ANALYTICAL CHEMISTRY
1740
Table 11. Effect of Bridge Frequency Resistance, Ohms
Water in ,Methanol,
a
%
60 cy c1es a
2.2 4.2 6.2 8.2 10.2
129.0 123.3 114.6 108.2 102.9
1000 cycles b 129.0 121.4 113.0 107.6 101.9
3.00 grams of 40-mesh SaC1, 5 minutes a t 600 r.p.m.
b 10.00 grams of 60- t o 100-mesh NaCl, 10 minutes a t 900 r . p . m .
ions, the p H of the soil may contribute to some of the discrepancies noted. Another source of difficulty in this study was the slow settling of some soil suspensions after stirring. When the conductivity was determined after short standing, some particles were still in suspension between the electrodes and some settled out on the upper surfaces of the horizontal electrodes during the measurement of resistance. The settling out of particles on the electrodes could be eliminated or greatly reduced by using a different type of conductivity cell having vertical electrodes. DISCUSSION
The majority of the studies described in this article were carried out during the summer of 1953. The operating temperature of 35.0' C. was chosen because it was about the lowest temperature that could be maintained \\-ithout refrigeration. A41thoughBurton ( 3 ) obtained good results with methanol1,i-dioxane mixtures as the water-extracting solvent, alcoholacetone mixtures were used in this study because acetone of high purity is more readily available and more economical than I,+ dioxane. I n the application of the results of this study to the determination of water in other materials, it is believed that small amounts of water in the water-extracting solvents present no difficulty, provided that the percentage is constant. Calibration with samples of known water content will correct for the initial presence of Lyater in the extracting solvents. %WATER
IN
SOIL
Figure 3. Conductivity of Ethyl AlcoholAcetone Water Soil Sodium Chloride Systems
-
-
-
alcohol-30.070 acetone mixture were added. The mixture was stirred with 3.00 grams of 40-mesh sodium chloride for 5 minutes a t 600 r.p.m. and then the conductivity was determined with the Model RC-1 meter. A 5-gram sample of air-dried soil was dried to constant weight a t 105" C. in an electric oven and the percentage of moisture was calculated from the lose in weight and the weight of the air-dried sample. The conductivities and percentages of moisture, as determined, are plotted in Figure 3. The majority of the points lie fairly close to a straight line, but some of them depart considerably from the line. Statistical treatment of the data yields the following values: correlation coefficient. 0.983; standard error of the correlation coefficient, 0.045. It is suspected that, because of the high conductances and mobilities of the hydrogen and hydroxide
ACKNOWLEDGMENT
The authors are grateful to John R. Eccles and Ralph E. Zerwekh, Jr., for aid in conducting the experimental wcrk which was performed in the laboratories of the Department of Chemistry, A. and M. College of Texas. LITERATU-RE CITED
(1) Boeke, J., Philips Tech. Rea., 9, KO.1, 13 (1947). (2) Burton, 31. B., Jr., A'1.S. thesis, A . & AI. College of Texas,
January 1953. (3) Koniarov, V. A , Russ. Patent 51,904 (Oct. 31, 1937). (41 Lange, S . A, "Handbook of Chemistry," 7th ed., p. 1416. Sandnskv. Ohio. Handbook Publishers. Inc.. 1949. .. (5) Lannung, 2. p h y s i k . Chem., A161, 269 (193i). (6) Nysels, K. J., J . Phys. and Colloid Chem., 51, 708 (1947). (7) Venkatanarasimhachar, S . , Proc. Indian Acad. Sci., 16A, 332 (1942). ~~~~
~
A:,
RECEIVED for review February G , 1954. Accepted September 1, 1954. Presented before the Analytical Chemistry Section a t the $MERICAN CHEMICAL SOCIETYRegional Conclave, New Orleans, La., December 10, 19.53.
Photometric Titrations ROBERT F. GODDU' and DAVID N. HUME Laboratory for Nuclear Science and Department o f Chemistry, Massachusetts
The principles of the photometric titration method are discussed and its advantages and disadvantages evaluated. Apparatus for the performance of photometric titration is described, and some of the fundamental factors limiting the accuracy are considered. Previous work in the field is reviewed.
