ANALYTICAL CHEMISTRY
560 Samples of the submitted data sheet and the final report ale shonn in Figures 1 and 2.
curvature viere high in concentration, accuracy decreased as evidenced by a departure from 10091, total concentration. CONCLUSIO\S
SOURCES AND COWTROL OF ERROR
In a complex multicomponent analysis and calculation, sources of error may be both numerous and cumulative. Therefore, it is essential to recognize every source of error. In the analysis discussed above, errors may be classified as those of measurement, calculation, and theory. Sources of measurement errors include dilution and spectrometry. When instrument temperature was maintained constant to 0.5” C., no significant wavelength shifts were observed. The instrument maker’s cIaim of less than 0.5% transmittance error was well substantiated. In the computation, human error may be involved in the keypunching of the data on cards. Use of the verifier should greatly reducc the probability of undetected error. Once the data are piope111 punched machine errors may be minimized by incorpoi ating numei ous automatic safeguards. The pessimistic assumption is made that the machines will make all possible e n ors The operation incorporates check methods which are printed on the final report. Thus, the machines will signal an e110 1 0 1 fail to print the proper check values in the event of a misplacwi or missing card, incorrect operation, machine part failure, etc. .1 final proof consists of the substitution of a column of the calihration matrix for the absorbence data. The results appear 0. There is a small systematic error of about 0 . 1 7 , which is the cumulative effect of dropping rather than rounding off the last significant figure in successive steps. By far the largest error is that introduced by the neglect of cuivature in the absorbence-concentration curve. Although it is possible to perform second-order corrections ( 2 )using the I B.M. machines, the increased machine time outweighs the inci eased accuracy for most process study programs. The effect of curvature was minimized by measuring all samples in dilute solution. The nominal concentration thus averaged 1 to 3 7 for any one component, When the compounds that evidenced the gi eatest
Use of automatic computing equipment reduced calculation time to 3 minutes from a minimum of 15 minutes by desk calculator or 11 minutes by analog computer. The 3 minutes represents combined operator and machine time per sample w\.hen calculated in groups of 25 samples. The machines require operator attention less than half of the time. The cost of materials consists primarily of 10 cents‘ worth of cards per sample computed. I n a 6-month period, 750 ten-component analyses and computations were performed without an undue strain on the spectroacopy group. The rapid accumulation of an array of analytical figures greatly facilitated the n-ork of the process study group. ACKNOWLEDG\IER[T
The w i t e r is indebted t o David J. Pye for his interest and criticism of this work. Thanks are due to R. E. Clement of the International Business Machines Corporation for his cooperation. The permission of The Dow Chemical Company to publish this material is gratefully acknowledged. LITERATURE CITED
(1) Beiry, C. E., Wilcox, D. E., Rock, S. II.,and Washburn, H. IT- , J . davlied Phus.. 17.262 (1946). Brattain: R. R.,kassmussen. R. ’S,, and Cravath, d. 51..Ihid.,
14, 418 (1943). Crout, P., Trans. A m . Inst. Elec. Eiigr.?., 60,1235 (1941). Eckert, IT. J., J . Chem. Education, 24,54 (1947). Eckert, W.J., “Punched Card Methods in Scientific Computation.” New York, Columbia University Press, 1946. Fry, D. L., Xusbaum, R . E., and Randall, H. hI., J . d p p l i r d Phys., 17, 150 (1946). International Business Machines Corp., Sew I’ork, “Poiriter 461.” King, G. TT., J . Chsm. Ediacution, 24, GI (1947). TTaugh, F. V.,and Dwyer, P. S.. A n n . M n t h . Stat., 16,259 (19453. ~ E I V E DSeptember
1, 1919.
Rapid Photometric Determination of Iron in High Temperature Alloys MICHAEL STEVENS PEP1 Fairchild Engine and Airplane Corporation, Farmingdale, Long Island, S. Y . A rapid method for the photometric determination of iron in high temperature alloys is based on the reaction of the ferrous ion with 1,lO-phenanthroline. The sample is dissolved in aqua regia and a few drops of hydrofluoric acid, and diluted to 500 ml. A 10-ml. aliquot sample is reduced with hydroxylamine hydrochloride and the orange colored complex is formed by the addition of 1,lOphenanthroline. The reproducibility is good and the average error is *0.02% of the amount present.
