V O L U M E 2 2 , N O . 9, S E P T E M B E R 1 9 5 0 (2) Barrett, C. S.,“Structure of Metals,” P. 118, New York, McGraw-Hill Book Co., 1943. (3) Bunn, C. W..“Chemical Crystallography,” p. 110, London, Oxford University Press, 1946. (4) Hofer, L. J. E., and Peebles, W. C., “X-Ray DiffractionPatternsof Solid Aromatic Hydrocarbons.” to be published in ANAL.CHEY.
1219 ( 5 ) Levin, I., and Ott. E., 2. Krist., 85,305 (1933). ( 6 ) McKinley, J. B., Nirkels, J. E., and Sidhu, S. S.,IND.ENO.
CHEM..AN.AI..ED., 16,304 (1944). (7) McLachlan, D., Jr., U.S.Patent 2,317,329(April 20,1943). ( 8 ) ”orse, J‘ K‘! op‘iea’ A m ’ t l6, 360 (1928). RECEIVED November 30, 1949
Interference of Methyl Anthranilate in Estimations of Parathion R. C. BLINN AND F. A. GUNTHER University of California Citrus Experiment Station. Riaerside. Calif. I T H the initial application of the insecticidal material wO,O-diethyl 0-pnitrophenyl thiophosphatc (parathion) to agricultural products h m coincided the introduction of a method for the quantitative estimation of its residues upon these products (1). The basis of this very sensitive method is the quantitative r e d u d o n of the nitro to the amino group, which is then diazotized and coupled with N-1-naphthylethylenediamineto give an intense magenta color (“dyed” parathion). However, Gunther and Blinn (S),Norris ( 4 ) , and Edwards ( 2 ) have reported that aniline and some of its analogs afford essentially the same magenta color by this procedure. This suggested that methyl anthranilate, reported by Power and Chestnut ( 5 )to be found in grapes and by Small (6) t o be found in citrus fruits, might int.erfere wit.h the determination of parathion residues on and in these products, particularly as the ,methyl anthranilate content may vary with both the age and the variety of the fruit. The present report deals with the spectral study of “dyed” methyl anthranilate. DISCUSSION
After being carefully purified, methyl anthranilate hydrochloride was subjected t o the exact dyeing procedure used for parathion estimations ( 1 ) ; the resulting int,ense magenta color was visually very similar to that produced by parathion. The absorption characteristics, determined on a Beckman spectrophotometer Model DU, in the visible range are compared with those given by dyed technical parathion in Figure 1. The molar extinction co6fficients were based UFO? the concentratioris of the undyed materials. Although the spectral characteristics of the two dyed compounds differ slightly, i t can be seen that methyl anthranilate would interfere seriously in a determination for parathion by the above-mentioned procedure. The maxima are separated only by 8 mp, but they differ in molecular extinction coefficient by about 800 units (2%). Maximum color development is achieved by methyl anthranilate well within the 10-minute period specified for parathion. The presence of methyl anthranilate in a “strip” solution can be demonstrated, even though intermixed with parathion, by the use of the dyeing procedure ( 1 ) without the preceding reduction step. Howevdr, any interference caused by methyl anthranilate can largely be removed from the strip solution by modifying a procedure originally reported by Gunthcr and Ulinn (3). T o illustrate, 100-ml. portions of benzene were each fortified with 81 micrograms of methyl anthranilate, then washed one, two, or three time.: with 25 ml. of 10% hydrochloric acid solution. After evaporation of the benzene in the usual mariner, the dyeing procedure was applied. If was found that one hydrochloric acid wash removed 60.5% of the methyl anthranilate present. With two and three washes with the dilute acid, there was left no detectable amount of methyl anthranilate in the benzene.
It is therefore suggested that strip solutions, in which methyl anthranilate is suspected, be washed at least twice with dilute hydrochloric acid.
It was incidentally noticed that the color characteristics of dyed methyl anthranilate behaved according to Beer’s law within the range of 18 to 360 micrograms of parent material. This
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