ANALYTICAL CHEMISTRY
918 (3)
Table 11.
Separation Factors for Partition Coefficients Corresponding to a Definite Ratio K..
Kb
Ka/Kb
S
0.6 0.9
0.4 0.6 1.0 4.0 6.0
1.5 1.5
110 99 98
1 5
6.0 9 0
1.5 1.5 1.5
172 230
Hodgman, C. D., "Handbook of Chemistry and Physics," 30th ed., pp. 204-8, Cleveland, Ohio, Chemical Rubber Publishing Co., 1946.
Lange, N. A, "Handbook of Chemistry," 6th ed., pp. 257-60, Table XXVb, Sandusky, Ohio, Handbook Publishers, 1946. (5) Martin, A. J. P., and Synge, R. L. M.,Biochem. J.,35, 1358-68 (4)
(1941).
(6) Mayer, S. W., and Tompkins, E. R., J. Am. Chem. Soc., 69, 286674 (1947).
(7) Williamson, B., and Craig, L. C., J. Biol. Chem., 168, 687-97 LITERATURE CITED (1) Craig, L. C., J . B i d . Chrm., 155, 519-34 (1944). ( 2 ) C'raig, L. C . , and Post, O., A X A L . CHESI.,21, 500-4 (1949).
(1947). RECEIVED February 7,1950.
Rapid Methods for Determining Fluoride in Waters WALTER E. THRUN, Valparaiso University, Valparaiso, Ind, A dilute solution of the aluminum lake of eriochromecyanineis used as a reagent for the rapid determination of fluoride. Small volumes of samples are required. The method should be useful for the field determination of low, optimum, and excess fluoride in potable waters. A rapid method for the distillation of fluoride is described. The results obtained directly and upon the distillate agree well.
B
EC'AUSE the fluoride content of potable water has a direct relationship to dental health, a rapid and simple method for determining fluoride is desirable. The method described below requires only a 10-ml. sample and a short time of standing before color comparisons can be made, whereas in the generally used official method, Sanchis' (4) modified by Scott (6) and Lamar (S), 100-ml. samples and 1-hour standing are required. In the colorimetric determination of fluoride in waters, those given above and those of Araujo ( 2 ) and Tageeva ( 7 ) , the alizarin red lake of zirconium is used as reagent. Because the fluoride ion a190 destroys the color of the aluminum lake of eriochromecyanine, it was expected that a buffered preparation would make a good reagent for the fluoride ion. Eriochromecyanine has also been used hy Saylor and Larkin (5) as an indicator in the titration of a fluosillcic- acid distillate with aluminum chloride.
Dilute lake solution was prepared by mixing 10 ml. of the stock lake solution with 90 ml. of water and 10 ml. of the buffer solution. PROCEDURE, DIRECT METHOD
Because the reaction is affected by pH, all very alkaline samples should be made slightly acid with a few drops of dilute hydrochloric acid. To determine whether the buffer is adequate, 2 ml. of the dilute lake solution are added to a 10-ml. sample. The mixture is tested with a paper and compared with a test on a dilute buffer solution. One or two drops of buffer may adjust the
RE4GENTS AhD APPARATUS
'%or a range of 0.1 to 1.1 p.p.m. of fluoride, 10 ml. of the sample water and 10 ml. of standard solutions are pipetted into the matched test tubes or specimen tubes. Then 2 ml. of the dilute lake solution are added. Comparisons are made 10 to 15 minutes after mixing. For a range of 1 to 6 p.p.m. of fluoride a 5-ml. sample and 5 in]. of standard solutions are pipetted into matched tubes. Then 5 ml. of the dilute lake solution are added, mixed, and compared 10 to 15 minutes later. The two ranges overlap.
