Direct Colorimetric Method for the Determination Of Chlorine Dioxide in Water H. W. HODGDEN' and
R. S. INGOLS
Georgia Institute o f Technology, Engineering Experiment Station, Atlanta, G a .
C
0.4
HLORIXE dioxide v,-as suggested as a sterilizing agent for water as early as 1900 by Berge ( 4 ) ,but it was not used on a plant scale until 1944. I t is now used to some extent in water treatment for controlling tastes and for the removal of manganese ( 6 ) ,and in the textile, m-ood pulp, and paper industries for bleaching. Methods currently used for the determination of the concentration of chlorine dioxide in water are basically the same as those used for the determination of hypochlorous acid and the chloramines. The relative merits of these methods of analysis have been discussed by Ingols ( 7 ) . Two of the available methodi (S, 6) are specific for chlorine dioxide but are indirect, while others ( 2 , 9, I O ) are direct techniques-ie., one may determine the concentration of chlorine dioxide in a pure solution-but the techniques do not differentiate chlorine dioxide from hypochlorous acid in a mixture of the two. It would be highly desirable, therefore, t o develop a direct specific method for the determination of chlorine dioxide in water. Studies by Ingols et al. (8) indicate that chlorine dioxide produces color when it is al-
0.3 U W
f 0.2
P Q
0.1
0 0.1 0.3 0.5 0.7 0.9 MOLAR RATIO OF TYROSINE TO CHLORINE DIOXIDE
Figure 2.
Effect of Increasing Tyrosine Concentration
Constant 1.2 p.p.m. chlorine dioxide concentration a t room temperature
Chlorine dioxide was generated from sodium chlorite with sulfuric acid. Chlorine-free, chlorine demand-free water was prepared by chlorinating a bicarbonate ion-buffered distilled water and then dechlorinating with ultraviolet radiation. The sodium chlorite was received from the Mathieson Alkali Works, Inc., and the tyrosine was purchased from the Eastman Kodak
co.
PREPARATION O F REAGENT BUFFER POC
520
400
440
WAVE LENGTH
I
560
(m-1
Figure 1. Photospectrograph of Chlorine Dioxide-Tyrosine Color Compound
Tyrosine (300 mg.) R-as dissolved in 100 ml. of O.L\- sodium hydroxide, and then diluted t o 1 liter with distilled water containing 97 ml. of concentrated acetic acid and 150 grams of sodium acetate. Reagent buffer must yield a final pH of 4.5 t o 4.6.
Taken with a B e c k m a n DU a t 5-mr intervals
lowed t o react with tyrosine, as was shown earlier by Aloy and Rabault ( I ) . This paper presents the optimum pH and reagent concentrations for the technique and an evaluation of reproducibility, sensitivity, and stability in the chlorine dioxide-tyrosine color reaction. METHOD O F RESEARCH
Chlorine dioxide was added t o a chlorine-free, chlorine demandfree water to give the desired concentration; this was determined by the method of Palin ( I O ) . Tyrosine reagent and a buffer for pH control were added t o a portion of the sample and the absorbance of the chlorine dioxide-tyrosine mixture was determined by a Photovolt colorimeter Model 450 with a 150mm. light path and a B-490 filter with a maximum transmittance at 490 mp. The choice of this filter is based on the spectrograph of Figure 1. It was found that cobalt nitrate gave a similar spectral absorption picture and that 140 p.p.m. of cobalt nitrate was equivalent t o 0.1 p.p.m. of chlorine dioxide as chlorine. Cobalt nitrate can be used as a permanent color standard for field work with the chlorine dioxide-tyrosine reaction technique. Studies were conducted a t temperatures of 22' to 24' C. and 4' t o s o C. 1
Present address, Florida State Board of Health, Jacksonville, Fla.
RESULTS
The data as presented in Figure 2 indicate that the absorbance of the chlorine dioxide-tyrosine compound reaches a maximum at approximately 0.5 mole of tyrosine to 1 mole of chlorine dioxide with no further change in absorbance between 0.5 and 0.8 mole of tyrosine t o 1 mole of chlorine dioxide. Higher concentrations of tyrosine cause no change in the color concentration. The data as presented in Figure 3 indicate that there is an increase in absorbance with a n increase of chlorine diovide in ratios up to 2.0 moles of chlorine diovide to 1 mole of tyrosine that is proportional t o the increase in concentration. From ratios ranging from 2.0 t o 3.3 moles of chlorine dioxide to 1 mole of tyro-ine there is a further increase in absorbance or color but it IS not in proportion t o the increase in chlorine dioxide concentration. At ratios ranging from 3.3 to 8 moles of chlorine dioxide to 1 mole of tyrosine, color is formed very rapidly but the colored compound is further oxidized by the excess chlorine dioxide to a colorless compound. The nature of chemical reaction is not knonm, but probably the ring is broken and a simpler substituted alanine is formed. It is important, therefore, that sufficient tyrosine reagent be present when this method is used for the determination of chlorine dioxide. 1224
1225
V O L U M E 26, NO. 7, J U L Y 1 9 5 4 The apparent equation of the chlorine dioxide-tyrosine reaction which produces color is: H H C=C 2C102
/
+ HOC,\
H 0
H
irOH
\
C-C-C-
//
+
2C10;
+0
/
1 3
T’iris H y ~ i o c h l o r o u s.Icid. 2 ti
0.25 0.19 0.13
.4hscrLnnce 0.01 0 13 0 12 0.01 0.01 0 10
.
