cause it is tiifficultly soluble in organic solvents (6). The results obtained by tlic proposed method for five samples of nitrocellulose that had been analyzed accurately by the nitrometer method by Picatinny Arsenal are shon-n in Table I. The results compared 1x11 with the results b y the nitrometer method. The precision for the proposed method (average about i0.09yo) is satisfactor>- but is not as good as that obtainable by the nitrometer method in the hands of an experienced operator. The source of the nitrocellulose did not affect the results obtained by the infrared method. ACKNOWLEDGMENT
The authors are indebted to Kilmer White for his assistance and Samuel Sitelman for his suggestions. Also, they
thank Milton Roth and Hyman Jadon-ita of Picatinny Arsenal for furnishing accurate standards needed for this project. LITERATURE CITED
(1) Allen, P. W., “Techniques of Polymer Characterization,” pp. 11, 12, 15,
Butterworths, London, 1959.
( 2 ) Barrow, G. hi., Searles, S., J . Am. Chem. SOC.75, 1173 (1953). (3) Doolittle, A. K. “Technology of
Solvents and Plaiticizers,” p. 527, Wiley, New York, 1954. (4) du Pont de Semours, E. I., and Co., LLPropertiesand Uses of Tetrahydrofuran.” Wilmineton. Del.. 1960. (5) Fisher Scientih Co., “Fisher Chemical Index,” p. 280, New York, 1959. (6) Hercules Powder Co., “Nitrocellulose, Prouerties and Uses.” . _UP. - 1,. 2,. Wilminaton; Del., 1955. ( 7 ) Kagarise, R. E., Weinberger, L. A “Infrared Soectra of Plastics a d Resins,” 1L’a;al Res. Lab. Rept. 4369,
X a y 1954 (U. S. Dept. of Comrnerce ltept. No. 111438). (8) Kuhn, L. P., ANAL.CHEM.2 2 , 276 (1950). (9) Military Standard, Propellants: Sampling, Inspection, and Testing, MILSTD-286, p. 56, June 1956. (10) Mitchell, J., Kolthoff, I. AT., Proskauer, E. S Weissberger, A., “Organic Analysis,” $01. 2, p. 102, Interscience, New York, 1954. (11) Pierson, R. H., Julian, E. C., ANAL. CHEM.31,589 (1959). (12) Pristera, F., Halik, hl., Castelli,. A., Fredericks, W., ”Analysis of Explosives by Infrared Spectroscopy,” Picatinny Arsenal Tech. Rept. 2254, May 1956. (13) Rosenberger, H. M., Shoemaker, C. J., ASAI,.CHEM.31,1313 (1959). (14) Shreve, 0. D., Heethcr, M. R., Knight, H. B., Swern, D., Ibid., 23, 277 (1951). HARRYLEVITSKY GEORGE NOR-WITZ Pitman-Dunn Laboratories Frankford Arsenal Philadelphia 37, Pa.
Conductometric Determination of Sulfate by the Nonaqueous Barium Acetate Method SIR: A method for the determination of sulfate has been reported in which the sulfate is precipitated in an acetic acid medium by the addition of an excess of barium acetate [Goldstein, G., Menis, O., Manning, D. L., ANAL. CHEM. 33, 266 (196l)l. The excess barium acetate is then determined potentiometrically by titration with perchloric acid. Conductometric titration of the excess barium acetate has since been found to be satisfactory and to offer a n advantage over the potentiometric method in that water does not have to be excluded completely from the sample. A Leeds and Sorth-
0
L
1
2
3
4
5
6
V O L U M E OF 0 . 0 3 N HCI04, ml.