llatched test tubes or specimen vials about 125 X 15 mm. were used. Standard sodium fluoride solutions contained 0.1 to 1.2 p.p.m. of fluoride with differences of 0.1 or even 0.05 p.p.m. and 1 to 6 p.p.m. with differences of 0.5 or even 0.25 p.p.m. Eriochromecyanine solution, 0.3% aqueous on the basis of a 36% ash, was prepared and purified as previously (8) reported. A preparation under the name of Eriochromecyanine R.C. obtained from Gei y & Co., Inc., 89 Barclay St., New York, N. Y., yielded 6 1 8 ash. A 0.5% solution of this waa found satisfactory. A preparation under the name of Alizarol Cyanine R.C., from the Xational Aniline Division of the Allied Chemical & Dye Corporation, yielded 59% ash and gave good results when a 0.5% solution was used. Aluminum chloride solution was prepared by dissolving 0.447 gram of the hexahydrate to make 1 liter of solution containing 0.01 mg. of aluminum per ml. Buffer solution was prepared by dissolving 50.0 grams of ammonium acetate in 100 ml. of water and 1.0 gram of ammonium benzoate and then adding 3 ml. of glacial acetic acid. One milliliter of this diluted to 20 should have a pH between 5.4 and 5.6. Composite reagent was prepared by mixing 3 volumes of the dye solution, 2 volumes of the buffer, and 1 volume of 0.1% g u m arabic solution. Stock lake solution was repared by mixing.50 ml. of the composite reagent, 50 ml. of t\e aluminum chloride solution, and 5 ml. of water and warming to 65" to 70" for 10 minutes with constant stirring before allowing to cool. It keeps for a t least 4 months.
Discussion The rate of color decrease varies with the temperature. Therefore more accurate results are obtained if the sample, standard solutions, and reagent are a t the same temperature. As the amount of fluoride increases, the color changes from a red purple to red, cherry red, peach pink, and orange. I n the lower range color differences corresponding to 0.05 p.p.m. can easily be distinguished, and standards with 0.05 p.p.m. differences in fluoride may be desirable. A piece of paper wrapped around each of two tubes that are held against each other facilitates comparison. Thus a blank determination is easily distinguished from a standard containing 0.025 p.p.m. of fluoride, but differences between standards of 0.025, 0.05, and 0.075 and 0.10 can be less easily distinguished. The color of the blank determinations remains constant. Thus a freshly prepared blank compared with blanks 15 and 30 minutes old showed no differences in color. For the higher range, standards of 0.25 p.p.m. difference may be used; it is better to view the tubes from above against a white background. Because the approximate fluoride content can be determined with two or three standards after standing 3 to 5 minutes, it is suggested that the operation be repeated with standard solutions narrowed to the proper range. I n the upper range the color changes continue to occur when more than 6 p.p.m. of fluoride are present, but the deep orange colors are not so easily distinguished.
V O L U M E 2 2 , NO. 7, J U L Y 1 9 5 0 Because the color change is rapid in the beginning, a time interval is required for the contents of the tubes to which the reagent was added later to catch up with the first tube. The change after 30 minutes is slow, and in standard solutions the color after 15 minutes is almost that of a solution which has stood 30 minutes. A special preliminary treatment of a hydrogen sulfide water consisted in shaking it thoroughly with air, allowing the sulfur precipitate to settle, or allowing the sulfur to redissolve. Interferences. Bicarbonate does not interfere except as it affects the pH. If the pH of reacting solutions are too high, the color will remain too deep and give low results. Phosphate up to 5 p.p.m. does not interfere but a t 10 p.p.m. low results are obtained. Chloride and nitrate a t 1000 p.p.m. do not interfere. Sulfate a t 760 p.p.m. does not interfere. Above 1 p.p.m., iron begins to give high results. Added aluminum up to 1 p.p.m. does not interfere. Added silicate as silica up to 6 p.p.m. does not interfere. Calcium at 168 p.p.m. as calcium carbonate gives results that are high by 0.7 p.p.m. of fluoride; a t 124 