A New Polarographic Method for the Microdetermination of Chloropicrin in Air BEN BERCK and JOHN SOLOMON Canada Department o f Agriculture Research Station, Winnipeg, Manitoba
b A new polarographic method using the dropping mercury electrode and a Ag-ASCI reference electrode was developed for direct determination of chloropicrin in air in amounts as low as 2 0 pg. The over-all precision ranged from k l . 1 to k5.070 in the to concentration range 4 . 2 7 X 1.22 X 1 O-5M. Solutions were stable and no interference was shown b y admixture of chloropicrin with 100 times its weight of carbon tetrachloride, methyl biomide, ethylene dibromide, ethylene dichloride, or chloroform. Acrylonitrile seriously affected the plateau of the chloropicrin wave. Results of representative analyses of air samples taken from fumigated grain, flour, and soil are presented.
s
of chloropicrin (CP) are toxic t o soil fungi, insects, nematodes, and weed seeds. C P is generally considered as the experimental standard when comparing soil fungicides ( 7 ) . Under suitable conditions it is a good grain fdmigant and it is also used as a spot fumigant in flour mills to treat insect-infested mill stocks, machinery, etc. (4). Small concentrations in air produce tears or coughing, and C P is therefore used as a warning agent in combination with other toxic gases, e.g., in 2YG w./vi. Ivith methyl bromide, 5% w./w. with hydrogen cyanide, etc. These and similar uses indicate the value of methods of measuring C P in problems such as the assessment of biological effectiveness, the distribution and persistence of C P in various systems, change in proportions after application of gas mixtures containing CP, C P residues in foodstuffs, and so on. This investigation stemmed from the need for a direct and rapid method of measuring micro quantities of chloropicrin in air t o assess the toxicity a t various temperatures of small amounts of C P applied to various species of insects, and to determine the sorption of C P by glass fumigation flasks (9). Polarography with the dropping mercury electrode (D.M.E.) was chosen for this purpose. Development of a direct method using the saturated calomel electrode as reference electrode was not successful a t the time and a n
#18Ag W i R E DeKHOTlNSKY CEMENT RUBBERPLUG
I
-1
I@K C I
.
nr
# 18 Ag SPIRAL
IOmm GLASS TUBING K N 0 3 - A G A R GEL
MALL AIfOUKTS
514
0
ANALYTICAL CHEMISTRY
Figure 1 .
Ag-AgCI
electrode
indirect polarographic method (1j, whereby C P was hydrolyzed t o C1-, was used instead. Amounts as low as 50 p g . of C P were thus measured. However, a time interval of 41/2 hours existed between the taking of a sample and the analytical result. Prior exploratory research with the spectrophotometric method of Feinsilver and Oberst (6) was abandoned because it was considered to be time consuming and not adequately reproducible a t low concentrations. During recent tests with a Ag-ilgC1 electrode as reference electrode, i t was found that C P could be measured directly in amounts as low as 20 pg. per 10 ml. of trapping solution, with an over-all precision that ranged from *l.l t o =t5.0% in the concentration range 4.27 X to 1.22 X lO-5M. Results could be obtained within 10 minutes after sampling. Test solutions to encompass the range 0.002 to 7.0 mg. of C P per ml. were stable a t room temperature for a t least 4 months. This report presents details of method, and representative analyses of air samples taken from soil, wheat, and flour that were fumigated with CP. APPARATUS A N D REAGENTS