0
F T H E various readily applied methods for the physico-
chemical determinations of titration equivalence point, that of quantitative measurement of monochromatic-light absorption has been one of the least exploited. Photometric titration has a number of attractive features which, if better known, would make it the method of choice in many applications.
institute o f
Technology, Cambridge'39,-Mass,
The idea of using monochromatic-light absorption measurements to determine titration end points is by no means new. Tingle (92), as far back as 1918, used a pocket spectroscope to isolate the color desired to detect end points visually. The advent of photoelectric colorimeters and spectrophotometers greatly increased the potential scope of the method, and many workers have pointed out the possibility of doing photometric titrations, although relatively few have actually investigated them. Muller and Partridge (66) deserve the credit for the pioneer work in the United States, developing their own apparatus and making several useful applications. The literature, up to the end of 1953, is summarized at the end of this paper. 1
Present address, Hercules Powder Co., Wilmington 99,Del.
1741
V O L U M E 26, NO. 11, N O V E M B E R 1 9 5 4 BASIS O F THE METHOD
The fundamental Ian7 of monochromatic-light absorption underlying photometric titrations is the Bouguer-Lambert-Beer law, A , = -log T = abc, in which A , signifies absorbance (optical density); T , transmittancy; a, absorbance index (extinction coefficient); b, length of light path through the absorbing medium; and c, concentration of light-absorbing constituent. The limitations of this la&-are given and discussed in Mellon’s recent book (61). The most important consequenre of the Beer’s law relationship for the present purpose is that absorbance, the quantity directly measured on a spectrophotometer, is proportional to the concentration of the absorbing ions linearly, rather than logarithmically as in potentiometric methods. This means that in a titration in which the titrant, the reactant, or a reaction product absorbs, the plot of absorbance versus titrant added will consist, if the reaction be complete, of two straight lines intersecting a t the end point. Theoretical titration curves are easily calculated from Beer’s law and the mass-action law if the appropriate equilibrium constants are known. Because of the linear response of absorbance to concent,ration, an appreciable break will often be obtained in a photometric titration, even though the changes in concentration are insufficient to give a clearly defined inflection point in :i pot,entiomc.t,ric titration. In this respect, photometric titrations are similar to amperometric and conductometric titrations;. l’hotometric titration has several distinct advantages over direct colorimetric determination. The presence of other substances absorbing at the same n-ave length does not necessarily cause interference, inasmuch as only the change in absorbancy is significant. The importance of this characteristic in practical analysis where samples may be colored or turbid is evident. The precision of locating the titration line by pooling the information derived from several points is greater than the precision of any single point. Finally, in favorable circumst’ances, particularly such as are found in titrations of the sort indicated in Figure l,a, c, and e, a very small deviation from the equivalence point is marked by a very large and easily measured photometric effect . Areas of particular applicability for the photometric titration method are seen t,o be i n solutions of low concentration, and with reactions which t,end to be appreciably incomplete a t the equivalence point-e.g., precipitation of moderately soluble substances, neutralization of very weak acids and bases, oxidation-reduction reactions involving couples with potentials not greatly differing in magnitude, and react,ions which are slow to come to equilibrium in the vicinity of the end point. All these circumstances tend toward a rounding off of the end-point breaks; but because no particular importance is attached to points taken in the near vicinity of the equivalence point, the straight-line portions of the curve may be extended to interciec,t for the accurate location of the end point. In precipitation reactions, photometric titration to maximum turbidity has distinct :idvantages over direct turbidimetric analysis. The multitude of experimental factors which contrihute to the lack of reproducibility of absorption characteristics of suspensions are relatively unimportant in a titration method. If a relatively stable colloid with a constant degree of dispersion is ohtained (often with the aid of a protective colloid such as gum arabic), an absorbance index reproducible from sample to sample is not necessary. Ringbom ( 7 6 ) ,in particular, has studied the particles of such tit,rations and evaluated some of the sources of error. The shape of a photomet,ric titration curve will be dependent on the absorbant properties of the reactant, titrant, and products of the reaction a t the wave length used. Figure l , a , for example, is typical of the titration where the reagent alone absorbs, as in the titration of ferrous iron with permanganate. Figure l,b, is characteristic of systems where the product of the reaction
absorbs (neutralization of a nitrophenol with alkali hydroxide); and Figure l,c, of systems where the substance titrated is converted to a nonabsorbing product. When a colored reactant is converted t o a colorless product by a colored reagent, curves similar to Figure l,e, are obtained (bromination of a red dyestuff ). Curves d and f might represent the successive addition of ligands to form two successive complexes of differing absorption. The several types of titration curves are not equally favorable for the achievement of high accuracy in locating the end point. As is shown in the discussion below on factors influencing the accuracy, the types characterized by Figure l,b, d , and f are more subject to some potential sources of error than the types shown in Figure l , a , c, and e .
