Determination of Ultramicro Quantities of Manganese by Catalytic Oxidation of Alizarin S by Hydrogen Peroxide T. J. Janjic, G . A. Milovanovic, and M. B. Celap Chemical Institute, Faculty of Sciences, University of Belgrade, Belgrade, Yugoslavia To utilize the oxidation reaction of alizarin S by hydrogen peroxide for determining ultramicro quantities of manganese, which catalyzes it, the kinetics of this reaction was examined. Equations for the kinetics of the catalytic and noncatalytic reaction were developed, the corresponding rate constants were calculated, and the appropriate energies of activation were determined. A method for determining ultramicro quantities of manganese was developed, using the method of tangents, the differential method, and a modified simultaneous comparison method, to determine manganese in concentrations from 0.30 x to 56.1 x wg per ml. Finally, the influence of foreign ions on the accuracy of the results was investigated.
TRACEDETERMINATION OF manganese by applying catalytic reactions was the subject of several authors. Shiokawa and Suzuki ( I ) found that the rate of disintegration of hydrogen peroxide is proportional to the concentration of manganese in the solution, and utilized this reaction to determine quantities of manganese between 20 and 100 pg. Blank and Voronova ( 2 ) used the catalytic oxidation of Eriochrome black T by hydrogen peroxide for trace determination of and in water manganese in salts and acids down to down to 5 X loFg%with an error of 1 5 %. Catalytic oxidations of some organic compounds-g-phenetidine (3),p-anizidine ( 4 ) , o-dianizidine ( 4 ) , p-toluylenediamine ( 4 ) , and toluidine (4)-by potassium periodate was also applied for trace determination of manganese. The sensitivity of these reactions is 1 X lW3pg of Mn per ml. Sensitivities of the oxidation reactions of dimethylaniline ( 4 ) and diethylaniline and 1 X pg of Mn per ml, re( 4 ) are greater (1 X spectively). For trace determination of manganese in blood serum, catalytic oxidation of leucomalachite green by sodium periodate (5) was used. The normal manganese content in the serum is between 0.36 and 0.90 X low3pg per ml. Finally, the catalytic oxidation reaction between potassium permanganate and oxalic acid was used for trace determination of manganese (6). The sensitivity of this method is 0.2 Babkin (7) used pg of Mn per ml with an error of this method for the trace determination of manganese in sulfates of different metals with an error of i10 In a recently published paper (8), Janjic established that manganese catalyzes the oxidation of alizarin S by hydrogen peroxide in a solution of ammonium carbonate. In the present study, we examined the kinetics of this reaction and applied it to the determination of ultramicro quantities of manganese.
+3z.
z.
(1) T. Shiokawa and S.Suzuki, J. Cliem. SOC.Japan, 72, 12 (1951). (2) A. B. Blank and A. Ja. Voronova, Zavodsk. Lab., 31, 1299 (1956). (3) L. Szebelledy and M. Bartfay, 2.Anal. Cliern., 106, 408 (1936). (4) J. Bognar, MTA Kern. Oszt. kozl., 7, 335 (1958). (5) A. Fernandez, C . Sobel, and S . Jakobs, ANAL.CHEM., 35, 1721 (1963). ( 6 ) I. M. Korenman and A. N. Lebedeva, Trudi PO khimii i khim. techriot., Gorkii, No. 2, 357 (1962). (7) M. P. Babkin, 211. Atlalit. Khim., 17,256 (1962). (8) H. Weisz and T. J. Janjic, Z . Anal. Chem., 227, 1 (1967).
