Determination of Camphor and Alcohol in Spirit of Camphor by Refractive Index and Specific Gravity ELMER M. PLEINl AND CHARLES F. POE College of Pharmacy, University of Colorado, Boulder, Colo.
plotted, several four-sided figures were formed and divided into smaller units in order to facilitate the use of the chart. Greater accuracy can be obtained with an enlarged chart with additional subdivisions. The more nearly horizontal lines represent camphor percentages from 7.5 to 11.5 and the more nearly vertical lines represent alcohol percentages from 70 to 90.
1N
EARLIER investigations the authors accomplished the analysis of spirit of camphor by means of 2,4-dinitrophenylhydrazine ( I ) and the optical activity of camphor (8). The method presented here uses the two physical constants, refractive index and specific gravity, and is applicable to synthetic camphor as well as the natural product. Schoorl (8) and Weber (4) used physical constants for the analysis of spirit of camphor official in the Dutch and German Pharmacopoeias, respectively. However, their works are not applicable to analysis of the United States Pharmacopoeial product because the preparations in the Dutch and German Pharmacopoeias contain 10% (by weight) camphor and about 60% (by weight) alcohol. The composition of those spirits therefore varies considerably from that of the U.S.P. produrt.
Table Camphor Present
EXPERIMENTAL
Samples of camphor were obtained from widely different aources over a period of 10 years. Each sample was purified a t least twice by sublimation. The first 10% and the last 5% of the sample were rejected each time. Several solutions containing varying percentages of camphor and of alcohol were prepared from each sample. The solutions studied were made to contain from 7.5 to 11.5% (weight to volume) camphor and from 70 to 90% (by volume) alcohol by the method described in a previous communication (8). The refractive indices of the solutions were determined a t 20' C. with a Valentine, Abbe-type refractometer and the specific gravities were determined with a 25-cc. pycnometer a t 200/20' c. From the refractive indices and the specific gravities of about 100 solutions a chart (Figure 1) was constructed in which the ordinates represent the refractive indices and the abscissas represent the specific gravities. By connecting the points as Present address, University of Washington, College of Pharmacy, Seattle 5, WYesh. 1
Alcohol
Present
%
%
7.50 7.50 7.50 7.75 7.85 7.92 8.00 8.75 8.80 8.90 9.00 9.35 9.40 9.75 9.80 10.00 10.00 10.00 10.00 10.00 IO.00 10.00 10.00 10.00 10.00 10.20 10.60 10.90 11.00 11.00 11.10 11.50 11.50
70.00 87.93 90.00 80.00 77.00 73.00 86.00 78.00 74.00 80.00 88.00 82.50 83.00 87.50 85.00 70.00 74.00 80.00 80.00 80.50 85.31 85.31 85.31 85.31 86.00 83.00 76.00 82.00 75.00 84.00 87.00 70.00 85.00
1.
Analysis of Natural Camphor
Refraotive Index
Speoifio Gravity
Camphor Deter- Varimined ation
%
%
%
1.3719 1.3715 1.3708 1,3726 1.3727 1.3726 1,3724 1.3738 1.3736 1.3739 1.3726 1.3742 1.3743 1.3732 1.3743 1.3747 1.3750 1.3751 1.3751 1.3750 1,3742 1,3743 1,3743 1.3744 1.3740 1.3749 1.3757 1.3756 1.3764 1.3754 1.3746 1.3764 1.3758
0.8780 0.8237 0.8153 0.8503 0.8580 0.8695 0.8297 0.8538 0.8658 0.8479 0.8194 0.8388 0.8365 0,8199 0.8300 0.8751 0.8640 0.8467 0.8465 0.8440 0.8285 0.8280 0.8287 0.8286 0.8250 0.8364 0.8572 0,8375 0.8601 0.8300 0.8188 0.8730 0.8257
7.50 7.41 7.49 7.60 7.75 7.90 7.99 8.74 8.72 8.87 9.05 9.38 9.58 9.64 9.92 10.05 9.94 IO.00 10.00 9.97 9.93 10.06 10.03 10.11 10.02 10.13 10.46 10.77 11.10 10.96 11.09 11.58 11.55
0.00 -0.09 -0.01 -0.15 -0.10 -0.02 -0.01 -0.01 -0.08 -0.03 +0.05 +0.03 +O. 18 -0.11 +0.12 +0.05 -0.06 0.00
70.00 87.80 89.97 79.75 77.08 73.08 85.94 78.05 73.98 80.00 88.00 82.47 83.19 87.52 84.87 69,97 74.00 79.90 79.89 80,64 85.28 85.30 85.20 85.12 86.06 82,84 76.20 82.12 74.85 84.20 86.86 70.00 85.11
0.00 -0.03 -0.07 +0.06
+0.03 +0.11 $0.02 -0.07 -0.14 -0.13
+o.