0.20 0.20 0.14
1.0
0.8 0.6
Tyro-ine Reagent, 111. 1 2 3
1
Chlorine Dioxide, P.P. M
HH
H H C=C C
!
H S
%-C’ H H
Table I. Absorbance of Tyrosine Reagent with Chlorine Dioxide with and without Hypochlorous Acid
0.23 0 19 0.13
1 3 P,P.AI. 7.0 ____
0.0 0.0 0.0
0.0 0.0 0.0
Extinction coefficient640.
H H O
\ I! C = C-C-COH
lngole et al. (S) reported that chlorine dioxide does not react
with the amino nitrogen atom of simple amino acid, rather, it oxidizes the benzene of the phenol ring. Hypochlorous acid, however, reacts with the nitrogen atom of amino acids and may also react with the organic portion of the acid but by substitution rather than oxidation. The data presented i n Figure 4 indicate that a pH of 1.6 gives the optimum absorbance in the chlorine dioxide-tyrosine reaction, while within the pH range of 4.3 to 5.2 only slightly less color is produced. ThuF, within these pH values one ran detrrmine chlorine diovide by this method of analysis. The data on reproducibility of this method of chlorine dioxide determination, presented in Figure 5 , indicate that at the very low concentrations of chlorine dioxide the coefficient of variation (C‘x = x ’X) shows that there is approximately a 12% variation
.I2
+
p
.IO
u_
! >
-5
.M
5
4
>
.04
.02 0
0.5
1.0 p+m.
1.5 2.0 2.5 CHLORINE DIOXIDE
3.0
Figure 5. Relationship between Chlorine Dioxide Concentration and Best Reproducibility for 10 Replicates Variability coefficient = ‘rat constant pH, X temperature, and time of contact
MOLAR RATIO CHLORINE DIOXIDE TO TYROSINE
Figure 3. Effect of Increasing Chlorine Dioxide Concentration With a constant 3.0 p.p.m. tyrosine concentration in developing color at room temperature
TIME MINUTES
Figure 6. Rate of Development and Stability for Color With 1.0 p.p.m. chlorine dioxide at pH 4.6 and room temperature
‘
45
5.0
5.5
60
PH
Figure 4.
Effect of Varying pH between 4 and 6 in Color Formation
Rith 0.76 p.p.m. chlorine dioxide at room temperature with 10 minutes’ contest
in reproducibility even under the most carefully controlled conditions. At the higher concentrations of chlorine dioxide the probable error is 2 to 3% a t best. A study was made to determine whether free chlorine would increase the color of tyrosine and chlorine dioxide. The results, shown in Table I, indicate not only that hypochlorous acid doe8 not increase the concentration of color, but that as the relative concentration of the hypochlorous acid increases, it competes for the tyrosine and prevents the formation of the colored compound unless an adequate amount of the tyrosine is present. Because an oxidized manganese ion can react with o-tolidine a t pH 2.0 to give a false “chlorine” residual, it was considered possible that the oxidized manganese ions could produce a colored tyrosine product. A natural water containing manganese was used with and without both chlorine and chlorine dioxide as the
1226
ANALYTICAL
CHEMISTRY
warmed to 20' C. one should wait 8 to 10 minutes but not longer than 15 minutes to compare or measure the color formed.
sample for testing for chlorine dioxide with the tyrosine reagent. The chlorine plus manganese either in natural water or in a bicarbonate solution gives no color with the tyrosine reagent. The chlorine dioxide oxidizes the manganous ions in the bicarbonate solution of natural water instantly, causing a dark brolvn color to form; when tyrosine reagent is added to the manganic solution or suspension after treatment with chlorine dioxide, no tyrosinechlorine dioxide color develops. The data of Figure 6 were obtained a t room temperature or about 25" C. When the temperature of the chlorine diolide solution was lowered to 4' C., 80 minutes were required to obtain the maximum color intensity.
