Spray Residues of Tartar Emetic on Citrus Leaves Determination by Iodometric Titration R. L. BUSBEY AND ROBERT A. FULTON Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, Whittier, Calif.
tartaric acid and titrated with iodine; 5.84 mg. of tartar emetic ARTAR emetic is now used to control certain species of were removed from the leaves compared with 5.78 mg. added. thrips, especially the citrus thrips, ~ c i r t ~ dtri ~ h ~ i The ~ ~correction factor for the leaves used was 0.02 mg. per 32.6 (Moult.), on lemons and oranges. When i t is used for the sq. cm. of leaf surface (average area of leaf). When the corcontrol of the citrus thrips, i t is combined with sucrose and rection factor was applied for the leaf material (0.26) the actual amount removed was 5.58 mg. compared with 5.78 mg. added. applied with a broom gun or a high-speed blower sprayer. In another test the leaves were allowed to stand for 3 days in a ~~~i~~ the 1940 in California a spray solution was standard moisture cage ( 2 ) . When they were removed, washed used containing 1.5 Pounds (680 grams) of tartar emetic, 2 with tartaric acid, and titrated with iodine, 8.82 mg. of tartar emetic were found compared with 8.51 mg. added. When the pounds (900 grams) of sucrose, and 100 gallons (378 liters) of above figure was corrected (0.02 X 17 leaves) for the leaf material, water. Davidson, Pulley, and Cassi1 (1) have proposed a 832 mg. - 0.34 mg. = 8*48mg. modified Gutzeit method for the determination of tartar emetic spray residues. However, i t was desired to develop a The use of the method is not valid in the presence of 81simpler method that would eliminate ashing of the leaf masenites, b u t these compounds are seldom, if ever, applied t o terial. citrus trees.
T
Procedure EMETIC DEPOSITS OS TABLE I. TARTAR
ORANGE
Replicate samples are collected from a plot of trees sprayed with tartar emetic by selecting a t random a few leaves from each of several trees until approximately 25 or 50 have been taken. The replicate samples need not come from the same trees. Similar samples are collected from uns rayed trees. The leaf material is placed immediately in a portatle ice box and taken to the laboratory, where it is stored in a refrigerator until analyzed. (Samples have been satisfactorily kept for 18 days.) As soon as practicable the leaves are washed with water containing 1 per cent of tartaric acid, first by agitation in a container and then individually by means of a wash bottle. The washings are made to 250 ml. for a 25-leaf sample and to 500 ml. for one of 50 leaves, Aliquants of 100 ml. are neutralized with solid sodium bicarbonate and enough is added to saturate the solution. It is immediately titrated with standard approximately 0.01 N iodine solution, using freshly prepared starch aolution as indicator. The iodine must be added at a uniform rate (approximately 10 seconds per ml.). After the leaves have been washed, their outlines are traced on paper and the area is determined with a planimeter. The results in this paper are reported in terms of residue per square centimeter of leaf, and not on the basis of total leaf surface. The correction to be applied is determined by carrying the unsprayed samples through the same procedure. For residues on lemons approximately 15 fruits are taken as a sample. They are assumed to be prolate spheroids, and the area is calculated from measurements of the major and minor axes. That the titration obtained is really due to antimony is confirmed by Reinsch's test, in which a strip of bright copper is boiled for 5 minutes in a portion of the solution to which has been added one sixth its volume of concentrated hydrochloric acid. A black or violet lustrous deposit is obtained.
FOLIAGE
(Sprayed with 1.5 pounds of t a r t a r emetic and 2 pounds of sugar in 100 gallons) KO.of Whole Leaves Taken Deposit" MMicrograms/sq. cm.
Time from Spraying t o Sampling Days
Plot 1 a t Redlands
0
50 50 48 50 49 50
9.4 7.8 10.3 6.6 10.7 7.0
50 50 50 51
2.6 3.0 1.9 1.5
25 25 27 24
1.9 1.3 1.5 1.2
~~
Rain 13
21
Plot 2 at Redlands
7
25 25 25 25
4.5 5.1 6.7 6.4
Plot 1 a t San Bernardino Rain
13
a
49 50
9.2 7.4
47 50
1.5 1.1
A correction factor, 1 80 micrograms per sq. om. for leaf material
Direct titration with iodine solution in the presence of sodium bicarbonate is a recognized means of determining antimony in solution in the trivalent form in which i t exists in tartar emetic [K(SbO)C4H40s. 1/zH20]. Preliminary experiments showed that this titration mas not significantly altered by the presence of sucrose, or by tartaric acid, which it was proposed to use as an aid to the removal of the spray from the leaves. Additional experiments showed that known amounts of tartar emetic applied to leaves could be quantitatively recovered by immediate washing n-ith 1 per cent tartaric acid solution. If the treated leaves were allowed to dry overnight, or were kept in a moist chamber for several days, the titer was greater than the tartar emetic applied, b u t when corrected for the leaf material the final recoveries averaged about 98 per cent.
TABLE 11.
TARTAR EYETIC
DEPosIrs
LEMOM
O S LEVON
FOLIAGE AND
( A t San Fernando, Calif., 12 days after spraying with 1.5 pounds of t a r t a r emetic and 2 pounds of sugar in 100 gallons) Sprayed Material Analyzed h'0. Deposit .Micrograms/sq. em. Leaves5 51 1.6 Lemonsa
49 14 14
2.4 0.9
0.7 A correction factor of 1.50 micrograms per sq. om. was used for leaves a n d 1.60 micrograms per sq. cm. for lemons.
Results With this technique tartar emetic deposits have been determined on citrus foliage and on lemons from groves in several sections of southern California. The results are shown i n Tables I and 11.
