Substituted 1,IO-Phenanthroline Ferrous Complex Oxidation-Reduction Indicators Potential Determinations as a Function of Acid Concentration G. FREDERICK SMITH AND FREDERIC P. RICHTER, Wm. Albert Noyes Laboratories, University of Illinois, Urbana, 111. This paper deals with determination of the variation in the potential at which the phenanthrolinium ion ir oxidized from the ferrous to the ferric form as a function of acidity. The data include those for the substituted complex ions in which the 5- or 6-position hydrogen i s replaced b y methyl, nitro, chloro, or bromo radicals, and for the complex ions in which the 5- and 6-position hydrogens have been replaced b y both the methyl and nitro groups.
Titration usin 0.1 N potmium dichromate dissolved in sulfuric acid (4 gram mokcules Of acid per liter) Frequently employed reference point potentials of various systems &s used at different acid concentrations are given in Table 11, GENERAL PROCEDURE FOR DETERMINATION OF FORMAL ELECTRODE POTENTIALS
For some of the phenanthrolinium ions the potential of the higher reference system is not sufficient to oxidize the ferrous to the ferric ion complex. To use a perchloric acid solution of perscribed by Walden, Hammett, and Chapman (8). The nitro chloratoceric acid because of its higher potential in some cases was substitution product was first studied by Hammett, Walden, and unsatisfactory because of the formation of insoluble ferrous perEdmonds (I),and its first practical application was in the deterchlorate complex phenanthrolinium ions. In other cases equally mination of oxalic acid, described by Smith and Get2 (6). The insoluble sulfuric acid complex ions resulted a t the higher acidities. synthesis of the materials is described by Smith and Getz (6) and The ferric complex henanthrolinium ions (with the exception Richter and Smith (4). The spectrophotometric Properties of of oxidized ferroin an$ methyl-ferroin) were not stable for more these products were studied by \loss, Mellon, and Smith (3). than a short interval, especially a t higher acid concentrations. In these cases solutions of 0.01 or 0.025 N sulfatocerate ion in solutions containing 1 to 8 gram molecules of sulfuric acid per Table 1. Physical Constants of Phenanthrolines and Their Substitution Products liter were prepared by dissolving Amount pure ammonium nitratocerate in Required for M . P . Common Name of looo of Formal concentrated sulfuric acid, (AnhyFerrous Sulfate 0 . 0 1 M Fe + + Oxidation, followed by gradual dilution to drous) Complex Mol. Wt. Complex E.M.F. the proper amount. The substiCompound c. Grams Voila' tuted ferroin indicator solutions 5-Nitro-1,lO-phenanthroline 202 Nitro-ferroin 225.20 6,7500 1.25 of 0.01 or 0.025M concentrations 5-Nitro5-methyl-l,10- henanthroline 289 Nitromethy1:ferroin 239.23 7.1708 1.22 were prepared by solution of the 5-Bromo-] 10-phenantfroline monohydrate 119 Bromo-ferrotn 277.11 8.3134 pro er weight of indicator base 5-Chloro-1'10-phenanthrolinemonohydrate 123 Chloro-ferroin 232.06 6.9800 (Take I) in 0.01 or 0.025 N 1,lO-Phena'nthroline monohydrate 117 Ferroin 198.22 5.9464 1.00 5-Methyl-1,lO-phenanthroline monohydrate 114 Methyl-ferroin 212.24 6 3673 1.02 ferrous ammonium sulfate soluFormal potential, when oxidized and reduced forms are equal, in sulfuric acid solution8 of one molecular weight tion. Measured portions Of the per liter (without reference to their possible incomplete ionization, hydrolysis, formation of complexes, etc.) and cerate solution (25.00ml.) were at 25' C. (7). placed in 400-ml. beakers and an
T
HE first application of the phenanthrolinium complex ion as an indicator in oxidation-reduction reactions was de-
EXPERIMENTAL WORK
