nitrate on the system was studied. These ions were added in proper amounts to solutions containing 4.12 p.p.m. of rhodium. The amounts of foreign ions which produce a varihtion in absorbance by =k2% have been taken as the tolerance limits. Results are described in Table I.
0 50 O
ACKNOWLEDGMENT
03 0 L 0
I
I O
30
2 0
4.0
50
Thanks are due to hIary L. Good for her kind interest during the course of this study.
PH LITERATURE CITED
Figure 3.
Effect of pH on the stability of the complex;
330 mp Concn. of rhodium, 3.09 p.p.m. Concn. of DAT, 5.9 X 10-%4
reproducible color intensity.
Hence,
a 10-ml. total volume of the heating
solution is recommmded. Effect of Reagent Concentration on Solution Absorbance. A large molar excess of the reagent over rhodium (>1:80) is necessary to produce maximum color intensity. For example, a solution containing 3.09 p.p.m. of rhodium required a t least 10 mg. of the reagent for maximum color development. Adherence to Beer’s Law. A series of mixtures containing varying amounts of rhodium, 2 ml. of the buffer, 5 ml. of the reagent, and distilled water t o give a total volume of 10 ml. was prepared and heated on a water bath a t 90” C. for 30 minutes. The solutions were cooled to room temperature and diluted to 25 ml. with water. Absorbances of these solutions were recorded a t 330 mp against reagent hlanks and plotted against rhodium concentration. Results show that Beer’s law is obeyed by the system between 0.3 and 15.4 p.p.m. of rhodium. Effect of pH on the Stability of Color. The variation in absorbance of the complex with change in p H is shown in Figure 3. The color is stable between p H 1.5 and 3.5. A sodium acetate - hydrochloric acid buffer of p H 3.0 was adequate for the
system to give reproducible values of absorbance. Other buffer systems of p H 3.0 including potassium biphthalate-hydrochloric acid affected the nature of the complex. The volume of buffer solution had some effect also on the absorbance values. Two milliliters of the sodium acetate-hydrochloric acid buffer were adequate for buffering capacity and for the consistence of absorbance values. Sensitivity and Precision. The sensitivity of the reaction is 0.0064 micron per square centimeter as described according to the notation of Sandell (8). The practical sensitivity based on an absorbance of 0.010 unit is 0.064 micron per square centimeter. The optimum range for the most accurate spectrophotometric measurements is 0.6 to 8.3 p.p.m. of rhodium. Ten different solutions containing 3.09 p.p.m. of rhodium when treated according to the optimum conditions already described gave absorbance readings which show average and maximum relative standard deviations of 1 0 . 6 3 and Al.26%, respectively, Interferences Due to Diverse Ions. The effect of a number of diverse ions including iron(III), cobalt(II), nickel (11), ruthenium(III), palladium(II), osmium(IV), iridium(IV), platinum (IV), copper (II), silver (I), gold (111), chloride, bromide, iodide, sulfate, and
(1) Ayres, G. H., Tuffly, B. L., Forrester,
J. S., ANAL.CHEM.27,1742 (1955). ( 2 ) Beamish, F. E., McBryde, W. A. E., Anal. Chim. Acta 18, 551 (1958).
(3) Berman, S. S., Ironside, R., Can. J . Chem. 36, 1151 (1958). (4) Berman, S. S., McBryde, W. A. E., Analyst 81, 566 (1956). (5) W. D.. ANAL. CHEM.32. . ,514Jacobs. (1960). (6) Maynes, A. D., McBryde, W. A. E., Analyst 79,230 (1954). (7) Pantani, F., Piccardi, G., Anal. Chem. Acta 22, 231 (1960). (8) Sandell, E. B., “Colorimetrk, Deter-
mnation of Traces of Metals. Interscience, New York, 1959. (9) Wagner, V. I., Jr., Yoe, J. H., Tnlanta
2,239 (1959). (IO) Wilson, R. B., Jacobs, W. D., ANAL. CHEM.33, 1652 (1961).
RECEIVEDfor review March 22, 1963. Accepted May 27, 1963. Work supported by U. S. Atomic Energy Commission under Contract Number AT-(40-1)-2576.
Correction Infrared Spectra-Structure Correlation Study of Vanadium-Oxygen Compounds In this article by Leo D. Frederickson. Jr., and Donald M. Hausen [ANAL, CHEM. 35, 818 (1963)l on page 821 captions 6 and 10 are in correct order but the spectra are reversed.
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