charts are read by taking the displacement of the DTA boiling point, in chart inches, from chart zero and plotting chart inches vs. the API boiling points of these compounds. The DTA boiling point of an unknown can then be located on this straight line plot calibrated in terms of the phenomena being measured. The boiling point for w-octadecane calculated by this bracketing method was 316.23° ± 0.09° C. as compared to 316.32° ± 0.2° C. obtained using the thermocouple response directly. Because of the narrowness of the bracketed range the plot is essentially linear. Importantly, the carborundum diluting agent apparently does not interact with the test samples. This is indicated by the accurate and consistent boiling points obtained with both benzenoid and aliphatic hydrocarbons. A discrepancy would be expected if significant interactions on a van der Waals level had occurred. Surface tension holding the sample to the diluent appears to be the only force at work. Agreement between API and DTA pressure boiling point data is extremely good, as shown in Figure 1. The DTA curves become even sharper at reduced pressures. An accuracy of ±0.2° C. can easily be maintained without special precautions. The DTA method is extremely rapid and precise for the determination of
applications. Although no decomposition problems were noted with any of the compounds studied, operation at reduced pressures would remove this problem if it should arise in future cases. The usefulness of the method extends well into the boiling point-pressure range below 20 torr. High molecular weight organic chlorides, nitriles, styrenes, and branched paraffins have also been successfully analyzed. LITERATURE CITED
Figure 1. tionship
Boiling point-pressure relaA. B.
C. D. E.
n-Decane n-Undecane n-Dodecane n-Tridecane n-Tetradecane
(1) API Project 44, Selected Values of Properties of Hydrocarbons and Related Compounds, Volume 3, Table 20K, Part 1, p. 2 (1954). (2) Barrall, E. ., II, Gernert, J., Porter, R. S., Johnson, J. F., Anal. Chbm. 35, 1837 (1963). (3) Barrall, E. ., II, Porter, R. S., Johnson, J. F., J. Phys. Chem. 68, 2810 (1964). (4) Barrall, E. ., II, Rogers, L. B., Anal. Chbm. 34, 1101 (1962). (5) Krawetz, A. A., Tovrog, T., Rev. Sci. Instr. 33, 1465 (1962). (6) Vassallo, D. A., Harden, J. C., Anal. Chbm. 34, 132 (1962).
Edward M. Barrall II Roger S. Porter Julian F. Johnson
C0I chart values.
Only three hours required per compound shown in Figure 1. The precision of ±0.2° C. is tenfold greater than that usually required for C0x charts in industrial was
California Research Corp. Richmond, Calif. Division of Petroleum Chemistry, 149th Meeting, ACS, Detroit, Mich., April 1965.
Determination of Trace Copper, Lead, Zinc, Cadmium, Nickel, and Iron in Industrial Waste Waters by Atomic Absorption Spectrometry after Ion Exchange Concentration on Dowex Sir
Spectrophotometric methods generally used for the analysis of heavy metals in industrial waste waters. These methods are cumbersome, requiring evaporation, acid fuming, and solvent extraction before the spectrophotometric measurements can be made. In addition, they are subject to serious interferences by even moderate concentrations of other cations and anions. Recently, trace heavy metals have been determined in various water samples by polarography (2), neutron activation analysis (4), and x-ray spectrometry (5), all methods based on a previous concentration of sample. Fabricand et al. (S) determined certain heavy metals in ocean water without concentrating by atomic absorption however, absorption spectrometry; values reported by them are low (l/¡ to D/4%). Heavy metals in industrial waste waters often need to be determined at concentrations lower than the limits of sensitivity generally reported for atomic absorption; therefore, a concentration step is in order. :
(1) are
1054
·
ANALYTICAL CHEMISTRY
Dowex A-l chelating resin is reported to absorb several heavy metal ions strongly above pH 4.0. These metals are in general held more strongly by this resin than they are by sulfonic acid resins like Dowex 50 (6). It was felt therefore, that Dowex A-l would be a good choice of resins for the concentration of heavy metal ion impurities in water. In the method presented here, water samples are buffered and passed rapidly through a column of Dowex A-l. The separated metals are stripped from the column with 8.0M nitric acid, concentrated accurately to a small volume, and analyzed by atomic absorption spectrometry. EXPERIMENTAL
Apparatus.
