July 15, 1941
ANALYTICAL EDITION
no bismuth was added, were also conducted. The analytical results are given in Table I. The complete procedure was put into the hands of a technician who obtained the results of Table I1 in duplicate and triplicate on known and unknown samples. These figures are submitted as evidence that the method is adaptable to clinical use in the hands of a technician. Results on other tissues have been found as precise as these shown.
Summary By means of a photoelectric colorimeter, the principal factors which affect the application of the potassium iodide method for the determination of bismuth in biological materials were evaluated. Procedures for a photoelectric determination of bismuth in urine, kidney, liver, muscle, and blood serum have been
465
devised with test analyses included to indicate the accuracy of such procedures.
Literature Cited (1) Autenrieth, W., and Meyer, A., MQnch. med. Wochschr., 71, 601 (1924). (2) Baggesgaard-Rasmussen, H., Jackerott, K. A . , and Schou, S. A., Biochem. Z., 193, 53 (1928); Dansk. Tids. Farm., 1, 391 (1927). (3) Hodgman, C. D., “Handbook of Chemistry and Physics”, 19th ed., p. 1563, Cleveland, Ohio, Chemical Rubber Publishing Co., 1939. (4) Leonard, C. S., J . Pharmacol., 28, 81 (1926). ( 5 ) Muller. R. H.. IND.ENG.CHEM..Anal. Ed.. 7.. 223 (1935). . . (65 Ibid., 11, 9 (1939). (7) Scholtz, J. R., and Chaney, A. L., Am. J. Syphilis Gonorrhea Venereal Diseases, 23, 759 (1939). SUBMITTED in partial fulfillment of the requirements for the degree of doctor of philosophy a t New York University.
Perchloric Acid Oxidation of Organic Phosphorus in Lake Waters REX J. ROBINSON Oceanographic and Chemical Laboratories, University of Washington, Seattle, Wash.
T
H E utilization of phosphate, dissolved in lake water, by growing phytoplankton attaches considerable importance to this element and to the phosphorus in the lake. Various studies have shown that only a small portion of the total phosphorus content is present as the readily available phosphate but a large potential supply exists organically bound. The Deni 6s ( 1 ) colorimetric method estimates only the phosphate phospforus. The amount of organic hosphorus is derived by deducting the phosphate hosphorus Prom the total phosphorus content. The methof as described by Robinson and Kemmerer (8) has served very well for the determination of total phosphorus. Briefly, the organic material in a 100-ml. water sample is digested with 0.2 ml. of concentrated sulfuric acid and 0.5 ml. of concentrated nitric acid t o convert the organic phosphorus to phosphate. Shortly before sulfuric acid fumes appear 3 ml. of concentrated hydrochloric acid are added t o destroy the excess nitric acid. Although the above method has proved its value, the following alternate procedure is proposed because of its greater simplicity. To the 100-ml. water sample contained in a 125-m1. Erlenmeyer flask, 0.2 ml. of 72 per cent perchloric acid is added and the sample is evaporated to fumes of perchloric acid. (More acid must be added to hard waters to gain an excess of the acid.) If oxidation of the organic material is slow, as is sometimes the case with water from extractive lakes, the flask may be covered with a watch glass t o prevent loss of perchloric acid and the heating continued until the colorationdisappears. The use of perchloric acid as the oxidizing agent has a number of advantages. Only one acid, rather than three, is measured. Undesirable fumes are not inhaled during pipetting or discharged during digesting. The excess nitric acid must be completely removed, as it causes fading of the blue phosphomolybdate complex; the excess perchloric acid does not cause fading. The flask may be covered with a watch glass during digestion to prevent loss of perchloric and phosphoric acids; this cannot be done with the nitric acid because
of the retention of the nitric acid. Consequently, with a covered flask there is less need for careful temperature regulation in the digestion to prevent loss of phosphoric acid. The nitric acid is destroyed and expelled a t a low temperature, the perchloric acid is present throughout; this means that difficultly oxidizable substances may be subjected to a higher oxidation temperature. Lastly, there is less phosphate impurity in perchloric acid than in the sulfuric-nitric-hydrochloric acid mixture. The perchloric acid oxidation has proved an efficient method of oxidizing organic phosphorus compounds. First it has been checked by the analysis of Eastman’s c. P. glycerophosphate, the phosphorus content of which had been verified by oxidation and gravimetric analysis of macrosamples. Amounts of glycerophosphate approximating the phosphorus content normally found in 100 ml. of lake water were used to simulate lake water conditions. Complete recovery was obtained, as indicated in Table I. Secondly, the efficiency of the method has been checked by analysis of lake waters which were also analyzed by the sulfuric-nitric-hydrochloric acid method. A comparison of the two methods is included in Table 11. Trout Lake water was particularly suited to a critical comparison of the two methods, because in it there was enough extractive organic material to make it more difficult to oxidize than the average lake water. The organic material was as quickly and efficiently oxidized by the perchloric acid as b y the nitric-sulfuric acid mixture. During the progress of this
TABLE I. ANALYSISOF GLYCEROPHOSPHATE Phosphorus Taken
Phosphorus Found
Mg./l.