Figure 1 . Effect of water and acetic anhydride on conductometric titration with perchloric acid of barium acetate in acetic acid Conditionr; Total volume of solution titrated, 50 ml. Ba(CHaC0O)t present, 0.1 5 meq.
rup conductance bridge (Catalog Xo. 4866) and two platinum electrodes (2 X 2 cm. and fixed 1 cm. apart) were used in all titrations. Effects of Water and Acetic Anhydride. T h e results of t h e conductometric titrations of barium acet a t e with perchloric acid are shown in Figure 1. T h e titrations were conducted in anhydrous acetic acid and also in acetic acid solutions t h a t contained 2 vol. yo water or 10 vol. % acetic anhydride. T h e reaction before t h e end point is t h e neutralization of the barium acetate ion with the perchloric acid. If i t can be assumed that the degrees of dissociation of barium acetate and of barium perchlorate in anhydrous acetic acid are approximately the same, then the small initial increase in conductance is probably due to the greater ionic conductance of the perchlorate ion. A leveling off of conductance with increasing concentration is typical of weak electrolytes. Conductances are greater in acetic acid solutions that contain 2% water or 10% acetic anhydride than in anhydrous acetic acid, because of the increase in the dielectric constant. The slope of the titration curve in the region beyond the end point is greater in the presence of 2% water than when water is absent. This small volume per cent of water is therefore beneficial in the conductometric titration b u t is detrimental in the potentiometric method. However, when the concentration of water is as high as 10 vol. yo, the initial conductance is very high, and the end
point of the titration is not clcnrly defined. Effect of Barium Acetate. T h e titration curves of solutions t h a t contained 0.07 meq. of sulfate a n d various amounts of excess barium acetate are shown in Figure 2. In general, a rather wide range i n concentration of excess barium acetate can b e tolerated without effect on t h e shape of t h e conductometric titration curves. For optimum conditions, however, i t is desirable to adjust the
c , ; 0
]
I
,
_A_--
1 2 3 4 5 VOLUME O F 0 . 0 3 N HCIO,,
6 rnl
Figure 2. Effect of excess barium acetate on conductometric titration of SUIfate with perchloric acid Conditions: Total volume of solution titrated, 50 ml. Volume of 0.05N Ba(CH3COO)t used, as indicated Sulfate present, 0.07 meq. VOL. 3 4 , NO. 9, AUGUST 1962
1169
samplc aliquot and the volume of barium acetate solution to back titrate an ewess of about 4 ml. of 0.05-V barium acetate in a total volume of approximately 60 nil. Under optimum conditions, the precision and accuracy are comparable to that obtained by the potentiometric method. Effects of Foreign Ions. T h e effects of various anions a n d cations in the potentiometric determination of sulfate have been evaluated [ANAL. CHEM.33, 266 (196l)l. T h e same anions will interfere regardless of t h e method used to detect t h e end point. Certain cations t h a t form basic acetates also interfere in t h e titration of barium acetate. Attempts were made to determine conductometrically the sulfate in potassium sulfate, nickel sulfate, and ferric sulfate to learn whether the corresponding acetates, which are produced by the reaction of barium acetate with the sulfate salt, can be distinguished from barium
y - v r - - - -
4 0 Y O
i
7-
---
--
I l l 2 3 4 5 6 7 VOLUME OF 0 0 3 N HCI04 , m .
8
Figure 3. Conductometric titration curves of various sulfates Conditions Total volume of solution titrated, 50 ml. Ba(CHaC00)Z present, 0.20 meq. Sulfate present, 0.05 meq.
acetate b y conductometric titration. The titration curves obtained are shown in Figure 3. I n each case, the theoretical end point is 5 ml. A correct
and well-defined end point was obtained for ferric sulfate. I n the case of potassium sulfate, a sharp break in the curve occurred only after both the potassium acetate and the excess barium acetate had been titrated. For nickel sulfate, there was no well-defined break at any point in the titration curve. It is apparent that in the conductometric titration barium acetate can be differentiated from the very weakly basic ferric acetate but cannot be distinguished from either potassium acetate, which is a somewhat stronger base, or nickel acetate, which is a somewhat weaker base. GERALDGOLDSTEIN D. L. MANNINQ H.E. ZI’ITEL Anal tical Chemistry Division Oak k d g e National Laboratory Oak Ridge, Tenn. The Oak Ridge National Laboratory is o erated by Union Carbide Corp. for the S. Atomic Energy Commission.