T
HE chief sources for the work reported in this paper are
Fortune and hiellon’s complete report on the spectrophotometric method for the determination of iron with 1,lO-phenanthroline (2), and the miter’s work on the determination of iron in aluminum alloys ( 4 ) . A number of papers ( 1 , S , 5 , 7 )have reported on the use of 1 , l O phenanthroline for the determination of iron in a variety of d e s . A summary of the work done with 1,lO-phenanthroline up io 1944 was made by Smith and Richter (6). The purpose of the work described in this paper was the de-
velopment of a rapid and accurate method for the determination of iron in high temperature alloys based upon the orange colored complex formed by ferrous iron and 1,lO-phenanthroline. EXPERIMENTAL WORK
The preliminary work covering the follotving problems is fully described by Fortune and Mellon ( 2 )and the writer ( 4 ) . A suitable reductant for iron. A 17‘ solution of hydroxylamine hydrochloride was reported as the most effective reductant.
V O L U M E 2 2 , NO. 4, A P R I L 1 9 5 0
561
rl wave length that 11ould produce maximum absorption 4900 A. was found the most suitable. Confoimity to Beer’s law. Beer’s law was followed by the color system and was proved by the straight line obtained when readings of the observed transmittancies at 4900 A. for roncentrations up to 5.00Tc iion were plotted.
The nen problems that arose in adapting the methods to high temperature alloj s weie: a suitable solvent for the material, sample size and aliquot portion, and interference from other elements present.
Tahle 1.
Determination of Iron i n ,411oys
Oilier M e t h o d s “ , Plintometri? IIethod, Alloy S o . ”r 1 R.4.E 103’2 (X-40) 1.04 I 10 2 RAE 1032 (X-40) 1.09 I 07 X RAE 1032 (X-40) I ox 1.04 1 RAE 1032 (X-40) 1 OX 1.03 .i RAE 1032 (X-40) 1.39 1 .AMs 5668 (Inconel) 7.47 7.48 R A E 1032 fX-40) 0.92 0.08 vitalliiim 1.60 1.60 9 Yitalliiiin 1 48 1.48 10 Trioonel X 6 , .54 6 . .5!2 Earl, raliir is a n average ( i f ten detPriiiination?.
Sainple S o .
c
4
.:m
k
a
Graviiiietrir a n d pernianiranate m?tliods.
A survej- of the present methods revealed that aqua regif1plus a few drops of hydrofluoric acid is generally used to dissolve high temperature alloys. This was suitable because there was no interference with the reaction of ferrous iron and 1,lO-phenanthroline. In order to obtain the intensity of the orange color produced which would be in the middle of the electrophotometer scale, a system of dilutions and aliquot portions mas devised. A 0.500gram sample was found suitable, and is described below. The first attempts to determine iron using 1,lO-phenanthroline involved complete separation of iron from the other elements present. This m s done because it appeared that the heavy concentration of cobalt, chromium, nickel, molybdenum, and tungsten might cause interference. The results obtained were favorable. The next step was to determine iron without separation from the other constituents. The results were also satisfactory, indirating t,hat i t was unnecessary to remove the other elements present. I-ery fe\v ions seriously interfere \vith the production of the quantitative color reaction. Fortune and Mellon studied fiftyfive possible interfering ions ( 8 ) . Bismuth and silver interfere because of the precipitate formed with 1,lO-phenanthroline, which also precipitates cadmium, mercury, and zinc. However. none of these elements is present in appreciable amounts in high tcniperaturc alloys. All photometric measurements were made with the Coleman Universal spectrophotometer Model 11; the optical cell thickness is 13 mm. For routine work t,he Fisher AC Model electrophotometer is used. The filter is 490 mp, the optical cell thickness is 23 mm. Reagent Required. Hydroxylamine Hydrochloride, 10%. Dissolve 10 grams of C.P. hydroxylamine hydrochloride crystals in 100 ml. of distilled water. (Store in refrigerator. Do not use if solution has a brown color.) Sodium Acetate. Dissolve 20 grams of C.P. sodium acetate crystals in 100 ml. of distilled water. 1,lO-Phenanthroline, 0.257,. Dissolve 0.500 gram of C.P. 1,lOphenanthroline monohydrate crystals in 150 ml. of boiling distilled water. Cool, t,ransfer to a 200-ml. volumetric flask, and dilute to the mark. (Store in refrigerator. Do not use if the solution has a brown color, as this indicates decomposition.) Standard Iron Solut,ion. Dissolve 1.000 gram of pure iron wire in 5 ml. of concentrated hydrochloric acid. Transfer to a 1000-ml. volumetric flask. Dilute to mark with distilled water (1 ml. = 0.ly0iron or 0.001 gram of iron). Method. Dissolve a 0.5000-gram sample in aqua regia (30 ml. of hydrochloric acid and 10 ml. of nitric acid) and a few drops of hydrofluoric acid, using a 250-ml. beaker. Filter into a 500-ml. volumet’ric flask, using Whatman X o , 41 paper. Wash five times