For example, 3.07 ml. of solution containing 5.78 mg. of tartar emetic were added to the surface of 13 leaves and allowed to dry overnight. The following morning the residue was removed with 37
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INDUSTRIAL AND ENGINEERING CHEMISTRY
38
Summary The antimony residues from citrus trees with tartar emetic and sugar can be removed from the leaves by washing with dilute tartaric acid solution and determined by titrating with standard iodine solution. The residues from orange foliage from a spray containing 1.5 pounds of tartar emetic and 2 pounds of sugar per 100 gallons were found to
Vol. 15, No. 1
contain antimony equivalent to 6.6 to 10.7 micrograms of tartar emetic per square centimeter immediately after spraying, but these residues were greatly reduced by rain.
Literature Cited (1) Davidson, J., Pulley, G. N., and Cassil, C. C., J. Assoc. Oficial Agr. Chem., 21, 314 (1938). ( 2 ) Munger, F., J. Econ. ~ n t o m o l .35, , 373-5 (1942).
Determining an Alkali Carbonate in the Presence of an Alkali Bicarbonate A Colorimetric Method W. TAYLOR SUMERFORD WITH THE TECHNICAL ASSISTANCE OF D.IVID DALTON AND ROBERT JOIINSON School of Pharmacy, University of Georgia, Athens, Ga.
T
H E carbonates and bicarbonates of the alkali metals are important industrial chemicals and useful chemical reagents, since they are the salts of a strong base and a weak acid and are the only readily available salts of these anions which are soluble in water. It is frequently necessary to distinguish between the carbonate and bicarbonate of an alkali metal, and to determine one in the presence of the other, since solutions of bicarbonates lose carbon dioxide to revert to the corresponding carbonate and solutions of the carbonates absorb carbon dioxide to become contaminated with the bicarbonate. The p H of an alkali carbonate solution is higher than that of the corresponding bicarbonate; hence, these anions may be distinguished by their behavior with an indicator such as turmeric (Y),which is reddened by solutions of an alkali carbonate but not by solutions of an alkali bicarbonate. Mercuric chloride (6), which gives a brownish-red precipitate with solutions of an alkali carbonate and a white precipitate with solutions of the bicarbonate, has been used to distinguish b e tween these anions; as has magnesium sulfate (6),which p r e cipitates at room temperature with alkali carbonates but not with the corresponding bicarbonates.
Qualitative Procedure I n a study of the tautomerism of p-nitrosothymol and thymoquinone monoxime (9) it was observed that a solution of sodium carbonate was alkaline enough to tautomerize the colorless p-nitrosothymol into thymoquinone monoxime with the simultaneous production of a red color due to the presence of the anion of the sodium salt of the oxime:
$OH
+ NatCOs = o@a
+ NaHCOs
0
A solution of sodium bicarbonate under the same conditions produces no color or a very faint yellow color, depending on the amount of carbonate contamination in the bicarbonate sample. Thus p-nitrosothymol can be used to distinguish between alkali carbonates and bicarbonates and provides a qualitative test for the presence of an alkali carbonate in a sample of an alkali bicarbonate. p-Xtrosothymol is available from the Eastman Kodak Company, Rochester, N. Y. It can also be prepared in almost
quantitative yields by the method of Kremers and Wakeman (3). Purification of p-nitrosothymol can be accomplished by recrystallization from benzene or from diluted alcohol with the use of activated carbon.
Quantitative Procedure There are standard procedures (10) for titrating an alkali carbonate in the presence of an alkali bicarbonate by the use of selected indicators. The accuracy of these methods depends upon several factors, especially the choice of the indicator, but under no condition is it exact when the amount of bicarbonate is proportionately large (2). For determining inadmissible amounts of carbonate in official samples of the alkali bicarbonates, the U. S. Pharmacopoeia XI (11) requires that a I-gram sample of the salt be not alkaline to phenolphthalein after it has been dissolved in 20 ml. of distilled water below 15" C. and treated with 2 ml. of 0.1 N hydrochloric acid. The British Pharmacopoeial method (1) is similar, except that thymol blue is used as the indicator. While these pharmacopeia1 methods serve the purpose for which they are intended, they are not quantitative.
The qualitative test using p-nitrosothymol was investigated to determine whether the intensity of the color produced with the indicator was in direct ratio to the amount of alkali carbonate present, so that it could be used for quantitatively determining an alkali carbonate in the presence of the corresponding bicarbonate.
Experiment a1 To a series of Nessler tubes, arranged in a rack fitted with a white porcelain base, were added equal volumes of sodium carbonate solutions of graduated molarity. To each tube was then added approximately, twice the calculated quantity of p nitrosothymol previously dissolved in enough neutral acetone or neutral dioxane to give a 0.35M solution. (The p-nitrosothymol was dissolved in the solvent to facilitate its admixture with the carbonate solutions.) The tubes mere shaken for from 10 to 15 minutes, and the excess p-nitrosothymol was filtered off. These filtrates provide the reference standards. An equal volume of a solution containing an unknown amount of alkali carbonate was treated in like manner, after which its intensity of color was compared to those of the reference standards for the determination of its alkali carbonate content. By this procedure, using a blank composed of p-nitrosothymol and distilled water, it was found that the color produced by the indicator in the presence of 0.0001 M solutions of sodium carbonate could be detected with the unaided eye. From this molarity the method is applicable in concentrations up to 0.1 M sodium carbonate, above which the color is too