p.p.m., 0.4 p.p.m. too high; at 106 p.p.m., 0.1 p.p.m. too high. hlagnesium as calcium carbonate a t 120 p.p.m. gives results that are high by 0.2 p.p.m.; a t 60 to 100 p.p.m., 0.1 p.p.m. high; at 40 p.p.m. there is no interference. Because of the greater dilution by the reagent in the upper range procedure, the limits of interference should be about 1.67 times as great and were so found experimentally. It was found that sodium salt solutions of 9000 ahd 5000 p.p.m. of chloride, nitrate, and sulfate lower the color of the aluminum lake. This is probably a salt effect and suggests that very hard or briny waters be diluted before the direct method is used. This also has the advantage of decreasing the amount of interfering substances. DISTILLATION METHOD
Water samples are distilled (1) when an excess of interfering substances is present or to eliminate unsuspected interferences. The standard (6) method, a modification of the Willard and Winter (9) procedure, required preliminary evaporation, and the distillation requires 1 hour. The procedure given below requires much less time and coupled with the above procedure requires less than an hour for a determination. Distillation Apparatus. A 300-mI. Kjeldahl flask is fitted with a two-hole rubber stopper. A bent glass tube is inserted through one hole, so that one end reaches near1 to the bottom of the flask. The flask is connected with a shalLw inverted U to an upright West type of condenser having a jacket 50 cm. long. The outlet should be slightly constricted. The U-tube should be 8 mm. in diameter and about 15 cm. wide, having one arm about 8 cm. lon and the other 12 cm. long. The short arm is inserted flush wit% the stopper in the distillation flask. The Ion er arm is inserted through a rubber stopper, so that it reacaes the constricted part of the condenser tube. The apparatus is supported with clamps on a tall ringstand. The flask is su ported on an asbestos board having a hole of 7-cm. diameter. %he heating is carried out with a Meker type of burner. The compressed air is led to the Kjeldahl flask through a 500-ml. gas-washing bottle containing water. A condenser having a 25-cm. jacket and a 40-cm. tube gives good results, but the condensate is much warmer. For a quicker operation a 100-ml. Kjeldahl flask may be arranged usin 6 m m . tubing to connect it to a shorter condenser. The asbestos %oclrdsu porting the flask should have a hole of 5cm. diameter. A smaEer burner is used. Distillation Procedure. A sample of 100 ml. of the water and 10 ml. of distilled water are pipetted into the 300-ml. Kjeldahl flask and 0.2 to 0.3 gram of silver sulfate and about 10 glass beads are added. Then 40 ml. of concentrated sulfuric acid are poured down the neck with a minimum of mixing. The water is turned o n to run rapidly through the condenser. The air supply and the condenser are connected to the flask. The outlet of the condenser tube is dipped into water. A 100-ml. graduate is placed under the outlet. The air supply is turned on to give high turbulence. About 30 seconds later a large flame is applied from a Meker type of burner and distillation is carried on at a rapid
919 Table I. Source of Sample Aurora, Ill. Aurora. fluoride added eqiiivalent t o 1 i.'.p.m. Aurora, fluoride added equivalent t o 20 p . p . m . Frankfort, Ind. Florida well
Comparison of Results
Direct Method. P.P.11. F
Diqtiliation Method, P.P..\I. F
0.7
0.7
1.55
1.65
20.0-
20.0+
I+ 0.7f
Hebron. Ind. Valparaiso, Ind.
0.3 0.1
0.3 0.1
Sheboygan, &-is,
1.1-
11+
Grand Rapids, hlich.
1.1-
1.1
Strongbow well
0.2
0.2
4.4+
4.4+
4.5
4.5-
0:3-
0.3+
4.5 3.2
4.5 3.2 4.2 2.25
Lowell. Ind. Diluted 1 Undiluted Small scale Lowell well
+3
2' 3
Remarks Hardness 322 p,p,m. Diluted for direct method
Distilled undiluted: distillate and s a m d e diluted 10 to 100 Slunicipal from wells 100-ft. well. 200 feet from a n East Central Florida beach We1 I From lake. hardness 80 P.P.~.
4.5
Lake Michigan u a t e r , fluoride added a t plant. 1 . G reported by official method LIunicipal. fluoride added a t plant. 1.09 reported by official method. A I 1.4 p.p.m. BO-foot well 1 mile E a s t of 'i'alparaiso, Ind. Well 200 feet, diluted 1 Slight HgS odor
+ 3.