Pertinent data concerning the materials of this discussion are contained in Table I. A procedure similar to that described by Walden, Hammett, and Chapman (8) was employed when both the ferrous and ferric complex phenanthrolinium ions were found to be stable in the various strengths of acid studied. This was true in the case of l,l0-phenanthroline and 5-methyl-l,l0-phenanthroline. The simultaneous titration of a mixture of ferrous sulfate and ferrous phenanthrolinium ions was carried out, using either a solution of sulfatoceric acid or potassium dichromate in solutions of sulfuric acid of concentration equal to that of the solutions of the ions being titrated. The range of acidity employed was from 1 to 8 moles per liter. The ceric-cerous and ferrous and ferric potentials were separately determined under the same conditions and the values of these two reference points reconfirmed. A typical sample titration graph is shown in Figure 1. Titration conditions used were: 10 ml. of an approximately 0.1 molar ferrous sulfate solution in sulfuric acid (4 gram molecules of sulfuric acid per liter) 15 ml. of an approximately 0.1 molar solution of meth 1-ferroin added to an equal volume of sulfuric acid (8 gram moLcules of sulfuric acid per liter) Dilution to 200 ml. by addition of sulfuric acid (4 gram molecules of sulfuric acid per Iiter)
twice the strength finally required was added. Dilution was made to 200 ml. with sulfuric acid of the same desired strength. A measured portion (50.00ml.) of the ferroin or substituted ferroin was then added in one portion with vigorous stirring. The potential of the resulting solution was read a t once, using a saturated calomel electrode and a bright latinum electrode as references. Any condition such as results Kom instability of the ferric phenanthrolinium ions was indicated by a adual fall of potential which could be observed without difficuEy. Such instability was more pronounced at higher acid concentrations and
50
MI. of
Figure 1. in 4
1
I5
titrdting solution
Simultaneous Titration of Ferrous and Phenanthrolinium Ferrous Ions
M sulfuric acid solution,
usin potassium dichromate in 4 sulfurfc acid tfrovrhoul
M
Table II. Formal Electrode Potentials of Various Systems in Sulfuric and Hydrochloric A c i d Solutions" Sulfuric Acid Concentrations (Molea per Liter) 1 2 4 0 8 E.M.F., Volts F e + + +cc F e + + 0.08 0.68 0.08 0.68 0.08 CrzOi +2Cr + ... 1.11 1.15 1.30 1.35 Ce(SOda--+Ce+++ 1.44 1.43 1.42 .. . 1.40 Hydrochloric Acid Concentrations (Moles per Liter) 1 2 3 4 E.M.F., Volts Fe + + ++Fe + + 0.09 0.08 0.07 0.00 CrlOl-- -F 2Cr + + + 1.09 1.11 1.19 1.15 a Determinations of present study are taken from Smith and Getz (6). Potential Determined +
581
ANALYTICAL EDITION
September, 1944
color change from red in reduced solutions to faint blue in oxidized solutions requires approximately 90% oxidation of the indicator ion before the red hue is eliminated. The oxidation potential is thus effectively approximately 60 millivolts higher than the values give in Table 111. The values given in Table I11 are claimed t o be valid to within *20 millivolts and in most cases better.
+
+
Table 111. Formal Oxidation Potential of Ferroin and Substituted Ferroin Indicators at Various Strengths of Sulfuric A c i d
Indicator Nitro-ferroin Nitromethyl-ferroin Bromo-ferroin Chloro-ferroin Ferroin Meth 1-ferroin 2 , Z drpyridyl-ferroin
Sulfuric Acid Strength 0 . 5 M 1 M 2 M 3 M 4 M BM S M Oxidation Potential, Volts 1.20 1.25 1.22 . . . 1.12 1.12 1.11 ... 1.23 .. ... , .. 1.13 . i.'ii i.'io " ' i.'04 0,'97 1 1 . . . 1.00 1 . 0 3 f.00 0 . 9 0 0 . 8 9 0 . 7 0 . . . 1.02 1.00 0.98 0.93 0.80 0 . 7 0 . 0.97 .. .. 0.92 .
.
.. ..
.
.. .
.. .
.
...
..
