Determination of Rotenone in Derris Root TH. M. MEIJER AND D. R. KOOLHAAS Laboratory for Chemical Research, Buitenzorg, Java, Netherlands Indies
T
DISTILLING OFF THE SOLVENT.The ether is distilled o f f in a 100-cc. centrifuge tube on a water bath; the tube is filled with the ether solution by means of a dropping funnel. The rotenone which may have separated during the extraction is transferred quantitatively to the tube, and the flask is rinsed out with ether a few times. The final solution in the tube must be 25 cc. The tube is then tightly closed with a cork. CRYSTALLIZATION OF ROTENOSE. To assure complete crystallization, the tube with the ether extract is kept tit room temperature for 1 day and then in a refrigerator for 2 days. The mother liquor is poured into a 50-cc. Erlenmeyer flask and the remaining crude rotenone is broken up with a spatula, with the addition of 10 to 15 cc. of ether. The tube and the Erlenmeyer flask are closed with a cork and placed in the refrigerator for another day. DETERMINATION OF ROTENONE.The rotenone is centrifuged in a laboratory centrifuge (Cenco) for 3 to 5 minutes at 3500 revolutions per minute, and the supernatant liquor is added to the mother liquor in the Erlenmeyer flask. The centrifuge tube with the crude rotenone is dried for 10 minutes in a water bath at 70" C., and after a slow current of air has been passed into the tube, it is dried in vacuo on a boiling water bath for 15 minutes. After cooling in a desiccator the tube is weighed. The difference in weight between the tube CALCULATIONS. with crude rotenone and the empty tube gives the amount of crude rotenone in 50 grams of powder. The purity of the crude rotenone is determined by the melting point, using an empirical table in which the correlation between the purity and melting point is given. If the melting point is lower than 140' C., the mass in the centrifuge tube is treated with another 10 cc. of ether, centrifuged, and dried, and the melting point is again determined. However, sometimes substances other than rotenone, possessing a melting point very near to rotenone (11),may separate from the ether extract. Therefore the authors determine the optical rotation, from which the purity of rotenone can also be determined (13). A correction is made for the amount of rotenone dissolved in the ether of the mother liquor and the ether used for washing. For each cubic centimeter of ether used 4.2 mg. of rotenone are added to the amount of pure rotenone. This multiplied by 2 gives the percentage of pure rotenone in the powder. The degree of purity when determined by the melting point is generally higher than when determined by polarization or alcohol recovery. If rotenone has separated from the mother liquor to which the wash ether has been added, after standing in the refrigerator for another night, it is centrifuged off and added to the crude rotenone. This is often the case with sarnples which contain a small amount of rotenone and a. great deal of ether extract. DETERMINATION OF ETHEREXTRACT. The amount of mother liquor in the Erlenmeyer flask is first determined in a measuring cylinder and then poured into a 500-cc. round-bottomed flask of known weight. The Erlenmeyer flask and the measuring cylinder are rinsed out lyith ether, which is also added to the bulk. The ether is distilled off on a water bath, and the last traces are removed in a vacuum in a water bath not exceeding 40" C. The contents of the flask are blown up to a voluminous mass, and placed in a desiccator over lime for 2 days, after which time constant weight has been reached. The difference in weight between the flask with resin and the empty flask gives the amount of resin. To this the amount of crude rotenone is added, giving the ether extract in 50 grams of the sample. The percentage of ether extract in the sample is found by multiplying the last figure by 2. DETERMISATION OF NOISTURE CONTEST. The moisture content of powdered derris root is determined by drying an accu2to 3-gram sample to constant weight in an rately weighed electric oven at 105' C. From the loss in weight the moisture content can be easily calculated.
