tioned previously, traces of Li in the base mix necessitated a blank correction which affected the accuracy of the Li determinations. Our analyses indicate the Li content of W-1 to be within the range 10 to 12 p.p.m., which may be compared with the recommended value of 12 p.p.m. ( 7 ) . For our quantitative work, we have used W-1 as a primary standard, adopt,ing the recommended value. To test the accuracy of the method further, rubidium was determined independently by x-ray fluorescence in some dolerites. For the x-ray determinations, pure rock powders vere briquetted as described by Baird (6) and analyzed in a Phillips PW 1540 vacuum spectro-
graph, using a molybdenum target tube (48 kv., 20 ma.), a topaz analyzing crystal, and pulse height analysis. Results were calculated according to the method of Reynolds ( 9 ) )using the rock standard G-1 (7), containing 220 p.p.m, of Rb, as reference standard. The results for this test are listed in Table 111; there is good agreement between the values obtained by the two methods. ACKNOWLEDGMENT
The authors express their gratitude to the C.S.I.R. (Pretoria) for its financial support and to L. H. Bhrens, Geochemistry Department, University of Cape Town, for helpful discussions.
LITERATURE CITED
(1) Ahrens, L. H., Taylor, S.R., “Spectro-
chemical Analysis,” 2nd ed., p. 75, Pergamon Press, New York, 1962. (2) Ibid., pp. 114-16. (3) Ibid., pp. 159-61. (4) Ibid., p. 175. (5) Annell, C., U. S. Geol. Survey, Prof. Paper 501 B, B 148-51 (1964). (6) Baird, A. K., iVoreZco Reptr. 8, 108 (1961). (7) Fleischer, M., Stevens, R. E., Geochim. Cosmochim. Acta 26, 525 (1962). ( 8 ) Heier. K. S.. Adams. J. A. S.. Phws. \----,.
faylor, S. R., Xature 205, 34 (1965).
RECEIVEDfor review May 9, 1966. Accepted August 29, 1966.
Spectrophotometric Determination of Chlorine Dioxide with Acid Chrome Violet K WlLLY MASSCHELEIN Service laboratoires, Compagnie lntercornmunale Bruxelloise des Eaux, Brussels, Belgium
b
The decrease in absorbance at
550 mp of 1,5-bis-(4-methylphenylamino 2 sodium sulfonate) 9,lO-
- -
-
anthraquinone (acid Chrome Violet K) enables the direct spectrophotometric determination of chlorine dioxide in aqueous solution. In a NHdCI-NHs buffer of pH 8.1 to 8.4, no interference of active chlorine, hypochlorites, chlorites, chlorates, aluminum, and fluoride, present individually or simultaneously, has been observed. The standard deviation of the method is 0.04 mg. of ClOz per liter. The method has been established for use in water treated by chlorine dioxide, but appears promising for research work on chlorine dioxide and application in other technical fields.
C
dioxide decolorizes many organic natural pigments and is widely used in bleaching. The purpose of the research reported here was to find an organic dye which is selectively decolorized by aqueous chlorine dioxide and to apply the reaction to the direct analytical determination of the latter. To be useful in water treatment practice, the method must present the following characteristics: HLORIXE
The determination should be capable of being made with ordinary equipment and should require minimum time and operations. The method should be applicable t o potable water and inorganic compounds normally found therein should not interfefe. Compounds to be particu-
larly considered for their interference characteristics are chlorites, chlorates, chlorine, chloramines, and any other active chlorine compound. A residual concentration of 0.2 to 0.25 mg. of CIOz per liter represents the minimum safety limit for the permanent bactericidal efficiency required for disinfection in transportation and preservation of palatable waters (7). To avoid taste and odor of chlorine dioxide, the residual dose must be less than 0.5 to 0.6 mg. of ClOz per liter (3, 4). Consequently, the method must be precise and accurate in the range of 0 t o 0.6 mg. of CIOz per liter. Taking into account the conditions for efficient generation of ClOz from a NaC102-Cl2 