A Jarrell-Ash Model
82-363 atomic absorption spectrometer equipped with three Beckman 4030 burners was used in this work. Acetylene-oxygen flames were used and a Nesco JY-110-2 5-inch strip
chart recorder
was used to record absorbances. Resin columns were prepared by pouring water slurries of Dowex A-l into 1-cm. i.d. columns and cylindrical separatory funnels were used as res-
ervoirs. Ammonium acetate Reagents. buffer was prepared by mixing 1:1 acetic acid and 1:1 ammonium hydroxide to give a solution of pH 5.5. Chelex 100 (50- to 100-mesh), a sized and purified form of Dowex A-l (BioRad Laboratories, Richmond, Calif.),
used without further treatment. A good grade of deionized water was used for dilutions and standards. Standards. Metal ion standards were prepared by diluting concentrated stock solutions of reagent grade metals or salts and were also made 4.0M in nitric acid. Each standard contained all of the metals. Composition of the i.OM nitric acid standards is shown in Table I. Procedure. Add 2 ml. of ammonium acetate buffer solution for each 100 ml. of water sample (pH should be 5.2 ± 0.2) and pass through a 1- X 10-cm. Chelex 100 column at a rate was
Table Standard 1
2 3
4 5
6
I.
Zn+2,
Cu+2,
Composition of Standards Cd+2,
Ni+2,
Pb+2,
Fe+3,
mg./liter
mg./liter
mg./liter
mg./liter
mg./liter
mg./liter
0.05 0.10 0.30 1.0 2.0 5.0
0.05 0.10 0.30 1.0 2.0 5.0
0.01 0.03 0.10 0.20 0.40 1.0
0.10 0.30 1.0 3.0 5.0 10.0
1.0 2.0 4.0 10.0 20.0 50.0
0.10 0.50 1.0 3.0 5.0 10.0
Table
Ni +
Water Samples
II.
Cu + Found Found Added, Added, mg./ mg./ mg./ mg. mg./ mg./ Sample liter liter liter liter liter liter No. 0.206 0.030 0.020 0.023 0.030 2a 0.200 0.024 0.213 0.035 0.020 0.030 4a 0.200 0.005 0.020 0.017 0.200 0.006 0.200 6 0.005 0.020 0.200 0.006 0.020 8 0.200 0.009 0.450 0.450 0.080 0.008 1» 0.080 0.009 0.094 0.450 0.480 0.008 3° 0.080 0.100 0.013 0.105 11-5 0.019 0.100 0.220 0.400 0.004 11-5-A 0.300 0.024 0.260 0.430 0.100 0.004 11-5-B 0.300 0.037 0.120 0.110 2-8 0.035 0.118 0.100 2-8 0.100 0.058 0.232 0.300 0.020 2-8-A 0.200 0.100 0.250 0.350 2-8-B 0.200 a level. at 2.5 Cr+3 also contained mg./liter Samples 4 N.A. not analyzed. 2
Cd + Found Added, 8
contained small amounts of Zn+2, Cd+2, and other heavy metal ions. To compensate for these, 4.0M nitric acid, made from the same concentrated acid used for samples and standards, was used to zero the instrument. Using this procedure and a 1-liter water sample, Cu"1"2, Cd+2, and Zn+2 can be determined to 5 p.p.b and Pb+2 and Ni+2 to 50 p.p.b. Fe+3 can be
Pb +
2
Added,
mg./ liter
0.500 0.500 0.625 0.625 0.088 0.088 0.250 0.250
0.40 0.40
Zn + Found Added,
8
Fe + 3
3
Found
mg./ liter 0.565 0.480 0.650 0.620 0.100 0.088
