V O L U M E 2 1 , NO. 1 2 , D E C E M B E R 1 9 4 9 43) Bullock, B., and Kirk, P. L., IND.ENG.CHEM.,A X A L E . D . , 7, 178 (1935).
Elving, P. J., and Ligett, W. B., Zbid., 14, 449 (1942). Grangaud, R., Bull. 8oc. chim., 10,236-8 (1943). 6 ) Niederl, J. B., and Niederl, V., “Organic Quantitative Microanalysis,” 2nd ed., pp. 157-9, New York, John Wilw 8~ Sons.
4) 5)
1942.
1553 (7) Sendroy, J., Jr., J . Biol. Chem., 120, 335 (1937). E N G .CHEM.,ANALED., (8) Sundberg, 0. E . , and Royer, G. L., IND. IS, 719-23 (1946). RECEIVED April 1 , 1949. Presented before the Division of Petroleum Chemistry, Symposium on Microchemistry in the Petroleum Industry. at the 115th Meeting of the AMERICAN CHEMICAL S O C I ~ T YSsn , Franaisco Calif.
Determination of Small Amounts of Water F. &I. ROBERTS AND HARRY LEVIN Beacon Laboratories, T h e Texas C o m p a n y , Beacon, N . Y . A m e t h o d , employing azeotropic distillation a n d subsequent d e t e r m i n a t i o n of the water in the distillate b y titration w i t h K a r l Fischer reagent, has been applied to samples of oils, greases, deposits, additive concentrates, etc., containing as little as 0.0002570 of water. The d e t e r m i n a t i o n is m a d e in a special distillation system protected f r o m atmospheric moisture, a f t e r the system has been dried by partial distillation of the azeotrope f o r m e r used in the analysis itself. The m e t h o d is accurate t o 0.3 mg. of water.
THE
reported chemical methods employing the Karl Fischer reagent for determining very small amounts of water in petroleum fractions or other liquids involve a direct determination of the water in the sample with the Fischer reagent. Aepli and MeCarter (I) detcrmined water in liquid petroleum fractions by titrating the sample directly in a large flask protected from atmospheric moisture. The method has disadvantages in that a large amount of sample is required, which makes direct titrations unwieldy, and the mixture in the titrating flask exists in two phases, necessitating the extraction of the water with Fischer reagent. Snyder and Clark (IO) also applied the direct titration procedure to petroleum fractions, using a solvent to effect a single phase in the titration vessel. This method also mvolves titration of large volumes of liquid, and it is necessary to prepare and keep uantities of dry solvent. Weaver and Riley 71,) have developed a method for determining water in gases by measuring the change in electrical conductance of a hygroscopic film. They have done a small amount of work on liquid samples; however, the amounts of water reported are not very low. Evans and Davenport (5) have described a manometric procedure for small amounts of water in insulating oils. Their method is limited to oils, and would not be applicable to greases or semisolid materials such as engine deposits. Benning, Ebert, and Irwin (4) applied infrared spectroscopy for water in Freons, using the strong absorption band of water a t 2.67 microns, but state that compounds containing hydrogen will also absorb a t this wave length. This rules out the application of the method to a wide range of organic liquids. Obviously, the A.S.T.M. distillation method ( 3 ) is not suitable for very small amounts of water, for direct visual volume measurement of the water is required. If water contents are very low, it is possible that the entire amount contained in the sample will remain dissolved in the distillate. During the course of this investigation, a paper by Suter (11) described a method for water in inorganic alkaline materials. Water was separated from the sample by distillation with xylene and determined in the distillate with Karl Fischer reagent. This procedure, although suitable for high water contents, does not allow the precision required for very small amounts of water; the blank determinations are greater than the total water often determined by the present method. I t was found in the present investigation that ground-glass joints, as found in Suter’s apparatus, could not be tolerated where small amounts of water were being determined. Opening th8 system to atmospheric moisture, as is done in the reported method, cannot be tolerated wherp amounts of water are low. The present method employs azeotropic distillation and determination of the water in the distillate with Karl Fischer reagent. The necessity for keeping a dry solvent, or correcting for the blank on the solvent, is eliminated. The determination LB made in a system completely protected from atmospheric water. The use of large samples is necessary; however, the
final titration is more convenient because the water is con. centrated into a comparatively small volume of liquid. Even in the case of dark samples the distillate is water-white; it is therefore possible to titrate the water without the aid of potentiometric devices for determining the end point. Snyder and Clark (IO)have reported a number of substances that interfere with the Karl Fischer reagent. These substance8 will interfere in the present method only if they are volatile under the conditions of the test. This method was developed primarily for new and used p e t r e leum products including greases, although by the choice of a proper azeotrope former, it may be applied to other substances The method has been applied over the past year to other organic liquids-for example, additive concentrates, and trichloroethyl. ene-and to engine deposits and sludges. REAGENTS
