H’, and H” calculated from the data of M, in Table 11. I t is readily found that all these quantities take a minimum point between 0.8 and 1.6 p1 of solute, while the increase in sample amount accompanies the monotonic increase in retention time (MI’ in the lower column of Table 11).This increase in the first moment suggests that the distribution isotherm in this experiment may slightly deviate from linearity to anti-Langmuir type (22, 23). As for the case of H’, this fact appears consistent with McNair’s result (24) that, in the case of anti-Langmuir type isotherm, the third moment takes minimum point with increase in solute amount. It is not clear why H” also passes the minimum point near 1.6 p1 of sample amount.
LITERATURE CITED (1)P. E. Porter, C. H. Deal, and F. H. Stross, J. Am. Chem. Soc., 78, 2999 (1956). (2)H. Clough, T. C. Gibb, and A. B. Littlewood. Chromatographia, 5, 351 (1972). (3)D. Macnaughtan, Jr., and L. B. Rogers, Anal. Chem., 43, 822 (1971).
B. E. Bowen, S. P. Cram, J. E. Leitner, and R. L. Wade, Anal. Chem., 45, 2185 (1973). C. N. Reilley, G. P. Hildebrand, and J. W. Ashley, Jr., Anal. Chem., 34,
1198 (1962). V. Maynard and E. Grushka, Anal. Chem., 44, 1427 (1972). T. H. Glenn and S.P. Cram, J. Chromatogr. Sci., 8, 46 (1970). L. H. Tung, Sep. Sci., 5 , 429 (1970). T. Provder and E. M. Rosen, Sep. Sci., 5, 437 (1970). E. M. Rosen and T. Provder. Sep. Sci., 5, 485 (1970). J. C.Sternberg, Adv. Chromatogr.,2, 205 (1966). R. N . Jones, R. Venkataraghavan, and J. W. Hopkins, Spectrochim. Acta, Part A, 23, 925 (1967). R . N. Jones, R. Venkataraghavan, and J. W. Hopkins, Spectrochim. Acta, Part A, 23, 941 (1967). R . W. Dwyer, Jr., Anal. Chem., 45, 1380 (1973). D. W. Kirmse and A. W. Westerberg, Anal. Chem., 43, 1035 (1971). K. Yamaoka and T. Nakagawa, J. Chromatogr., 93, 1 (1974). (17)K. Yamaoka and T. Nakapawa. J. Chromatoor., 100. 1 (1974). (18)J. E. Oberholzer and L. B.-Rogers, Anal. Cheh., 41, 1234 (1969). (19)S.N . Chesler and S. P. Cram, Anal. Chem., 43, 1922 (1971). (20)S.N. Chesler and S. P. Cram, Anal. Chem., 44, 2240 (1972). (21)K. Yamaoka and T. Nakagawa, J. Chromatogr., 92, 213 (1974). (22)K. Yamaoka and T. Nakagawa, J. Phys. Chem., 79,522(1975). (23)K. Yamaoka and T. Nakagawa, J. Chromatogr., 103, 221 (1975). (24)H. M. McNair and W. M. Cooke, J. Chromatogr. Sci., I O , 27 (1972).
RECEIVEDfor review November 19, 1974. Accepted June 24, 1975.