Recording polarograph. A Radiometer Model POa (Radiometer Co.,
Copenhagen, Denmark) with a galvanometer sensitivity of 0.00035 pa. per mm. full scale was used to record polarovalues of graphic waves. The mz'3t1!6 the D.M.E. capillary lvere 2.414, 2.449, 2.467, 2.461, and 2.453 mg.2i3sec.-If2 a t +0.2, 0.0, -0.25, -0.50, and -0.i5 volt us. S.C.E. a t 25" C. in a medium of 80% methanol with 0.08.Y HNOI and 0.057G gelatin. Ag--4gC1 electrode. -4d g - d g c l electrode was used as reference electrode (Figure 1). Pure silver wire, 18 gage, was spiralled bo a convenient length (12 turns), and thoroughly cleaned with mild det'ergent solution and rinsed. The helis was hooked up to :i 11,'2-volt cell as a receptor electrode (anode) u i t h another piece of d g wire as cathode. N t ' h the electrode tip and helix immersed in saturated KCl solution, the current polarity was alternately reversed bo clean and recoat the receptor, until i t turned violet. After rinsing n-ith distilled water, the lead wire was put through a tight-fitting rubber plug and sealed with DeKhotinsky cement. The tube ivas then clamped in a n inverted position and 1.21 KC1 solution was put in by syringe to the level s h o m . K i t h the tube still inverted, a hot mixture of 3N KN03 and 37, wv./v.agar ivas dispensed v i t h a syringe and B 6-inch 18gage hypodermic needle over the KC1 solution in such a way that no air bubbles were occluded in the gel mixture. This was done by placing the needle tip a t the liquid/air interface and then s l o ~ l ydischarging the contents of the syringe while bringing the needle up, but always below the surface of the mixture. After the tube was filled and the agar mixture had gelled, the electrode was thoroughly rinsed and then preconditioned by testing with 5 or 6 replicate samples prior to regular use. A spare electrode was constructed. The electrodes were stored in test tubes containing 1% KXOs solution that was changed twice per week. Polarographic cells and gas absorption apparatus, as in ( 1 ) . Sample tubes. Borosilicate glass, 125 X 16 mm. 0. D., without rim (Cat. No. 46048, Kimble Glass Division, Owens-Illinois Glass Co., Toledo 1, Ohio), calibrated to a 10-ml. mark. Glass syringes, in lo-, 20-, 30-, 50-, and 100-ml. sizes, fitted with mechanical stops, after Chaney (S), and calibrated by weighing the volumes of water delivered. Hypodermic needles, ao-gage, Luerlok, in 2-, 4-,and &inch sizes (Becton. Didkinson and Co., Rutherford,. N. J.):
for comparison of stability after storage a t 3" C. in the dark us. storage a t room temperature exposed to light.
.03 mg./ml.
2.1
,x'
+5 1.4
PROCEDURE
K
a 2
0
0.7 0 +0.2
0
-0.2 -0.4 -0.6 APPLIED € . M I , volts
-0.8
Figure 2. Typical current-voltage curves for chloropicrin Medium in polarographic cell consists of approx. 80% v./v. methanol with 0.05% gelatin solution as maximum suppressor and 0.08N nitric acid solution os supporting electrolyte. Ag-ASCI electrode os reference electrode a t 25' C.
