Table II.
Results From Steel Samples
700 Determined on Separate Days
Sample
Mill ingot” 0,083 Stainless 410b 0.039
0.084 0.042 0,010 0.014 0.015 0.018
0,087 0.046
0.091 0.035 0.010 0.017 0.015 0.018
Stainless 32lC 0.010 0.008 TBS No. 1040d 0.019 0.025 0.015 0,019 0.019 0.017 0.016 0.018 0.018 0.023 .Ueehenv Ludlum Steel Coro.. X = 0.094. .IllGhen$ Ludlum Steel Corp.; X = 0.039. c Allegheny Ludlum Steel Corp., X = 0.012. d XBS certified yo 0 = 0.018, TRlCA4av. = 0.0185.
0.094 0.033 0.006 0.022 0,019 0.014 0.023
Rang=
9
0.011 0.013 0.004 0.011 0.004 0.005
0.088
0 007
0.039
0.008
0,019 0,017 0 017 0 021
Leaks are less of a problem, since the vacuum svstem is more compact. The spied of analysis achieved with this equipment is believed to be due to the use of the platinum flux technique combined with an apparatus designed for rapid unobstructed transfer of gases from the furnace into the analytical system. The duplicate analytical sections allow analysis of the collected gases to keep pace with thc rapid estraction obtained in the furnace. ACKNOWLEDGMENT
yolving 80 determinations madc on 40 coiisccubive working days. ’l’his apparatus and tcc.hniquc h a w hccii tried on all of t h r wrious coinmcwi:il alloys of t’itaniiim v-ith no evit i c w ~ , of interference ti\- alloying r,lcnwiits. This agrees with thc findings of the Task Force on 0s)-gen Analysis iii their report to the Panel on Methods of .lnalysis of the hlctallurgical AdG o r y Committee on Tit’anium, in n%ich thcy stated that in using tlic 111:itinum flux tcchniquc.. “no rlmient p~c*scntin commercially amilablr tit:inium rnctal or alloys 1i:is bccn obstwwl to interfere.” I his apparatus should be d d t . to clc~tcwiiineosygen in any n x t a l to d i i c l i tht. wcuuni fusion nirtliod is applicable. TLthlr I1 cont>ninsth(>data obtained in ~uiininga series of atwl saiiiplcs. It i i ~ j lw noted that the d u w ol)t,ainctl
,.
on the Kational Bureau of Standards sample are in good agreement with the certified value of 0.01S70 oxygen and that the results on the three samples from Allegheny Ludlum Steel Corp. agree quite well with the ralucs reported b y them. Due to the use of resistance heating and the simplified vacuum system, the cost of this apparatus is lcss than that of conventional vacuum fusion equipment. The low cost of the equipment and the short time per deterniination have reduced the cost of determining oxygen in metals to a very reasonable value. This equipment has been found to operate with less “down time” than the conventional apparatus. Only 1 hour is rrquired to change crucibles and outgas as oompared Trith approximately 4 hours for thc conrcntional apparatus.
The authors arc indebted to E. I>. Dilling and R. L. Pow11 for contribution of ideas and suggestions; to 11. J. Miles for data on interlaboratory agreement and strel samples; and to U.L. Smith for efficient operation of the equipment. LITERATURE CITED
(1) Bennett, S. J., Covington, 1., C., ANAL.CHEM.30,36J (1958). (2) Fassell, V. .4., Tabeling, R. \V,, Spectrochim. Acta 8 , 201 (1956). (3) Hansen, IT. R., Alallett, M. W., Battelle Memorial Institute, Columbus, Ohio, Memorandum on Determination of Oxygen in Titanium, February 25, 1957. (4)Hansen, W. E., hlallett, 11. W., Trzeciak, hI. J., Aix..ar,. CHEM.31, 1237 (1959). RECEIVEDfor review January 6, 1960. Accepted May 9, 1960.
Extraction of Chromium(III) with 2-Thenoyltrifluoroacetone Direct Spectrophotometric Determination in the Orga nic Phase SANTOSH
K.
MAJUMDAR and ANlL
K.
DE
Deparfment o f Chemistry, Jadavpur University, Calcufta 32, India
b A simultaneous extraction and colorimetric method for milligram amounts o f chromium(lll) i s based on the formation of an orange chelate with 2thenoyltrifluoroacetone, which i s extractable b y an organic solvent such as benzene. The resulting orange solution conforms to Beer’s law a t 430 mp over the range of 8 to 200 y of chromium(lll) per ml. A single extraction b y TTA-benzene a t pH 5.0 to 6.5 removes about 8070 or more of chromium(III) from an aqueous solution. The colored system i s stable for a week. Moderate amounts of silver, aluminum, mercury(ll), and citrate d o
not interfere, whereas iron(lll), uranium, thorium, zirconium, bismuth, tartrate, and EDTA interfere more or less seriously. However, interferences of iron(lll), thorium, and zirconium can b e eliminated b y a preliminary extraction from fairly acidic solution. The method i s accurate and reproducible to within f 270.