Vol. Reagent
Val Reagent
(b)
(0)
VOl Reagent
(e)
’Val.
Reagent
if)
Figure 1. Possible Shapes of Photometric Titration Curves A clear distinction should be made between direct photometric titration, where it is the color change of the substance being determined or the reagent that is observed, and titrations involving indicators. Indicator titrations may be done photometrically. and with advantage, if the color change is not sharp, or if other substances present contribute to the total control of the solution. Mika (62) has sholvn that the use of a photometer to detect an ordinary indicator end point, in general, involves no increase in accuracy over visual observation. In order to take proper advantage of the potentialities of the photometric method, a relatively large amount of indicator should be added, so as to obtain a good straight line beyond the equivalence point. As is shown in a subsequent paper, the choice of indicator may also be different, in neutralization reactions, an indicator is chosen whirh ha3 its maximum color change not at, but after the equivalence. An important application of the photometric titration technique to indicator titrations is in those systems where the color change is gradual, owing to incomplete reaction a t the equivalence point. Here again the extrapolation of the straight-line portiona of the curve locates the end point without reliance on data taken in the uncertain immediate vicinity of the equivalence point. Many workers, however, have not gone to the trouble of plotting absorbance, or some related quantity, against volume of titrant, but have merely taken a large deflection as the end point. As a result, they have lost accuracy and limited them-
1142
ANALYTICAL CHEMISTRY
selves to the type of titration where either the excess reagent absorbs or an added reagent changes color. Alternative to the plotting of absorbance values is the possibility of plotting transmittancy or a quantity proportional to it, such as photocell output. This was the practice of the earlier workers (65, 71, 77,105),and under the proper conditions a curve very similar to a potentiometric titration curve is obtained. I n common with the potentiometric curve. this t m e of plot has all the disadvantages inherent in the use of the inflection point t o locate the end of a titration and the compression involved in a logarithmic plot. The authors feel t h a t the plotting of absorbance is preferable, especially where end-point breaks are not large. APPARATUS AND TECHNIQUE
It was considered desirable to use a commercially available spectrophotometer rather than to construct a photometric titration unit, as has been done by many authors. An adaptation of the Coleman Model 14 spectrophotometer has been described (69),hut this instrument does not allow convenient use of light of wave length less than 400 m#: and in the particular adaptation desoribed, there was no way to reaero the instrument once a
not be determined, so long RE it is within the range of linearity of the instrument. The buret is placed 60 t h a t the tip extends into the solution and the atmosphere of the cell compartment is swept with nitrogen if necessary. The stirrer is turned on and the turbulence (stirring cone) adjusted so t h a t it does not obstruct the light. The titration is then commenced by adding an increment from the buret, waiting until the absorbance reading is constant, and noting t h a t value. More increments are then added and the absorbances noted. For exploratory work, 0.2-ml. or 0.4-ml. increments are desirable; but once the shape of the titration cnrve is known, it is usually necessary to take but three to four points on each side of the end point. A plot of absorbance vs. milliliters is then made and the best straight lines are drawn between points taken well before and after the equivalence point; the intersection is taken 8s th8 end paint I n general, i t is desirable to have the buret t,ip immersed in the solution, in order to avoid the drop error, and as a rule no difficulty due to diffusion is encountered. Occasionally, however, there may be serious difficulty due to convection, as where there is an appreciable density difference between solution and reagent. This is most likely to happen in titration involving nonaqueous solutions. An upturned tip must then be attached to the buret or Some simple mechanical arrangement providedfarremaving and hanging drops. FACTORS AFFECTING ACCURACY
Dilution Error. If relatively large volumes of titrant are added after the color has started to appear, it is necessary to correct for the dilution of the solution by the titrant. This may be done by multiplying the observed absorbancies by the factor(*),
where
V is the volume a t the start of the titration, and v is the volume added. If the
Figure 2.