HE analysis of derris and cube root for commercial purposes has been a source of unpleasant experience. A
number of claims have risen owing to the different methods used b y various laboratories, and the difficulty of sampling this material has also caused trouble. The present article deals with results obtained b y the methods now in use for the estimation of rotenone and presents a n illustration of the different results which may be obtained when a sample of powdered derris root is analyzed by various laboratories. Early in 1937 a sample of powdered derris root from a wellmixed lot was sent b y the director of the Netherlands Indies Government Plantations a t Batavia to a number of laboratories throughout the world, which deliver certificates on the analysis of derris and cube root, in order to compare the results and to get information. Since t h a t time methods have been improved. Table I gives the outcome of this experiment, and shows t h a t differences of about 4 per cent in the nominal value of the rotenone content may occur. It is curious to note the great differences in the moisture content found by these laboratories; the total ether extract does not show such differences. This undesirable variation can be changed only b y the adoption of a uniform method of analysis. The authors have studied and compared the methods proposed for the determination of rotenone in derris roots, and found that a number of thein give results concordant with the method used in their laboratory. They are convinced that all methods in which extraction is complete and sufficient attention is paid to the crystallization of rotenone or the rotenone-carbon tetrachloride solrate should give practically equal results. Suitable solvents for extraction are ether, benzene, chloroform, ethyl acetate, and trichloroethylene. Carbon tetrachloride should not be used, especially for samples with a high rotenone content, as Seaber (13) and Jones (7) have shown. For a comparison of a few methods of analysis a n article b y Braak (1A) should also be consulted. Jones and his co-workers (3, 6, 7 ) have extensively studied the use of various solvents for extraction and the conditions for the best crystallization of rotenone from carbon tetrachloride.
TABLE I. ROTENONE DETERMINATION Laboratory
Moisture
Total Ether Extract on DryMatter Basis
%
%
%
18.2 19.35 19.1 17.9 18.95 19.2 18.8 18.13 19.16
8.1 8.59 9.75 7.67 8.39 7.5 10.3 6.34 9.8
6
11.32 10.4 9.4 9.3 9.9 5.15 7.18 9.6
Rotenone
on Dry-Matter Basis
Procedure The following method (8) has been in use in this laboratory for some time, during which a few thousand samples have been analyzed. $t least 75 per cent of the powdered root used for analysis must pass an 80-mesh sieve.
DETERMINATION OF ROTENOKE PRESENT. Although the figures obtained by this method in many cases are higher than those found by ot'her laboratories, riot all of the rotenone can be removed from the extract by crystallizat'ion. I n order to get a n idea to what extent rotenone can be extracted from this so-called derris resin, this resin has been fractionated in various ways. One of these efforts was the following:
EXTRACTION.Fifty grams of powder are percolated with ether in a Soxhlet, without a thimble but with cotton wool at the bottom, for 65 hours. The heat used for boiling the ether comes from a 60-watt electric bulb. During the extraction rotenone separates against the wall of the flask in the case of a sample with high rotenone content. 205
INDUSTRIAL AND ENGINEERING CHEMISTRY
206
The resin of the 50-gram sample as it is obtained from the analysis is boiled under reflux in a 500-cc. round-bottomed flask
TABLE 11. ROTENOSEPRESENT IS RESIN Rotenone in Resin Compared with
Originally Found Sample DL.84 D0.18 P.171 DO.155.4 P.133/139 D0.155B DL.203 D0.19 DL.205 KdE.5 P.234 KdE.4 P.223/33 Kdj.3
,f in.4ir-Dried 100 Grams Root Rotenone Resin Grams Grams 7.6 7.7 11.3 10.8 9.7 7.4 11.6 10.5 4.0 6.9 12.6 17.1 20.4 1.4 8.1 13.9 12.8 15.2 1.0 12.6 11.1 7.0 13.1 1.1 5.4 8.8 8.5 9.4
R~~~~~~~ ~~~~d i n Resin
%
%
8.1 5.4 8.5 9.0 2.6 8.5 9.9 6.3 8.6 13.5. 15.9 10.G 3.0 4.4
8.2 5,1 6.5 8.1 4.5 14.3 143 10.8 10.2 17.0 11.7 119.0 4.8 4.8
Grams
TABLE
Pure Rotenone by Koolhaas Method
I %
Sample DO.155
;;:i}ll,2
%
%
10.6;
10.6)lO.G
9.1' 8.8) 8.9
so.500.4 60.509B DL.2179 P.957
99:;) E:;)
$;:j ;:;j
9.4
:;;;> 8 9
P.958 P.1001
E:;}
P.1006
8.6 9.01
21.3
41
8.2
38
g.9
8.3
-0.2
2.9
...