10
-0.04 -0.01 +o. 08 +0.05
Alcohol Deter- Vanmined ation
% 0.00
-0.13 -0.03 -0.25 +o. 08 +0.08 -0.00 +0.06
-0.02 0.00 0.00 -0.03 +0.19 +0.02
-0.13 -0.03 0.00 -0.10
-0 1 1
+0.14 -0.03 -0.01 -0.11 -0.19 +0.06 -0.16 +0.20
+0.12 -0.15 +0.20 -0.14
0.UO
+o,
11
The chart was used for the analysis of samples of spirit of camphor of known composition. The refractive index and specific gravity of each solution were determined. The point of intersection on the chart found from these two constants was located by reference to the respective ordinate and abscissa. From this point of intersection the percentage of alcohol was determined by following along the nearly vertical lines from the point of intersection to the outside of the four-sided figure, either top or bottom. The percentage of camphor was determined by following the nearly horizontal lines to the outside, either right or left. For example, the refractive index of 1.3740 and the specific gravity of 0.8500 may be selected. After the point of intersection has been found, the alcohol COIItent may be read as 79.29% and the camphor content as 8.92y0.
Figure 1.
Thirty-three samples of spirit of natural camphor of known composition were analyzed by uqe of a chart similar to Figure 1 ; the results are given in Table I. The determined values are in accord with the theoretical values. The camphor content shows variations from -0.15 to +O.lS% and the alcohol content !from -0.25 to +0.20%. Since synthetic ramphor is now used to a considerable extent, several samples of spirit were prepared with the synthetic product col-
Determination OF Camphor and Alcohol
168
ANALYTICAL EDITION
March, 1944 Table
So. 1 1 1
2
2
2 3 3 3 4
1 4 .i .i
.i fi
6
; ;J 8 8
11.
Camphor Present %
Alcohol Present %
10.00 10.00 10.00 10.15 10.00 10.40 9.70 10.00 10, 00 9 30 10.00 11.10 8.00 10.00 10.90 10.00 10.00 10.50 10.00 10.00 9.70 10.00 10.50 9.70
85.56 85.56 85.56 77.00 85.56 84.00 79.00 85.56 86.00 84.00 85.54 81 .OO 80.00 85.56 80.00 85.40 80.00 85.60 85.40 86.00 79.00 85,40 85,60 79.00
Analysis of Synthetic Camphor RefracCamphor tive Specific Deter- Vari-. Index Gravity mined ation
% 1.3741 1.3742 1.3741 1,3754 1.3743 1.3749 1.3749 1.3742 1.3741 1,3739 1,3744 1.3763 1.3730 1.3742 1.3760 1.3743 1.3751 1.3746 1.3742 1.3741 1,3749 1,3742 1.3745 1.3750
0.8275 9.92 0.8279 9.98 0.8277 9.90 0.8549 10.15 0.8278 10.08 0.8321 10.33 0.8501 9.75 0.8278 9.98 0.8260 10.03 0.8341 9.31 0.8277 10.17 0.8406 11.22 0.8486 8.00 0.8277 10.00 0.8147 10.85 0.8284 10.03 0.8467 10.00 0.8250 10.54 0.8286 9.91 0,8250 IO.07 0.8601 9.76 9.91 0,8286 0.8250 10.45 0.8500 9.82
Alcohol Deter- Varimined ation
%
%
%
-0.08 -0.02 -0.10 0.00 4-0.08 -0.07 4-0.05 -0.02 4-0.03 f0.01 4-0.17 4-0.12 0.00 0.00 -0.05 10.03 0.00 +0.04 -0.09 +0.07 4-0.05 -0.09 -0.05 eo.12
85.50 85.35 85.48 77.00 85.34 83.88 78.91 85.43 85.94 83.98 85.33 80.93 80.15 85.45 80.00 85.18 70.90 85.70 85.20 85.97 78.91 85.20 85.77 78.78
-0.06 -0.21 -0.08 0.00 -0.22 -0.12 -0.09 -0.13 -0.06 -0.02 -0.21 -0.07 4-0. 15 -0.11 0.00 -0.22 -0.10 io.10 -0.20 -0.03 -0.09 -0.20 $0.17 -0.22
169
lected from eight different sources; Table I1 shows the results of the analyses, Again these are in accord with the theoretical values. SUMMARY
h chart has been constructed from which the percentagea of alcohol and camphor in spirit of camphor may be determined when the refractive index and specific gravity of the spirit are known. Analyses of different samples of spirit of camphor, whether prepared from natural or synthetic camphor, by the proposed method show close agreement with the theoretical values. LITERATURE CITED
(1) Plein, E. M..and Foe, c. F.,
[email protected].,-4s.k~.ED., 10, 78-80 (1938). (2) Plein, E. M., and Poe, C . F., J. Am. Pharm. Assoc., 3 2 , 89-95
(1943). ( 3 ) Bchoorl, N.,Pharm. Weekblad., 66, 977-86, 1001-9 (1929); Phurm. Presse Wiss. prakt. Heft, 1930, 33. (4) Weber, E., Deut. Apoth. Z t g . , 50, 042-4 (1935).