Stirrer and Cell Holder for Photometric Titrations with Beckman Model B Spectrophotometer
dilution by excess titrant is considerable, curvature in the titration plots is very evident; but if the dilution is of the order of only a few per cent, the lines appear straight. Failure tomakevolume corrections under such circumsi,snces
titration was begun. The rate of mixing was not as rapid &s desired, and the spectrophotometer itself had serious inherent limitations due to stray light and insensitivity. A more satisfactory apparatus was obtained by providing an attachment far the Beckman Model B spectrophotometer. The cell carriage and the cover and floor t o the cell comprtrtment were removed and the annaratus shown in Fieure 2 was inserted. A conventional magh;?tie stirrer with its-top removed provides very rapid mixing in the 150-ml. beaker. The covers or and the s n m o r t far the beaker are easilv made from ~ wood ~ ...~ . .. ~ opaque plaiiic. Small blocks and a~sprcngelsmp may b< attached t o the beaker shelf to aid in the accurate positioning of the beaker. AU parts should fit as well as possible and be painted black to minimize light leeks. The appearance of the instrument with the light cover in place is shown in Figure 3. A 5-ml. mieroburet which extends throueh ~~~
~~~
into the celi ookpartment. Anoiher hole in the'&
~~
~
.
;over sh&d
~~~~~~
aperating Technique. The spectrophotometer is set to the desired wave length and allowed to warm up, and the dark current is adjusted. The sample to be titrated is placed in the light path and the instrument s e t to read zero absorbance or some other starting value. As only changes in absorbance are involved in locating the end point,, the absolute value of the absorbance need
Figure 3.
Model B Spectrophotometer Set Up for Photometric Titrations
V O L U M E 26, N O . 11, N O V E M B E R 1 9 5 4
l
8%
n
$
, 6-
0
0
qc
I 2t
"
2rd
1743
"
"
:265ml.
concentration (failure of Beer's law). Even n-ith instruments of good quality, the deviations may he very considerable, as s h a m by Vandenbelt, For.syth, and Garrett (95) and more recently by Goldring ef nl. (31). The effect of a photometric titration of the type shown in Figure 1,h is a gradual rounding of the upward Ijranch of the curve. If the cause of this is
1744
ANALYTICAL CHEMISTRY
even faintly colored solutions are as a rule found to absorb rather strongly, and it is rarely that the wave length of an adsorption peak is suitable for a titration. More often the wave length is selected well down on the lower part of the curve. Even then the absorption is sometimes too great, and some device such as a glass spacer may need to be inserted to shorten the light path (Figure 7 ) . GRAPHICAL DETER.IlIN.4TION O F E N D POIKT
Because the end point in a photometric titration is found graphically, some attention must be given t o the proper choice of graph paper and scale, lest these become a limiting factor in the precision of the determination. For titrations in which there is little curvature in the vicinity of the equivalence point, a few points comprising a relatively small part of the titration may be plotted on a fairly large scale and the intersection of the straight lines located with considerable ease and accuracy. Typical examples are: titration of strong acid with baseand asingle-color indicator, or the titration of iron with permanganate, either of which may be done with a precision of a few tenths of a part per thousand.
Although the surressive-derivative or differential method commonly used in potentiometric titrations for the exact location of the end point may, in principle, be applied to photometric titrations no advantage is gained by it. This method of treating the data requires good measurements near the vicinity of the equivalence point; and, as Irith aniperometric and conductonietric titrations, the data are poorest here. A sharp cusp can indeed be obtained as the second derivative of a photometric titration curve end point, but only if the original curve showed a break sharp enough SO that the end point could be located readily anyway. REVIEW OF PRIOR WORK
The literature on the techniques and applications of photometric titrations has been growing rapidly in the past 10 years; and as the field has never been extensively reviewed, a survey embodying some degree of completeness appears to be in order. Many of the early investigators did not determine actual titration curves, but attempted to match indicator colors or titrated to the occurience of a large deflection. Sonetheless, these papers are included in the reviem, as the methods involved will in moht circumstances give ‘308 0 “ Theoretical end win1 3 75 ml. 0 as good or better results on application of presentday techniques. The literature coverage is be/ o O lieved to be essentially complete up to the end of 1953; and for most of the readily available jour/ O nals, to mid-1954. Attention should be called to the very recent review article by Underwood (94) which appeared while this manuscript was in press. Apparatus and Technique. Instruments, mainly filter photometers, suitable for the performance of photometric titrations, have been described by a number of authors (1, 17, 21, 32, 34, 35, 37, 50, 51, 62-67, 69,70, 78-80, 82, 83, 105). The “heterometer” of Bobtelsky (9) is a simple turbidimeter designed for titration work. Spectrophotometers, by reason of their superior selectivity and sensitivity, are to be preferred to filter photometers, and adaptations of commercially available instruments are therefore of particular interest. The use of the Coleman Universal (28,29),Beckman Model B (28,60,87), + & s = - - - ~ 9 4 - z z / - - - - ‘365 ~ - I i I 1 I I I I I and Beckman DU (15, 88) spectrophotometers 41 8 12 16 20 24 28 32 36 40 44 48 has been described recently. ml. 0 I20 N N c O H An interesting development closely analogous Figure 6. Titration of p-Nitrophenol i n Water to the photometric titration technique is the use
-
:
E
0
10.0 ml. of 0.450N p-nitrophenol in 100 ml. of Cot-free water under nitrogen a t various wave
lengths
For the less favorable systems where the straight-line portions must be extrapolated from regions far from the equivalence point, a large portion of all of the curve must be plotted. Here “millimeter” paper is desirable; and if the point is in the vicinity of 100 to 150 divisions, estimation to half a division is equivalent to about 0.5y0. The angle of intersection and the uncertainty of the individual points govern the accuracy with which the end point may be located on a given type of graph paper. The accuracy of the spectrophotometric measurements is no greater than + l % in the middle range or k0.002 unit in the low-absorbance region. The uncertainty of the location of the lines is, of course, less than this because each line represents the average of a number of points. I n general, the location of the intersection of two experimentally determined lines with an angle of intersection of 90” + 30” would seem to involve no greater uncertainty than the location of an individual point. If one of the lines is a base line, and therefore subject to less uncertainty, the uncertainty in the intersection will be correspondingly decreased.
/
20mm Glass Tubing
Figure 7. Device to Reduce Light Path through 150-M1.Beaker
V O L U M E 2 6 , NO. 1 1 , N O V E M B E R 1 9 5 4 of a fluorimeter, reported by Willard and Horton, to measure the fluoresence of a titration product (101). Of interest in this connection is a list of the properties of a number of fluorescent acidbase indicators (20). The feasibility of photometric detection of an end point through the use of a chemiluminescent indicator has been demonstrated by Kenny and Kurtz ( 5 2 ) . The use of photoelectric detection of the end point has long appealed to designers of automatic titration apparatus. Muller and Partridge ( 6 6 ) , as early as 1928, described such a device to shut off reagent flow automatically when an indicator changed color, and other? (36, 50, 6 3 ) have follomed similar lines. A very recent development is the use of photometric detection of end points in automatic coulometric titration (102, 1013). MalmPtadt and Gohrbandt (69) have described the use of the Cary spectrophotometer with a Lingane-type constant-flow reagent delivery syringe for recording absorbance automatically as a function of added reagent. Marple (60) has described a simple accessory for the Beckman Model B spectrophotometer which makes it into a recording instrument suitable for automatic photometric titrations. Neutralization Reactions. The variety and versatility of acidbase indicator systems have resulted in a number of applications to neutralization reactions. Titrations using single-color indicators may be performed straightforwardly with advantage (63, 70, 97), while two-color indicators may offer no advantage over visual methods or may he superior, depending on the choice of wave length and the manner in which they are used (48,51,56,62, 68, 72, 75, 77, 79, 85). The theory and practice of direct photometric titration of n-eak acids and bases, singly and in mixtures, have been studied by Goddu (68, 30). The advantages of the photometric titration method for locating indicator end points in practical applications where solutions may be highly colored have been demonstrated by Osborn, Elliott, and Martin (69) and others (39, 56). Applications to the determinat,ion of the acid and saponification numbers of resins ( 6 9 ) and the titration of amino acids in alcohol-acetone media (105) have been made. Oxidation Reduction Reactions. Nost of the workers in this field have demonstrated the feasibility of photometric detection of the end point in the standard reactions such as iron-permanganate, iron-dichromat,e, and iodine-thiosulfate (27, 54,50, 51, 75, 79, 83-85, 97). I n addit,ion, it has been shown that the determination of vanadium in steel (29, 49, 82) and manganese in steel and other