60-foot well, 1 mile east of Lowell. Very slight smell of H& Diluted 5 to 100 nil. Shaken until S ppt. was dissolved. Contains 13:s
rate until 90 mi. have been collected. The gas is turned off and the air allowed to go through for a few seconds longer. The condenser is disconnected and rinsed with about 3 ml. of water from a pipet into the graduate. One or two drops of a concentrated ammonium carbonate solution are added to the distillate, and it is allowed to cool to room temperature. About 0.5 ml. of the buffer solution is added and then the distillate is diluted to 100 ml. I t is mixed and the fluoride determined as given above. The actual time for distillation is about 14 minutes. The operation on a smaller scale requires a 35-ml. sample, 5 ml. of water, and 15 to 16 ml. of sulfuric acid in a 100-ml. Kjeldahl flask; 35 ml. are distilled into a 50-mI. cylinder. After neutraliaing and cooling, it is made up to 40 ml., and mixed and the fluoride is determined as above. The actual time for distillation is about 7.5 minutes. The parts per million of fluoride determined are multiplied by 1.14 to get the parts per million in the original. Discussion. Known added amounts of fluoride were added to several water samples and recovered in the distillate. The rapid addition of air causing great turbulence and the application of a large flame are essential. With smaller flames and slower distillation, the recovery is low, especially when the fluoride content is above 0.5 p.p.m. During the distillation some steam escapes. There is no increase in recovery of fluoride when the bottom of the condenser tube is immersed in water, and some steam escapes just the same. In the outlet of the condenser tube there is always some distillate hanging by capillary attraction, through which the vapors are blown. The addition of silver sulfate makes the distillation smoother and possibly retains sulfide in water containing a trace of it and some chloride. The extra water is added to give the distillate a larger volume and to collect less hydrogen chloride. A standard solution containing 10 p.p.m. of fluoride as sodium fluoride was distilled and the distillate made up to 100 ml. One volume of this was made up to 10 volumes and compared with a 1 p.p.m. standard which it matched. Blank determinations using distilled water, 0.3 gram of silver sulfate, and ten 5-mm. soft glass beads gave results that showed negligible fluoride content; the maximum was equivalent possibly to 0.001 p.p.m. RESULTS
The results by both methods on a variety of waters are given in Table I. In two cases they are compared with the standard
ANALYTICAL CHEMISTRY
920 method. There is excellent agreement between the two methods within the precision that can be expected. The precision in the lower range is less than 0.05 p.p.m., and in the upper range less than 0.25 p.p.m. Such precision is adequate for all health purposes. The presence of aluminum ions should deepen the color of the lake, and silicate ions (8) should destroy its color. Therefore, it is reasonable to assume that the aluminum and the silicate ions are tied up in natural waters and are not freed to any extent at pK 5.4 to 5.6 in 15 minutes. The escape of some steam during the rapid distillation is disconcerting, but the results in recovering added fluoride (as sodium fluoride) justify confidence in the method. For both methods Great Salt Lake water was diluted 1 t o 10 before the determination was made.
LITERATURE CITED
(1) Am. Public Health Assoc. and Am. Water Works Assoc., “Standard Methods for the Examination of Water and Sewage,” 9th ed., p p . 76-8, 1947. (2) Araujo, T. L., Rev. faculdade m e d . cet., Univ. Sdo Paulo ( B r a z i l ) , 2, NO. 2, 15-17 (1942). (3) Lamar, W. L., and Seegmiller, C. G., IND. ENG.CHEX.,ANAL,
ED.,13, 901-2 (1941). (4) Sanchis, J. M., Ibid., 6 , 134 (1934). (5) Saylor, J. H., and Larkin, ,M. E., ANAL.CHEM.., 20, 194-6 (1948). (6) Scott, R. D., J . Am. W a t e r Works Assoc., 33, 2018 (1941). (7) Tageeva, N. V., J . A p p l i e d Chem. (U.S.S.R.), 15, 56-9 (1942). 20, 1117 (1948). (8) Thrun, W. E., ANAL.CHEM., ANAL.ED., (9) Willard, H. H., and Winter, 0. B., IND.ENG.CHEM., 5, 87 (1933). RECEIVED January 14, 1949.