Mg./1.
0.028 0.02s 0.028 0.028
0.029 0.027 0.027 0,027
INDUSTRIAL AND ENGINEERING CHEMISTRY
466
Vol. 13, No. 7
It is known that the residual acid from the digestion has a small but definite inhibiting effect upon the formation of the blue reduction complex. This effect may be prevented by neutralization of the excess acid before development of the TrouL Lake blue reduction color. Analyses of Trout Lake are given in Table I11 to show the effect of neutralization. Using either Lake Washington methyl red or phenolphthalein as the indicator, the acid was carefully titrated with N ammonium hydroxide, followed by Green Lake N hydrochloric acid until the acid form of the indicator was TABLE111. TOTALPHOSPHORUS IS TROUT LAKE,SAN JUAN just prevalent. The colorimetric comparisons were made with the Zeiss-Pulfrich photometer as described by Wirth and ISLANDS, WASH. Robinson ( 3 ) . Interference by the methyl red was entirely --Phosphorus FoundUnneutralized Neutralized elimir@ed by the S-72 color filter (average wave length XQ./l. Mg./l. 7200 A.). Estimations were also made in Nessler tubes when HzSOI + H S @ s + HC1 0.024 0.026 phenolphthalein had been used as the indicator in the neu0.024 0.027 0.024 tralization. Although the inhibiting effect of the excess acid 0 , 2 ml. HC104 0.023 0.028 is not large, greater accuracy is undoubtedly obtained when 0,022 0.027 the acid is previously neutralized. TABLE 11.
TOTAL PHOSPHORKS IN LAKEWATER
--
Phosphorus FoundHClOi H?SOI-HSO~-HCI .lfQ./l. .MQ./l. 0.025 0,026 0.02i 0.027 0.018 0.017 0.017 0.017 0.024 0.026 0.026 0,025
0 . 5 ml.
“ 3 0 4
0.019 0,016
0,026
Literature Cited work the oxidation always proceeded quietly and never with violence, probably because of the quantity and nature of the organic compounds present in lake water, together with the gradual oxidation during evaporation and digestion.
(1) DenigBs, G., Compt. rend. soc. bid., 84, 875-7 (1921). (2) Robinson, R. J., and Kemmerer, George, Trans. Wisconsin Acad. S C ~ 24, . , 117-21 (1930). (3) Wirth, H. E., and Robinson, R. J., IWD. ENG.C H m r . , Anal. Ed., 7, 147-50 (1935).
The Mixed Indicator Bromocresol Green-Methyl Red for Carbonates in Water ST.UVCIL S. COOPER. Washington University, St. Louis, hIo.
The mixed indicator bromocresol greenmethyl red has been applied to the detection of the end point of bicarbonate titrations in concentrations which are found normall!- in natural or commercial waters. Electrometric titration curves for waters of various compositions show that the final equivalence point pH is definitely dependent on the carbon dioxide content there existing. A method is presented whereby the pH value to be obtained at the final end point can be ascertained before that point is reached. This allows the selection of the proper indicator color at the end point. The glass electrode, bromocresol greenmethyl red, methyl orange, and methyl orange-xylene cyanole are compared in titrations of carbonates of various concentrations.
T
HE estimation of carbonates in extremely dilute solution with methyl orange as indicator is unsatisfactory for two reasons: The color change is difficult to observe in solutions Those pH is changing slowly, and the equivalence point in the majority of titrations of this type comes a t pH values too high to permit this indicator to respond correctly. The pH a t the final equivalence point is a function of the car-
bonic acid concentration existing there and this in turn is dependent on the neutralized bicarbonate as well as on the initial carbon dioxide content. In the titration of such solutions methyl orange leads to high results if the carbonic acid content a t the final equivalence point is lower than about 1.2 millimoles per liter (73 p. p. m. of carbonic acid). This limit is realized if the end point color is read when the indicator shows its first definite cast of orange (pH = about 4.6). For example, if 0.0200 N acid is used this indicator shows a minimum positive error of 4.6 per cent for total carbonate and of 7.2 per cent for bicarbonate when used in a solution initially containing 21.6 p. p. m. of carbonate and 17.5 p. p. m. of bicarbonate. In the official method the carbonic acid end point is determined by the use of methyl orange (1, 3, d), methyl orangexylene cyanole (S), or erythrosin (1, 5 ) . Methyl orange is subject to the errors pointed out above and erythrosin requires special technique in its use. For low carbonates, methyl orange-xylene cyanole leads to higher results than does methyl orange alone. Furthermore, the official method using methyl orange has been shown to be unreliable when carbonates are low ( 1 2 ) . Therefore, an indicator which would respond more nearly a t the carbonic acid equivalence point, when solutions of carbonates or bicarbonates are titrated yielding less than 1.2 millimoles of carbonic acid per liter, would prove useful. I n such titrations the solutions are fairly well buffered as the equivalence point is crossed. Any indicator which is to reveal this point correctly must respond over a very narrow pH range. A distinct characteristic of mixed indicators is that they tend to show sharp color changes within narrow pH limits.