8.3 8.2
0.I 0.5
;;;j 9 , 1 i::! 3 . 1
8.71 8.5 8.31
8.6
8.2
$:;}
3.0
22.5
40
8.9
8.3
22 3
4%
10.4
10.0
22.8
44
20.0
42
8.4
7.7
-0.1
20.0
41
9.7
9.9
9.3
-0.2
22.7
43
8.1
9.8 6.5 6.7
9.4 6.2 6.0
-0.6 -0.3 -0.2
9.9
-0.6
;;:' 3 0 . 5
9.5 10.3 11.4 9.3
9.0 9.8 11.0 8.9
7.9
8.8
8.2
11.2 8.5 5.1 9.9 6.0 1.9 0.8 2.7
-0.8 -0.1 -0.1
9.0
8.3
1.1
8.0
7.7
1.0
8.3
7.8
0.9
8.9 8.4 6.8 2.1 9.9 5.6 9.1 6.4 14.8 8.7
8.4 8.0 6.5 2.0 9.3 5.1 8.4 6.0 14.3 8.2
0.4 -0.6 -0.3 0.4 0.4 -0.4 0.5 -0.3
::}
9.8
;;:;!10.3 8.5 5.3 9.9 6.1 2.0 0.8 2.8
8.3 4.9 9.6 5.8 1.9 0.7 2.6
....
20.3
43
.....
24.6 17.0 16.8
37 36 39
..... .....
23.9
42
22.1 22.6 25.3 22.7
39 44 45 43
.....
.....
.....
..... .....
.....
.....
21.6
37
..... ..... ..... ..... .....
..... .....
28.4 9.3 26.5
41 41 44
..... .....
21.1
48
19.3
47
..... ..... ..... ..... .....
21.5
43
20.7 21.8 18.5 6.7 20.5 18.0 22.1 15.2 33.7 21.2
45 36 35 37 29 43 40 44 40
22.9
49
18.2 12.9 21.8 18.1 5.9 2.8 8.6
47 40 45 33 32 29 32
-0.9
11.4 3.6 11.3
9.0 9.4 8.9} 9 ' 2 9.3 7.8 6.5 2.5 10 3 5.2 9.6 6.1 14.8 8.5
-0.9 -0.3 -0.1 0.3
12.4 3.9 11.8
98::)
....
0.3
8.5
8.6 10.0 11.3 9.8
10.1
P.1377 P.1321 P.1361 DN.13 DN.14 DN.15 DS.16
% 46
8.3
P.901
P.1298
% 24.5
...
11.6 3.8 11.7
P.863 P.1310 P.1313 P.1300 Kd'.34 Kdb.33 P.1339 P.1340 DL.2229 P.1345
;;:;}10.1
7.8
P.1243 P.1285 P.1296
P.845
88:;) E::)
;::;:10.9
8.4
9.9
D0.83
;:;]
%
8.4
P.936
78:;)
::3
O.G
%
RotenoneEther Extract Ratio
...