Punched Card Catalog of Mass Spectra Useful in Qualitative Analysis PAUL D. ZEMANY Research Laboratory, General Electric Company, Schenectady, N. Y . A method for indicating the prominent features of a mass spectrum on punched cards and the way these cards can be used as an aid to qualitative analysis with the mass spectrometer are described in detail. Further aids for the identification of peaks observed on the mass Spectrometer are the measurement of mass defects and correlation of relative peak heights with known isotopic distribution.
UNCH cards of the Keysort variety (Keysort cards manufactured by McBee Company, Athens, Ohio; Rocket cards manufactured by Charles R. Hadley Company, Los Angeles, Calif.) have been used in many chemical applications (8, 4-7) particularly in bibliographies, but other kinds of information can also be put on punched cards. An isotope file (IO), for instance, is coded to permit sorting out the cards for isotopes having some particular property. Wright ( 2 6 ) introduced the use of punched cards for Lhe presentation of infrared data, and infrared charts can now be obtained (Samuel P. Sadtler & Son Co., Philadelphia, Pa.) printed on punched cards which indicate the absorption bands by means of a direct index. During the past two years the author has used a punched card system for cataloging mass spectra. Besides being a convenient method for filing, these cards have been useful in the identification of mixtures of compounds. Several hundred spectra of compounds of special interest have been put on these cards, and, in addition, mass spectra reported in the literature have been incorporated in the file. The mass spectra given in A.P.I. Project 44 publications (I), for example, have been included. Although the h e r details of a spectrum will differ from one instrument to another, the main features are similar, and hence data obtained on other kinds of spectrometers are useful for qualitative and rough quantitative work. DESCRIPTION OF CARDS
The cards used for this catalog of mass spectra are the 5 X 8 inch McBee Keysort cards with single rows of holes at the sides and double rows a t the top and bottom (Figure 1). A card for a given compound includes a copy of the spectrum as recorded on the General Electric photoelectric recorder, pasted directly on the card if the spectrum was obtained in this laboratory, or a transcribed record of peak heights if from the litera-
ture. Other recorded data are sensitivity (peak height ratio of an arbitrary prominent peak per unit pressure on the leak to the peak height per unit pressure for some peak of a reference substance under identical conditions), references to more detailed data on the spectrum of the compound, a description of the conditions under which the spectrum was obtained, a designation of the five or six highest peaks, and any other pertinent data. The spectra are generally obtained a t a single attenuation setting of the amplifier, so that the highest peak will be nearly full scale. In this way, the various features of the spectrum retain their proper perspective. In comparing the spectra obtained on different spectrometers, the relative peak heights for adjacent ions are more likely to be similar than comparisons of peak heights far apart in mass. This is due to the fact that the focusing may not be equally effective a t the various parts of the spectrum, particularly if magnetic scanning is used, whereas with voltage scanning the sensitivity varies with the accelerating voltage. For most of this work magnetic scanning with a single setting of the focus was used, giving the best focus at mass 44, the geometric mean of the range 12 to 160. This range will include a majority of the compounds cataloged. The attenuation due to focusing a t the extremes of this range was about 2. The cards are punched under two headings (Figure 1). First, a means is provided for sorting the card of a desired compound. The molecular weight of the compound is used as the basis for this c:assification and the hundreds (below 7 ) , tens, and units holes on the left side of the card are reserved for it. The convention has been adopted of using the nearest integral weight of the most abundant natural isotope-i.e., CI = 35, Br = 79, Ge = 74. By this convention all cards of a given moIecular weight can be quickly separated and hand sorting of the few cards so separated gives the desired compound. Isomers, of course, fall into a common group. Although this method of