URTHER extraction studies in this laboratory using 2-thenoyltrifluoroacetone (TTA) (1-5) have been applied to chromium(II1). Kork by
11IcKavaney and Freiser (6) ,ihon.etl that chromiuni(II1) does not readily form a complex with acetylacetone. The solution containing chromium must be adjuded to pH 7.0 aiid heated under reflux with acetylacetone for 30 iniiiuteq before the complex can be measured 111 the organic layer cpectrophotometrlrally a t 560 in@. When TTA ib substituted for acetylacetonc and ‘I’TAbenzene 1- uietl for the extraction, thc chromium chelate forms readily after 15 minutes’ shaking and the resulting orange color can be measured spectrophotometrically. The procedure is simple and rapid for the extraction and VOL. 32, NO. 10, SEPTEMBER 1960
0
1337
Table I. Distribution Ratios of Chromium(Il1)-Thenoyltrifluoroacetonate between Benzene and Aqueous solution a s Function of pH Chromium(111) Extracted IJH 1.5 1.9 2.3 2.7 3.1 3.5 3.9 1.3 4.7 5.1 5.3 5.5 5.7 5.75 5.9 6.1 6 .5
into Benzene, 3.8 5 6.8 9 12.5 17.5 24 33.5 48 84 92 96.4 99.2 100 97.5 91 78
u
7c
0 098 0 13
0.18 0.25 0.36 0.53 0.79 I .26 2.31 13.12 28.75 66.94 309.9 97.5 25.28 8.85
APPARATUS AND REAGENTS
The apparatus has been described previously ( I ) . Unless otherwise mentioned, all the chemicals used were chemically pure or reagent grade materials. T T A (Columbia Organic Chemicals, Columbia, S. C.) solutions in thiophenefree benzene, about 0.15iM, were used. A stock solution of c7hromic sulfate was prepared by dissolving about 12 grams of the sulfate in 500 ml. of water containing -0.OIN sulfuric acid. The solution was standardized iodometrically and contained 4.74 mg. of chromium per ml. This stock solution was diluted tenfold (0.01N in sulfuric acid) for spectrophotometric runs so that the chromium content was 474 y of chromium per ml. Approximately 1M buffer solutions were prepared (9) : potassium chloride-hydrochloric acid buffer (pH 2.0) and acetate buffers (pH 4.0, 5.0, and 6.5). GENERAL PROCEDURE
The general extraction and measurement procedures were as follows: A suitable aliquot (5 ml.) of the chromic sulfate solution, containing 474 y of chromium per ml., was mixed with 20 ml. of buffer solution at p H 6.0 in a ANALYTICAL CHEMISTRY
**ut
Figure 1 . A
B.
ItNCTH.y
Absorption spectra
Chramium(lll)-TTA system VI. reagent blank (pH 5.75): Cr = 1.83 X 1 0 - 3 M and TTA = 1.5 X 1 0 - l M Reagent blank vs benzene (pH 5.75)
a
determination of chromium :it the milligram level. Acetylacetone (pK, = 9.7) is more basic than T T A (pK, = 6.2) and so it generally forms more stable chelates. But again this leads t o a smaller reagent anion concentration from the former than from the latter at any p H value. The reagent anion concentration appears to influence chelation to a greater extent than does the stability factor. This possibly explains why T T A chelates form to a greater extent than do those of acetylacetone in general (8) and also why in this case chromium(II1) forms R chelate with TTA so readily.
1338
, 40”
250-nil. keparatory funnel. For pH studies, the appropriate buffer solution of desired p H was employed. For the fitudy of diverse ions, the solution containing the desired ion was introduced prior to the buffer solution. The aqueous phase was immediately shaken for 15 minutes with 10 ml. of a benzene solution (0.15M) of TTA. The benzene layer was separated and collected in a 25-ml. volumetric flask; the aqueous layer was then rinsed twice with 5-ml. portions of benzene and the benzene extracts were withdrawn as before into the volumetric flask. The combined benzene extracts were diluted to 25 ml. with benzene and the absorbance of this solution was measured a t 430 m p against a reagent blank. The corresponding chromium concentra t‘ion was read directly from the calibration curve described below. The aqueous layel. after extraction was saved for p H measurements.