Figure 1. Test tube with container for hydrogen peroxide
EXPERIMENTAL
During the oxidation of alizarin S by hydrogen peroxide the solution gradually loses its color, so that one can observe the progress of’the reaction spectrophotometrically by measuring the absorbance of the solution at a wavelength of 335 mp every minute for 10 minutes from the reaction start. We used the Beckman D U quartz spectrophotometer with an auxiliary thermostatic apparatus and 1-cm cells. The solutions were thermostated at 20” + 0.1 “C before the beginning of the reaction. A radiometer 4 pH-meter was used for measuring the pH values of the solutions. The solutions of manganous sulfate (1.8 X lO-4M) and alizarin S (1.5 X 10-3M) were prepared from recrystallized analytical reagent grade reagents. To 1 ml of the manganous sulfate solution was added 1 ml of 0.1N H&O4 and the solution was diluted to 100 ml. Ammonium carbonate was purified by sublimation and its carbon dioxide content was determined by the indirect method (9). The ammonium carbonate solution was 1.8Nand its pH was 9.35. The hydrogen peroxide solution was 9.8M and its concentration was determined by the permanganate method. Redistilled water was used for preparing these solutions. To determine the order of the catalytic and noncatalytic oxidation of alizarin S by hydrogen peroxide, we investigated the dependence of the reaction rates on the concentrations of components which participate in these reactions. The influence of the hydrogen ion concentration on the rate of catalytic and noncatalytic reactions was investigated by observing the reactions at different pH values. The corresponding buffer solutions were prepared by adding different volumes of 1 M sodium carbonate solution to solutions of 1M sodium bicarbonate. Manganese was determined in test tubes where measured volumes of manganous sulfate, alizarin S, and ammonium carbonate solutions were diluted to 5 ml. The hydrogen peroxide solution was added to the test tube solution at the start of the reaction by means of a glass container attached to the upper part of the test tube (Figure l), by shaking the tube (the modified simultaneous comparison method). The reaction was started simultaneously in 13 test tubes, 10 of which contained different quantities of manganous sulfate standard solution. In the other three tubes, different amounts of the examined solution were present. The determination (9) F. P. Treadwell, “Manuel de Chimie Analytique,” Vol. 11, “Analyse Quantitative,”Dunod, Paris, 1943, p. 350.
ANALYTICAL CHEMISTRY, VOL. 42, NO. 1, JANUARY 1970
27
Table I. Reaction Rate Constants for Catalytic and Noncatalytic Reactions f = 20 f 0.1 OC
x
[HCOI-] X 10 Catalytic Noncatalytic moles/l moles/l 1.80 0.13 9.80 1.00 1.30 0.18 9.80 0.96 0.92 0.22 9.80 0.93 0.31 9.80 0.88 0.50 0.25 3.60" 9.80 0.83 0.30 0.35 3.605 9.80 0.78 0.81 0.47 3.60" 9.80 1.60 1.61 0.89 3.60" 9.80 3.20 9.80 4.80 1.20 1.60 3.60 5.88 1.50 3.60 7.80 1.60 1.14 1.60 3.60 15.60 0.65 1.60 3.60 19.60 0.61 1.60 7.20 9.80 1.69 1.60 1.80 9.80 0.54 Mean value. K = 1.16 A 0.05 X lolo; KO = 0.43 & 0.02 X We. 0 Manganese concentration by determination of tga of catalytic reaction. tga
[Mne+]X 108 moles/l 3.60" 3.m 3.60"
102
[H~OZ] X loa
[H+] X 1O1O moles/l 14.80 7.60 3.71 2.23 1.40 1.10 2.23 2.23 2.23 2.23 2.23 2.23 2.23 2.23 2.23
K x 10-lo 13/2m01e-3/9 min-1 1.27 1.33 1.40
1.38 1.04 0.91 0.93
KO X lo6 1l/?mole-1/9 min-1 0.49 0.51 0.45 0.52 0.36 0.44 0.44
0.41 0.37
1.02 1.03 1.18 1.38 0.92 1.23
The kinetic equation for the noncatalytic reaction under the same conditions may be written as follows:
01
I
#
*
lo 2
4
l2
[MnSOdxl# m o l l 1
6
Figure 2. Dependence of tg a on manganese concentration in oxidation of alizarin S by hydrogen peroxide Initial concentrations. Alizarin S = 6.2 X 1C6M , HIOn = 9.8 X 10-2 M , (NH&COs = 0.18 M , pH = 9.35, t = 20" -f 0.1'C
On the basis of these equations the rate constants for the catalytic and noncatalytic reactions were calculated (Table I). The influence of temperature on the reaction rate was investigated. The linear relation between the logarithm of the rate constant and the reciprocal of the absolute temperature was found for the catalytic as well as the noncatalytic reaction. The activation energies were found to be 10.31 kcal per mole for the catalytic reaction and 13.71 kcal per mole for the noncatalytic reaction. The minimum concentration of manganese which could be determined by this method may be calculated by the method given by Yatsimirskii (11):
On the basis of our kinetic investigation we formulated a kinetic equation for the oxidation of alizarin S by hydrogen peroxide in the presence of ammonium carbonate and with managese as a catalyst, provided the concentrations of hydrogen peroxide are higher than 5.88 X 10-2M:
where K and KOare the rate constants for the catalytic and noncatalytic reactions. As can be seen, it would be more efficient to determine manganese from solutions of lower pH values. However, COZ is liberated from solution at pH under 8.3, which induces changes in the solution composition. Because the standard solutions of manganese had to be acidic, and considering the acidic properties of hydrogen peroxide, we decided to work under less efficient conditions-Le., with an ammonium carbonate solution (pH 9.35). From the equation it can also be seen that it would be most efficient to operate with lower concentrations of hydrogen peroxide, but because we were attaining linear relations between the logarithm of absorbance and time only at concentrations higher than 5.88 X 10-2M, we made all our tests at 9.80 X 10-2M. By entering these values in the upper equation we pg find Cmin= 0.17 X lo-* mole per liter, or 0.94 X per ml.