samples ( 4 6 , 49,81) is feasible. Among other determinations reported are those of cobalt with peroxide (84), gold with st,annous chloride (58) or potassium iodide (bo), iodate with iodide ( 3 7 ) )manganese and cerous cerium with permanganate in a neutral pyrophosphate medium (eo), and uranium and iron with ceric sulfate ( 1 6 ) . Increased sensitivity t.hrough use of the ultraviolet was achieved by Bricker and Sweetser ( 1 5 ) in the tit,ration of arsenic and ceric sulfate. The same authors have made an extensive study ( 8 6 ) of the w e of bromate-bromide reagent in acid medium, and have shown t h a t good results are obtained in addition reactions of olefinic compounds, substitution reactions involving phenols and aromatic :imines, and oxidations such as the determination of arsenic and antimony, separately and together. Narple ( 6 0 ) has compared the theoretical and practical limitations of photometric and potentiometric titration methods for oxidation-reduction reactions, and has shown that the photometric technique has certain advantages where the potentials of the titrant and reactant c.ouples are not well separated. Precipitation Reactions. The photometric titration technique h:ts been applied to many precipitation reactions, occasionally with the aid of indicators or for the location of a clear point, but usually for the purpose of titration to maximum turbidity. The fundamental investigations of Ringbom have already been mentioned ( 7 5 ) and in the field of applications, papers by Hirano and Bobtelsky are particularly numerous. Among the reactions which have heen studied are the precipi-
1745 tation of lead and molybdate (58), sulfide (45),or as the chlorofluoride ( 1 8 ) ; the precipitation of mercury with sulfide (CY); zirconium and hafnium with cupferron ( 2 6 ) ; palladium with iodide (90); silver with chloride ( 4 1 ) ; calcium with oxalate ( 2 6 ) ; nickel with dimethylglyoxime ( 7 , 8); selenium with iodide ( 4 7 ) ; bismuth with phosphate ( 1 8 ) ; magnesium with phosphate ( 7 ; ) ; and zinc with ferrocyanide (24, 5 8 ) . Recent papers have described determinations of aluminum with oxine (9),magnebiuin with oxine ( I O ) , zinc with quinaldic acid ( 5 ) , copper with exine (11, 12), and lead with citrate (6). The behavior of copper, iron, chromium, thorium, and aluminum with phthalate, and the reactions of copper and thorium with malonate, maleate, and succinate, have been reported by Bobtelsky and Bar-Gadda (2-4,11). Anion constituents determined include fluoride, precipitated with thorium (18, 29); chloride with mercuric salts ( 5 7 ) ; chloride, bromide, and iodide with silver ( 4 2 ) ; cyanide with silver ( 5 7 ) ; sulfide with lead, mercury, or bismuth (43); citrate with lead ( 1 5 ) ; and, of course, sulfate with barium or lead (17, 23, 76, 89, 91, 100). Ncotine may be determined by titration with silicotungstic acid ( 3 3 ) . Other developments include Klevens’ method for the determination of critical micelle concentration (65, 7 3 ) , and applications have been made to the determination of detergents and the surface areas of pigments and latices. Two papers report the determination of cationic and anionic soaps (54,681. Complexation Reactions. Cntil very recently, the majority of photometric titrations involving complex-formation reactions have been designed to determine the combining properties of the reagent, rather than to provide an analytical result. Xoteworthy examples include: the titration of iron with 1,2-dihydroxybenzene 3,5-disulfonate (1O4), palladium with pararosaniline hydrochloride (98), and cobalt with thiocyanate (99);the determination of the oxidation states of neptunium ( 3 6 ) ; and studies on the starchiodine reaction (21, 66). Aside from the determination of nickel with cyanide ( I S ) , all the recent work has involved the use of ethylenediaminetetraacetic acid. Sweetser and Bricker (87, 88) were the first to show the great advantages of the photometric titration technique in the use of the reagent, and they have applied it to determinations of iron, copper, nickel, magnesium, calcium, zinc, cadmium, titanium, and zirconium. Under\\ ood (93) has determined iron and copper simultaneously in aluminum alloys by this technique, and Malmstadt and Gohrbandt (59) have used it in the automatic titration of thorium, with copper present as an indicator substance. Fortuin, Karsten, and Kies have very recently published an important study on the theory of photometric complexone titrations with indicators ( 2 2 ) . The versatility of ethylenediaminetetraacetic acid as a reagent, and the advantages of the photometric titration technique, promise to make this one of the most fruitful fields of titrimetric research in the near future. ACKNOW LEDGMEhT
The authors are indebted to the Atomic Energy Commission for partial support of this research, and to the Procter & Gamble Co. for a fellowship for Robert F. Goddu. REFERENCES
(1) Alyea, H.
K.,J. Chem. Educ., 18, 57 (1941).
