ead Determination Using an Anion Exchanger and Sodium Chloranilate SIR:In our article in AXAL. CHEM. 33, 807 (1961), we stated that a t that
time we were unable t o increase the range for the determination of lead below 50 fig. We have since been able to use a salting-out effect, which makes the general procedure applicable to concentrations less than 50 p.p.m., using the original substrate. Where the lead concentration is known t o be less than 50 p.p.m., the following technique should be used.
After the addition of the sodium chloranilate, let the blank and samples in the centrifuge tubes stand for 30 minutes. Add 0.3 gram of ammonium chloride. Stopper and shake to dissolve the ammonium chloride. Centrifuge for 30 minutes as before, and continue with the original procedure. The addition of the ammonium chloride to the blank and unknown apparently facilitates the precipitation of the lead chloranilate. At the same time, the salt releases entrapped soluble sodium
chloranilate to permit elimination of false increased absorbance when the lead is chelated by tetrasodium EDTA. More than 0.3 gram of ammonium chloride will cause the salting out of sodium chloranilate, which will also give false readings. Less than the stated weight reduces the sensitivity seriously. EDWlN
A. WYNNE
RUSSELL D. BURDICK Chemical Manufacturing DiVision Fisher Scientific Co. Fair Lawn, N. J.
Ultrasonic Method for Fluorescence Determination of Phthalates SIR: Although analysis for phthalates is important in a wide variety of fields including polymers and propellants, the available methods (g-2-6) are not highly sensitive. A simple new method which is sensitive down to a concentration of 0.05 pg. of phthalate per ml., and is linear a t least up to 6 pg. per ml., is described. The new method is based on the observation that ultrasonic irradiation of potassium acid phthalate in aqueous solution gives a fluorescent product, which is believed to be the 3-hydroxyphthalate. A quantitative determination suitable for the 10-44 concentration range was worked out readily; the details are given below. PROCEDURE
A 20-ml. sample of each concentration of potassium acid phthalate (0.4, 0.8, 1.2, 1.6,and 2.0 X 10-6M) was treated with ultrasound for 5.00 minutes, with a convergent-beam Brush hypersonic generator, Model BU-204, operating a t a fre uency of 400 kilocycles and a d.c. catlode current of 160ma. Then a sample was withdrawn, and the fluorescence peak in the vicinity of 440 mp was measured in the Aminco-Bowman spectrophotofluorimeter, using an excitation wave length of 315 mp. The fluorescence was a linear function of phthalate concentration, within a relative error of *5%. Unknowns of various concentrations of potassium acid phthalate were analyzed in duplicate by the same procedure, carrying along a 2 X 18-6 M standard in each set, and computing the unknown concentration from the simple ratio of fluorescence intensities. Minor variations from day to day made it advisable to standardize daily. aecautions. A single
32 X 200 mm. borosilicate glass test tube was used for all the irradiations, and i t was positioned the same way each time. Before any quantitative work was undertaken, the ultrasonic generator was stabilized by operation a t full power for a t least 20 minutes. A standardized time schedule of operations was followed. During each irradiation, the tuning dial was adj usted to maintain maximum turbulence in the solution. 'Under the conditions used, the acoustic power dissipation inside the test tube amounted to approximately 20 watts. RESULTS AND DISCUSSION
Good results were obtained in the analysis of the unknowns, as is shown in Table I. The error is less than 6%, which is as good precision as can be expected in sonochemical reactions ( 7 ) . Both the emission spectrum (for 315mp excitation) and the excitation spectrum (for 440-mp emission) of the fluorescent substance produced by ultrasonic treatment of phthalate are very similar to those of 3-hydroxyphthalate prepared synthetically (1). The formation of this product is understandable, in view of the known production of OH free radicals in water subjected to ultrasound of sufficient intensity to cause cavitation (6). Neither positive nor negative interference is caused by equal concentrations of aliphatic di-acids such as succinic, adipic, maleic, or fumaric, but aromatic carboxylic acids (such as benzoic, isophthalic, and terephthalic) give interfering fluorescences, although with somewhat different excitation and emission peaks. A 10-minute irradiation period gave slightly higher fluorescence readings
than the 5-minute period specified, but with no significant increase in sensitivity or precision. Exposure to ultrasound beyond 10 minutes under our conditions gave a slow decline, indicating gradual destruction of the fluorescent material. The pH of the potassium acid phthalate solutions was close to 6. Adjusting the pH to 4.5 or 11 with phosphate buffers before irradiation resulted in decreased fluorescence. Table I. Analysis of Potassium Acid Phthalate Solutions
Concentration M) Taken Found 0.28 0.50 0.52 0.80 1.04 1.20 1.32 1.44 1.80
Relative %Error
0,284 0.50 0.548 0.76 1.08 1.27 1.34 1.36 1.80
1.4 0 5.4 -5.0 3.8 5.8 1.5 -5.5 0
LITERATURE CITED
(1) Eliel, E. E., Burgstrahler, A. W., Rivard, D. E., Haefele, L., J.Am. Chem. SOC.77,5092(1955). (2)Fassinger, W. P., Gonter, C. E., ANAL.CHEM.31,1324(1959). (3) Hall, M. E. McNutt, R. C., Ihid., 32,1073(19601. (4)Stalcup, H.,McCollum, F., Whitman, C. L.,Ihid., 29,1479 (1957). (5) Swann, M.H.,Zbid., 29, 1352 (1957). (6)Weiasler, A., J . Am. Chem. SOC.81, 1077 (1959). (7) Weissler, A.,Cooper, H. W., Snyder, S., Ibid., 72, 1769 (1950). ALFREDWEIBSLER BARBARA WASILESXI Laboratory of Technical Development
National Heart Institute Bethesda 14, Md.
VOL. 33, NO. 13, DECEMBER 1961
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