9.2 6.2 6.5
P.1291
79
Total Ether Extraci
9.7
P.1050 P.1160 P.1213
P.1265 P.1271 P.1277 P.1290
9.0
I - I1
Rotenone by Seaber Method Crude Pure
10.2
l;; $0.2
E::}
3.0
Table I1 gives the amounts of rotenone which were found in the resin. The amount of rotenone still present in the resin is consitlerable especially in cases of low rotenone content and high ether extract. The mean of all the determinations shows that the quantity of rotenone present in the resin amounts to 9 per cent of the quantity originally found, leaving out of consideration the excessive value of samples DL.203 and
9.9:
9.1
9.1
3.0
Gemengd
;:;)
with 100 cc. of petroleum ether (b. p. 60-80" C,). This is decanted after cooling and the residue boiled with 100 cc. of cyclohexane. This also is decanted and the remaining sticky mass, after removing the last traces of cyclohexane in a vacuum on a water bath, is dissolved in the smallest possible amount of carbon tetrachloride. In all cases the authors noticed separation of the rotenone-carbon tetrachloride solvate; this ryas then placed in the refrigerator for one night and the solvate was collected, washed with carbon tetrachloride saturated with rotenone at 0" c.,dried, and weighed. The purity was determined by polarization.
111. DETERMINATIOX O F ROTEXONE
Rotenone by Jones-Graham Uethod Crude I1 Pure
10.6) DL.1228/36
originally Amount Found
T'OL. 12, NO. 4
..... .....
.....
..... .....
.....
...
-0.2 0.9
...
-0.2
...
-0.1 -0.1
...
-0.1
..... .....
.....
.....
.....
.. .. .. ..
50
APRIL 15, 1940
ANALYTICAL EDITION
KdE.4. I n the method proposed by Jones and Graham (6) an excess of rotenone would be added to the extract in the case of such low-rotenone samples as DL.203, KdE.5, and KdE.4 in a n effort to induce more complete crystallization. The amount's of rotenone Jvhich could be detected in t'his way do not represent all the rotenone that was present in the resin, for although petroleum ether and cyclohexane are poor solvents for rotenone, considerable rotenone will dissolve in a solution of the resin in one of these solvents. The amount of rotenone present in the resin may also be determined by means of a chromatogram. About 2.5 grams of the resin are dissolved in 25 cc. of benzene and this solution is passed through a column 15 cm. long and 2 cm. in diameter, filled with Frankonit KL (an activated fuller's earth of the Pfirschinger Pvlineralwerke, Kitzingen-am-Main, Germany). This adsorbate contains traces of iron that can be noticed, owing to the different colors that the phenolic substances present in the resin give with iron salts. The authors noticed a deep green color at the top layer, probably due to toxicarol-like substances, a broxn-purplish color next to it, which may be caused by sumatrol, followed by a vellowish-green zone. This chromatogram is developed with benzene until the yellowish-green zone is washed out. The solution in the suction flask, which is only slightly yellow, is evaporated to dryness, and the last traces are removed in a vacuum. The residue is dissolved in the smallest possible amount of carbon tetrachloride, and worked up in the v-ell-known way. The amount of rotenone obtained in this way was of the same order of magnitude as in the previous determination.
207
TABLE IV. EFFECT OF FINENESS OF POWDER
Sample
Rotenone Content E1 her Koolhaas Jones-Graham Extract 8020080200SO200mesh mesh mesh mesh mesh mesh
% D0.155 P.901 P.1298
DL.2179
P.1277 P.1285 P.1313 P.1339
%
11.2 14.6 10.1 ,. 11.2 1 0 . 2 1318 11.3 .. 3.8 .. 6.5 ,, 9.6 ..
%
%
%
%
9.9 8.3 9.8 9.7 11.0 3.6 6.5 8.4
12.1 8.2 9.5 12.0 12.9 5.6 8.8 9.5
24.8 21.1 22.9 22.8 25.3
31.3 20.9 22.2 30.6 31.4 15.8 26.3 26.3
9.3 18.5
20.5
Chloro-
form Extract :!OO-
Mesh
%
Loss of
1Iaterial on Grinding t o POO-lIesh
% 7.4
4.1 , .