Chloropicrin. Khite label, No. 1426 (Eastman Organic Chemicals, Rochester 3, s. I-,). Polarographic maximum suppressor. Two types were used : A . Gelatin solution, 1% w./v., prepared in a boiling water bath and stored a t 3" C. A fresh solution was made after 5 dq-s. The gelatin solution was used for teat samples that nere to be analyzed nithin 1 week. in which case the gelatin solution was added a t the rate of 0.5 nil. to 9.5 nil. of the methanol -nitric acid solution used for gas trapping. B. AlLyl aryl polyether alcohol, 0.47, aqueous solution (Southwestern Analytical Chemicals, Austin 2, Tex.), This m s used for test samples to be stored for more than 1 week, in which case the suppressor solution was added a t the rate of 0.5 ml. to 9.5 ml. of methanol-nitric acid solution. Gas-trapping solution. This consisted of 940 ml. of 85% v. /v. methanol, 50 ml. of maximum suppressor (Type A or B ) and 10 ml. of 8.0-47 nitric acid solution per liter. The final mixture contained approximately 80% v./v. methanol. Nitrogen for osygen removal. Tank nitrogen, high purity, dry, 99.99% pure, (Lnion Carbide Canada Ltd., Linde Gases Division, Toronto, Canada), presaturated with blank solution, was used for deaeration of the test solution in the measurement cell. Fumigant standards. Twelve C P standard solutions, for use in preparation of standard calibration curves and for periodic check tests, were made from serial dilutions of a stock solution prepared by weighing 1.000 gram of C P in a 100-nil. volumetric flask and diluting to the mark with 85% methanol. Each standard was made up to 100 ml. with the inclusion of 5 ml. of maximum suppressor ( A or B ) and 1 ml. of 8.0.l' nitric acid solution and was stored in 4-oz. clear flint glass prescription bottles with Bakelite screw caps fitted with polyethylene liners. The concentrations of the standards were: 2, 5, 10, 30, 50, 100, 200, 300, 400, 500, 600, and 700 pg. of C P per ml. of solution. Two sets of standards were made
From standard solutions described above, prepare a calibration curve for the range 0.002 to 0.7 mg. of C P per ml. Transfer a 4- to 10-ml. portion of each standard solution to the electrolysis cell. (Exact volume of aliquot is not important when standards are prepared as indicated). Deaerate for 4 minutes with nitrogen a t a flow rate of 30 cc. per minute (longer periods may be used). Record the wave in the range S 0 . 2 to -0.8 volt, with the Ag-AgC1 electrode as anode. Plot the diffusion current values, deducting the residual current of the blank. Air samples may be taken conveniently with glass syringes fitted with mechanical stops. Dispense 10 ml. of gas-trapping solution by calibrated syringe or automatic pipet into sample tubes and chill in an ice bath or refrigerator. Discharge the air samples into the trapping solution manually, or semiautomatically by controlled vacuum ( I ) , a t a rate of 30 to 33 cc. per minute through 20-gage 6-inch stainless steel hypodermic needles. Stopper the tubes with polyethylene stoppers (or cork stoppers lined with polyethylene sheeting), and store in a refrigerator until required. For analysis, transfer a Sample, or a portion thereof, to the polarographic cell, deaerate with nitrogen for 4 minutes, and record the wave in the range $0.2 t o -0.8 volt, using the Ag-AgC1 electrode as anode a t 25" C. RESULTS A N D DISCUSSION
Figure 2 shows typical currentvoltage curves in the range +0.2 to -0.8 volt a t 25" C. Instrument sensitivity of 1/100 was used, the wave height being measured a t -0.6 volt in this instance. For moderately low concentrations, such as in Figure 2, gelatin may be omitted, but a t higher concentrations it is beneficial in suppressing maxima and flattening the plateau with no loss in wave height. A high concentration may nevertheless show a double wave, in which case the diffusion current shown by the second or main wave is measured. The prewave generally occurs a t concentrations greater than 3 mg. of C P per 10 ml. of test solution and may in any case be eliminated by dilution of the sample, or by using a new and smaller air sample. The E1/z values (approximating -0.15 volt a t low concentrations) become somewhat more negative as the concentration increases, whereupon wave height may be measured on the plateau a t -0.7 volt in accordance with the concentration level. Prolonged deaeration with nitrogen does not alter the wave height. The current-concentration relationships shown by two companion calibration curves were linear and reproduc-
