(11) Baker and Adamson, Reagent Grade, No. 1212. Fractionally distilled from conc’d. HzS04 (15 ml. per liter of MeOH), fractionally distilled from alkaline AgNO3 (5 grams/liter), refluxed with freshly ignited CaO, refluxed (900 ml. of it) with M g methylate (5 grams of M g per 60 ml. of limetreated MeOH plus 0.5 gram of Iz), fractionally distilled. Method as given in (9). (12) Matheson, Coleman, and Bell, No. 5051. Fractionally distilled, steam distilled, dried with CaC12,recrystallized, dried over P20a,fractionally distilled at Z m m . pressure. Method as given in (8). RESULTS
Some values of dielectric constant obtained at 25.0” C. with the instrument and liquids described above are listed in Table I. With one major exception, methanol, the observed values agree with published values to within & l % ; in most cases the agreement is much better. In the cases of worst agreement
i t is believed that impurities in the compounds are the main source of error, in spite of the reasonable (but not exhaustive) care with which each compound was purified. The other major source of error is believed to be the error involved in the manufacturer’s tolerance of the capacitors used in the fixed-step tuning capacitor, Clezl. The tuning indicator is exceptionally sensitive and a given reading is very reproducible, hence these are not considered to be significant sources of error. This instrument has been used very easily by students in the physical chemistry laboratory, and it is simple enough in design so that unusual knowledge of electronics is not required to understand its principle of operation. The students have used this instrument for both dielectric constant and dipole moment determination.
rendered in the purification of the liquids used and in some of the test procedures applied to the instrument. LITERATURE CITED
(1) Bender, P., J . Chem. Ed. 23, 179 (1946). ( 2 ) Daniels, F., Rilliams, J. W., Bender, P., Alberty, R. A., Cornwell, C. D.,
“Ex erimental Physical Chemistry,” S i x 8 Ed., pp. 223-230, McGraw-Hill, Xew York, 1962. (3) Fischer, R. B., ANAL.CHEM.19, 835 (1943 ( 4 ) Harris, H . , J . C h e m S o c . 1925,1049.
( 5 ) Maryott, A. A., Smith, E. R., Table of Dielectric Constants of Pure Liquids, Sat’l. Bur. Stand. Circ. No. 514, Aug. 1951, Supt. of Documents, U. S. Gov’t. Printing Office, Washington 25, D. C. (6) Miller, J. G., J . Am. Chem. SOC.64,
ACKNOWLEDGMENT
117 (1942). ( 7 ) Richards, T. W., Shipley, J. W., Zbid., 41,2007 (1919). (8) Sugden, S.,J . Chem. SOC.1933, 76s. (9) Wright, R. W., Stuber, L. S., Albright, P. S., J . Am. Chem. SOC.61, 228 (1939).
We acknowledge with appreciation the assistance which Roger A. Smit,h
RECEIVEDfor review April 23, 1963. Accepted September 10, 1963.
Determination of Moisture in ion Exchange Resins by Karl Fischer Reagent FRANK X. POLL10 Rohm & Haas Co., Philadelphia, Pa.
b Application of the Karl Fischer method to determination of moisture associated with ion exchange resins is described. The method of analysis involves direct titration of the resin in either methanol or pyridine solvent. Use of the Fischer reagent overcomes many of the limitations of both oven drying and azeotropic distillation techniques commonly used for detection of moisture in resins.