Solvent or Azeotrope Former. In the present work, benzene wab used for all samples except greases. Pyridine waa used for greases Karl Fischer Reagent. The reagent may be prepared (9, 19) or purchased. It should be equivalent to 1.5 to 2 mg. of water pel milliliter of reagent. Water-in-Methanol Solution. This solution should contain 1.5 to 2 mg. of water per milliliter. Because commercial anhydrow methanol sometimes contains as much as 1 mg. of water pei milliliter, its water content should be estimated and adjusted to thr desired concentration. APPARATUS
The apparatus, shown assembled in Figure 1, consists of a dis. tilling flask, a receiver and titration flask, and two 25ml. automatic burets, the tips of which pass through 18/9 ball joints whicb fit on the titration flask. One automatic buret is for Karl Fischei reagent, the other for water-in-methanol. A magnetic stirrer (Arthur H. Thomas Co.), a heatin ‘mantle, and a Variac are also required, as well as an instrument for determining the end point of the titration. The dead-sto method described by Foulk and Bawden (6)is satisfactory, and tge Fischer Titrimeter or any p H meter may be used. This part of the apparatus is not absolutely necessary, as the end point may be determined visually. PROCEXWRE
Standardization of Reagents. The apparatus, except the distilling flask, is assembled aa shown in Figure 1 and the reagents are standardized according to the procedure of Almy, Griffin, and Wilcox (9). It is more convenient t o use this method than a distillation. Table I shows that factors obtained by both procedure are essentially the same.
ANALYTICAL CHEMISTRY
1854 Table I. Factor, mg. of HnO/ml. of reagent
Standardization of Reagent Direct Procedure 3.02 2.98
Distillation 3.06 3.00
Determination of Water. The apparatus is completely assembled, and 500 to 600 ml. of the solvent to be used as the azeotrope former are introduced into the distilling flask and distilled until 50 to 75 ml. of distillate have been collected. The heat is reduced so that the solvent does not distill, and a small excess of Karl Fischer reagent is added to the distillate in the receiver and back-titrated with water-in-methanol. The distillation and titration are repeated and continued until a 50- to 75-ml. portion of distillate contains no water. At this point the apparatus is anhydrous and ready for the sample to be introduced into the distilling flask. If the sample is liquid, it may be conveniently added, without opening the system, from a separatory funnel with a long stem passing through a glass stopper fitted with a rubber sleeve a t the top of the distilling flask. The funnel is placed in position with the tip of the stem above the top condenser prior to the initial dehydrating step. To add sample, the funnel is lowered until the tip of the stem passes through the upper condenser and the desired amount of sample is allowed to run in. Sample weight is obtained by weighing the funnel before and after sampling. For greases, a piston and cylinder arrangement as shown in Figure 2 is used. As above, this apparatus is placed in position before the initial dehydration, and is lowered through the top condenser to add the sample. Sample weight is obtained by weighing the grease sampler before and after adding sample. The distillation is allowed to continue for 30 minutes, during which time 50 to 75 ml. of distillate are collected. The distillation is stopped, and a small measured excess of Karl Fischer reagent is added to the distillate in the receiver and back-titrated with water-in-methanol. The distillation is repeated and continued until a 50- to 75-ml. portion of distillate contains no water. The first distillate usually contains all of the water; however, if the water content is comparatively high (0.1%), additional distillation may be necessary. Six or seven distillations may be made from a 500 to 600-ml. charge of azeotrope former. Calculations. The per cent by weight of water is calculated from the equation: (A-BR)F $& water = -__ 10c where A
=
No special attempt was made in this work to fractionate the vapors, the excess of benzene acting aa a solvent for any water that might separate when the vapors are cooled in the bottom condenser. In addition, the inner surfaces of the distilling flask were carefully cleaned initially, so that condensing vapors drained completely, thus further ensuring the complete collection of the water in the receiver. If the water content of the sample is so large that water separates from the condensed vapors, a smaller sample should be taken or a method more suitable for large concentrations should be applied. Ground-glass joints or
Table 11.
