alkyl bromides and for the simplification of the chromatograms of complex mixtures. Figure 2 demonstrates the use of this technique for analysis of unknown mixtures of alkyl bromides. Figure 2, a, shows the chromatogram obtained from a mixture of 13 C1 to Cs monobromo alkanes using firebrick in the reaction eone and a 2.5-meter column packed with Tween 60. Under the conditions of
analysis, 2-bromobutane and l-bromo-2methylpropane are not resolved, l-bromobutane and 2-bromo-2-methylbutane are not resolved, and three of the bromopentane isomers overlap one another. Figure 2, b, shows the chromatogram obtained from the same mixture using a silver nitrate reaction tube. All secondary and tertiary bromides have reacted with the silver salt and the resulting chromatogram is much simplified.
LITERATURE CITED
(1) Fredericks, E. M., Brooks, F. R., ANAL.CHEY.28, 297 (1956). ( 2 ) James, A. T., Martin, A. J. P., Biochem. J. 50, 679 (1952). (3) Michael, Arthur, Carlson, G. H., J. Am. Chem. Soc. 57, 1268 (1935). RECEIVEDfor review April 11, 1958. Bccepted August 4, 1958. Contribution from Research Chemistry Branch, Atomic Energy of Canada, Ltd., Chalk River, Ont., Canada. Issued as A.E.C.L No. 710.
Differential Spectrophotometric Determination of Hydrogen Peroxide Using 1,I 0-Phenanthroline and Bathophenanthroline ROBERT BAILEY and D. F. BOLTZ Wayne State University, Detroit, Mich.
b A differential spectrophotometric method for the determination of traces of hydrogen peroxide is based on the decrease in absorbance due to the iron(l1) phenanthroline complex in the presence of hydrogen peroxide. 1 r l 0Phenanhroline is used in determining 0.1 to 2.5 p.p.rn. of hydrogen peroxide and 4,7-diphenyl-1 r l O-phenanthroline is used for the 0.03- to 0.1 p.p.m. range.
permanganate (I), and (6) have been described.
molybdate
EXPERIMENTAL
Apparatus and Solutions. A Beckman Model DU spectrophotometer and a Warren Spectracord with 1.00-cm. Corex cells were used in all the absorbance measurements. A tungsten fila- ment lamp was used. Standard Titanium(1V) Solution. Dissolve 4.5 grams of potassium titanyl oxalate dihydrate and 8 grams of ammonium sulfate in 50 ml. of concenwo rapid differential spectrophototrated sulfuric acid. Heat a t the boilmetric methods have been deing point for 15 minutes to effect solution. Dilute to 1 liter. Standardize veloped for the determination of hyby transferring an aliquot to a beaker drogen peroxide. They involve the and precipitating titanyl hydroxide oxidation of iron(I1) to iron(II1) with with ammonium hydroxide. Weigh the hydrogen peroxide and the subsequent ignited precipitate. A solution so preaddition of either 1,lO-phenanthroline Dared contained 0.5515 mn. of titaniumor bathophenanthroline (4,7-diphenyl(IV) per ml. 1,lO-phenanthroline) to react with the Standard Hydrogen Peroxide Sohexcess iron(I1). The decrease in color tion. Dilute 20 ml. of the 30% analvtas compared to the color of the blank ical grade (stabilized with acetanilide 0.02% by weight), to 1 liter with boiled indicates the amount of hydrogen perredistilled water. Add 20 mg. of oxide present. These methods are apacetanilide. Standardize either titriplied to the determination of hydrogen metrically (iodometrically) or spectroperoxide in the 0.03- to 2.5-p.p.m. photometrically utilizing the peroxyconcentration range. titanic acid method. The spectroHydrogen peroxide can be estimated photometric method was used in this by several colorimetric methods. Perinvestigation because the instability of haps the most common method utilizes the hydrogen peroxide necessitated freperoxytitanic acid (2, 3, 8 ) . This yelquent, time-consuming, standardization. In this method, add an excess of standlow complex shows an absorbance maxiard titanium(1V) solution to an aliquot mum a t 415 mp. Hydrogen peroxide portion of hydrogen peroxide, dilute to has been determined by utilizing the volume in a 100-ml. volumetric flask, color produced when a starch-potasand measure the absorbance a t 415 mp. sium iodide mixture is alloR-ed to react These spectrophotometric results are with the peroxide (9, 1 1 ) . Coloricompared with titrimetric results (Table metric methods using thiocyanate (4, I). The molar absorptivity of the fluorescein (la), phenolphthalin ( 7 ) , peroxytitanic acid system computed 2-chlorodihydroxyphenylenediamine(6), from experimental data is 731 a t 415
T
-
Table I. Comparison of Titrimetric and Spectrophotometric Methods for Standardization of Hydrogen Peroxide
Sample
Titrimetric Method
Spectrophotometric Method
1 2 3 4
0,278212.’ 0,2783N 0.2784.11 0.2783N 0.2783N
0.2785N 0.2786N 0.2789N 0.2780N 0.2785N
KO.
