584
ANALYTICAL CHEMISTRY
When tests were repeated in the absence of cyanides, none of the solutions listed developed any color. However, a solution containing 1000 p.p.m. of mixed phenols, such as can be recovered from gasoline caustic washes, developed a color equivalent to 1 p.p.m. of cyanide. Sulfides, which are usually present in refinery waste waters, will form a black precipitate with the nickel, completely masking any color development made by cyanides. The sulfides can be removed satisfactorily by treating the neutral or slightly acid waste water with cadmium nitrate to precipitate the yellow cadmium sulfide, which can be filtered. The results must then be corrected for the amount of acid and cadmium sulfide solution added. Sulfide concentrations up to 100 p.p.m. have been removed by this method. Higher concentrations have not been encountered. Obviously cations such as iron, aluminum, and magnesium, which give hydroxide precipitates in alkaline solutions, will interfere with the test. Hydroxide formation of some of the heavy metals can be suppressed by complexing with citric or tartaric acid, but complete removal by ion exchange is preferable. Amberlite 100-H, a laboratory grade resin, and Catex 12, a commercial carbonaceous exchanger, have been used satisfactorily. Two techniques have been employed. The waste water can be percolated through a column packed with the ion exchange material in the sodium form. The first 100 ml. collected are discarded and the second 100 ml. are used for test purposes. A column 1 inch (2.5 cm.) in diameter and 12 inches high can be used for 25 to 100 determinations and can be regenerated by contacting the material with a 5% salt solution for 15 minutes and washing with distilled mater until free of chlorides. If only a few samples are to be run, the batch method may be preferable. To 150 to 200 nil. of waste water in an Erlenmeyer flask about 25 grams of sodium ion exchange material are added and the solution is sxTirled gently for 5 minutes. Then 100 ml. of the water are decanted and the test is continued.
Turbid solutions must be clarified before making the test. The suspended solids in refinery waste water are mostly colloittal and cannot be filtered. For most analytical tests they are iemoved by a filter aid such as activated carbon or Attapulgus clriy. In other cases a heavy metal and a hydroxide are added. The heavy metal hydroxide precipitates and removes the suspended solids on settling. These methods all removed a portion of the cyanides. Magnesium hydroxide had a particular affinity for cyanides, completely adsorbing them from the dilute solutions tested. It was found, however, that a pulp of ashless filter paper (Whatman No. 40) would clarify the waste waters without afferting the cyanide concentration. To 200 ml. of waste water in u graduate cylinder, about 1 gram of filter pulp was added. The cylinder was shaken and the pulp allowed to settle. The supernatant liquid was decanted for further treatment. CONCLUSIONS
A colorimetric method for the determination of cyanidea has been developed, which does not require preliminary distillation and is sensitive in the range of 0.5 to 3 p.p.m. of cyanide. 9 1 though it was developed piimarily for use on refinery wastc waters containing alkaline cyanides, the method could be applied to other problems requiring the determination of trace quantities of cyanides. Soluble cyanides other than alkaline cyanides offer no problem, as they can be converted to the alkali form by an ioii wchange method. LITERATURE CITED
(1) American Public Health Association, K’ew York, “Standard Methods for the Examination of Water and Sewage,” 9th ed., p. 90, 1946. (2) Cooper, R. A., J. Chem. M e t . Mining SOC.S. Africa, 25, 296 (3)
(1925). Feigl, F., and Feigl, H. E., Anal. Chim. Acta, 3, 300
(1949).
RECEIVED.4pril 4, 1951. .iooepted October 5 , 1951.
Direct Determination of Oxygen in Organic Compounds by Elementary Isotopic Analysis A. V. GROSSE AND A. D. KIRSHENBAUM Research Znstitute of Temple University, Philadelphia, Pa.
HE! development of am accurate method for the determiT nation of oxygen in organic compounds has become of increasing importance. A good direct method would have
The per cent oxygen, in a sample of weight a, is calculated as follows :
%O=
b X ( m - n) x 100
obvious advantages over the usual procedure of reporting the amount of oxygen in a compound as the difference between 100% and the percentage sum of all-over determinations. Recently a number of publications have appeared on the direct determination of oxygen in organic compounds by the “classical” methods of quantitative analysis (1-5, 8-10, 12,13). The authors reported (7) a n isotopic method for determining oxygen, which in principle does not require any quantitative separation of oxygen compounds but nevertheless is potentially more accurate than any of the classical procedures. At that time heavy oxygen was available only in 1.2 atom % concentration. Heavy oxygen is now available in the concentration range of 5 to 10 atom %, and the ratio of two isotopes in the low mass range can now be measured precisely t o the sixth decimal place by the Nier-Consolidated mass spectrometer (11). These advances have greatly increased the accuracy obtainable, which is demonstrated by the results shown in Table I.