mixture (5, 6 ) , the possible concentration ranges in stock solutions for water treatment are approximately 0 to 0.75 gram of ClOz per liter, 0.65 to 1.0 gram of Clz and 0 t o 0.75 gram of C l 0 ~ -per liter, with minor amounts of chlorides and chlorates. An analytical method for chlorine dioxide must account for such possible concentrations and the substances coexisting with the chlorine dioxide must not interfere. Previous methods are mostly indirect techniques which are unreliable when chlorine and chlorites may be present (6, 7, 9). For this reason, the use of chlorine dioxide in water treatment has been considered questionable (8). EXPERIMENTAL
Standard Solutions. Chlorine dioxide was prepared by well known procedures (6, 6) and the concentration
was tested immediately before and after its use. The iodine formed by iodide oxidation at neutral p H in 8 weight % phosphoric acid was always required t o be in the molar ratio 1 to 5 ( 5 ) . Chlorine, sodium chlorite, sodium hypochlorite, and calcium hypochlorite solutions were made in tap water and controlled iodometrically. Analytical grade sodium chlorate was weighed and dissolved in distilled water without further control. The tap water used in this work had the following composition: Resistivity. 1750 ohms/sq. cm./cm. (18’ C.) pH. 7.90 Dissolved solids (105” C.). 448 mg./l. Total silica. 14.8 mg./l. Chemical oxygen demand (KhIn04). 0.13 mg. 0 2 / 1 . Cationic content, mg./liter. Cat2 104.4; Mg+2, 18.9; Na+, 10.6; K+: 2.0. Fe, 0.007 Anionic content, mg./liter. C1-, 21.9; Sod-2, 55.9; HCOa-, 317; Koa-, 17.4 Acid Chrome Violet K stock solution was prepared by suspending 175 mg. (hlichrome No. 1047, Edward Gurr, London) in an aliquot of distilled water. To the suspension were added subsequently 20 mg. of chemically pure sodium hexametaphosphate, 48.5 grams of analytical grade ammonium chloride, and 1.6 grams of ammonia. The solution was finally diluted t o 1 liter with distilled water and set aside for 24 hours. When preserved in an amber bottle, the solution is useful a t least a month. After tenfold dilution with the water to be analyzed, the pH of the solution must be maintained between 8.1 and 8.4. With a 5-cm. cell, the absorbance VOL. 38, NO. 13, DECEMBER 1966
0
1839
.
Table 1
Determination of Chlorine Dioxide in Presence of Possible Interferences
AA x 103. Mg. C1. mg./liter (2108- as CIOz- as A = 550 mM. As CL As NaOCl As Ca(OC1); NaCIOa. mg./l. NaCIOz. mg./l. cell = 5 cm C102/l. found Watera C102. mg./l 0.78 ... ... 151 0.80 2.7 ... ... D 0.89 0.80 ... ... ... 173 ... 3.0 147 0.76 3.0 0.80 2.7 ... ... ... ... 155 0.80 2.7 ... ... ... 0.83 ... 163 0.84 ... ... ... 5.0 0.83 ... ... 153 0.79 ... 2.7 5.0 0.83 ... 270 1.39 ... ... ... 5.0 1.40 ... 262 1.35 2.7 ... ... 5.0 1.40 ... ... 339 1.75 ... 8.0 ... 1.70 1.79 ... 0.53 1.70 347 ... ... ... 0.53 1.67 ... 4.65 ... 5.0 1.70 324 0.53 322 1.66 8.0 4.65 5.0 ... 1.70 ... 409 2.11 2.7 ... ... ... 2.12 2.22 ... 431 5.0 ... ... ... 2.12 2.13 ... 2.7 5.0 ... ... 413 2.12 0.18 35 ... ... 0.05 0.5 0.19 ... T 34 0.18 ... 0.66 1.0 0.5 ... 0.19 0.66 39 0.20 1.32 ... 1.0 0.5 0.19 0.22 0.05 ... 43 ... ... ... 0.19 0.20 1.33 2.00 ... 1.0 39 ... 0.19 0.23 45 2.64 ... ... ... 1.5 0.19 0.27 52 0.53 ... ... ... ... 0.29 ... 0.28 54 0.93 ... 0.5 0.53 0.29 0.2 0.30 58 ... 0.93 0.5 0.29 ... 0.31 60 ... ... ... ... 0.5 0.29 ... 211 1.09 1.33 ... ... ... 1.03 ... 0.1 1.00 3.94 0.93 ... 1.0 1.03 ... 1.03 200 0.93 ... 1.0 1.03 ... ... 0.02 1.03 200 2.76 1.5 1.03 ... ... ... ... 1.36 264 2.67 1.38 0.4 0.93 ... 2.0 1.36 264 2.67 1.38 1.34 260 ... ... ... 0.93 2.0 1.38 ... 1.42 275 ... ... ... 2.0 1.38 0.2 70 0.36 ... ... ... 0.34 2.7 DF ... 1.0 0.2 68 0.35 ... 2.7 0.34 0.30 0.2 58 ... 0.93 ... 1.0 0.34 0.84 ... 0.2 163 2.7 ... ... 0.84 0.79 ... 0.2 1.0 153 ... 2.7 0.84 0.78 0.93 0.2 ... 1.0 151 ... 0.84 ... ... 0.2 66 0.34 0.34 2.7 ... TF 0.2 ... ... 2.0 76 0.39 0.34 2.7 0.38 0.2 1.86 ... 2.0 74 0.34 2.7 0.2 0.95 ... ... ... 