CONCLUSIONS
Tyrosine is selective for chlorine diouide, producing a color with which there is no interference from hypochlorous acid, chloramines, and manganese. The method for the determination of chlorine dioxide is simple and rapid. The reproducibility is adequate for higher concentrations. The sensitivity is poor for the chlorine dioxide Concentrations less than 0.2 p.p.m. sometimes used in water treatment. LITERATURE C I T E D
Aloy, XI. A1 , and Rabault, C., Bull. soc. chzm. Paris, Ser. 4,
RECOMMENDATIONS
111,391 (1908). Am. Public Health Assoc., Xew York, "Standard AIethodn for the Examination of Water and Sewage," 9th ed., 1946. Aston, R. N., J . A m . Wuter Works Assoc , 42, 151 (1950). Rerge, XI. A., MBm. sot. ing. civzls France, V 1900, Part I, B 475. Haller, J. F., and Listek. S. C., AXLL.CHEM.,20, 639 (1949). Harlock, C. R., Water & Sewage Works, 100, 74 (1953). Ingols. R. S., J . Inst. Water Engrs., 4, 581 (1950). Ingols, R. S.,Wyckoff, H. A., Kethley, T. .I.,Hodgden, H. W., Fincher, E., Hildebrand, J. C., and Mandel, J. E., Ind. Eng. Chem., 45,998 (1953). Marks, H. D., Williams, D. B., and Glasgow, G. G., J . Am. Wuter Works Assoc., 43, 201 (1951). Palin, A4.T., J . Inst. Water Engrs., 3, 100 (1949).
I t is recommended that 2 ml. of reagent be used per 100-ml. sample for concentrations up to 2.5 p.p.m. of chlorine dioxide plus hypochlorous acid and that with higher concentrations, the sample be diluted below 2.5 p.p.m. or proportionately more reagent be used. Permanent cobalt nitrate standards can he prepared for comparison of color produced in the chlorine dioxidetyrosine reaction. I t is recommended that cobalt nitrate standards contain 140 p.p.m. of cobalt nitrate for every 0.1 p.p,m. of chlorine dioxide. Because in the chlorine dioxide-tyrosine reaction the maximum amount of color is produced to 6 in 8 minutes at 20" C. Ivhile beyond 15 minutes the color begins to fade, after the solution is
RECEIVED for review September 17, 19.53. Accepted March 18, 1954. Investigations supported in part by a research grant from the National Institutes of Health.
Detection of Bismuth by Dithizone in Molten Naphthalene JACK K. CARLTON and WALTER C. BRADBURY Institute o f Science and Technology, University o f Arkansas, Fayetteville, Ark.
T
HE organic reagent, dithizone (diphenylthiocarbazone), is well known for itR use in the detection and determination of certain metal ions (2). The reagent is commonly employed in a chloroform or carbon tetrachloride solution and is used as an extraction medium for the desired metal ions. I n applying the reagent, selectivity is attained by masking the interfering ions with appropriate complexing agents, by the careful adjustment of pH, or by a combination of these methods. I n certain cases double extractions have proved advantageous; the metal ions are extracted into the dithizone-chloroform medium and the organic phase is then extracted by an aqueous solution the pH of which has been adjusted to favor the solubility of the desired metal dithizonate. Feigl and Baumfeld ( 1 ) found that several metsls foinied colored complexes in molten 8-quinolinol and have suggested this as a method of detection for several of them. West and Granatelli (3)studied the reaction of metal salts with molten 8-quinolinol microscopically and have established that the characteristic crystals formed by a number of cations and anions offer an extremely sensitive method of detecting them. During an investigation of various reactions in nonaqueous media the authors found that a solution of dithiaone in molten naphthalene reacted v-ith bismuth salts very rapidly to yield a brilliant red color. Bismuth concentrations in the range of 0.004 y are easily detectable. Reactions of the dithizone-naphthalene reagent with other metal ions and the nature of interferences and their masking were studied. REAGENTS
Dithizone, Matheson Co., a 0.025% solution in Baker's naphthalene.
6.p.
Bismuth chloride, J. T. Baker Chemical Co., prepared in 1 . O J I hydrochloric acid to contain 1007 per drop. Dilutions were made from this stock solution. Reagent grade chemicals were used in the interference studies and nere made up to contain 5007 per drop and were used in this concentration. acid was added where needed to retain hydrolyzable ions in solution. EXPERIMENTAL
Because of the intense color of dithizone, maximum sensitivity could not he obtained using this reagent undiluted in the molten state. In addition, its melting point is relatively high and its stability is lowered at higher temperatures. Consequently, naphthalene ivas selected as an inert, low melting solvent for the reagent. The reagent solution was prepared by dissolving 16 nig. of dithizone in 75 ml. of chloroform, mixing with 66 grams of naphthalene, and finally evaporating the chloroform from the mixture. Dilutions of the stock bismuth chloride solution were made to establish the limit of identification of this ion. One drop of the test solution was evaporated on a spot plate previously heated to about 90" C. and a few milligrams of the reagent were added. The red color of the bismuth dithizonate was clearly disrerned a t a concentration of 0.0047 of bismuth. Limits of identification of other metal ions Rere determined following the same procedure. Observations of the reactions between various cations and the reagent are listed in Table I. RIany of these gave salts analogous to those obtained employing the chloroform solution of dithizone, while others vary considerably. In some cases the color changes required long periods of time and relatively large concentrations of the metal ion. Cadmium, tin, mercury, zinc. and silver gave almost instantaneous reactions.