33:6 17.2 28.7 30.3
13: 3 13.3 14.6 16.2 8.5
Comparison of Rlethods Jones and Graham ( 6 ) have proposed a method for the determination of rotenone in derris and cube, in which the powdered root is extracted with chloroform and rotenone is determined by means of its carbon tetrachloride solvate. Similar methods have pre\-iously been described in the literature. Chloroform has been used as a solvent by Danckwortt and Budde ( X ) , Rowaan ( l e ) ,Beach ( I ) , and Seaber ( I S ) , and gives practically complete extraction a t room temperature. The chloroform extract is about equal to the benzene extract ( 7 ) . Therefore "the total extract content" represents the total amount of extractives obtained by one of these three solvents, which for chloroform is the cold extractive content. The extra determination of the ether extract is unnecessary when chloroform and benzene h a r e been used as solvents. The authors have analyzed 40 samples of derris root of varying composition according to their method and the method of Jones and Graham. The first six samples were also analyzed by Seaber's method ( I S ) . Table I11 shows that values for pure rotenone according to the authors' method are practically equal to those for crude rotenone according to Jones and Graham. The mean difference for 35 analyses amounted to only -0.04 per cent. Samples P.1001, P.1050, P.936, P.1265, P.1290, KdE.33, DL.2229, and P.1345 consisted of powder about 80 to 90 per cent of which passed a 200-mesh sieve, whereas of the other samples a t least i 5 per cent passed a n 80-mesh sieve. I n all these cases, except P.1290, the Jones-Graham values for the crude rotenone content are higher than or equal to the authors' values for pure rotenone. This indicates that the extraction of the very fine powder is much more effective. I n order to investigate the influence of the fineness of the powder the authors analyzed a few samples of derris root which were first ground to such a fineness that a t least i 5 per cent passed a n 80-mesh sieve. An average sample was taken and then the remaining powder was again ground to such fineness that a t least i 5 per cent passed a 200-mesh sieve. With this operation a considerable loss takes place, as is shown by the last column of Table IT.'. The loss is mainly due to the very fine dust during grinding in the disintegrator; this dust has the
highest rotenone content. The figures obtained by the analysis of the remaining powder will therefore be rather too low than too high. I n most cases the influence of the fineness of the powder is very great. The increased rotenone content of the powder goes parallel with an increased ether extract. It is remarkable that in samples P.901 and P.1298 this effect of the greater fineness is not noticed; the difference may be caused by the structure of the root, probably depending on the age of the root, so that the cells are more or less easily penetrated by the solvent. Lately Jones (4) has published a titrimetric step in the determination of rotenone. The carbon tetrachloride solvate is converted into the solvate of dichloroacetic acid, containing 1 mole of rotenone to 1 of acid and titrated with standard alkali. The authors have analyzed a series of samples according to this method and have also determined the purity of the carbon tetrachloride solvate as in the Jonea-Graham mode of analysis by alcohol recovery and by polarization, dissolving 0.5 gram of the carbon tetrachloride solvate in 25 cc. of benzene and determining the optical rotation in a 1-dm. tube. From this the specific rotation is calculated; the figure obtained divided by the specific rotation of rotenone x 100 gives the purity of the solvate. I n Table 5' the purities of the solvates found by the three methods are compared and the rotenone contents of the samples of derris root investigated are given. All analyses were done in duplicate. Bccording to Table 5' there is very little difference in the purity of the carbon tetrachloride solvate as determined by the three methods; the alcohol recovery generally gives the lowest values and the polarization the highest, while the titration keeps the middle. The rotenone contents calculated from these purities also show but small differences. If the rotenone is not very pure and contains about 20 per cent of other substances, which is very often the case in the ether method previously described, the titration method
208
INDUSTRIAL AND ENGINEERING CHEMISTRY