curve (Figure 2 and Table 1). The extraction virtually starts from p H 1.5, gradually increases, becomes 100% at p H 5.75, and then drops. A p H range from 5.0 to 6.5 is suitable for about 80% or more e-xtraction. Extraction occurs to the extent of 78% at pH 6.5, whereas a t higher p H (> 7.0) the hydroxide precipitate tends to persist and inhibit the extraction. The influence of acetate buffer on extraction is interesting. If the solution of chromium, after mixing with acetate buffer, is allowed to stand for a while, a violet chromium(II1)-acetate complex is formed which resists, to a certain extent, extraction by T T A sulution. This difficulty is overcome by shaking the aqueous solution rvith organic phase immediately after addition of the acetate buffer. The latter procedure of extraction gives absorbance readings about 150% higher than those obtained by the former method. Use of :icetate buffer also helps to keep
Figure 2. Extraction of chromium(ll1)TTA chelate by benzene a s function of PH
RESULTS AND DISCUSSION
Absorption Curve. T h e absorption spectrum of a solution of chromium(111)-TTA compkx (chromium = 1.83 x l O - M ) , extracted as above at pH 5.75, is shown in Figure 1 against a reagent blank. The orange chroinium(II1)-TTA solution exhibits 4rong absorbance below 410 mp where the reagent blank also absorbs strongly. Then the absorbance steadily decreases and becomes negligible beyond 550 inp. The reagent blank, however, shows insignificant absorbance from 420 mp onward. All absorbance measurements were carried out a t 430 mp. The absorptivity a t 430 mp is 421.5 i 9.8, calculated on the basis of chromium content. The orange chromium (111)-TTA chelate is stable for 1 week. Effect of pH. T h e liquid-liquid extraction bchavior of t h e chromium(111)-TTa4 system was investigated over t h e p H range of 1.5 t o 6.5. The distribution ratios, D, were calculated 3 s described ( I ) from the extraction
chromium (.- 2 mg.) in solution even up to p H 6.5, which is a n advantage for the extraction process. Calibration Curve. A t various wave lengths-420, 430, 450, and 460 nipt h e absorbances of different ainounts of chromium(III), extracted as above a t pH 5.75, were noted against a rca-
Table II.
Effect of Reagent Concentration
TTA Added, Absorbance at Concn., M M1. 430 Mfi
TTA
0.015 0.15 0.15 0.15 0.15
10 2 5 10 20
0.15 0.49 0.63 0.78 0.79
3370 of chromium(II1) after extraction by TTA-benzene a t pH 5.75 gives an absorbance 0.770 & 0.014 in 25 ml. Qf benzene.
gent blank. I n each case thr, solution ot chromium(II1) was exhaustively extracted so that the aqueous phase was dear and colorless. The results proved that the chromium(II1)-TTA system conforms to Beer’s law a t 430 nip over the concentration range of 8 t o 200 y of chromium per ml. Reagent Concentration. The T T A concentration was varied from 0.015 to 0.15M (Table 11), keeping other variables constant. T h e optinium concentration is 0.15M. With higher wnrentrations the absorbance is essentially constant, whereas dilute solutions- -e.g., O.Ol5M-lead to incomplt.te extraction. Period of Extraction. Iiecping othei factors constant, tht. period of extraction was varied froni 5 t o 20 niinutes. T h e optimum tinits is 15 minutes (Table 111). Diverse Ions. Thrl following ions ( 5 t o 25 mg.) were carried through t h e procedure: Ag+, CoA2, Ni+2, Bif3, illf3, Fe+3, Th+4, Zr,f4, Uf6, citrate, tartrate, and EDTA The results
Table 111.
Effect of Period of Extraction
[Chromiuni(III) = 2370 y st pH .5 701 Extraction Period. Absorbance at. Min. 430 3Ip 0.10 2 0.29 5 0.54 10 0.78 15 0.78 20
(Table IV) show that chromium (-2 mg.) can tolerate up t o 5 mg. of silver and aluminum and 25 mg. of mercury(11) and citrate. Uranium and iron(II1) give color reactions whereas cobalt(I1) and nickel(I1) form orange and green precipitates, respectively, in the organic phase. Thorium (IV), zirconium (IV) , and E D T A also interfere. Although it is reported in the literature (IO) that the violet chromium(II1)-EDTA chelate is formed only on heating the solution (acidic) t o boiling, the present authors observed, however, that this chelate is formed even during extraction and hence it actuallj, interferes. Interferences from thorium and zirconium can be eliminated b y extracting these first a t pH 1.0 and then chromium from the residual aqueous phase a t higher pH--viz., 5.75.
