670
ANALYTICAL CHEMISTRY
flame spectrophotometer. Reliable results can be obtained for sodium and Sample Sodium, P.P.M. Potassium, P.P.M. Calcium, P.P.M. potassium, while calcium can be deter(Rivers) Original Added Found Original Added Found Original Added Found mined with sufficient accuracv to war28(33) 10 41 10 13 57 (55) 10 69 1 rant application of the method for most 49(48) io 62 {Ej5) io 13 3o 10 67 68 2 3 6(9.7) 30 38 2(4) 30 32 routine work Radiation buffers have 50 57 50 54 50 90 4 been developed which serve to minimize 6 11’(9‘.9) 30 41 3 (3,‘5) 30 35 2f (31) 30 62 6 ... 50 61 ... 50 55 ,,. 50 83 interfering effects of diverse ions. The 1. Verdigris River concentrations of the ions sought are 2. Verdigris River 3. Spring River determined by reference to semiperma4. Spring River nent calibration curves. Small quanti5. Neosho River 6. Neoaho River ties of sample are sufficient and no Valuea in parenthesea, chemical analysis by U. 6. Geological Laboratory in Stillwater, Okla. chemical treatment of the samples is necessary. The calibrations as well BS the determinations can be done by an operator without extensive chemical or Analytical Determinations. Table V compares analytical deinstrumental experience. The development of a higher flame terminations made with the flame spectrophotometer to those temperature might permit the application of this method to magobtained with classical methods of chemical analysis. It can be nesium determinations as well. seen that the results obtained are in general agreement. In pracACKNOWLEDGMENT tically every instance the deviations between reported values and the experimental findings are within the limits common t o internal The authors wish to express their appreciation to the Division checks in duplicate analyses of waters by chemical procedures. of Research Grants and Fellowships of the U. S. Public Health Where deviations exist, final interpretation should be tempered Service for financial support of this investigation. by the thought that chemical analyses may not be absolute and LITERATURE CITED repeated checks by both methods might reconcile apparent difBarnes, R. B., Richardson, D., Berry, J. W., and Hood, R. L., ferences due t o method. IND.ENG.CHEM.,ANAL.ED., 17, 605 (1945). Recovery Studies. Four samples of the waters listed in Table Berry, J. W., Chappell, D. G., and Barnes, R. B., Ibid., 18, 19 VI were selected for recovery studies; Table VI1 tabulates the re(1946). sults of these determinations. The additional concentrations of Brode, W. R., and Silverthorn, R. W.,“Proceedings of Sixth Summer Conference on Spectroscopy and Its Applications,” minerals in the samples were obtained by adding the necessary pp. 60-6, New York, John Wiley & Sons, 1939. amount of appropriate standard to the original solution. (The Duffendack, 0.S., Wiley, F. H., and Owens, J. S., IND.ENG. calculations were based on the original concentration as deterCHEM.,ANAL.ED., 7, 410 (1935). mined with the flame spectrophotometer.) .vanov, D. N., Zavodskaya Lab., 10, 401 (1941). Parks, T. D., Johnson, H. O., and Lykken, Louis. ANAL.CHEM., 20,822 (1948). SUMMARY Table VII.
Analytical Recoveries of Added Ions
;E[yi
The small quantities of sodium, potassium, and calcium normally found in water can be easily and quickly determined with a
Colorimetric Determination of
RECEIVEDNovember 3, 1949. Presented before the Division of Water, Sewage, and Sanitation Chemistry a t the 117th Meeting of the AMERICAN CHEMICAL SOCIETY,Detroit, Mioh.
0-
and m-Dihydroxyphenols
HOBART H. WILLARD A N D A. L. WOOTEN’ University of Michigan, Ann .4rbor, Mich.
I
N PREVIOUS work ( 1 ) on the volumetric determination of resorcinol it was found that on iodination in the presence of catechol a dark insoluble precipitate formed. It has been found that this reaction is very selective for m- and o-dihydroxyphenols, After the excess iodine is destroyed the precipitate is dissolved by the addition of acetone and the resulting grape-blue color is measured. Beer’s law is obeyed over the range 0 to 75 p.p.m. REAGENTS
Iodine Solution, 0.1 N. Six and one-half grams of iodine and 10 g r a m of potassium iodide are dissolved in a little water and diluted to 1 liter. It is not necessary to standardize this reagent. Sodium Thiosulfate Solution, 0.1 N. Twenty-five grams of sodium thiosulfate are dissolved in 1 liter of freshly boiled water containing 0.1 gram of sodium carbonate. It is unnecessary to standardize this reagent. Starch Solution. A 1% starch solution containing 2% potassium iodide. Buffer. The buffer is acetic acidsodium acetate, molar in acetate ion. For the determination of resorcinol or catechol pH should be 5.7; for the determination of phloroglucinol, 6.0. 1
Present address, Reichhold Chemicals, Inc., Ferndale, Mich.
Reagent grade acetone, 0.05% resorcinol solution, and 0.05% catechol solution are used. PROCEDURE
Determination of Resorcinol. Take a neutral sample of no more than 15 ml. containing no more than 0.75 mg. of resorcinol, and add 10 ml. of buffer, 10 ml. of 0.05% catechol solution, and 15 ml. of 0.1 N iodine solution. After 1 minute titrate the excess iodine with sodium thiosulfate and starch. Transfer the sample to a 100-ml. volumetric flask, add 50 ml. of acetone to dissolve the precipitate, and dilute to 100.0 ml. with distilled water. hfeasure the intensity of the color a t 725 mp. Refer to a standardization curve for the resorcinol content. Determination of Catechol. The same procedure is followed, except that 0.05% resorcinol is added rather than catechol. Although the prbduct is the same in both cases, separate standardization curves are necessary. Determination of Phloroglucinol. The resorcinol procedure is followed, except that a buffer of p H 6.0 is necessary. A new standardization curve is required.