Av.
mp. In a series of eight determinations, a 0.1940M hydrogen peroxide solution R-as standardized with a standard deviation of 1.3 X 10-3M. Standard Iron(I1) Solution. Dissolve 0.2100 gram of Mohr’s salt in distilled water, add 5 ml. of 72% perchloric acid, and dilute the resulting solution to 1 liter. After dilution, add approximately 5 grams of 1/16-inch aluminum rod cut into 1/2-inch lengths. A solution stabilized in this manner resists excessive oxidation for at least 10 weeks. 1,lO-Phenanthroline Solution. Dissolve 50 mg. of 1,lO-phenanthroline monohydrate in 100 ml. of distilled water and heat to effect solution. Bathophenanthroline Solution. Dissolve 20 mg. of 4,7-diphenyl-1,10-phenanthroline in 50 ml. of 95% . _iron-free ethyl alcohol. 0.5N Sodium Acetate. Dissolve 67.0 grams of the trihvdrate salt in water and &lute to 1 liter. ” Vacuum distilled (72%) perchloric acid was used. Calculations Involved in Proposed Differential Spectrophotometric Method. The oxidation of iron(I1) with hydrogen peroxide in acidic solution is illustrated by the equation VOL. 31, NO. 1, JANUARY 1959
117
2Fe+2
+ H2OS + 2 H T ~i 2Fe‘3 + 2H20
When either of the plienantbrolines is added to a solution containing iron(I1) and hydrogen peroxide, the color developed depends on the excess of iron(I1) present. The follon ing relationship is applicable: A = ab(C1 - 0.5 C2), where A is absorbance, a is molar absorptivity of the iron(I1) complex, b is cell thickness, C1 is the original molar concentration of iron(II), and Cp is the molar concentration of the hydrogen peroxide. Because the molar ratio of hydrogen peroxide to iron is 0.5 and the AC term must be expressed in terms of the molar concentration of iron, the factor, 0.5, must acconipany the CPterm. It can be seen from this expression that to determine the hydrogen peroxide concentration, the concentration of iron(I1) must be knon-n. This necessitates a standardization of the iron(I1) solution. Furthermore, it has been found experimentally that the concentration of excess of iron(II), as given by the expression [C, - 0.5 C,] cannot exceed 0.03 nig. per ml. \\-hen 1,lO-phenantliroline is used. A large excess of iron(I1) will produce a color too optical1~-dense t o be measured
Table II. Determination of Hydrogen Peroxide Using 1,lO-Phenanthroline [Concentration (calcd.) 1.94 X Concn., AA, at X 10-5 Error, Yo. 510 M p (Exptl.) X lo-’ 1 0.1118 2.02 +8 2 3
4 5 6
7 8 9 10
0.1079 0.1057 0.1118 0.3090 0.1085 0.1107 0.1101 0.1079 0.1085
1.94 0 -3 1.91 2.02 +8 1.96 +2 1.96 1 2 1.99 i 5 1.98 $4 1.94 0 1.96 $2 Mean 1.97 X 10-6M Error = 1.670 u = 3.5 X lo-’, or 1.8%