Recommended Procedure. T r e a t a n aqueous solution containing 0.5 t o .5.0 mg. of chromium(II1) with 20 ml. of buffer solution of pH 6.0 and immediately evtract in a separatory funnel n i t h 10 nil. of 0.15M TTAbenzene solution for 15 minutes. After the 13yerk hare settled, transfer the benzenr. layer to a 25-nil. volumetric flask. Rime the aqueous layer with two 5-nil. portions of bciizene and collect the benzene phases as before in the volumetric flask. Dilute these benzene extracts to 25 m1. n-itli benzene and measure the absorbanre a t 430 mp against a reagent blank. Occasionally chromium(VI) ia encountered. In such a case reduce the .lightly acidic solution of chromium(V1) 15-ith sodium bisulfite until the solution turns green, boil off escess sulfur dioxide, cool to room temperature, adjust the pH, and evtract nq usuil. Thi,
reduction procedure does not affect the colorimetric method. The usual reducing agents-viz., iron(I1) and iodide --employed for the reduction of chromium(VI) in analysis cannot be used here since both of them nil1 interfere with the colorimetric measurement. From eight runs n i t h 2.37 mg. of chromium(III), the absorbance measured was 0.770 =t0.014. The standard deviation was + 1.8%. Different amounts of chroniium(II1) were analyzed by the recommended procedure. The rrsults (Table V) qhow an accuraq to within 3- 2.2%.
Table V. Accuracy of Method Absorbance Chromium(II1) at 430mp Taken Found Error, 70 0.22 -4.2 710 680 f2.1 0.30 950 970 0.40 1190 1200 f0.8 0.61 1900 1850 -2.6 0.78 2370 2370 0 0 1 22 3570 3600 $3 5 AV. &2.2%
The propowl method requireb only inoderatrl amouriti of time (23 to 30 minutes for c x h run). rls little as 5 y of chromium(II1) Iirr ml. ran he detected. ACKNOWLEDGMENT
The authors thank the Council of Scientific and Industrial Research, India, for sponsoring this projcct and awarding a fellowship to one of them
(S.K.lT.). LITERATURE CITED
(1) Khopkar,
Table IV.
Diverse Ions [Chromium(III) = 2370 y a t pH 6.75;
Foreign Ion None . . xg+
co +a Ni +P Bi +a .\i
+3
Fe +a Fe +a Th+4 Zr +4
Ion Concu., Mg.
5 5 4.5 5
5
2 2 4.5
25 4.8 25 25
Added as AgNOa C0(NO3)*.6Hn0 NiSO4.7 HzO BiOCl Alz( Son),.18 HzO Fez(SO4)s.(NH4)ZSOa.24 HzO F ~ z ( S O (NH4)?S04 ~)~. 24 H20 Th(S03)a. 4Hz0 ZrOCL U0~(?1703)~.6H& Citric acid Tartaric acid EDTA (disodium salt)
thsorbance at 430 mp 0 770 & 0 014 0.76 0.42a
0.20” 0.15 0 75
Intense color 0.60h 0.30 0.03
Intense color U +E Cit-8 0.80 Tart-’ 0.52 (EDTA)-’ 30 0 02 Precipitation of chelate. 5 Iron(II1) was first separated by extraction a t pH 2.0 and then chromiuni(II1) extracted from the aqueous phase after adjustment to pH -5.8, buffering, etc. Recovery of chromium -80%.
S. hl., De, A. K., l h . 4 ~ . CHEM.32,478 (1960). (2) Khopkar, S. M., De, A. K., Anal. Chim. Acta 22, 223 (1960). ( 3 ) KhoDkar. S. M.., De., A. K.. Anc12ust 8 5 , 376 (1960). (4) Khopkar, S. M., De, A. K., Chern. &: Ind. (London) 1959, 291, 854. (5) Khopkar, S. M., De, A. K., %. c~nnl. Chetn. 171, 241 (1959). (6) McKavaney, J. P., Freiser, H., A s a L . CHEX.30, 1965 (1958). (7) Morrison, G. F., Freiser, H., “Solvent Extraction in Analytical Chemistry,” p. 12, Wiley, New York, 1957. (8) Ibid., p. 27. (9) yogel, A. I., “A Textbook of Quantitative Inorganic Analysis,” Longmans, London, 1953. (10) Welcher, F. J., “The -4nalytical Uses of Ethylenediamine Tetraacetic Acid,” Van Sostrand, Princeton, N . J.. p. 248,1958. I
RECEIVEDfor review January ‘LO, 1060. Accepted Nay 2.1960.
VOL. 32, NO. 10, SEPTEMBER 1960
1339