Titrimetric Determination of Fluorine Following Volatilization J . K . Wilkeyson Eutectic Corporation, 40-40 172nd Street, Flushing, N. Y. 11358
Many different analytical methods exist for the determination of fluorides by instrumental techniques (1-3). However, the classical wet method first introduced by Wohler and later by Adolph ( 4 ) appeared best suited for our particular needs. I t is a simple, relatively fast procedure that did not require the purchase of additional laboratory equipment. Briefly, in the original procedure, all fluorine is converted to gaseous silicon tetrafluoride (SiF4) which, when passed through water, is converted to fluosilicic acid (HzSiFS). This acid solution is then titrated vs. a standardized sodium hydroxide solution and percent fluorine calculated. The reactions are as follows:
+ HzS04 xso4 + 2HF Si02 + 4HF 2H20 + SiF4 3SiF4 + 2H20 2HzSiFs + Si02 6NaF + Si02 + 4Hz0 HZSiFe + 6NaOH XFz
---
+
(1)
(2) (3)
(4)
This procedure works very well for many types of inorganic samples except those that contain chlorides. In this case, when the sample is reacted with acid, hydrogen chloride (HCl) is also generated and is also absorbed by the water in the collection flasks. This yielded higher fluorine results due to the excess of acid when titrating. This problem made it necessary to modify the classical procedure and will be discussed. Although an alternate method proposed by WillardWinter ( 5 ) encompasses a wider variety of samples, our procedure does not require that the sample be put into solution or separated from other components,
the collection flasks to absorb hydrogen chloride. 2) An Allihn condensing tube containing glass beads (F) was used in place of Utubes. This change was required when it was discovered that a heavy sulfuric acid spray was being carried over to the collection flasks. 3) The drying train (A, B, and C ) was simplified because compressed air was used in place of a water pump. The system utilizes all Pyrex glassware, heat resistant stoppers (Stoppers were of the silicone type suitable up to 450 OF.), and tubing. A Drechsel bottle containing sulfuric acid and two 3-inch U-tubes containing glasswool and Drierite, respectively, are employed in drying the compressed air and catching the sulfuric acid spray from (A). A heating mantle is used to react the sample in a 100-ml boiling flask. Two 125-ml Erlenmeyer flasks containing 100 ml of distilled water each are used to collect the silicon tetrafluoride. (When a second collection vessel was added, it also absorbed some silicon tetrafluoride.) The concentrated sulfuric acid used to react with the sample was treated to remove as much moisture as possible. Powdered quartz is used as a source of silicon, however, feldspar, glass beads, or other silicon bearing materials may be used. The final titration is performed with 0.1N sodium hydroxide. Procedure. The reaction flask (D) should be cleaned and dried before each analysis. The best results are obtained when the sulfuric acid in the reaction flask is limited to maximum temperature of
Figure 1. Apparatus (A) Drechsel bottle containing concd
EXPERIMENTAL Apparatus a n d Reagents. Referring to Figure 1, the following changes were made to the original apparatus described by Adolph: 1) A 5-inch U-tube containing zinc shot ( G ) was added just before
H2S04;
(B) U-tube containing
glasswool;
(C) U-tube containing Drierite; (D) Reaction flask with thermometer; (E) Erlenmeyer flask containing concd H2S04; (F)Allihn condensing tube Containing glass beads: (G) U-tube Containing zinc shot; (H) Erlenmeyer (2)flasks con-
taining distilled water
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
2053
Table I. Comparison of Results Fluorine, Sample
Calcium fluoride Sodium fluoride Potassium fluoride Cryolite (impure) NBS 120b
(Phosphate Rock) Sodium fluorosilicate Laboratory mixture I Laboratory mixture 11" Laboratory mixture IIIn a
Contain Chlorides.
\+'eight, g
0.1122 0.1049 0.1071 0.1023 0.1038 0,1122 0.1084 0.1022 0.1056 0.1011 0.1118 0.1006 0.1025 0,1019 0.1017 0.1010 0.0558 0.1045 0.1331 0.1010 0.1093 0.1100 0.1027 0.1050 0.1023 0.1078 0.1045
c/.
for another 15 minutes at approximately 1 l./min. The fluosilicic acid (HzSiF6) is then titrated vs. 0.1N sodium hydroxide using phenolphthalein as an indicator.
