ANALYTICAL CHEMISTRY
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Table 11. Transmittance Values for 2,4-D in Water .Mg. of 2,4-D
% Transmittance
Nil 0.10 0.25 0 50 0 7.5
93.9 80.3 61.8 41.3 27.1
known to be completely free of 2,4-D where the zero point by this determination is 91.1% transmittance while for distilled water it is 93.9% transmittance. This small difference is attributed to a minute amount of milk solids still present with the 2,4-D residue which chars slightly when hratrd with the concentrated sulfuric acid. I~1SCUSSION
Read the milligrams of 2,4-D present in the sample of milk on a graph made from data obtained by analysis of milk to which known quantities of 2,4-D had been added. Data obtained by the authors are given in Table I and portrayed graphically in Figure 1. CALCULATION
Calculate the parts per million of 2,4-D present in the milk as follows (assuming density of milk to be 1):
ANALYTICAL DATA
Various amounts of 2,4-D up to 0.75 mg. were extracted from an acidified aqueous solution with two 10-ml. portions of carbon tetrachloride. The carbon tetrachloride was evaporated off and the colorimetric determination described in the above procedure was made. The data are given in Table I1 and portrayed graphically in Figure 2. Comparison of the trro sets of data (T:hles I iind I1 and Figures 1 and 2) indicates that the 2,4-D is completely extracted from the milk. The slope of the line in each case is piactically the same. The diffrrence shows up most in the blank determination on milk
The color reaction of chromotropic acid in concentrated sulfuric acid is not entirrly specific for 2,1-D. According to Frecd (W), phenoxyacetic acid and its various halogen derivatives will give a wine-purple color. Aromatic acids such as benzoic acid and phenylacetic acid do not give a characteristic color, whereas their halogen derivatives do. However, data on this reaction with various compounds obt'ained from a table in the reference show that the color reaction with chromotropic acid is sufficiently characteristic for the detcrniination of 2,4-D. It is possible to detect 0.2 p.p.m. of 2,4-D and probably even less in milk by this analytical procedure. Interferences b y other compounds, such as those mentioned above, were not experienccxd The buffered extraction solution, with a pH of 6.7, extracts the 2,4-D from the h a 1 ether solution with only a minute amount of other acidic niateri:il originally prrsent in the milk that may char when hcated with coiicentrated sulfuric acid during the color developnirnt nith chromotropic acid. 1.ITER.ATURE CITED
( 1 ) Bandurski, R . S.,Bofun. Gnz., 108, 446-9 (1Y47). (2) Freed, V. H., Science, 107, 98-9 (1948). (3) Swanson, C. P., Botun. Guz., 107, 507-9 (1946).
RECEIVED April 10, 1950.
Spectrophotometric Determination of Nickel Using 1,2-Cycloheptanedionedioxime RAYRIOND C. FEKGUSON AND CHARLES V. B 4 " S Institute f o r Atomic Research and Department of Chemistry, Iolozra State College, Ames, Iowa
ECACSE 1,2-cycloheptanedionedioxime (heptoxime) was B found t o be a very satisfactory analytical reagent for both the macro- (4) and microgravimetric determination of nickel,
produce reddish-broa n complexes similar to those produced by 1,2-cyclohexanedionedio\inie (nioxime) and dimethylglyoxim~
ita reaction with nickel wm studied in the presence of oxidizing agents in strongly basic solutions.
Absorption Spectra. .4 solution for study with the Cary spectrophotometer was prepalrd as follows:
APPARATUS
A 10-ml. portion of the standard nickel solution (15.4 micrograms of nickel per ml.) was pipetted into a 100-ml. volumetric flask; 5 ml. of saturated bromine water, 10 ml. of concentrated ammonium hydroxide (specific gravity, 0.90), and 3 ml. of 0.47% heptoxime solution were added and mixed. Then 5 ml. of bromine water were mixed in, and, after 1 minute, 10 ml. of concentrated ammonium hydroside were added. The flask was filled to the mark with distilled water, the contents were mixed thoroughly, and the pH was found to be 11.3. The solution warn placed in a 5.0-cm. absorption cell and was scanned from 330 t o 700 mp against distilled water. Scanning curves were run a t intervals of 10 minutes for the first hour, and at hourly Intervals thereafter (Figure 1).
(8)
The Cary automatic recording photoelectric spectrophotometer, Model 12, was used for all the absorption spectrum measurements. Matched sets of 5.000-em. Corex cells were used for the solutions and blanks. REAGENTS
Bromine water, saturated solution. 1,2-Cycloheptanedionedioxime(heptoxinie), saturated aqueous solution (0.47%). 1,2-Cyclohexanedionedioxime (nioxime), saturated aqueous eolution (0.8%). Dimethvlglyoxime solution, 1% solution in 95% ethyl alcohol. Nickel solutions. A stock solution was prepared from Mond nickel dissolved in aqua regia. A standard nickel solution, containing 15.4 micrograms of nickel per ml., mas -prepared by diluting the stock solutron. Reagent-grade chemicals were used throughout the work. COLOR REACTION
1,2-Cycloheptanedionedioxime (heptosime) reacts with nickel n the presence of oxidizing agents in strongly basic solutions t o
(1).