(10) H. Weisz, Mikrochim. Acta ( Wien), 1954, 460, 785.
(11) K. B. Yatsimirskii, Zh. Analit. Khim., 10, 299 (1955).
was achieved by the method described by Weisz as ring colorimetry (IO). When the tangents and differential methods were used, the solution was poured into a cell and the absorbance was measured spectrophotometrically each minute. The concentrations of the test solutions at the beginning of 0.18, and between the reaction were: 6.20 X IOw5, 9.8 X 0.36 and 17.8 X lo-* mole per liter, for alizarin S, hydrogen peroxide, ammonium carbonate, and manganese, respectively. RESULTS AND DISCUSSION
28
0
ANALYTICAL CHEMISTRY, VOL. 42, NO, 1, JANUARY 1970
~~
A 12
IO
-
Table 11. Trace Determination of Manganese by Kinetic Methods
-
Concentration, pg/ml X lo3 Actual Found
Method Tangents
8-
-
Ne x P
4 6 -
Differential L-
3.60 3.60 3.60 5.60 5.60 5.60 0.30 0.30 0.30 0.88
2..
0
I
0
0.80 0.80 0.80
1
2
3
I
1
5
Simultaneous comparison
I
6 [MnSO&] xl$m?I/l c
On the basis of the investigations described, we were able to use the oxidation of alizarin S by hydrogen peroxide for the trace determination of ultramicro quantities of manganese by kinetic methods. The method of tangents (J2), the differential method (J3), and the modified simultaneous comparison method (14) were applied. The calibration plots are shown on Figure 2 (tangents method) and Figure 3 (differential method). Results are given in Table 11. The application of the oxidation reaction of alizarin S by hydrogen peroxide allows the determination of manganese in (12) K. B. Yatsimirskii, “Kineticheskie Metodi Analiza,” 11 Izd., Izdatelstvo “Khima,” Moscow, 1967, p. 55. (13) Zbid.,p. 64. (14) J. Bognar, Mikrochim. Acta, 1963, 801.
0.88 0.88 1.76 1.76 1.76 56.10 56.10 56.10
0.80 0.80
0.74 3.60 3.50 3.54 5.60 5.20 5.06 0.34 0.30 O . 30 0.90
Standard deviation of average
x
103
10.02 k0.05 k0.30 10.01 1-0.04
0.90
0.86 1.76 1.72 1.76 56.20 56.00 55.30
=tO.Ol
i2.10
concentrations from 0.30 X lopa to 56.1 X pg per ml while the smallest quantities were determined by the differential method with the highest degree of accuracy. The influence of other ions on the accuracy of the method was tested at the end. Table I11 shows that the presence of most of the ions investigated (Ca2+,Mg2+,Cd2+,Ni2+,C O ~ + , Zn2+, Pb2+, Bi3+, and Fe3+) decelerates the reaction only at concentrations 1000 times higher than the manganese concentration. Potassium, copper, tartrate, and oxalate ions in higher concentrations accelerate the reaction, while chloride, nitrate, phosphate, and sulfate ions do not influence it, even when present in a 2.5 X lo5to 1 ratio. RECEIVED for review June 23, 1969. Accepted September 8, 1969.
ANALYTICAL CHEMISTRY, VOL. 42, NO. 1, JANUARY 1970
e
29