cannot very well be used. The impurities interfere nith the crystallization of the dichloroacetic acid solvate. AS the determination of the optical rotation of the carbon tetrachloride solvate in the Jones-Graham method of analysis is even less time-consuming than the titration and the outcome is practically the same, the advantage of this titration method is not apparent although its originality is acknowledged. Jones and Graham (6), discussing the difficulty of extraction when the ratio of rotenone to total extractive material is 40 per cent or more, state, "Another factor that appeared to influence the ease of extraction was the ratio of rotenone to total extractive material. I n samples in which the ratio of rotenone was high, extraction was difficult. The present method will give satisfactorily complete extraction, provided this ratio does not exceed 40 per cent. Fortunately derris and cube samples with a ratio higher than this are rarely encountered." The last column of Table I11 shows that many of the samples analyzed had a ratio higher than 40 per cent. Among the derris roots grown on the estates of Java and bumatra these ratios are not a t all rare and tons of such roots are available. The market will soon get used to these types of derris, as the estates tend to propagate highly selected derris roots, IThich show a fairly constant composition with high ratio of rotenone to total extractives (9). For derris roots with such a high ratio of rotenone to total extract, Jones and Graham recommend four successive treatments of the powdered roots with chloroform. A less time-consuming procedure probably would be to regrind the roots to a greater fineness. Comparison of the t v o methods leads to the conclusion that the pure rotenone content found by the authors' procedure is practically equal to the crude rotenone content by the Jones-Graham method. The rotenone value should not be lowered by applying a correction for the purity of the crude rotenone, as the solvate obtained in the Jones-Graham method is already fairly pure. As the rotenone present in the resin that escaped determination amounted to at least 9 per cent of the estimated rotenone value, the authors suggest using the crude rotenone content by the Jones-Graham method as the figure for rotenone content. The authors have also endeavored to determine the "escaped rotenone" in the resin obtained from the Jones-Graham method. The mother liquor of the crude solvate is evaporated t o dryness and the last traces of solvent are removed in a vacuum on a water bath. The residue is taken u p in 25 cc. of benzene and run on a column of Frankonit KL. From the result the rotenone already accounted for in the rotenone content due to the solubility in carbon tetrachloride, and the rotenone present in the carbon tetrachloride saturated with rotenone, used for washing the solvate, are subtracted. This was done in two cases: I n sample DY.13, in which 5.5 per cent of rotenone was found with the Jones-Graham method, 0.65 gram of pure rotenone for 100 grams of root was recovered. I n sample DN.16 with 2.5 per cent of Intenone (Jones-Graham) the amount of "escaped" rotenone was 0.4 gram for 100 grams of root. As expected, these values are of the same magnitude as recorded above for the resin using the authors' method. The ether-extraction method as described has certain disadvantages, one of the chief of which is the length of time required. This has been partly overcome by an installation in which 24 samples can be analyzed a t the same time. A satisfactory uniform method might be based on the Jones-Graham method, but it must be adapted to samples with a high ratio of rotenone to total extractives. This may be done by grinding the samples to such a fineness that a t least 75 per cent of the sample passes a 200-mesh sieve or by extracting the root several times with chloroform.
VOL. 12, NO. 4
The authors propose to take for the rotenone content the amount of crude rotenone as it may be calculated from the solvate.
Moisture Content of Powdered Derris and Cube Root Jones and Graham (5) make the following remark with regard to drying samples of derris a t a high temperature: "In cases in which a preliminary drying has been made the results for rotenone have usually been slightly lower than on the undried root. There are indications also that drying renders extraction more difficult. Some samples were dried at 100" C. and others a t 50" C. under vacuum." The authors noticed astonishing effects when heating powdered derris root a t 60" and 80" C.(IO). Fifty-gram samples of a lot of powdered derris root, 90 per cent of which passed a 200-mesh sieve, were heated at 60" and 80" C. for 0.5, I,and 2 hours. The samples before heating contained 10.6 per cent of rotenone and 23.6 per cent of ether extract. Table VI shows the results. It is obvious from these figures that heating the sample above 50" C. before analysis in order to diminish the moisture content must be strongly discouraged.
TABLE VI. EFFECT OF DRYING Drying
Rotenone
Ether Extraot
Hours At 40' C .