The first absorption spectrum obtained was nearly identical to those obtained ~ i t h1,2-~yclohexanedionedioxirneand with dimethylglyoxime and had the shape characteristic of the metastable complex A reported by Furman and RlcDuffie (3). The larger maximum was at 445 mp and the smaller one a t about 530 mp. There was negligible change in the curve during the first hour after mixing but within 2 hours shifts in the maxima had begun. 9rather broad maximum formed a t 455 to 465 m w after
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1
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colored system. The solution for this study mas prepared as above, except that 10 ml. of 6 N sodium hydroxide solution were wbstituted for the final 10 ml. of concentrated ammonium hydroxide. After mixing, the pH wm 12.1. This solution was scanned in 5.O-cm. cells a t intervals of 20 minutes until 3 hours had passed. The first curve obtained had the shape characteristic uf the stable complex B reported by Furman and McDuffie ( 3 ) . The absorhancy, over the range from 440 to 700 mp, increased steadily for 1 hour, remained essentially constant for about an hour, and at 3 hours had again increased by a small amount. The maximum Ras found at 457 to 4130 mp. Sensitivity. A comparison of the sensitivity of the reaction of nickel with three of the vicdioxinies in the presence of an oxidant and id , , I ammonium hydroxide is shown in Table I. 1 1 450 500 553 61C ji? 400 330 350 These molar absubancy indexes were calcuW A V E LENGTH, rnp lated from scanning curves obtained within IO Figure 1. Absorption Spectra to 15 minutes after mixing; thus they are for the form knou-n as complex A. Solutionu containing 1547 of nickel per 100 ml., heptoxime, bromine water, and ammonium hydroxide. Cary instrument, using 5.0-cm. cells Although heptoxime seems to have no 1. 10 minutes; 2, 1 hour; 3, 2 hours; 4, 3 hours; 5, 4 hours; 6, 5 hours; 7 , 6 hours particular advantage over dimethylglyoxime or nioxime with respect to stability of the color produced, Table I indicates that it provides a more scnsitive Table I. Calculated AIolar Absorbancy Indexes for method for the spectrophotometric determination of nickel. Oxidized zic-Dioxime Complexes of Nickel
j
Ware LenRth,
Molar Absorbancy Index,
Diinet hylglyoxi me
453 536
1L 0 6 1
fTeptoxime
443
13.3
Reagent
Siorime
mp
LITERATURE CITED
aJ/ X
531 448
6 4 1.7 0
537
5.7
~
-
~
essentially constar,t until about 4 hours. ~ h peak k the last curve was run 6 hours after mixing. Sodium hydroxide was used in an attempt to stahilize the
(1) Ferguson. R. C.. and Banks, C. V., AXAL.CHEM., 23, 448 (1951). (2) I'erguson, R . C., Voter, R. C., and Banks, C. V., M i k ~ o c i i e , r ~ i ~ T P T , Jlikiochim. Acta, 38, 11 (1951). (3) I'ui,man, S . H., and McDuffie, B., Atomic Energy ( ~ o m m i s s i u ~ i rlassified Report AEC-M-4234 (1947). V o t e r , R . C_ . , aiid Banks, C . V., ANAL.CHEM., 21, 1320 (1949). _ R E C E I V E DOctober 12, 1950. Contribution 129 from the Institute for Atomic Rwearch a n d Department of Chemistry, Iowa State C o l l r g ~Ames, , Iowa. TYork uerformed in the Aines Laboratory of the Atoinir Energy Comniiasion.
Estimation of 0,o-Diethyl,o-p-Nitrophenyl Thiophosphate Modified Semimicro Method C. W. WILSON, RODGER BAIER, DALE GENUNG, AND JAMESMULLOWNEY California Fruit Growers Exchange, Ontario, Calif.
HE:
01 iginal procedure for estimating small quantities of parathion (0,O-diethyl, 0-p-nitrophenyl thiophosphate, Thiophos 3422) was that of Averell and Norris (1 ). It involved reduction of the nitro group to form an aniline derivative, and formation of a dye therefrom by diazotization and coupling with a naphthylethylenediamine. The method was modified by Gunther and Hlinn ( 2 )for routine operation. ?;either the original method nor the modification was found satisfactory for the determination of parathion in citrua oils. I n addition, losses of parathion were known to occur during decolorization of the benzene solutions with clay and evaporation of the benzene. In the modification described, citrus oils and benzene extracts of plant materials may generally be used without any pretreatment, and the quantity of sample required is drastically reducede g., to 0.2 ml. for citrus oil. Isopropyl alcohol has been substiTr
tuted for ethyl alcohol lwause it is equally suitable and more readily obtainable by cornmeirinllaboratories. EXPERIMENTAL
Preparation of Sample. Citrus oils are used without any prrtrratment other than clarification if necessary. Solid materials may be extracted or nashed with benzene to obtain solutions for analysis. Each class of sample material will no doubt require some modification of estraction methods, but a method that is suitable for dried citrus peel, and probably suitable for dry materials in general, is outlined below. Reduction. The nitro group of parathion is reduced by the use of zinc and hydrochloric acid. Possible losses of parathion here may result from volatilization before it is converted to the less volatile amine hydrochloride, and inconiplete reduction because part of the parathion might remain in the oil phase. Car-
