tion constant were calculated. These varied from 2 X 10-l2 to 18 x lo-'*, the most reliable figure being about 9 x lo-'*. DISCUSSION
The greatest obstacle to be overcome in the BTT extraction is the carrying over effect of the TBTC and the TBT. For example, a t a pH of 2.2, BTT is extracted well by itself, but when the higher butyltin compounds are present, they are extracted into the chloroform layer and tend to pull along the BTT, From a practical standpoint, it should be possible to remove and concentrate butyltin chlorides from various materials by a chloroform extraction. Even though it is unlikely that inorganic ions as such would be extracted appreciably with organotin chloridcs, a brief study showed that one extraction with EDTA was sufficient to keep the following ions from interfering with the determination
of DBTD: Zn(II), Mn(II), Fe(I1, III), Pb(II), Cu(1, 11), Cd(II), and Sn(I1, IV) . The success of the recommended procedure in being able to determine only DBTD in the presence of a mixture of the various butyltin chlorides is due to the selective extraction of BTT with EDTA. As noted in Table IV, DBTD as well as BTT is extracted in varying amounts a t the higher pH's. Conccivably the TBTC would not be extracted within this range and it could then be determined with dithizone by the method of Aldridge and Cremer ( 1 ) . These methods should be investigated for other series of alkyltin chlorides. ACKNOWLEDGMENT
One of us, R. T. S., gratefully acknowledges the financial assistance received from a National Science Foundation Undergraduate Research Assistant-
ship. The organotin compounds were supplied by Metals and Thermit Corp. LITERATURE CITED
(1) Aldridge, W. K., Cremer, J. E., Analyst 82,37-43 (1957). ( 2 ) Barbier, R., Belluco, U., Tagliavini, G., Ann. chim. (Rome)48, 940 (1958). (3) Barnes, J. M., Stoner, H. B., Brit. J. Ind. Med. 15 ( l ) ,15-22 (1958). (4) Brit. M e d . J . 2,639 (1954). (5) Farnsmorth, M., Pekola, J., ANAL. CHEM.31,410-14 (1959). (6) Faulkner, C. J., Brit. Patent 743,119 (July 27, 1955). (7) Hudson, P. B., Sanger, G., Sproul, E. E., J . Am. Med. Assoc. 169, 1549-66 (1959). (8) Osmundson, J. A,, N . Y . Times 1, March 28, 1959. (9) Snable, G. L., senior thesis, Princeton University, May 1959. (10) Toropova, V. F., Saikina, bl. K., Sbornik Statei Obshchei Khirn. Akad. Nauk. S.S.S.R. 1, 210 (1953). RECEIVEDfor review June 17, 1960. Accepted November 7 , 1960.
N e w Spectrophotometric Method for Molybdenum ARTHUR H. BLACK and JAMES D. BONFIGLIO' Department o f Chemistry, University o f Toledo, Toledo 6, Ohio
,b A spectrophotometric method is presented for the rapid determination of molybdenum in low-alloy steels. Molybdenum is separated from the bulk of the sample b y use of Amberlite IR-l20(H) resin, after which the complex of molybdenum and phenylfluorone is formed. The red-orange complex follows Beer's law and exhibits a maximum absorbance at 550 mp over a range of 0.33 to 1.67 pg. of molybdenum per ml. This method produces excellent results for low-alloy steels containing between 0.1 and 0.5% molybdenum.
C
OLORIMETRIC METHODS for
the determination of molybdenum have been reviewed recently (1, 5, 8, 9). Khere applications to lon--alloy steels have been made, either precipitation or extraction procedures were involved in the separation of the molybdenum from the bulk of the sample. This investigation was instigated to develop a new and different colorimetric procedure for molybdenum. Luke (3) and Luke and Campbell (4) elucidated photometric methods for tin and germanium with the reagent phenylfluorone. The molybdate ion in each 1 Present address, National Cash Register Co., Dayton, Ohio.
of these procedures was an interfering color-producing substance. As a result of the literature review, this investigation became concerned with the feasibility of an ion exchange method for the separation of molybdenum (6, 7 ) and the subsequent determination of the molybdenum as the phenylfluorone complex. APPARATUS AND REAGENTS
Colorimeter, Spectronic 20, Bauhch
8: Lomb.