The liquid samples were distilled into the platinum tube as described previously ( 7 ) . Solid samples were weighed in a small platinum boat inserted into the platinum tube and the latter was sealed to the system.
PRINCIPLE OF METHOD AND APPARATUS
RESULTS
The method and apparatus have been described in detail ( 6 ) . A photograph of the equipment now used a t the Research Institute is shown in Figure 1 .
The results are given in Table I. The first two analyses were obtained with a standard Consolidated instrument, while for the rest the more precise Nier-
where b is the weight of added oxygen, containing m atom % excess 0 1 8 , and n is the atom per cent excess of OI8 in the mixture after high temperature equilibration in a platinum tube. SUBSTANCESANALYZED
Acetic Acid. A heart cut of pure glacial acetic acid was used. Both the refractive index and melting point agreed with the best literature values. Sucrose, C.P. Baker’s analyzed grade, dried in a desiccator. Benzoic Acid, C.P. Baker’s analyzed grade, melting a t 122.8’ C . 1-Naphthol, C.P. crystals, melting point 95.5” C. METHOD O F INTRODUCING SAMPLES
V O L U M E 24, NO. 3, M A R C H 1 9 5 2 Table I. Oxygen Determination in Organic Compounds 1' 2' Standard Mass Bpsotrometer .4eetie acid, Acetio acid, C&O* c.x.n.
a. weight of sample, m g 02 added st NTP,CC. a, OP added. mg. m. atom % Ouabove normal G O . 2 0 in 0 n ) k At-? ,% 0 1 8 in equilibrium
-
d
37.8( 8.4:
41.82 6.78 9.69
12.0!
9.37 3.040 3.045 3 005
7.2; 2.97 2.9f
O.".U
" "-" .,."I* 3.017 3.050
0.018
+ 0.012
2.850 6.520
2.97 2.159
4.516
2.230 5.045
2.676 2.462
2.975 2.163
11.305 53.66 51.98 26.31 51.41 26.21 11.11 53.28 0.185 0.38 0.10 0.57 1.61 1.11 0.38 0.12 0.71 at the 113th meeting AMDR~CAN CXEMKAI. EOCIETY.Chicam, April Results of these snalyaes were presented b emi e, the ~ ~ Divirinn ~ ~ of . . . Orzanie ~ .ChemisBy, ~ 19 to 23 1948. b Ex& values for normal Om oontent were obtained with each analysis.
53.54 53.28
0.26
I"
~~~
~~
Consolidated mass spectrograph (If) was used. The Nier isotopic ratios are given to only three decimal places because the instrument's full precision was not employed. The average deviation from the true oxygen content of all six analyses in the table is equivalent to 0.74% of the oxygen content, while the average probable error of the method, as usually delined, is =t0.15% of the oxygen content. This is z little better than the average precision which waa previously anticipated (7) a6 *O.l% for 20 atom % 0". Tho accuracy and precision of the method could be improved still further. Such improvements would involve greater precision in weighing of samples ( *1microgram); greater precision in determining the volume of heavy oxygen (i-1 eu. mm.) added;
elimination of, or correction for, traces of air which may he dissolved in the sample, may leak into the apparatus during a ' determination, 01.may contaminate the equilibrium sample; and taking full advantage of the precision in determining the isotope ratio obtainable with the Nier instrument. ACKNOWLEDGMENT
Acknowledgment is due to A. 0. Nier of the University of Minnesota for the gift of some heavy oxygen samples, to the Sun Oil Go. and the Houdry Process Corp. for generously donating their thermal diffusion plants for isotope separation, and to (11 Alume. V. .4., Allen, H . K.. Conway, S., Harris. C. C.. Jones,W. H., d Smith, W. H., ANAL.CHEM.. , 53&3 (1951). ie, Y. A., Hall. R. T.,Staats, F, C..and Beoker, Vi, W., I b i d . ,
ipparatus for Determination of Oxygen Isotopic Analysis 1
tube is in electrie fum*os.
Bulb with hsery
0.