SUMMARY
Formal oxidation potentials of the ferric-ferrous and the dichromate-chromic systems have been determined in 1 to 8 M sulfuric and hydrochloric acid solutions. The use of such data in the selection of the proper indicator systems for determination of reaction and points is suggested. A general procedure for use in determination of the formal electrode potentials of reversible oxidation-redhction indicators of the ferroin and substituted ferroin group is described. The oxidation potential of the phenanthrolinium ion and nitro, bromo, chloro, methyl, and nitromethyl phenanthrolinium ions is given in various sulfuric acid strengths from 1 to 8 M . For the system of indicators studied the range of oxidation potentials found varies from 0.7to 1.26 volts, with all gradations between represented. LITERATURE CITED
with ferric phenanthrolinium ions of highest electrode potential. The systems showed no appreciable change in potential during the time required for reading the potential of the first mixing. The data obtained are found in Table 111. By determination of potentials in many cases by both procedures, the values were shown to be reliable within 0.02 volt. The values obtained by either procedure duplicated those of Walden, Hammett, and their co-workers as corrected by Hume and Kolthoff (2). As previously assumed (b), the oxidation potential of the bipyridylinium ferrous complex ion is not so high as that of ferroin. I n using the data of Tables I1 and I11 as a guide t o titrations employing visual equivalence point determinations rather than potentiometric observations, it must be kept in mind that the
Hammett, Walden, and Edmonds, J. Am. Chem. SOC.,56, 1092 (1934).
Hume and Kolthoff, Ibid., 65,1895 (1943). Moss, Mellon, and Smith, IND.ENO.CHEM.,ANAL.ED., 14, 931 (1942).
Richter and Smith, J. Am. Chem. Soc., 66,396 (1944). Smith and Getz, C h m . Reviews, 16,113 (1935). Smith and Getz, IND.ENQ.CHEM.,ANAL.ED.,10, 304 (1938). Swift, "System of Chemical Analysis, Molal and Formal Potentials", pp. 540-3, New York, Prentice-Hall, 1939. Walden, Hammett, and Chapman, J. Am. Chem. SOC.,55, 2649 (1933). ABSTRACT of a. portion of 8 thesis presented in partial fulfillment of the requirements for the Ph.D. degree in the Graduate School, University of Illinois.
Use of Synthetic Detergents in the V a n Slyke Determination of Oxygen Capacity CARL S. VESTLING AND MARTIN A. SWERDLOW, University of Illinois, Urbana, 111.
M
ODIFICATIOKS of the original Van Slyke procedure (6, 7) for the determination of blood oxygen capacity have been concerned chiefly with mechanical and manipulative improvements (1, 2, 3, 6, 8, 9). It occurred to the authors to test several synthetic detergents, of different types, as possible substitutes for the saponin prescribed by Van Slyke as the hemolytic agent. The results below indicate that several common detergents may conveniently be used in place of the less readily available, more expensive, and mildly irritating saponin. Sendroy's procedure (2) has been used in these determinations on rabbit and horse blood. It is reasonable to assume that the modified method can be extended to the blood of other species. A saturated solution of each of the deter ents, with the exception of the R9-C, was prepared in a fresay made potassium ferricyanide solution containing 23 grams per 100 cc. The saturated solutions were prepared by adding one volume of potassium ferricyanide of twice the desired concentration to an equal volume of detergent solution containin 16 grams per 100 cc. and filterin The source of each of the feter ents used can be aacertainedfy reference to the 1943 list (4). f n the case of the RO-C (a cationic detergent of the alkyldimethylbenzyl
Ox gen Capacity Determinations on Fresh Oxalated Rabiit Blood Diluted with l%*NaCI Solution Detergent Type Volume % 01
Table I.
Saponin Duponol WA Aerosol O.T.
Natural polycyclic glucoside, Merck Long-chain alcohol sulfate Sodium dioctyl sulfosuccinate
11.99 12.08 11.72
ammonium chloride type, Winthrop Chemical Company), 8 grams per 100 cc. were used, an amount equal to that of the saponin prescribed by Van Slyke. The RO-C reacted slowly with potassium ferricyanide and is not considered suitable for use with it as the oxidizin a ent. The results in k b f e I suggest that Duponol WA may be readily em loyed in place of sapomn, but that the use of Aerosol O.T. yiebs slightly low values. A favorable check in this analysis is t 0 . 2 volume % (8). All determinations< including blanks, were carried out in duplicate. Table I1 indicates that each of the three detergents tested will give satisfactory results on fresh oxalated rabbit blood diluted with 1% sodium chloride. The use of Nacconol FSNO, an alkyl aryl sulfonate type, led to similar values. A freshly prepared
*