I O N EXCHANGE COLUhfN. A Jones Reductor tube, 18 mm. in inside diameter, packed to a height of 15 em. with Amberlite IR-12O(H) cationic resin of 50 to 100 mesh. Prior to use the column was eluted with 250 ml. of 4iv hydrochloric acid. The excess acid was removed from the exchanger with deionized water until the eluent was neutral t o litmus. ~IOLYBDEXUII SOLUTION.A standard solution of molybdic acid equivalent to 1 mg. of molybdenum per ml. was prepared by dissolving 1.8i50 grams of molybdic acid monohydrate (Climax Molybdenum Co., Climax, Colo.) in deionized water and diluting to 1 liter. The solution was standardized gravimetrically by precipitation with 01benzoinoxime ( 2 ) . PHENYLFLUOROSE SOLUTIOK.A solution was prepared by dissolving 0.075 gram of the solid (Eastman Organic Chemicals) in 75 ml. of methanol and 1 ml. of 12N hydrochloric acid. The
solution was diluted to 500 ml. with methanol. Guhi ARABIC. One gram of gum arabic was dissolved in 100 ml. of boiling deionized water, filtered, and stored for use. PROCEDURE
For steels containing between 0.1 and 0.5% molybdenum, weigh a 1-gram sample, place in a 250-ml. beaker, and dissolve in 50 ml. of 1 t o 5 sulfuric acid. If a standard calibration curve is being run, a t this point add 1, 2, 3.5, and 5 ml. of the molybdic acid standard solution to each of four 1-gram samples of a low-alloy steel which contains no molybden urn. Add a minimum of nitric acid (1 ml. for a 1-gram sample) to the hot solution. Boil gently to remove the oxides of nitrogen, dilute to 100 ml. with deionized water, and add 1 gram of ferrous ammonium sulfate to reduce any vanadic or chromic acids present. Add 50 mg. of citric acid ( 7 ) , and transfer the sample to a 250-nil. volumetric flask. Dilute to approximately 200 ml. Adjust the pH to 2 with 257, sodium hvdroxide. using a narron- range pH paper. Dilute t o volume Ind mix thoroughly. Pipet a 25-m1. aliquot into the ion exchange column. Place a 500-ml. glass-sGppered graduated cylinder containing 30 ml. of phenylfluorone and 5 ml. of gum arabic beneath the column. Allow the solution to stand several minutes in the column, then let it drain VOL. 33, NO. 3, MARCH 1961
rn
431
Table I.
Per Cent Molybdenum in Five Analyzed Steels AV.
Sample -1 B C
1 0 405 0 215
0 206 0 093
1)
Runs 2 0 0 0 0 0
396 223
200
100
Values, 3 0 396 0 218 0 192 0 096 0.065
% 0 0 0 0 0
399
219 199 096
E 0 067 060 064 Metallurgj- Laboratory, Electric Auto-Lite Co., Toledo, Ohio.