Analysis of Samples of Known Water Content
Sample Lithium grease Sodium grease Calcium grease Sodium-calcium grease Oil 1 2 3 4 5 Trichloro- -.....-.ethylene0 Tri chl oroethylenea
Solvent Pyridine Pyridine Pyridine Pyridine Benzene Benzene Benzene Benzene Benzene
Sample
H20 Added
Gams.
%
20
10
0.0261 0.0670 0.159
20
0.173 0.00022
20
600
415 300 300 300
0.00038
0.00377 0.00755
0.0219
Benzene
29.32
...
Benzene
29.32
._.
Last two samples are different batches.
H20 Recovered % 0 . 240 0.0699 0.161 0.171 0.00021-0 .00019 0.00034-0 ,00038 0.00374 0.00748 0.0220 0.004 0,004 0,000
0.000
nil. of Karl Fischer reagent
B = ml. of water-in-methanol R = ratio of Karl Fischer reagent to water-in-methanol F = factor, mg of HzOper ml. of Fischer reagent C = weight of sample, grams DISCUSSION
A suitable solvent or azeotrope former for use in this method should be a good solvent for the 8s-ainple. Its azeotrope with water should be rich enough to bring about complete removal of water from the sample in a minimum number of distillations. It should hold the removed water in solution in the distillate. The benzene-water azeotrope boils a t 69.2" C. and contains 8.8% water ( 7 ) . The solubility of water in benzene is 0.057% a t 20" C. (8). Thus, benzene, being an excellent solvent for many substances, is suitable as an azeotrope former when very small amounts of water are determined.
Figure 1. Apparatus for Determination of Water A. B. C. D. E. F. G.
Figure 2. Grease-Sampling Apparatus
Distilling flask Drying tube 25-ml. automatic burets Magnetic stirrer Electrodes Receiver and titration flask Heating mantle
V O L U M E 21, NO. 12, D E C E M B E R 1 9 4 9 Table 111. Results Obtained by Present and A.S.T.M. Distillation Methods Sample Calcium grease Sodium greaee Sodium grease Lithium grease
% Ha0. A.S.T.M. 0.8
1.0 None Less than 0.1 Less than 0.1
% IIZO, Karl Fischer 0.91 0.92 0.038 0.040 0.098
1555 tent. Table I11 shows a comparison of results obtained on different greases by the present method and by the A.S.T.M. distillation method. ACCURACY
The method is accurate to 0.3 mg. of water, as shown by the data in Table 11, which are t,ypical results obtained from a large number of determinations.
0.100
0,099 0.103
stopcocks should not, be used in the direct path of the dist.illing vapors, as they will hold, by capillary action, part of t,he first water-rich distillate, and complete recovery of water will not, be accomplished. Although benzene was found to be a suitable solvent, for most subst,anres analyzed, it was difficult to disperse some greases in it, even on prolonged boiling. Greases were much easier t,o disperse in pyridine and formed a clear solution xith the boiling solvent. The pyridine-water azeotrope boils at. 96.7” C., and contains 43% water, and because water is miscible with pyridine, even large amount,s will remain dissolved in the distillate. In the analysis of greases difficulty with foaming was overcome by the addition of a few milligrams of an antifoam agent t o the pyridine prior to the initial dehydration. The commercially available DC Antifoam A was found to be excellent for this purpose. Table I1 shows the results of a series of samples of known water content. These samples were prepared by first dehydrating the solvent and sample as described in the procedure, cooling the mixture, and adding a weighed amount of water, either from a weighing pipet, or by adding more solvent of known water con-
LITERATURE CITED (1) Aepli, 0. T., and McCarter, W. S.W., IND. ENG.CHEM.,ANAL. ED.,17, 316 (1945). (2) Almy, E. G., Griffin, W. C., and Vilcox, C. S.,Ibid., 12, 392 (1940). (3) Am. SOC.T d n g Materials, Philadelphia, “A.S.T.M. Standards on Petroleum Products and Lubricants,” v . 60, 1947. (4) Benning, A. I?., Ebert, A. A . , and Irwin, C. F., ANALCHEM., 19, 867 (1947).
