formate showed the chloroformate content to be 0.190%, this value being 96.670 of its theoretical content. For the determination of allyl chloroformate (b.p. = 110' C.), a column temperature of 25' C. is required. I n Figure 2, Curve A is the chromatogram for allyl chloroformate (without solvent dilution) a t 1 X 10-9 ampere whereas Curves B and C represent the chromatographic peaks obtained for 0.224 pg. of allyl chloroforniate a t sensitivity and 1 X settings of 1 X ampere, respectively. At the 1 X ampere setting, the allyl chloroformate calibration curve is also linear over the 0.05 to 0.25 pg. concentration range investigated. As noted in this study, little or no
decomposition was observed for the chloroformates as well as the organic dicarbonate ester monomer which lends itself readily to quantitative analysis a t 133" C. Furthermore, 0.05 pg. of either allyl chloroformate or diethylene glycol bis(ch1oroformate) per 1 p1. of injection yields an easily observed and measurable peak height. Lower detection limits for these materials are possible by increasing the volume of material injected into the chromatograph. ACKNOWLEDGMENT
The author thanks J. P. R. Levesque, American Optical Company, Southbridge, Mass., for the commercial monomer samples and the allyl chloro-
Microboiling Point Determination at Thermal Analysis SIR: The use of differential thermal analysis (DTA) for determining boiling points a t atmospheric pressure is well known; see for example the work of Vassallo and Harden (6). Extension of the technique to subatmospheric pressures was suggested by Krawetz and Tovrog, who cited data on toluene in the 65-760 torr range (6). Their boiling temperature was the algebraic sum of the cell temperature a t the endothermal boiling peak and the peak height in degrees centigrade, usually 2-10'C. This work demonstrates the use of DTA, employing two different calculation techniques to determine boiling points, over a pressure range of 30-760 torr for hydrocarbon samples with atmospheric boiling points of 175'-325' C. Sample sizes are such that fractions from analytical gas chromatographs may be used. EXPERIMENTAL
The differential thermograph and auxiliary equipment used in this study have been described previously (8-4). The heating rate used in all cases was 8' C. per minute. Purified carborundum (4) was used as a diluting agent and as the inert DTA reference material. Using a calibrated medicine dropper, a 0.02-ml. sample was placed in a DTA sample tube containing 0.15 gram of 500-mesh carborundum. The powder was mixed intimately with the liquid using a quartz rod 1 mm. in diameter. A semidry powder with the liquid spread evenly over the granules was obtained after a few moments mixing. The ceramic thermocouple probe was introduced and the sample compacted gently. A 0.15-gram carborundum reference was prepared by the same com-
formate and diethylene glycol bis(chloroformate) compounds used as standards. LITERATURE CITED
( 1 ) Gudzinowicz, B. J., Driscoll, J. L., ANAL.CHEM.33, 1508 (1961). ( 2 ) Hishta, C., Bomstein, J., Ibid., 35, 65 (1963). ( 3 ) Levesque, J. P. R., American Optical Go., Southbridge, Mass., private communication, January 1965. ( 4 ) Muskat, I. E., Strain, F. (to Pittsburgh Plate Glass Co.), U. S. Patent 2,370,571 (Feb. 27, 1945). ( 5 ) Zbid., U. S. Patent 2,384,115 (Sept. 4, 1945).
BENJAMIN J. GUDZINOWICZ Research Department Jarrell-Ash Co. Waltham, Mass.
30 to 760 Torr by Differential
paction technique. The thermograms were run in nitrogen using a mercury manometer to determine the system pressure within the bell jar containing the DTA cell (4). American Petroleum Institute Project 44 n-Clo, n-Cll, n-C1*, n-Cla, n-C14, n-Clb, n-decylbenzene, and Eastman Kodak White Label 1-phenyldodecane were used. The normal boiling point values for these compounds are shown in Table I. Boiling points by DTA were measured by extending the base line, prior to the boiling endotherm, into the boiling point region. Another straight, line was drawn on the chart through the steepest (and most linear portion) of the boiling endotherm. The intercept of these two straight lines was taken as the boiling point. The temperature a t the intercept was determined by measuring its distance from the recorder zero with a vernier rule. The distance was translated into millivolts using a recorder factor plus the known bucking potential. Thermocoudes had been calibrated as described previously (4).