Table Ill. Determination of Hydrogen Peroxide Using Bathophenanthroline [Concentration (calcd.) 1.94 X Concn.. AA, a t X 10-A Error, Yo. 533 Mp (Exptl.) X 10-8
4 3
6
7 8 9
10
118 *
0.0215 0.0209 0.0214 0.0223 0.0209 0.0218 0.0214 0,0227 0.0218 0,0205
1.91 1.88 1.91 1.99 1.88 1.94 1.91 2.03 1.94 1.83
-3 -6 -3 +5 -6
0 -3 +9 0 -11 Mean = 1.92 X Error = 2.47, u = 5.3 X 10-8, or 2.8%
ANALYTICAL CHEMISTRY
accurately when the color forming reagent is added. Consequently, if the hydrogen peroxide concentration were changed by a small increment, a corresponding change in the iron(I1) concentration would be necessary. However, two hypothetical relationships can be formulated: ,41 ab (Ci - 0.5 C,) AP = ab (61- 0.5 C,)
(1) (2)
I n these expressions -Il,4 2 , a, b, and Cl h a r e the same connotations as before, and Ca and Ca denote different hydrogen peroxide concentrations. If Equation 2 is subtracted from Equation 1, and appropriate simplification is made, Equation 3 is obtained. 0.5 Cs - 0.5 C2 = ‘41 - Az/a
(3)
If C, is made to equal zero, Equation 4 results. 0 5 C3 = A1
- -&/a, C
or 2(Ai - A ) / a
=
(4)
Equation 4 is especially useful because standardization of the iron(I1) solution is unnecessary, the specific amount of original iron(I1) solution used is not critical, and a differential spectrophotometric determination requires only one absorbance measurement. Hence, AI - .42 may be read directly by using a n iroii(I1) solution of final concentration C1 and an excess of colorforming reagent in the sample cell, and by using a solution of iron(I1) concentration of Cl (prior to oxidation), the unknown hydrogen peroxide, and an excess of color-forming reagent in the reference cell. Comparisons of experimental and calculated results using 1.10-phenanthroline and bathophenanthroline are given in Tables I1 and 111, respectively. Equation 3 may be used advantageously when higher concentrations of hydrogen peroxide are to be determined. If volumes of hydrogen peroxide solution VI and V z are used in preparing colored solutions of identical volume, Equation 5 is applicable. (?/a) ( A ,
- A?) = c1 - C? = KV, - V2) Jf/V/I
(5)
In Equation 5, n/r is the molar hydrogen peroxide concentration and V , is the final volume of colored solution. EFFECT
OF SOLUTION VARIABLES USING 1,lO-PHENANTHROLINE
Iron(I1) and Hydrogen Peroxide Concentration. il wide range of concentrations of hydrogen peroxide and iron(I1; may be used, if iron(I1) is in excess by not more than 0.03 mg. per nil. When the general single reading method is used, as suggested by Equation 5 , hydrogen peroxide concentrations in the 0.1- t o 2.5-p.p.m. range can be determined (Table 11).