%
%
10.6 10.3
23.6 23.0
10.3 9.6 8.1
23.0 22.2
6.2 5.4 5.2
15.7 14.6 14.4
0.5 2
A t 60' C . 0.5 1 2
At
so0 c.
0.5 1 2
19.1
Summary and Conclusions The analysis of finely powdered derris root by the etherextraction method has been compared with the method of analysis proposed by Jones and Graham. The pure rotenone content by the former method was equal to the crude rotenone of the latter. I n samples with a fineness of 80 to 90 per cent through a 200-mesh sieve the crude rotenone content by the Jones-Graham method was generally higher. For complete chloroform extraction of samples in which the ratio of rotenone to total ether extract exceeds 40 per cent, a greater fineness than the one given in the Jones-Graham method will be required. The purity of the carbon tetrachloride solvate as it is obtained in the Jones-Graham method is determined by titration of the dichloroacetic acid solvate into which i t has been converted, b y polarization, and by alcohol recovery. Results by these three modes of determination did not differ greatly. A method has been devised for determining the rotenone in the resin which has escaped estimation, involving the passage of the solution of the resin in benzene through a column of Frankonit KL. From a number of samples of resin a t least 10 per cent of the original rotenone could be recovered. Heating derris powder a t 60" and 80" C. for definite periods considerably lowered the rotenone and total ether extract contents.
Acknowledgment The authors wish to thank the analysts, F. Zimmer and J. TVillemsen, for carrying out the various analyses.
ANALYTICAL EDITIOK
APRIL 15, 1940
Literature Cited Beach, D. C., Soap, 12, 109 (1936). .) Braak, H. R., Economisch Weekblad, 8 , No. 18 (1939). Danckwortt, P. W., and Budde, H., Deut. tierarztl. Wochschr., 41, 677 (1933). Jones, H. A,, IND.Exo. C ~ M .Anal. , Ed., 9, 206 (1937). Ibid., 10, 684 (1938). Jones, H. A., and Graham, J. J. T., Ibid., 10, 19 (1938). Jones, H. A., and Graham, J. J. T., J . Assoc. Oficial Agr. Chem., 21, 148 (1938). Jones, H. A., and Sullivan, V. N., J . Econ. Entomol., 31 (a), 400 (1938).
209
(8) Koolhaas, D. R., Bull. j a r d i n botan. Buitenzorg, Series 111, 12, 563 (1932). (9) Koolhaas, D. R., and Meijer, T. M.,Bergcullures, 12, 1045-53 (1938). (IO) Meijer, T . M., Ibid., 12, 1562 (1933). (11) Meijer, T. M., and Koolhaas, D. R., Rec. trav. chim., 5 8 , 207 (1939). (12) Rowaan, P. A., Chem. Weekblad, 32, 291-5 (1935); 34, 605 (1937). (13) Seaber, W. M., J . SOC.Chem. Znd., 56, 168T 1:1937). COMMUNICATION 63 of the Laboratory for Chemical Research, Buitenaorg, Java, Netherlands Indies.
Starch-Iodide Method of Ozone Analysis J
CLARK E. THORP Ozo-Ray Process Corporation, Chicago, Ill.