(5) Evans, R. N., and Davenport, J. E., IND.ENG.CHEM.,ANAL.
ED.,14, 732 (1942). (6) Foulk. C. W.. and Bawden, A . T., J . A m . Chem. Soc., 48, 2045 (1926). (7) Horsley, L. H., ANAL. CHEM.,19, 508 (1947). (8) International Critical Tables, Vol. 111, p. 389, New York, MrGraw-Hill ~ . - . - Book Co.. 1928. (9) Smith, D. My, Bryant, W. SI.D., and Mitchell, J . ,J.A m . Chem. Soc., 61, 2407 (1939). (10) Snyder, R. E., and Clark, 12. O., paper presented before Division of Analytical and Micro Chemistry, 112th Meeting of AM. CHEM.Soc., New York, N. Y., 1947. (11) Suter, H. R., r l s a ~CHEM., . 19, 326 (1947). (12) , , Weaver. E. R.. and Rilev. R.. Ibid.. 20. 216 (1948) (13) Wernimont, G’., and Hopkinson, F’. J.; IND.‘ENG: CHEM., AN~L. ED., 15, 272 (1943). RECEIVED April 1, 1949. Presented before the Divisions of Petroleum Chemistry and Analytical and Micro Chemistry, Symposium on M i c r o chemistry and the Petroleum Industry, at the 115th Meeting of the AMERICAN CHEMICAL SOCIETY, San Francisco, Calif.
Report on Recommended Specifications for Microchemical Apparatus Carbon-Hydrogen, Dumas Nitrogen, Sulfur, and Halogen Committee for the Standardization of 3licrochemical Apparatus, Division of _AnalyticalChemistry, h l E R I C - i N CIIEYIIICAL SOCIETY i L STEYERMARK, Chairman, Hoffmann-LaRoche Znc., .l’utley, iV. J . 11. K. ALBER, Arthur H . Thomas Company, Philadelphia, Pa. V. i. ALUISE, Experiment Station, Hercules Powder C o m p a n y , Wilniington, Del. E. W. D. HUFFRIAR’, Huffman Microanalytical Laboratories, Denver, Cola .I. A . KUCK, College of t h e C i t y of .Yew Y o r k , New Y o r k , \. I-., and 4mericcin Cyanamid C o m p a n y , Stamford, Conn.
.I. .J. MORAN, Iiimble Glass, Division Owens-Zllinois Glass Company, I inplnnil,
V. J .
C:. 0. WILLITS, Eastern Regional Research Luboratory, Philadelphia, Pa.
R
ECOhfMESDED specifications for microchemical apparatus t o be used in connection with the carbon-hydrogen, Dumas nitrogen, halogen, and sulfur determinations have been published by the Committee for the Standardization of Microchemical Apparatus, which was f i s t appointed in 1937 (5-7). At the 112th Meeting of the AMERICAS CHEMICAL SOCIETYheld ~ ~ ~in~September 1947, a in I $ - York by P. J. Elving, then chairman of the Division of Bnalytical and hiicro Chemistry, t o continue this work. This committee has declared its intentions to be as follows ( 1 ) :
1. Where needed, to revise apparatus rerommended by the
former Coninlit tee for t h e 8t:irict:irtlixiition of 1Iicrochsnlical .‘pparatus. 2. T o recommend specifications for other items of quant,itaive micro-, semimicro-, and ultr:tmicroRpparatus. .&iter this, field, attention will be given t,(, thr All recommendations will be made with t,he understanding that the specificat’ionsrepresent the best thought at the present time. Additional revisions will be made when necessary. Primary consideration be given to glass apparatus. The committee has held twelve meetings and has revieweti all of the previously recommended specifications. Changes are being presented for many items to increase efficiency, add