A plot of dl - A 2 us. p.p.m. of hydrogen peroxide is linear with this range. Higher concentrations of hydrogen peroxide may be determined using the differential spectrophotometric method. Data for hydrogen peroxide concentrations exceeding 2.5 p.p.m. are not included because existing colorimetric methods are adequate for these higher concentration ranges. The absorption spectrum of the iron(I1)-1,lO-phenanthroline system exhibits maximum absorbance a t 510 nip. The molar absorptivity of the complex a t 510 nip has been reported to be 11,100 liters per mole-em. (13). pH. The maximum color is developed in pH range of 2 t o 9; a pH of 4 was used throughout this study. Diverse Ion Concentration. Sandell ( I O ) has indicated the ions which interfere in the determination of iron with 1,lO-phenanthroline. These interferences include cobalt(II), zinc, and copper(II), which should not exceed 10 p.p.m. Cadmium, beryllium, tin(IV), and phosphate ions must not exceed 50 p.p.m. The limits for merciirj-(II) and nickel(I1) are 1 and 2 p.p.m., respectively, Fluoride, chloride, and sulfate ions do not interfere in moderate amounts, The effect of these diverse ions was studied in relationship to the determination of hydrogen peroxide and found to be essentiallv the same, with the exception of cobalt (11) 15 hich interfered at concentrations lonrr than 1 p.p.m,, presumably because of its oxidation by the hydrogen peroxide. Some additional ions which interfere because of their ease of oxidation are mercury(I), tin(II), and ovalate ions. PROCEDURE USING 1,lO-PHENANTHROLINE
Preliminary Test. One preliminary test must be made to approximate the concentration of hydrogen peroxide. An aliquot of the hydrogen peroxide solution t o be determined is added t o a n excess of color-forming reagent and approximately 10 nil. of a sodium acetate-acetic acid buffer in a 5O-ni1. volumetric flask. After being diiuted almost t o volume iyith distilled ivater, the iron(I1) solution is titrated into a flask from a microburet until an absorbance suitable for determination is acquired by the solution. This amount of iron(I1) is used to calculate C1, and cited in Equation l. I n the recommended procedure, the hydrogen peroxide is added to the iron(11)solution prior to the addition of the color-forming reagent because of the preferential reaction of iron(I1) with 1,lO-phenanthroline. Procedure. Add from a microburet t o each of tmo 50-ml. volumetric flasks the required volume of iron(I1) solution t o give a concentration of C1. Add the desired volume of hydrogen peroxide solution to one flask. Add 0.1 ml. of 72% perchloric acid FTith 10 ml. of the sodium ace-
tate-acetic acid buffer and 5 ml. of the color forming reagent to both flasks. Dilute both flasks to the graduation mark. If more than one sample is to be analyzed, it is advisable to Fork with one sample a t a time. The sample(s) should stand for 15 minutes to allow the color to develop. The solution containing hydrogen peroxide is used in the reference cell and the other solution is used in the sample cell to determine the quantity AI - Aa, as given in Equation 5. The absorbance is measured at 510 mP. If higher concentrations of hydrogen peroxide are desired, the procedure can be modified slightly. After adding iron(I1) from a microburet to each of two 50-ml. volumetric flasks, add different volumes of the hydrogen peroxide solution-e.g., 1 and 1.5 m1.-to the flasks. Add 10 ml. of the buffer solution and the 1,lO-phenanthroline reagent and dilute to volume. The solution containing the least hydrogen peroxide is used in the sample cell. Checking Precision of 1,lO-Phenanthroline Method. Exactly 0.50 ml. of 0.194111 hydrogen peroxide solution was diluted t o 1 liter. This 9.70 X l O - 4 M solution was used in the subsequent investigation. The color was developed in the following manner. Add 2 ml. of the iron(I1) solution, 2 drops of concentrated sulfuric acid, 10 ml. of the hydrogen peroxide qolution, 10 ml. of the acetate buffer solution, and 10 ml. of the 1 , l O phenanthroline reagent to a 50-ml. volumetric flask, and dilute to volume. Allow this solution to stand 15 minutes for complete color development. This order of addition is recommended, and if more than one sample is to be analyzed, it is advisable to deveIop each color separately. The results obtained are shown in Table 11.