T
HE Karl Fischer reagent offers a relatively simple, fast, and reliable chemical means for quantitatively determining moisture present in a wide variety of substances. Since the discovery of the specificity of this reagent for water in the mid-thirties ( f ) , i t has proved highly successful for the determination of water associated with either organic or inorganic materials. I n addition, the Karl Fischer reagent has served as a useful tool in following the course of chemical reactions in which water appears as a reagent or one of the products formed (3). With the introduction of macroreticular resins (4),the utilization of ion
2164
ANALYTICAL CHEMISTRY
exchange resins as catalysts or adsorbents in organic systems has received added impetus principally because of the favorable physical and chemical attributes of these exchangers in nonaqueous media. T o assure maximum efficiencies of these materials, it has often been necessary to know the moisture levels associated with the resins before utilizing them as either catalysts or adsorbents in moisture sensitive systems. The Karl Fischer reagent has recently been found satisfactory for this purpose. The Karl Fischer reagent is a solution of iodine, sulfur dioxide, and pyridine in methanol, with the strength of any preparation being dependent on the iodine concentration. As the Fischer reagent reacts with water in a particular sample, the red-brown color of iodine is consumed until all the water has been reacted. The reagent thus serves as its own indicator during visual titrations. EXPERIMENTAL
Apparatus. Though elaborate visual or electrochemical Karl Fischer titration units are available commercially (typical supplier A. H.
Thomas Co., Philadelphia, Pa.), the apparatus in its simplest form consists of a buret (5- or 10-ml. capacity), a reservoir for the Fischer reagent, a 125-ml. Erlenmeyer flask, and a magnetic stirrer plus stirring bar. A Drierite tube, placed above t h e reservoir, serves t o protect t h e reagent from atmospheric moisture contamination. The tip of the buret delivery tube is inserted through a rubber stopper placed into the mouth of the Erlenmeyer flask containing stirring bar plus the contents to be titrated. A small slit, cut into the rubber stopper, facilitates gravity flow of Karl Fischer reagent during titration. Reagents. Karl Fischer Reagent. May be prepared using t h e method of Smith, Bryant, and Mitchell ( 7 ) , or more conveniently, may be purchased as a single stabilized solution (Harleco Chemical Products). The reagent undergoes slow deterioration on standing and therefore should be standardized periodically, preferentially before use. Sodium Tartrate Dihydrate ( S k ca400 2Hz0). Primary mater standard (Harleco Chemical Products). Though pure r a t e r or a standard solution of water in methanol may be used for standardization purposes (6),sodium tartrate dihydrate is preferred. This
-
Table 1.
Amberlyst 15 Moisture Determinaiion
Moisture found, yo Karl Fischer Zplol titration distillat,ion 0.9 0.9 1.1 2.7
0.4 0.8 1.0 2.4
stable crystalline hydrate possesses an accurately known water composition (15.66 =t 0.05% H20) after 3 hours' drying at 150' C. (6). Methanol. Reagent grade (,J, T. Baker Co.). Pyridine. Reagent grade (J. T. Baker Co.). Procedure. I n t o :t d r y 125-ml. Erlenmeyer flask, pipet 25 ml. of pyridine or methanol. Connect t h e flask t o t h e t i p of a 10-nil. buret (Teflon stopcock equipped) with a rubber stopper. Titrate the contents of t h e flask wii,h standardized Karl Fischer reagent while the contents of t h e flask are agitated by means of a magnetic :;timer. Record the milliliters of titrant required to produce a light cherry-red end point which persists in intensity for a t least 60 seconds. T o the Erlenmeyer Rask add an accurately weighed 1 to 5 grams of resin sample, the size of the sample depending on the mcisture level expected and on the strength of the Fischer reagent. Resume the titration until the identical end poinb color observed for the pyridine (or alcohol) blank is attained. Record the total volume of titrant used for the blank plus the sample. The per cent H20in the resin sample may then be calculated. The procedure employed for qtandardizing the Fischer reagent is the same m the one used for the moisture determination of a resin sample, except that a 0.5- to 1.0-gram sample of Na2C4H406. 2Hz0 is used in place of the resin sample. RESULTS AND DlljCUSSlON
I n Table I are rtipresented some typical data obtained during moisture analysis of Amberlys; 15, a macroreticular hydrogen-for m sulfonic ion exchange resin based on a styrenedivinylbenzene matrix. Results from both the Karl Fischer technique described and zylol azeotropic distillation ( 2 ) are recorded. The Karl Fischer technique was used successfully during a drying study for hmberlyst 15 resin to determine the minimum drying time that would be required to d r y unde- vacuo a completely hydrated Ambldyst 15 sample or a sample in toluene containing a relatively low moisture level. Data obtained during the study are tabulated in Table 11. The reliability of the Fischer titration values was checked out in several instances by addition of
small known quantities of water to the titrated resin samples and then reevaluating the samples for moisture. The added water was accounted for in each case within the reasonable experimental limitations of the method (Table 111). Precision. An indication of t h e reproducibility of t h e method may be obtained from a n examination of t h e d a t a in Table I V which records moisture values from a series of independent moisture determinations for a n Amberlyst 15 sample made in either methanol or pyridine solvent. -1s seen from the data of Table IT', the average deviations differ by less than &0.75% of the mean values of the individual sets of determinations, with no independent measurement deviating more than +1.5% from the means. Oven drying of four replicates of the same Amberlyst 15 sample, on the other hand, gave a mean moisture value of 10.2501,, with an average deviation from the mean value of *2%. The lower moisture values obtained from zylr 1 azeotropic distillation and oven drying of Amberlyst 15 samples are probably attributable to incomplete release of moisture from the internal poreq of the macroreticular resins
Table IV.