(2) Bobtelsky, M., and Bar-Gadda, I., Anal. Chim. Acta, 9, 446 (1953). (3) Bobtelsky, M., and Bar-Gadda, I , Bull. SOC. chzm., 1953,276. (4) Ibzd., p. 382. (5) Bobtelsky, b l . , and Bihlev, L., Anal. Chzm. Acta, 10, 260-4 (1954). (6) Bobtelsky, M., and Graus, B., Ibid., 9, 163 (1953). Ibzd., 9,281 (1953). (7) Bobtelsky, M.,and Welwart, Y., (8) Ibid., p. 374. (9) Ibid., 10, 151 (1954). (10) Ibid.. p. 156. (11) Ibzd., p. 459. (12) Ibzd.. p. 464.
ANALYTICAL CHEMISTRY Boyer, W.J., IXD.ENQ.CHEY.,ANAL.ED., 10, 175 (1938). Nellon, M. G., Ed., “Analytical Absorption Spectroscopy.” Bricker, C. E., personal communication. New York, John Wiley & Sons, 1950. Bricker, C. E., and Sweetser, P. B., ANAL.CHEM.,24,409 (1952). Rlika, J., 2. anal. Chem.. 128, 159 (1948). Ibid., 25, 764 (1953). Muller, F., 2. Elektrochem., 40, 46 (1934). Campo, A. del., Burriel, F.,and Escolar, L. G., Anales soc. Muller, R. H., IND.ENG.CHEM.,-4NAL. ED., 11, 1 (1939). espaR., fis. y quim., 34, 829 (1936); Bol. Acad. Clienc. (65) RIullBr, R. H., and McKenna, 11. H., J . Am. Chem. Soc., 58, ( M a d r i d ) , 2, No. 7, 10 (1936). 1017 (1936). Cheuelevetskii. M . L.. Zavodskava Lab.. 11. 498 (1945). (66) lluller, R. H., and Partridge, H. M., Ind. Eng. Chem., 20, 423 Chebelevetskii, 11. L., Rubinova, S. S.,an‘d Evelina, B. B., (1928). Ihid., 11, 783 (1945). (67) Sichols, M. L., and Rindt, B. H., ANAL.CHEM.,22, 781 (1950). DeMent, J., J . Chem. Educ., 30, 145 (1953). (68) Ibid., p. 785. Field, J., 2nd, and Baas Becking, L. G. XI., J . Gen. Phusiol.. 9, (69) . . Osborn. R. H., Elliott, J. H.. and Martin. A. F.. IXD.ENG. 445 (1925). CHEM.,-4x.4~.ED.,15, 642 (1943). Fortuin, J. 11. H., Karsten, P., and Kies, H. L., A n a l . Chim. (70) Partridge, H. M., Ibid., 2, 207 (1930). Acta, 10, 356 (1954). (71) Partridge, H. 11., and Smith. R. d.,Mikrochemie, 11, 311 Frey, H., Ihid., 6, 28 (1952). (1932). Frey, H., Z . anal. Chem., 132, 276 (1951). ( 7 2 ) Raeder, 11. G., Kgl. Korske T’idenskab. Seiskabs, Skrifter, Ibid., 133, 328 (1951). 1942-1945, NO.3. Fujiwara, S., J. Chem. Soe. ( J a p a n ) , 72, 77 (1951). (73) Raison, hl., Compt. Rend., 235, 1129 (1952.) Gaukhman, 11. S., Reznik, B. E.. and Gansburg, G. >I., (74) Reznik, B. E., and Fedorova, G. P., Zhur. Anal. Khim., 3, 92 Zavodskaya Lab., 16, 1045 (1950). (1948). Goddu, R. F., Ph.D. thesis, Massachusetts Institute of Tech(75) Ringbom, A., Chimie et Industrie, 45, So. 3, bis 304-8 (1941). nology, 1951. (76) Ringbom. -4., Z . anal. Chem., 122, 263 (1941). Goddu, R. F., and Hume, D. X., ANAL.CHEM.,22, 1314 (1950). (77) Ringbom, A., and Sundman, F., Ibid., 116, 104 (1939). Ibid.,26, 1679-84 (1954). (78) Ronland, G. P., IND.ENG.CHEM.,ANAL.ED., 11, 442 (1939). Goldring, L. S.,Hawes, R. C., Hare, G. H., Beckman, d. O., (79) Russell, W.W., and Latham, D. S., Ibid.,6, 463 (1934). and Stickney, M . E., Ibid., 25, 869 (1953). (80) Somiya, N., and Kamada, H., J . Japan. Chemistry, 1, 63 Gonzales, F., I X Congr. Intern. Quim. Pura Apilcada ( M a d r i d ) , 11947). 