with hot distilled water, cool, and dilute to the mark with divtilled water. Pipet 10 ml. of solution into a 100-ml. volumetric flask if the sample contains up to 2.00% iron; or 5 ml. of solution if the sample contains over 2.00% iron. .4dd 1 ml. of hydroxylamine hydrochloride and mix. Add 10 ml. of sodium acetate and mix. Add about 50 ml. of distilled water and then 10 ml. of 1 , l O phenanthroline. Dilute to the mark with distilled water and let stand for a t least. 15 minutes. Using the Coleman spectrophotometer, set wave-length dial a t 490 and measure the color density of the solution. If a Fisher electrophotometcr is used, a 490 mp filter is required. Use distilled mater as a reference solution. A shortage of standard samples made it necessary to develop a method by which a pure iron solution could be used. This was possible because of the absence of interfering elements. h 1.000gram sample of pure iron wire was dissolved in 50 ml. of hydrochloric acid, then transferred to a 1000-nil. volumetric flask, and diluted to t,he mark with distilled watw. All results obtained in this investigation are calculat,ed on the basis of using a pure iron solution as a standard. Results arc shown in Table I. DISCUSSION
=\ method of analyzing high temperature ;tllo>.sfor iron content has been developed and found highly successful when used on various t,ypes of high temperature alloys. The formation of the complex when ferrous iron reacts with 1,lO-phenanthroline is represented by the radical (CizHsl\T2)3Fe. This is an orange colored compound whose intensity varies with the concentration of iron present. The ferrous phenanthroline complex will not develop a t a pII below 2, and the reduction of iron with hydroxylamine is slow a t a pH above 3. The p H a t xhich the determinat>ionis made is 2.8; thus a final d j u s t m e n t of pH is unnecessary. Another important advantage of this method is the elimination of tedious separations which are usually required in other methods for the determination of iron. These separations are a source of error where speed is required in the analysis. The .murres of errors of the proposed method are the instrument, and transfer and dilution of samples. With all the possihle sources of error> the average error \vas +0.0270 of the amount present. SUXIMARY
An orange colored solution is foriiied when 1,lO-phenanthroline react,s with ferrous iron. The color intensity varics with the iron concentration. The iron is reduced from ferric to ferrous by hydroxylamine hydrochloride. Kone of the elements present in high temperature alloys interferes with the reaction of iron and 1,lO-phenanthroline. A shortage of sdandard samples resulted in making use of pure iron solution as a standard. The proposed method takes less time to complete t,han the standard volumetric and gravimetric method for the deterniinat,ion of iron in high temperature alloys. ACKNOWLEDGMENT
The author grat efully ackno~vledgesthe many helpful suggestions and constructive criticism of this report given him by Richard B. Faurote, chief chemist, Ranger Ihgines Division, Fairchild Engine and Airplane Corporation. LITERATURE CITED (1) (2)
Blau. F.. Monntsh.. 19. 648 (1898). Fortune, R. B., and Mellon, 11.G.. IND.ENG.CHEM.,ANAL.ED.,
10. 60-4 (1938). (3) Mehl&J. P:,and Hulett, H. R., Ibid., 14, 869-71 (1942). (4) Pepi, M. S., Ibid., 18, 111-12 (1946). ( 5 ) Saywell, L. G , and Cunningham, B. B., Ihid., 9, 67-9 (1937). (6) Smith, G. F., and Richter, F. P., “Phenanthroline and Substi-
tuted Phenanthroline Indicators,” Columbus, Ohio, G. Frederick Smith Chemical Co., 1949. (7) Walden, G. H., Hammett, L. P., and Chapman, R. E’., J . Am. Chem. SOC.,53,3908 (1931). R E C E IF~D September 2 4 , 1949.
