMENT
The authors are grateful to H. E. Hawkes and Vance Kennedv of the U. S. Geological Survey for assistance in collecting the samples.
Determination in Laboratory and Field of Antimony in Idaho Soils Sample N o .
LITERATURE CITED
Antimony, P.P.M. Laboratory Field’
1
1 2 4
2 3 4
2~. 5
5 6
34 41
40
7 8 9 10 11
70 140 135
75 112
350 260
Cannon, H. L., A m . J . Sci., 2 5 0 , 7 3 5 (1952). Clarke, F. W., U. S. Geol. Survey, Bull. 770, 423 (1924). Clarke, S. G., AnaLysf,5 3 , 3 7 3 (1928). Edwards, F. C., and Voigt, A. F.,. ~ N A L .CHEM.,21, 1204 (1949) Eegriwe, E., 2. anal. Chem., 70, 400 (1927). Frederick, W.G., IND. ENG.CHEM.,ANAL.ED., 13, 922 (1941). Goldschmidt, 1‘. hl., Skrifter A’orske Videnskaps-Akad. Oslo, I . Mat.-Naturv. KZ.,KO.4 , 99 (1937). Hawkes, H. E., Econ. Geol., 44, 706 (1949). Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” 2nd ed., p. 283, Kew York, John Wiley & Sons,
0.5 3 8 30 ~~
40 160
350 350
1953.
I n the range covered by the data in Table V, the precision is well within the requirements set forth by Youden (19). The standard deviation of the soils varies from 0.5 to 1 p.p.m. and about 68%three out of four-of the values obtained on each sample (soils and rocks) is within 1 standard deviation of the mean value. As the method is proposed for field as well as routine laboratory work, a comparison of results obtained in the field and laboratory is appropriate. Cuts from 11 soil samples analyzed for antimony in the field were brought into the laboratory and antimony determinations were made under more ideal conditions. ilbsorbancies of the isopropyl ether solutions of the antimony-rhodamine B compound were measured instrumentally, and the quantities of antimony were determined from a previously established standard curve. The results obtained in the field and in the laboratory are shown in Table VI. The agreement between field and laboratory determinations is
Huff, L. C., Econ. Geol.. 47,517 (1952). hIcChesney, E. W.,IND.ENG.CHEM.,ANAL. ED., 18, 146 (1946).
hlaren, T. H., Bull. Johns Hopkins Hosp., 77, 338 (1946). Maren, T . H., ANAL.CHEM..19, 487 (1947). Rankama, Kalervo, and Sahama, Th. G., “Geochemistry,” p. 738, Chicago, University of Chicago Press, 1950. Sandell, E. R., “Colorimetric Determination of Traces of Metals,” 2nd ed., pp. 165, 167, New York, Interscience Publishers, 1950. Webster, S. H., and Fairhall, L. T., J . Ind. Hug. Toxicol., 27, 183 (1945).
West, P. W., and Hamilton, W. C.,
; ~ N A L . CHEM.,24,
1025
(1952).
Willard, H. H., and Diehl, Harvey, “Advanced Quantitative .I\nalysis,” p. 346, Kew York, D. Van Nostrand Co., 1943. Youden, W. J., “Statistical hfethods for Chemists,” p. 12, S e w York. .John Wiley & Sons, 1951. Young. Philena. AN.AI.. CHEM., 24, 152 (1952). RECEIVED for review September 1 4 , 1953, Accepted
April 14. 1054.
Determination of Sesamin, Sesamolin, and Sesamol MORTON BEROZA Entomology Research Branch, Agricultural Research Service,
The determination of sesamin and sesamolin, pyrethrin synergists found in sesame oil, is of importance in the insecticide field. Existing procedures for their determination may sometimes be in error. -4method for the determination of sesamin, based on its separation in pure form by chromatography on silicic acid, is described. Solutions of ethyl acetate in 2,2,4-trimethylpentane are used to develop the chromatogram and the sesamin in the effluent is detected and identified by means of its ultraviolet absorption. Sesamolin and sesamol determined by the method of Suarez et al. gave less color than anticipated. I t is recommended that a solution of known concentration be run under identical conditions as the unknown, so that the concentration of the unknown may be based on the color developed by known. Chromatographic studies indicate that sesamolin is the only compound, exclusive of sesamol, that gives the Villavecchia color reaction.
U. S. Department o f Agriculture, Beltsville, Md The chromatographic procedure for sesamin, although time-consuming, is accurate, reproducible, and specific, The proposed modification of the sesamolin and sesamol procedures eliminates interferences found in the previous method.
S
ESAME oil, obtained from the seed of Sesamum indicum (L.), increases the insecticidal potency of pyrethrins ( 7 ) .
One of the constituents of the oil responsible for this activity was found by Haller et al. (8, 9) to be sesamin. More recently Beroza ( 2 ) found that sesamolin, another constituent of sesame oil, is a much more potent synergist than sesamin and, although present in lesser amount, it usually accounts for most of the synergistic activity of sesame oil with pyrethrins. The determination of both constituents is therefore of importance in the insecticide field. 1Iethodp for the determination of sesamin and ~esaniolinin