6, 70 (1934). (81) Somiya,‘T., J . Soe. Chem. Ind. ( J a p a n ) ,Supplemental Binding, Goodhue, L. D., ISD.ENC.CHEX,ANAL.ED., 10, 53 (1938). 40, 412B (1937). Havemann, R., Chem. Zentr., 1944, 11, 1304. (82) Somiya, T., and Nakamura, Y., Ihid., 38, 262B (1935). Hickman, K., and Sanford, C. R., IND.ENG.CHEX, ;Is.AL. (83) Somiya, T., and Shjraishi, S., Ibid., 33, 300B (1930). ED.,5, 65 (1933). (84) Ibid., 41, 314B (1938). Hindeman, J. C., bfagnusson, L. B., and La Chapelle, T. J.. (85) Ibid., p. 422B. J . Am. Chem. Soc.. 71. 689 (1949). (86) Sweetser, P. B., and Bricker, C. E., ,Is~L. CHEM.,24, 1107 (1962). Hirano, S., J . S O ~&em: . I n d . ‘ ( J a p a n ) ,Supplemental Binding, \----,37, l77B (1934). (87) Ibid., 25, 253 (1953). Ibid., p. 178B. (88) Ibid., 26, 195 (1954). Ibid., p. 145B. (89) Takagi, K., and Yamada, M., J . Electrochem. Soc. ( J a p a n ) , 18, Ibid., 6.561B. 9 (1950). Ibid., p. 754B. (90) Tananaev, I. I-., Zhur. Anal. Khim , 4, 67 (1949). Ibid., 38, 175B (1953). (91) Tananaev, I. V., and Rudanev, V. A., Ibid., 5, 82 (1950) Ibid.. D. 598B. (92) Tingle, rl.,J . Am. Chem. SOC.,40, 873 (1918). Ibid.; 646B. . 25, 1910 (1953). (93) Underwood, A. L., A N ~ LCHEX., Ibid., p. 648B. (94) Underwood, A. L., J . Chem. Educ., 31, 394 (1954). Ibid., 40, 412B (1937). (95) Vandenbelt, J. M., Forsyth, J., and Garrett, A,, ISD.ENG. Ibid., 41, 266B (1938). CHEX,4 x 4 ~ED., . 17, 235 (1945). Ibid., 46, 223 (1943). (96) Walter, R. N., ANAL.CHEY:., 22, 1332 (1950). Hirano. S..and Kakamura. Y.. Ihid.. 37. 147B (1934). (97) Weber, 0. H., Die Chemie, 55, 364 (1942). Juliard, A., van Cakenberghe, J., and Heitner, C., Ind. chim. (98) West, P. W., and Amis, E. S.,IND.ENG.CHEM..AN.AL.ED.,18, Belge, 17, 25 (1952). 400 (1946). Kasai, Y., and Takii, S., Repts. I m p . I n d . Research Inst. (99) West, P. W,, and de J’ries, C. G., B N ~ LCHEY., . 23, 334 (1951). (Osaka, J a p a n ) , 16, No. 3, 1 (1935). (100) Wickbold R., Angew. Chem., 65, 159 (1953). Kenny. F.. and Kurtz, R. B., ANAL.CHEM.,24, 1218 (1952). (101) Willard, H. H., and Horton, C. A , , ANAL. CHEM.,22, 1194 Klevens, H. B., J . Phys. Collotd Chem., 51, 1143 (194T) (1950). (102) Wise, E. S . , Gilles, P. W.,and Reynolds, C. A, Jr., Ibid., 25, Lambert, J. XI., J . Colloid Sei., 2, 479 (1947). Linnane. J. J.. ANAL.CHEX. 20. 285 (1948). 1344 (1953). Lur’e, Y. Y., and Tal, E. ill., Zaz’odskaua Lab., 9, 702 (1940). (103) Ibid., 26, 779 (1954). Ibid.. 11, 504 (1945). ENG.CHEM.,ANAL.ED., 16, (104) Yoe, J. H., and Jones, A. L., IND. 111 (1944). Ibad., p. 788. CHEW., . 26,442 (105) Zamecnik. P. C., Levin, G. I., and Bergman, R.1. J., J . Biol. Malmstadt, H. V., and Gohrbandt, E. C., A N ~ L Chem., 158, 537 (1945). (1954). hlarple, T. L., Ph.D. thesis, lIa?sachusetts Institute of TechR E C E I V Efor D review July 29, 1954. Accepted September 27, 1954. nology, 1954.
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