184 0.94 2.7 ... 0.93 1.0 0.2 0.88 171 0.94 2.7 1.00 ... 1.86 3.0 0.2 194 ... 0.94 0.2 1.48 ... 1.33 287 2.7 ... 1.56 2.0 0.2 ... 1.58 1.33 306 ... 1.56 0.2 1.58 1.33 3.0 ... 306 ... 1.56 ... 0.2 101 0.52 ... ... 0.54 ... DA ... ... 0.2 103 0.53 2.7 ... 0.54 . . . 1.0 0.54 0.2 105 ... 0.54 2.7 1.04 ... 0.2 202 ... ... ... 1.08 1.10 ... ... 0.2 213 2.7 ... 1.08 1.0 1.10 ... ... 0.2 213 1.08 2.7 0.43 1.86 ... ... ... 83 2.7 0.39 TA 0.27 0.35 ... ... 3.0 68 ... 0.39 ... 0.44 ... ... 3.0 85 2.7 0.39 3.0 ... 207 0.27 1.07 2.7 ... 1.10 1.07 0.2 3.0 207 ... ... 1.10 2.7 1.71 0.2 ... 332 1.33 ... ... 1.68 DAF 1.74 ... 3.0 0.2 338 ... 2.7 1.68 1.64 1.0 0.2 318 1.33 ... 2.7 1.68 2.0 0.20 ... 0.2 39 ... ... 0.20 TAF 0.22 2.0 0.2 43 ... ... 2.7 0.20 2.0 0.18 1.86 ... 0.2 35 0.20 ... 0.20 2.0 38 1.33 0.2 ... ... 0.20 0.78 151 0.2 ... 1.86 ... 2.7 0.80 0.79 0.2 2.0 153 ... 1.86 2.7 0.80 0.85 165 1.33 2.0 0.2 ... ... 0.80 0.81 0.2 157 3.0 0.67 ... 0.80 2.7 1.23 238 2.0 ... ... ... 1.20 3.0 1.27 246 0.67 ... 3.0 ... 1.20 ... 1.20 233 3.0 0.67 ... ... 3.0 1.20 Tap water containing aluminum . TA . 0. D . Distilled water . DAF. Fluorided distilled water containing aluminum. T. Tap water . TAF . Fluorided tap water containing aluminum. DF . Fluorided distilled water . A A 103 = l o 3 (absorbance of blank dilution-absorbance of decolorized sample) TF. Fluorided tap water . DA. Distilled water containing aluminum
.
~
.
e
ANALYTICAL CHEMISTRY
I
.
.
duced subsequently. The analysis was performed under ordinary conditions that the stock solution is still useful. and the concentration found was comProcedure. STANDARDIZATION.pared with the amount introduced Twenty milliliters of the acid Chrome (Table I). Violet stock solution are introduced To test the method for interference of into a 200-ml. volunietric flask. A fluoride and aluminum, the ions were known aliquot of CIOz is added, takadded separately or together as NaF ing care t h a t it drops directly into and A1(NOJa. 9Hz0in amounts to ensure the reagent without running along the walls of the vessel. This prea concentration of 1 mg. of F- per liter caution is essential in order to avoid and 1 mg. of A1 per liter in the distilled loss of chlorine dioxide before it reacts water used for dilution. Experimentally with the dye. The solution is diluted fluorided tap water ( I ) , containing 1 to 200 ml. with either distilled or tap mg. of F- per liter, was used also and 1 water. The absorbance a t 550 mp mg. of A1 per liter was eventually introis recorded, using the dilution water duced. Known amounts of chlorine without any reagent for the adjustment dioxide were determined in such water of lOOyo transmittance. The absorb(Table I). ance of a blank dilution of the acid Chrome Violet without chlorine dioxide is always measured simultaneously. DISCUSSION The reaction takes place almost imIf the difference of absorbance bemediately and the absorbance is eonstant for a t least 30 minutes. The tween the blank solution and the parvalues of LA (absorbance of the blank tially decolorized dye solution is less solution minus absorbance of the dethan half of the value observed in the colorized sample) vary linearly with the blank solution, the method presents the concentration of chlorine dioxide, a t following characteristics: standard deleast when 4.4. is less than half of the viation, 0.04 mg. of CIOz per liter; absorbance observed for the blank solurange, 0 to 2.5 mg. of CIOz per liter in tion. ANALYSIS OF CIOz STOCKSOLUTIOKS. the final dilution. I n this range, the absorptivity on the base of CIOz is Chlorine dioxide in stock solutions for water treatment is determined in the 38,800 f 1500 liters per gram cm. The same manner as the standardization. sensitivity of the technique is 0.04 mg. The aliquot which reacts with the dye of CIOz per liter when 5-cm. cells are is such that the concentration of ClOz used with a Zeiss PMQ I1 spectrophoin the final dilution is less than 2.5 mg. tometer (8). per liter. I