slon-ly through the resin (2 to 3 ml. per minute). When the level of the initial aliquot is just above the top of the resin, wash down the wdls with deionized water, and adjust the flow rate to 8 to 10 ml. per minute until the total volume collected is slightly less than 300 ml. Adjust to p H 2 with 4N sodium hydrazide. Finally dilute the effluent to 300 ml. with deionized water which has been passed through the column. Mix the solution thoroughly and let stand for several minutes for full color development. Transfer a portion of the red-orange complex to a sample tube and place in the colorimeter previously set a t zero absorbance with water at a ware length of 550 mp, the wave length of maximum absorbanre for the complex. RESULTS AND DISCUSSION
At a wave length of 550 mp, absorbances for the standard samples containing 0.100, 0.200, 0.350, and 0.500%
Certified Values,"
% 0 41 0 22 0 20 0 090 0 07
molybdenum were 0.132, 0.220, 0.350, and 0.490, respectively. The standard low-alloy steel also contained l.OOyo chromium, 0.80yo manganese, and O.lti7' nickel. The absorbance readings of the standards correspond to transmittance values of from 73.5 to 32.3%, which are very close to the optimum operating range for the Spectronic 20. The results obtained from the analysis of five loralloy steels are shown in Table I. These values were obtained from a t least triplicate samples in every case. Duplicate aliquots were run for each of the triplicate samples. The phenylfluoronemolybdate complex was stable a t p H 2 for 24 hours but tended to show some decomposition after standing for longer periods of time a t room temperature. During the development of the procedure, it was found that molybdate ion TI as not completely removed from
the coluinn. Hoiwver, by adding a small amount of citric acid t o the solution as suggested by Klenient ( y ) , molybdate ions \vcre rffectirely removed from the resin. From the results obtained by Luke and Campbell (4), LT-ho ran tests on 59 metals to determine which ones yielded stable colored phenylfluorone chelates, it \\-as concluded that our procedure gave an effluent free froin interfering ions. S o further studies on inberierences \!--ere niade. LITERATURE CITED
( I ) Goldstein, G., Manning, I>. C., llenis, O., h x . 4 ~C. H m f . 30, 539 (1958). ( 2 ) Kolthoff, I. N.,Sandell: E. B., "Textbook of Quantitative Inorganic Analysis," 3rd ed., p. 692. Macniillan,
Sew York, 1952.
(3) Luke, C. L., A X A L . CEEM.28, 1276
(1956).
(4)Luke, C. L., Campbell, 11,E., Ibid., 28, 1273 (1956).
( 5 ) Otterson, D. h.,Graah. J. If-., Ibid., 30, 1282 (1958).
( 6 ) Pecsok, R. L .,--Parkhurst. It. AI., Ibid., 27, 1920 (193s). ( i )Samuelson, O., "Ion Exchangers in -4nalytical Chemistry," p. 153. Kiley, Sew Tork, 1953. (8) Katerbury, G. R., Bricker. C. E., AYAL.CHEM.29, 129 (1957). (9) Kill, Fritz, 111, Poe, J. H.. Ibid., 2 5 ,
1363 (1953).
RECEIVED for review January S. 1Bti0. .\ecepted December 8, 1960. Division of .\nalytical Chemistry, 135th Meeting, .1CS, Boston, AIass., Ipril 1959.
Spectrophotometric Determination of Phosphate in the Presence of Highly Labile Phosphorus Compound LEWIS C.
MOKRASCH'
Neurochemistry Laboratory, Section on Experimental Neurology, Deparfmenf of Medicine, University o f Kansas Medical Center, Kansas City 72, Kan.
b By substituting N,N-dimethylformamide for most of the water in the phosphate assay, the hydrolysis of labile phosphorus compounds is virtually arrested and b y reading the color a t 335 mp, a much more sensitive method i s obtained. The molar absorptivity for phosphate in this procedure i s 17,500. Applications and permissible variations in procedure and sources of interference are discussed.
N
uhmxows colorimetric methods for phosphate are based on the reduction of phosphomolybdate, of which three differ in some essential respect (1, 5 , 6). These methods have certain defects which limit their universal ap432
ANALYTICAL CHEMISTRY
plication, such as too high acidity, sensitivity to sulfhydryl compounds, or the need for extractions. I n a n attempt to find a phosphate assay milder than the Lowry-Lopez method and more sensitive, the possibility of combining the molybdenum blue color with benzidine blue in an acidic alcoholic medium was investigated. Although no blue color appeared immediately, the strong yellow color found in the samples containing phosphate was much more intense than the normal color of phosphomolybdate. Efforts to improve the reliability resulted in the evolution of a simple method which is suitable for the determination of phosphate in the presence of labile phosphorus compounds. ;iscor-
bic acid is the reducing agent, replacing benzidine, and acetic acid-acetate is the buffer system in a diniethylformamide medium. MATERIALS
K,HPOI was recrystallized and dried 2 hours a t 110' C. for use as the phosphate standard. A-,S-Dimethylforniamide (DAIF) vias redistilled through a 1S-em. Widmer column a t about 50% reflux and the fraction boiling a t l53O + 0.5' was collected. Conimercial diniethylformamide may give aatis1 Present address, Research Laboratory, AlcLean Hospital, Belmont, RIass.