Theorcticnl Experimental
48.7 45.2 32.7 ~54.0 3.8 60.6 6.8 25.3 26.1
47.8 48.5 48.6 45.6 45.3 45.0 32.6 32.3 32.9 53.0 52.9 53.2 3.9 3.8 4 .O 60.8 60.5 60.4 6.3 7.2 7 .O 24.3 23.4 26.5 26.5 24.7 26.4
220 O C for not more than 30 minutes. Anhydrous copper sulfate is employed to absorb the moisture created from the reaction itself. Silicon is present in the form of powdered silicon dioxide and, along with the sample, is dried at 110 OC for 8 hours. After all the reagents are dried and the system is purged with air, the reagents are placed in the reaction flask as follows: 0.1 g sample, 1.0 g CuSOd (anhydrous), 5.0 g SiOz, and 25 ml H2S04. The sample flask is heated for thirty minutes, and the air is allowed to purge
RESULTS A N D DISCUSSION In establishing the procedure, it was of concern to note the effect carbonates would have on the analysis as they might create carbonic acid and produce high results. This was prevented by simply agitating the reaction flask for a few minutes followed by a brief flow of compressed air before attaching it to the apparatus. (Hydrogen fluoride is not generated until the sample is heated.) A much more serious problem was found with chloride bearing samples. These samples gave high fluoride values due to the formation of hydrogen chloride. Addition of a zinc filled U-tube, placed just before the collection flasks, reacted with the gaseous hydrogen chloride and eliminated this interference. The reactions are as follows: XCL t H2SOr XHS04 t HC1 (5) 2HC1 t Zn ZnCln t Hz (6) Calcium fluoride (99.95%) was used in first establishing the procedure. I t was then expanded to the samples shown in Table I. The results show that this modified procedure will produce accurate results with CaF2, as was first intended, and also on a variety of inorganic compounds, whether present in a mixture or as pure fluorides. I t would appear that this procedure would also work well on some organic compounds but this is not within the needs of our laboratory. ACKNOWLEDGMENT The author thanks Bernard Brachfeld and Richard Edgar for their assistance in writing this paper. LITERATURE CITED
-. -+
(1) Wolfgang J. Klrsten and 2. H. Shah, Anal. Chem., 47, 184 (1975). (2) Blanche L. Ingram, Anal. Chem., 42, 1825 (1970). (3) H. E. Mewln, Am. J. Scl. No. 4, 28, 119 (1909). (4) W. H. Adolph, J. Am. Chem. Soc.. 37, 11, 2500 (1915). (5)H. H. Wlllard and 0. B. Wlnter, lnd. Eng. Chem., Anal. Ed., 5 , 7. (1933).
RECEIVED for review April 29, 1975. Accepted July 3, 1975.
Use of Copper-PAN in the Selective Titrimetric Assay of EDTA and Its Alkali Salts W. W. White and P. J. Murphy Industrial Laboratory, Kodak Park Dlvlslon, Eastman Kodak Company, Rochester, N. Y. 14650
Many hundreds of papers have been published on the analytical uses of EDTA but they have been primarily concerned with the metals they chelate. Little attention, however, has been given to a preferred complexometric method for assaying the acid or its alkali salts. Cheng and Bray ( I ) proposed the use of 1-(2-pyridylaz0)-2-naphthol (PAN) to determine copper in the presence of calcium, magnesium, and iron. However, the purpose of this paper is to show that the copper-PAN titrimetric system offers a more selective assay method by which the anion of EDTA (Y)can be determined in the presence of other ligands. Doran (2) has identified many of the by-products and intermediates present as impurities in the preparation of EDTA by electrophoretic techniques. However, there is lit2014
tle reason to believe that small quantities of ethylenediamine (EDA), 3-oxo-1-piperazineaceticacid (U-KP) or 2oxo-1-piperazineacetic acid (S-KP) would interfere with the copper-PAN assay of EDTA. The latter two compounds represent the cyclized forms of N,Nethylenediglycine and N,N'-ethylenediglycine and in solution form weak complexes with copper (2,3).The theoretical (ethylenedinitri1o)triacetic acid (ED3A) is very difficult to isolate and is known to cyclize readily to form 2-0~0-1,4-piperazinediacetic acid (3-KP). (Benik-Sas-Berezowsky (3) claims to have formed ED3A by refluxing 3-KP for 24 hours in a strongly basic sodium hydroxide solution.) No interference due to the presence of 3-KP has been experienced in the assay of EDTA by the copper-PAN method.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