Table 1. Concentration of Chloropicrin a t Surface of Fumigated Flour, Wheat, and Soil a t 25' C. (Mg. per liter of air)
Hrs. after Application 1 3
Flour
Wheat
10.0 7.4
38.4 44.4
Soil 11.1 11.0
12 24 30 48 54 72 96 120
7.8 5.6 4.8 4.0 2.7 1.9 1.3 0.8
24.0 12.6 9.3 6.5 4.6 2.4 1.6 1.2
8.6 4.1 3.3 1.5 1.1 0.5 0.1 0.0
ible. The smaller curve enabled measurements in the micro range, and was obtained with an instrument sensitivity of 1/70. It was thereby possible to determine 2 pg. of C P per ml. of solution (equivalent to 20 pg. of C P per 10 ml. of gas-trapping solution). JT'ith 20 pg. set as the lower limit, the over-all precision in the range 7.0 to 0.02 mg. of C P per 10 ml. (equivalent to 4.27 X 10-3 t o 1.22 x lO-5M) Bas + l . l to =t5.0%. Less than 20 pg. was measured on occasion, and in such instances the method of standard addition (6) was used to offset loss in precision. When deviations greater than .t596 were noted, a new pair of samples was obtained if possible, or the performance of the reference electrode was checked against that of the spare Ag-AgC1 electrode that was made for standby purposes. Reproducibility and wave contours, as well as comparative length of "foot" of the polarographic wave, 75-ere somewhat more satisfactory with the Ag-AgC1 than with the S.C E . as reference electrode. (In subsequent tests, it was found that 0.08147 HzSO4, but not HC1 or acetic acid, could be satisfactorily substituted for 0.08-h' HNOs as supporting electrolyte.) The specificity of measurement of CP in the presence of other fumigant gases was examined. Acrylonitrile seriously affected the plateau of the C P wave. Sulfur dioxide, particularly a t high concentrations, interfered with true wave height of CP, although the SO1 wave itself was affected to a negligible extent. No interference, however, was shown by admixture of C P with 100 times its weight of carbon tetrachloride, methyl bromide, ethylene dibromide, ethylene dichloride, or chloroform, regardless of whether these concomitants were present singly or all mixed together. The method was used to check the reproducibility of sampling air taken VOL 34, NO. 4, APRIL 1962
515
from 24 all-glass Strand fumigation flasks to which C P had been applied in the range 0.25 to 10.0 mg. per liter ( 2 ) . Such flasks are commonly used in fumigant research and have an average capacity of about 6.25 liters. Duplicate air samples ranging from 25 t o 100 cc. in volume and dispensed semiautomatically ( 1 ) were consistently in good agreement. A gas concentration as low as 0.2 mg. per liter (equivalent to 29.7 p.p.m. of C P at 25” C. and 760 mm. of Hg) could readily be determined in a 100-cc. sample. The relative sensitivity may obviously be lowered in instances where larger samples may be taken, as in investigations of atmospheric pollution, where samples of 20 to 100 liters are commonly used. Results of a test run of the analytical method on fumigated flour, wheat, and soil are shown in Table I. For purposes of the test, three heavy-walled domestic polyethylene dishpans, 103/4 X l F / 4 X 5’/4 inches, were each filled t o a 0.2cu. ft. mark (approximately 3 inches depth) to contain respectively, 3.63 kg. of flour, “second patent” grade, 13.5%