P
OTASSIUM iodide has been used as a reagent for the detection of ozone for more than 97 years (8). While a common reagent in the analysis of a score of other compounds, it presents a number of disadvantages in ozone analysis, and for this reason many investigators have proposed other reagents (3, d , 6). Many of these methods have been used in this laboratory and found satisfactory, but potassium iodide is preferred whenever a quick and convenient method is desired. Ozone is usually determined quantitatively in air by passing the gas through a neutral solution of potassium iodide, acidifying the solution with acid, and titrating the free iodine with standardized sodium thiosulfate. The greatest sensitivity that could be attained by this method in this laboratory was the detection of 0.0013 mg. of ozone per cc. of 2 LV potassium iodide solution. Air containing as little as 0.1 part per million (by weight) of ozone must commonly be analyzed. This concentration required that 9.9 liters (0.35 cubic foot) of air be passed through each cubic centimeter of potassium iodide test solution before any ozone could be detected by the above method. For quantitative analysis, therefore, enough air should be passed through the sample to bring the error down to less than 0.5 per cent. Various methods have been tried to increase the sensitivity of the potassium iodide reaction (2, 7 ) . The use of thiocyanate ions as described by Ernst may increase the sensitivity of potassium iodide to some compounds, but was found by the author to decrease its sensitivity to ozone. Decrease in the pH of the potassium iodide test solution decreases the stability of the solution to decomposition, but the use of free acid to lower the pH introduces another error due to the formation of hydrogen dioxide. This sets free additional iodine and too high a reading is obtained ( 5 ) . The use of a buffer solution was found by the author greatly to increase the sensitivity of the potassium iodide reaction without introducing an error such as is caused by the addition of free acid. This solution consists of 5 grams of aluminum chloride hexahydrate and 1 gram of ammonium chloride, made up to 1 liter. Five cubic centimeters of this solution are added to each 100 cc. of potassium iodide test solution before the test is run. The solution should not be acidified during the titration. The use of the aluminum chloride solution as outlined above will give a minimum sensitivity of 0.00062 mg. of ozone per cc. of potassium iodide. The potassium iodide solution so treated will have a stability of over 3 hours, which allows plenty of time for the ordinary analysis. Exclusion of light
from the solution will greatly increase stability. Samples of the solution treated as above have been kept for over 40 hours in brown glass bottles before a trace of free iodine could be detected. The ozone sample is drawn through 100-cc. gas-washing bottles each fitted with a Jena glass disk (9) until a definite deep iodine color is noticed in the first bottle. Titration is made with sodium thiosulfate solution standardized against c. P. resublimed iodine. The thiosulfate solution should not exceed 0.01 LV, and a 2-cc. microburet is recommended for greater accuracy. For ozone concentrations of less than 0.5 part per million, the gas-mashing bottle should preferably be of the semimicro type and the test solution should not exceed 10 cc.
Precautions KO cork or rubber should be used in contact with ozone. S o t only does ozone destroy these substances, but they will seriously affect the accuracy of the determination. Groundglass connections are preferable, but neoprene or rubber and cork coated heavily with shellac or lacquer mrty be used. Only ultraviolet light will produce pure ozone. An ozonizer that uses sparks of any kind will produce impurities in the form of oxides of hydrogen and nitrogen. Potassium iodide will liberate free iodine in the presence of these gases also. The author has made numerous ozone analyses on commercial ozonizers, and has found oxide impurities as high as 75 per cent of the total yield. ,4n ozonizer frequently produces as much of the oxides of nitrogen as of ozone, especially in generators which have been in use for some time. To make sure that only pure ozone reaches the potassium iodide bottle ( I ) , an absorption tube containing chromic acid and a tube containing potassium permanganate should be provided before the potassium iodide absorption bottles.
Literature Cited (1) Bamberger and Trautal, Z . anal. Chem., 64, 9 (1924). (2) Baskerville and Crozier, J . Am. Chem. Soc., 34, 1332 (1912). (3) Benoist, L., A m l u s t , 44, 183 (1919). ( 4 ) Briner and Perrollet, Helv. Chim. Acta, 20, 293-8 (1937). (5) Dennis, L. M . , “Gas Analysis”, p. 192, New York, Macmillan co., 1911. (6) Dobson, G. A I . B., “Photo-Electric Cells and Their Applications”, by J. S. Anderson, p. 185, London, Physical and Optical Societies, 1931. (7) Ernst, Biochem. Z . , 232,346 (1931). (8) Schonbein, Verhandl. N a t . Ges. Basel, 4, 58 (1842). (9) Thomas, M. D., IND. ENQ.CHEM., Anal. Ed., 5 , 193 (1933).