Effect of Solution Variables Using Bathophenanthroline. The solution variables are essentially the same as in the 1,lO-phenanthroline method. The iron(I1) concentration may not be in excess by more than 0.015 mg. per ml. when bathophenanthroline is used. Ethyl alcohol is used as a solvent because of the limited solubility of bathophenanthroline in aqueous solution. The molar absorptivity of the complex has been reported as 22,400 liters per mole-em. a t 533 mp ( I S ) . Diverse Ion Concentration. It was found that 100 p.p.m. of the following ions did not interfere: chloride, nitrate, acetate, sulfate, perchlorate, arsenate, nickel(II), zinc, cadmium, copper(II), mercury(II), titanium(IV), lead, bismuth, and tin(1V). Silver ions in excess of 30 p.p.m. causes a turbidity. Cobalt(I1) interferes because of formation of a yellow complex. PROCEDURE USING BATHOPHENANTHROLINE
This procedure is identical to the one using 1,lO-phenanthroline except that 95% ethyl alcohol is used for dilutions. The absorbance is measured a t 533 mM. Checking Precision of Method Using Bathophenanthroline. The color wasdeveloped in the follon-ing manner: Add 1 nil. of iron(I1) solution, 2 drops of concentrated sulfuric acid, 1 ml. of hydrogen peroxide solution, 20 ml. of the acetate buffer solution, and 5 ml. of the bathophenanthroline solution to a 50-ml. volumetric flask. Dilute t o volume with 95’% ethyl alcohol. Allow the solution to stand 20 minutes for
complete development of color. The results are shown in Table 111. SUMMARY
The proposed procedures for determining hydrogen peroxide are more sensitive than the peroxytitanic acid method because of the high molar absorptivities of the iron(I1) phenanthroline complexes. As indicated in Tables I1 and 111, to 10-6M solutions of hydrogen peroxide can be analyzed with satisfactory precision and accuracy. LITERATURE CITED
(1) Allen, Nelson, IND.ESG. CHEJI., ANAL.ED. 2, 55 (1930). (2) Bonet-Maury, P., Compt. rend. 218, 117 (1944). 1 3 ) Eisenberc. G. M.. ISD.ENG.CHEJI.. ANAL.ED.%, 327 (1943). (4) Erdmann, H., Seelich, F., Z. a n d Chem. 128, 303 (1948). (5) Hartmann, S., Glavind, S., d c t n Chem. Scand. 3, 954 (1949). (6) Isaacs, M. L. , J. Am. Chenz. Soc. 44, 1662 (1922). \
z
( 7 ) IlcCabe, S., Ind. Eng. Chem. 45, 111.1 (September 1953). (8) Miller, MacPherson, N.,Natl. Research Council Can. At. Energy Project Div. Rpsearch C R d 352 (N.R.C. KO. 1617). (9) Ownston. T. C. J., Rees, TI-. T., - --Analyst 75,’204 (1950). (10) Sandell, E. B., “Colorimetric Determination of Traces qf Metals,” 2nd ed., na.. 376-7, Interscience. Yew Tork. _ 1950. (11) Savage, J., Analyst 76, 224 (1951). (12) Schales, Otto, Ber. 71, 447 (1938). (13) Smith, G. F., Richter, F. P., “Phe\
,
nanthrolineand Substituted Phenanthroline Indicators,” G. Frederick Smith Chemical Co., Columbus, Ohio, 1944. RECEIVED for review May 1, 1958. Accepted August 4, 1958.
Polarographic Determination of Chlorate LOUIS MEITES and HENRY HOFSASS Polytechnic Institute o f Brooklyn, Brooklyn, N. Y. ,An investigation of the polarographic characteristics of chlorate in various mineral acid media has led to the development of a polarographic method for its determination, based on the rapid stoichiometric reaction between chlorate and excess ferrous iron in 3F hydrochloric acid. It is accurate and precise to about & l % . Chlorate solutions as dilute as 10-W can be analyzed.
D
the very positive value of the standard potential of the halfreaction ESPITE
C103-
+ 6 H + + 6e = + 3H20; E” = + 1.47 volt ( 4 )
C1-
chlorate ion is not reduced a t the dropping mercury electrode from alkaline, neutral, or moderately acidic solutions ( 2 , 12). This evidently reflects the existence of an extremely slow step in the reduction process. Consequently the polarographic determination of chlorate could only be accomplished by increasing the rate of the electroreduction (either by adding a catalyst or by using a strongly acidic supporting electrolyte) ,or by converting the chlorate into an equivalent amount of some other
substance which n-ould give rise t o a polarographic wave. The first of these approaches was employed by Koryta and Tanygl (S), who found that the catalytic current obtained in an acidic oxalate medium containing 10m,ll titanium(1V) was proportional to the chlorate concentration from 1 t o 15mX. This concentration of titanium(1T’) is so high that an accurate correction for its diffusion current would become extremely difficult in the analysis of chlorate solutions much more dilute than 1mM. This paper reports the results of investigations of both of these possible VOL. 31, NO. 1 , JANUARY 1959
119