n the range 0 to 200 mg. per liter of ANALYSIS OF C102 RESIDUALS. For acid Chrome Violet in the stock solution, the determination of chlorine dioxide the use of other concentrations than residuals an aliquot of the acid Chrome that given here has no real influence on Violet solution is diluted ten times with the sample water. Blank dilution can the method. However, with higher conbe made either with distilled water or centrations, the precision of the spectrowith the sample water from which photometric readings can be less, and CIOn has been eliminated by the inwith much lower concentrations, the troduction of 5 mg. of phenol per liter. range of the method is limited. The second technique is preferred. The absorption band used presents a hypsochromic shift by the discoloration Interferences. By a procedure with CIOz. The wavelength of 550 mp identical with that for standardizaselected here is a compromise which tion, the acid Chrome Violet reagent corresponds to the maximum observed was allowed to react separately with in the presence of about 0.5 mg. of CIOz chlorine, hypochlorite (Na and Ca), chlorite, and chlorate. For concenper liter. Under the conditions described here, trations up to 10 mg. per liter in the 2 moles of chlorine dioxide react with 1 final solution, no interference was mole of acid Chrome Violet. This charobserved within 30 minutes for absorbance measurements at 550 mp. acteristic appears to be constant, probably stoichiometric. Local excess of Higher concentrations were not tested. chlorine dioxide is of no importance for When unbuffered with ammonium chlothe stoichiometry of the reaction and the ride-ammonia, chlorine slowly discolors dye may be partially diluted before the the dye. This reaction is completely avoided by the technique described here. reaction with chlorine dioxide. I n further examination of interferThis selective and constant reactivity of acid Chrome Violet K cannot be enences, the substances to be tested were tirely explained in view of what is known added first to the reagent and known about the reactivity of chlorine dioxide amounts of chlorine dioxide were introa t 550 mp is between 0.75 and 0.85. A check may thus be made t o be sure
with organic compounds. However, a selective attack of the anthraquinoid nucleus appears probable. NaOsS
This reaction is likely to be much faster than other possible reactions of functions still present in the already decolorized dye, and disproportionations of chlorine dioxide appear to be avoided. Standardization and application of the method proposed here are identical in distilled water and tap water. Because of the composition of tap water, the method is valuable for most drinking waters, and minor temporary changes in inorganic content can be neglected. As shown in Table I, fluoride and aluminum at 1mg. per liter introduce no change. Furthermore, no interference of active chlorine compounds, chlorite, and chlorate has been observed even a t concentrations much higher than the doses commonly present in water treatment. The method is useful for the determination of significant residuals of chlorine dioxide as well as for stock solutions and reactor operation control. The technique presents excellent possibilities for application in research work and use in technical fields other than water treatment. LITERATURE CITED
(1) Buydens, R., Tech. Eau (Brussels) 200, 33 (1963). (2) Davis, 0. L., “Statistical Methods in Research and Production,” Oliver and Boyd, London, 1961. (3) Draves, H. J., Public Works 79, 36 (1948). (4) Enger, M.,Gas Wasserfuch 101, 340 (1960). (5) Feuss, J. V., J . Am. Water Works Assoc. 56, 607 (1964). (6) Granstrom, XI. L., Lee, G. F., Ibid., 50, 1456 (1958). (7) Ingols, R. S., J . Inst. Water Eng. 4, 581 (1950). (8) Karge, H., 2. Anal. Chem. 200, 57 (1964). (9) Middlebrooks, E. J., Water Sewage Works 112, R.122 (1965).
RECEIVEDfor review June 3, 1966. Accepted August 8, 1966.
VOL. 38, NO. 13, DECEMBER 1966
1841