Table
Amberlyst 15 Drying Study
(Drying conditions 100" C. < 1 mm. Hg) Moisture, 70 Drying Water Toluene time, wet wet resin resin hr. 0 1 2 3 4 5 6 5 S
53.30" 1.41 0.54 0.29 0.19 0.22 0.16 0.18 0.10
1,210 0.34 0.21 0.21 0.20 0.19 ... 0.14 0.12
Weight per cent moisture determined on samples drained of excess solvent (before drying). 0
Table 111. Determination of HzO Added to Karl Fischer Titrated Amberlyst 15 HzO found by
H 2 0 added, yo 1.25 5.04 9.68 13.08
Karl Fischer titration, yG 1.29 5.12 9.53 13.20
Amberlyst 15 Moisture Precision Data
Pyridine solvent Moisture found, $7' Deviation
Methanol solvent Moisture found, Deviation 11.2s 11.09 11.29 11.22 11 .22 (mean)
II.
0.06 0.13 0.07 0.00 b 0 . 0 7 (av. dev.)
during the distillation and drying processes. Sulfonic resins, especially when in the hydrogen form, are noted for their abilities to hold onto the final residual amounts of moisture rather tenaciously even after prolonged drying, This behavior is apparent from the data of Tables I and 11. Inherent disadvantages of both oven drying and azeotropic distillation methods are that, they are time consuming and incapable of satisfactorily handling unstable and heat sensitive resins. I n addition, the presence of volatiles other than water can lead to serious errors at low moisture levels. Direct Karl Fischer tit,ration of the resin samples should considerably overcome the moisture detection limitations of the customary physical methods a t low resin moisture levels. The Fischer reagent appears better suit,ed for determining tightly bound residual moisture which otherwise may escape detection.
11.06 11.25 11.12 11.24 11.17 (mean)
0.11 0.08 0.05 0.07 1 0 .OX (av.rdev.)
Though analysis of moisture associated with resins of different structural types was not investigated, no serious interferences should be expected in the case of standard type products available commercially. LITERATURE CITED
(1) Fischer, Karl, Angew. Chem. 48, 394 (1935). (2) Harel, Simcha, Talmi, Alon, AXAL. CHEM. 29, 1694 (1957). (3) Johansson, Axel, Ibid., 26, 1183 (1954). (4) Kunin, Robert, Meitzner, E. F , Bortnick, N.M . , J . Am. Chem. SOC.84, 305 (1962). (5) Mitchell, J., Jr., Smith, I). M., "Aquametry," p. 66, Interscience, New York, 1948. (6) Neuss, J. D., O'Brien, M. G., Fredani, H. A,, h A L . CHEY.23, 1332 (1951). (7) Smith, D. M., Bryant, W. A I . , Mitchell, J., Jr., J . Am. Chem. Soc. 61, 2407 (1939). RECEIVEDfor review May 9, 1963. Accepted September 5, 1963. VOL. 35, NO. 13, DECEMBER 1963
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