moisture content; 4.89 kg. of Mindum wheat (a durum variety), 12.6% moisture content; and 7.17 kg. of potting soil, 28% moisture content. Each container was covered with polyethylene sheeting, I’/z mil (0.0015 inch) thickness, which was taped on to provide a tight cover. The cover m s marked in a n X-pattern a t 5 equidistant points. The cover was successively pierced by a 1-ml. Chaney-type syringe fitted with a 6-inch needle to dispense 1 ml. of C P liquid in five 0.2-ml. portions to within inch of the bottom of the container. The holes were immediately covered with cellulose tape. The containers were placed in a fume chamber and 25-cc. samples of the “supernatant” air-Le., just above the surface of the treated commoditywere taken a t periodic intervals by introducing the syringe needle through the center hole. The data in Table I do not necessarily reflect field or natural conditions, but the experimental procedure nevertheless is a simple and rapid method of demonstrating differences in sorption patterns. The main objective was to
obtain additional performance data. C P residues as such were not determined, but the polarographic method described herein should be adaptable for such purposes. LITERATURE CITED
(1) Berck, B., J . Agr. Food Chem. 10,
158 (19621. (2) Beick, ’B., Liscombe, E. -4. R., Solomon, J., unpublished data. (3) Chaney, A. L., IND.ENG.CHEX., ANAL.ED. 10,326 (1938). (4)Cotton, R. T., “Insect Pests of Stored Grain and Grain Products,” 2nd ed., Burgess Publishing Co., Minnea o h , Rlinn., 1950. (5) Feinsiyver, L., Oberst, F. W., AKAL. CHEM.25, 820 (1953). (6) Kolthoff, I. M., Lingane, J. J., “Polarography,” 2nd ed., Chap. XVIII, Interscience, Kew York, 1952. (7) Munnecke, D. E., “The U. C. System for Produein!, Healthy ContainerGrown Plants, Chap. XI, Manual 23, University of California Agricultural Ex erimental Station, Los Angeles, CaEf., September 1957. RECEIVEDfor revie%. July 31, 1961. Accepted December 4, 1961. Contribution No. 95, Can. Dept. of Agriculture, Research Station, Winnipeg, Man., Canada.
Determination of 2-lsovaleryl-1,3-indandione with 2,4-Dinitrophenylhydrazine Rodenticide Analysis CALVIN M. MENZIE, VYTO A. ADOMAITIS, and WILLIAM L. REICHEL Pafuxenf Wildlife Research Center, U.
S. Fish
b At present, three 2-alkyl-lI3-indandiones (PMP, pival, and diphacinon) are widely used as rodenticides. Because analytical procedures now in use are empirical and do not furnish adequate or positive means for distinguishing among these closely related compounds, studies were undertaken to develop a sensitive and specific method for the determination of PMP. The relation between KCN and the 2,4-dinitrophenylhydrazone of PMP was investigated and shown to b e A deeply sensitive and specific. colored solution is produced with an absorption maximum a t 540 mp. This solution obeys Beer’s law over a wide range. The molar absorptivity for the developed color was calculated to b e 3.0 X lo4. This reaction can b e used also as a spot test to detect as little as 1 pg. of PMP.
516
ANALYTICAL CHEMISTRY
and Wildlife Service, laurel, Md.
A
PRESENT, three 2-alkyl-1,3-indandiones-PMP [2-isovaleryll,3-indandioneIl pival [2-pivalyl-1,3indandione], and diphacinon [2-(2,2diphenylacetyl) - 1,3 - indandionelare widely used as rodenticides. Analytical procedures now in use (3, 4) are empirical and do not furnish adequate or positive means for distinguishing among these closely related compounds (Figure 1). Increased use of P M P has made the need for a sensitive and specific method of analysis more apparent. Preliminary tests with 2,4-dinitrophenylhydrazine indicated that the reactivity of the PAIP derivative differed markedly from that of the other compounds. Quantitative studies were made to determine the applicability of this reaction to routine analysis. T
PROCEDURE
Reagents. 2,4-Dinitrophenylhydrazine, 100 mg. dissolved in 85 ml. of 95% ethyl alcohol and 15 ml. of concentrated HC1; alumina, washed with dilute HC1 and then with distilled water t o the p H of the water; 10% aqueous K C N ; P M P , 1 mg. per ml. of 9.5% ethyl alcohol. The best available PRIP (about 9575) was recrystallized several times to obtain crystalline material with minimal melting point range 66.567’ C. As Spot Test. On a piece of filter paper, place a drop of the ethyl alcohol solution of the rodenticide. Add 2 drops of 2,4-dinitrophenylhydrazine solution. Allow t o dry. Karm gently. Add 2 drops of 10% K C N and warm until dry. Then add 10 drops of ethyl alcohol slowly and dropwise to t h e center of the spot. Upon drying, a purplish color appears in the presence of PMP; a yellowish