8
Deter mina tio n of Ethy le ned ia mine in 2-Met hy Ipipe ra zi ne SIR: Near infrared spectrometry has been very useful in organic quantitative analysis. Kaye (1, 2) in his reviews of near infrared spectroscopy points out t h a t this region of the spectrum is concerned primarily with hydrogenic stretching vibrations of CH, NH, and OH, their overtones and combinations. I n a general study conducted in this laboratory on methods of analysis of amine mixtures, a striking difference was observed in the near infrared spectra of ethylenediamine and 2-methylpiperazine. This difference was then used to develop a method for the determination of ethylenediamine in 2-methylpiperazine. A t a wavelength of 2.02 microns, ethylenediamine exhibits a strong absorption band which is not present in 2methylpiperazine. A further investigation showed that although 2-methylpiperazine does not exhibit a strong
Table 1.
Differential Analysis of Ethylenediamine
Ethylenediamine, Moles/Liter Added Found 0,019 0.028 0.039 0.051 0.059 0.070
0,019 0.028 0.038 0.050 0.058 0.071
1 170
0
Deviation, Moles/ Liter
Deviation, Mole %
0.000
0.0
0.000
0.0
0.001 0.001 0.001
2.6
0.001
ANALYTICAL CHEMISTRY
2.0 1.7 1.4
band at 2.02 microns, increased concentrations of 2-methylpiperazine caused an increase in the background transmission. It was possible to eliminate this interference by differential analysis. This technique has been discussed by Robinson (4) and McDonald (3) in their publications. Washburn and Scheske (6) have applied i t to the determination of traces of ketone in a carbinol. Differential analysis is particularly suited for use with double beam instruments. The effect of the interfering material in the sample solution is compensated by placing a solution of the solvent and interfering material in the reference beam. The resulting absorbance is due to the desired constituent only. EXPERIMENTAL
Apparatus. A Perkin-Elmer Spectracord 4000 double-beam spectrophotometer equipped for use in the near infrared with 10-mm. silica cells. Reagents. Although reagent grade carbon disulfide and carbon tetrachloride are excellent solvents for use in t h e near infrared, neither can be used with amines because amines react rapidly with carbon disulfide and slowly with carbon tetrachloride. M a n y solvents were found for ethylenediamine and 2-methylpipera~ine~ b u t most of them absorbed too strongly t o be of use. Pyridine, reagent grade, although exhibiting strong absorbance in the near infrared, was found to transmit sufficient energy at 2.02 microns to permit its use as solvent for this system. Both ethyl-
enediamine and Zmethylpiperazine are readily soluble in pyridine. Beer’s law. Solutions of varied concentrations of ethylenediamine in pyridine were prepared and t h e transmittance was measured at 2.02 microns. Ethylenediamine i n pyridine obeys Beer’s law at 2.02 microns as demonstrated b y t h e constant absorptivity. For 12 solutions examined, the average deviation of t h e absorptivity was +0.77%. Procedure. Solutions of 2-methylpiperazine in pyridine were prepared with varied amounts of ethylenediamine from 0.019 to 0.071 mole per liter of pyridine plus 2-methylpiperazine. A reference solution was prepared containing approximately the same amount of Zmethylpiperazine in pyridine ea the sample. The differential absorbance between the reference solution and the sample solution was measured at 2.02 microns and the results were calculated as ethylenediamine. The data obtained are presented in Table I. The average deviation of ethylenediamine in moles per liter is 0.0007 or 0.7 mole %. The data presented in Table I correspond to a concentration range of approximately 3% to 18% ethylenediamine in 2methylpiperazine. DISCUSSION
Effect of Water. Water exhibits a strong absorbance at 1.94 microns. Its effect on t h e absorbance of ethylenediamine at 2.02 microns was investigated b y preparing solutions of 2-methylpiperazine and ethylenediamine in pyridine with varied