V O L U M E 2 2 , NO. 5, M A Y 1 9 5 0
671
If a m-dihydroxyphenol is iodinated in the presence of an o-dihydroxyphenol, a dark colored addition compound is formed. This precipitate dissolves on the addition of an equal volume of acetone to give a grape-blue color. The intensity of this color is proportional to either the m- or o-dihydroxyphenol, depending on which is present in the lesser amount. The optimum concentration range is 0 to 50 p.p.m. This could be made considerably smaller by use of more concentrated reagents. Of 25 phenols tested, only the 0- and rndihydroxyphenols gave this reaction.
EXPERIMENTAL
Table I shows that the color body is formed from equal amounts of resorcinol and catechol. The color produced by resorcinol in the absence of catechnl is due to aristol formation. A blank in the determination of catechol corrects for this. Resorcinol alone gives a red or pink color; in the presence of catechol the color is blue-violet. This blank may be eliminated by the use of a spectrophotometbr. In the experiments reported in Tables I1 to VI11 the variables in the determination of resorcinol were tested one by one. The
procedure given herewith was followed using 0.750 mg. of resorcinol. Very similar results were obtained in the determination of catechol and phloroglucinol.
Table VII.
Effect nf Acetone-Water Ratio
Acetone. % by Volume 35 50 60
Optical Density 420 520 516
Table \ W I . Formation of Color Body
Table I. Resorcinol, mg. Catechol, mg. Optical density
0.00
3.00 0.5
Table 11.
0.60
2.40 362
1.20 1.80 740
1.50 1.50 890
2.40 0.60 520
1.80 1.20 780
a.oo
0.00 185
Catechol, Mg. 0.750 1.500 2.290 3.750 6.000
Molar Ratio, Catechol/ Resorcinol 1.0 2.0 3.0 5.0 8.0
Optical Density 452 520 522 522 518
Table 111. Effect of Amount of Buffer Bu5er Added, MI. 2.0 4.0 6.0 8.0 10.0
Optical Denaity 480 503 512 526 525 ~~
Table IV.
Effect of pH on Rate of Reaction T i m e of Reaction, Minutes 0.25 0.50 1 .oo 2.00 5.00 10.00 20.00 30.00 1 .oo 2.00 3.00
:?tg: 5.3 5.3 5.3 5.3 5.3 5.3 5.3 5.3 5.7 5.7 5.7
Optical Density 385 435 440 452 470 504 520 525 530 525 527 ~~~~
Table V.
Effect of Amount of Iodine
Iodine, MI. 1.5 3.0 6.0 9.0 12.0 15.0
Table VI.
1.0
5.0
'
Optical Density 17.7 114.0 212.3 308 420 500
Effect of Cxtechol-Resorcinol Ratio
Resorcinol, Mg. 0.750 0.750 0.750 0.750 0.750
Excess Sodium Thiosulfate, M1. 0.0
Standardization Curve
Reaorcinol, Mg. 0.000 0.150 0.300 0.450 0.600 0.750
Optical Density 455 460 477 509 525 525
Effect of Excess Sodium Thiosulfate After0.5 mln. 525 526 520
Density Aftef 1 . 0 After5.0 min. min. 525 525 526 525 520 495
After 1 0 . 0 min. 525 519 467
DISCUSSION
& Table I1 indicates, a t least twice the theoretical amount of catechol must be preseni if the reaction is to be complete in 1 mirute. In the procedures above, the amount specified is about five times the theoretical. A blank should, of course, be run on the catechol alone. One batch that contained 0.75% resorcinol was analyzed by this method. The amount of buffer specified is about 25% more than the minimum necessary (Table 111). The pH of the buffer is critical (Table IV). The buffer should be rechecked frequently. It is surprising that such a large excess of iodine is necessary to complete the reaction (Table V). Approximately an eightfold excess is necessary. The procedure specifies a tenfold excess. The bleaching of the color in the presence of e x c w thiosulfate is not surprising. The mere acidification of the sample is sufficient to bleach the color with the liberation of free iodine. Resorcinol has been determined by this method in the presence of 50 times as much of each of the following phenols with an error of less than 1%: o-cresol, m-cresol, p-cresol, phenol, o-phenylphenol, p-phenylphenol, o-tert-butylphenol, p-tert-butylphenol, p-tert-amylphenol, salicylaldehyde, p-hydroxybenzaldehyde, m hydroxybenzoic acid, phydroxybenzoic acid, salicylic acid, p aminophenol, m-aminophenol, o-aminophenol, o-nitrophenol, and m-nitrophenol. Hydroquinone interferes in this large excess, but not when it is present in the same order of magnitude as the resorcinol. ACKNOWLEDGMENT
One of the authors wishes to express thanks to Reichhold Chemicals, Inc., for the financial aid that made this work possible. LITERATURE CITED
(1) Willard, H. H., a n d W o o t e n , A. L.,
ANAL.CHEM.,22,585
(1950).
RECEIVED August 31. 1949. From a dissertation submitted b y A. L. Wooten to the Graduate School of the University of Michigan in partial fulfillmen8 of the requirements for the degree of doctor of philosophy in chemistry.