Precision and Accuracy of Colorimetric Procedures as Analytical Control Methods Determination of Aluminum ALLEN L. OLSEN, EDWIN A. GEE,
AND
VERDA McLENDON Md.
Bureau of Mines, Eastern Experiment Station, College Park,
A colorimetric procedure for the determination of aluminum, calculated and represented as aluminum trioxide and involving the formation of the red complex b y the interaction of the aluminon reagent and the aluminum ion, has been developed to meet the special requirements in the rapid analysis of leach liquors in pilot-plant operations. The factors influencing color intensities have been investigated and the requisite techniques for a precision and an accuracy of a control character are described. Employing these techniques in the analysis of an aliquot of the leach liquor, precision and accuracy studies as applied to ordinary and refined laboratory techniques have been made on typical analytical data. Statistical reasoning based on the standard deviation is applied to the acquired data. Applying ordinary laboratory techniques, the average precision, measured b y the average deviation of the single results from the mean, i s of the order of 1 % or 10 parts per 1000, while the overall accuracy i s of the order of 1 to 3%.
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LMEROUS literature references (7, 8, 12) and recently published books (3, 6, 17') describe in detail the procedures involved in colorimetric determinations. Although the colorimetric method has been used for the rapid estimation of small quantities of many inorganic substances, not a great deal of emphasis has been placed on the precision and accuracy that might be expected in its use as an analytical control method. In quality control work, speed is so essential that precision and accuracy are often sacrificed; however, since intelligent conclusions in plant operations have to be based on the analytical data, it is essential to ascertain the precision and accuracy of the control methods. Recent investigations in this laboratory have been concerned with the colorimetric procedures involving aluminum, titanium, silicon, and sodium. The procedures are, for the most part, adaptations of previously published methods; however, as a
matter of convenience, deviations from standard procedures are necessarily made from time to time, and the subsequent effects of the variables on precision and accuracy are briefly considered. Statistical reasoning based on the standard deviation is applied to the acquired data (1). The purpose of this investigation ie therefore twofold: to describe satisfactory laboratory techniques in colorimetric procedures as applied to aluminum and to evaluate the precision and accuracy that might be expected in routine analyses. The usual procedure in the colorimetric determination of aluminum involves the formation of the red complex by the interaction of the ammonium salt of aurin tricarboxylic acid (aluminon) and the aluminum ion in a carefully buffered solution (3). I n the investigation of aluminum in plants, Winter, Thrun, and Bird (16) conclude that maximum color is obtained in the presence of 10% ammonium acetate when the solution is maintained a t a temperature of 80" C. for 10 minutes and pH 4 (approximately). In the presence of 25 ml. of both ammonium acetate and ammonium chloride, they find that the dye changes color a t about pH 7. Roller (10) states that the red color which aluminum ion gives with aurin tricarboxylic acid is much more sensitive if made a t about pH 6.3 instead of in alkaline solutions aa recommended by Poe and Hill (16). The latter authors, investigating the procedure under different experimental conditions, cite five factors that affect the test for aluminum with aluminon: time, temperature, volume, concentration, and the presence of vther ions. Lampitt, Sylvester, and Belham (5) sug est the use of glycerol to stabilize the lake formed. Thrun ( I S ) %as investigated the use of protective colloids in colorimetric determination of certain metals as lakes of dyes and recommends the use of a gum arabic solution to keep the aluminum lake of aurin tricarboxylic acid in solution. The colorimetric method presented here for the determination of aluminum, calculated and represented as aluminum trioxide, has been developed at this station to meet the special requirements in the rapid analysis of leach liquors in pilot-plant operations. The sample taken for analysis must be free from inter-