The effect of sample size on apparent boiling point by DTA was evaluated using n-decylbenzene in the concentration range 0.01-0.02 mlJ0.15 gram carborundum. The locat'ion of the boiling point was unaffected from 0.010.07 m1./0.15 gram sample on the carborundum. Duplicate runs on 0.01, 0.02, 0.04, and 0.06 m1./0.15 gram samples were repeatable to =t0.5' C. The extremely small sample size permits measurements of boiling points on fractions collected from a conventional analytical gas chromatograph. Use of such fractions provides a rapid method of collecting high purity samples not readily available from other sources. RESULTS AND DISCUSSION
The DTA data were examined both by reading the chart directly and using only thermocouple calibration factors and by bracketing with API hydrocarbons. The latter treatment removes any possible error arising from thermocoude calibration. The bracketed
Table I. Comparison of Normal Boiling Points Determined by Differential Thermal Analysis with Literature Values
Compound Literature ( 1 ) n-Decane 174 12 n-Undecane 195 89 n-Dodecane 216 278 n-Tridecane 235 434 n-Tetradecane" 253 515 n-Decylbenzene 297 88 n-Octadecane 316 33 1-Phenyldodecane 327 611 a Phillips 99 mole per cent. * Bracketed by DTA.
Normal boiling point, "C. Found by DTA 173 93 195 90 216 65 235 48 252 92 297 82 316.23 -f: 0 09* 327 70
Error -0
+o +o fO -0 -0 -0
+o
VOL. 37, NO. 8, JULY 1965
19 01 37 05 59 16 10 09
1053
charts are read by taking the displacement of the DTA boiling point, in chart inches, from chart zero and plotting chart inches us. 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 n-octadecane calculated by this bracketing method was 316.23' f 0.09" C. as compared to 316.32' i 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 a t 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 =t0.2' C. can easily be maintained without special precautions. The DTA method is extremely rapid and precise for the determination of
1000
applications. Although no decomposition problems were noted with any of the compounds studied, operation a t 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.
800.
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400
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LITERATURE CITED
60-
40-
E PO 1.8
D
C
B
A
" " " " " ' 20
22
24
26
28
1
Cox chart values. Only three hours was required per compound shown in Figure 1. The precision of kO.2' C. is tenfold greater than that usually required for Cox charts in industrial
(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. >I., 11, Gernert, J., Porter, R. S., Johnson, J. F., ANAL. CHEM.35, 1837 (1963). ( 3 ) Barrall, E. XI., 11, Porter, R. S., Johnson, J. F., J . Phys. Chem. 68, 2810 (1964). (4) Barrall, E. R.I., 11, Rogers, L. B., ANAL.CHEW34. 1101 119621. ( 5 ) Krawetz, A. A., Tovrog,' T., Rev. Sci. Instr. 33, 1465 (1962). ( 6 ) Vassallo, D. A., Harden, J. C., ANAL. CHEM.34, 132 (1962)
EDWARD XI. BARRALL I1 ROGERS. PORTER JELI.4N F. JOHNSON California Research Corp. Richmond, Calif. DIVISIONof 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 A-1 SIR: Spectrophotometric methods ( I ) are 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 ( d ) , neutron activation analysis ( 4 ) , and x-ray spectrometry (6),all methods based on a previous concentration of sample. Fabricand et al. (3) determined certain heavy metals in ocean water without concentrating by atomic absorption spectrometry; however, absorption values reported by them are low ( l / 2 to 11/4yo).Heavy metals in industrial waste waters often need to be determined a t concentrations lower than the limits of sensitivity generally reported for atomic absorption; therefore, a concentration step is in order. 1054
ANALYTICAL CHEMISTRY
Dowex A-1 chelating resin is reported to absorb several heavy metal ions strongly above p H 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-1 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-1. The separated metals are stripped from the column with 8.OM 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 t o record absorbances. Resin columns were prepared by pouring water slurries of Dowex A-1 into 1-em. i.d. columns and cylindrical separatory funnels were used as reservoirs. Reagents. Ammonium acetate buffer was prepared by mixing 1 : l acetic acid and 1 : l ammonium hydroxide to give a solution of p H 5.5. Chelex 100 (50- to 100-mesh), a sized and purified form of Dowex A-1 (BioRad Laboratories, Richmond, Calif.), was 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.OM in nitric acid. Each standard contained all of the metals. Composition of the 4.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 ( p H should be 5.2 i 0.2) and pass through a 1- x 10-em. Chelex 100 column a t a rate
