ANALYTICAL CHEMISTRY
210 When the end point was approached as indicated by the change t o a light brown color, 2 ml. of the starch solution were added from a buret, the sides of the beaker were washed down, and the titration was continued t o a colorless solution. This part of the procedure was conducted in a fume cupboard because of the formation of hydrogen cyanide. No colored particles of the cadmium complex should be present in the bottom of the beaker. This procedure \ws used for 1 to 75 mg. of cadmium oxide. 1 to 20 mg. required 0.0078 M potassium iodate 20 t o 40 mg. required 0.0156 M potassium iodate 40 to 75 mg. required 0.0312 -1.I potassium iodate
For amounts of cadmium oxide greater than 75 mg. it is recommended that aliquots of the solution obtained after the wet destruction of the filter be used. I n the development of the method aliquots of the standard cadmium solution and a filter paper were added to the conical flasks and the samples were treated as described above. Table I includes some of the results obtained. When the weight of the fume was required, the following procedure vias carried out: Whatman No. 50 (5.5-cm.) a t e r papers were dried in an oven a t 75' C. for 2.5 hours in preparation for weighing, removed from the oven with forceps, and placed immediately in a weighed, flat, polished, metal ointment tin (about 6 cm. in outside diameter), and the lid was tightly closed. The box and the papers were then weighed. The tin was handled and kept clean with a chamois. After the fume had been collected, the paper and fume were dried in the oven, placed in the box, and weighed as described above. The tins were wiped with a chamois before each weighing. The cadmium method outlined above was used for over 1500 determinations in the study of the toxicity of cadmium and cadmium oxide fumes. About twenty-five determinations could be made by one person in 8 hours.
Table I. Sample NO.
Results of Cadmium Determinations C d Recovered as Oxide M p.
Remarks
Mo. 1.00 25.05 1.97 1.00 5.00 10.01 10.02 25.02 9.85 9.85 9.85 7.43
1.06 25.13 1.95 1 01 5.12 9.90 9.99 25.03 9.70 9.75 10.10 7.47
10-minute settling 10-minute settling 15-minute settling 20-minute settling 20-minute settling 20-minute settling 20-minute settling 20-minute settling 30-minute settling 30-minute settling Overnight settling Standard procedure, 2.5
13
9,85
9.80
14
9.85
9.75
Standard m g . of Cu procedure, 10 mg. of Cu, 12 mg. of A1 Standard procedure, 10 -mg. of Cu, 12 mg. of Zn Standard procedure, 25 mg. of Cu
1 2 3 4 5 6 7 8 9 10 11 12
15
Cd Added as Oxide
74 3
i3 8
droxide instead of 2 N ammonia. The titration was made in the presence of the asbestos and any undissolved complex waa revealed by its purple color after the solutions had become colorless. Pass and Ward used sulfurous acid before the removal of the interfering metals. The complete removal of sulfur dioxide is time-consuming and, if not completely boiled out, sulfur dioxide is reduced during the generation of hydrogen and cadmium sulfide is formed. This proved to be a frequent source of difficulty in the initial experiments. The authors found that the sulfurous acid was not necessary at this point. Ten to 15 minutes rather than one hour was found to be sufficient time for the quantitative formation of the complex. ACKNOWLEDGMENT
DISCUSSION
To dissolve the p-naphthoquinoline complex Pass and Ward used 2 N ammonia and filtered t o remove the asbestos. The authors found this method unsuitable because of the lengthy treatment required. This difficulty was overcome by grinding the asbestos before use, transferring the mat and the precipitate to the original beaker, and using concentrated potassium hy-
The authors wish to acknowledge the assistance of J. E. Currah, J. R. Mills, and D. S. Russell. LITERATURE CITED
(1) Pass, A., and Ward, A. M., Analyst, 58, 667 (1933). (2) Silverman, L., and Valenzuela, C., J. I n d . Hug. Tozicol., 28, 3, 107 (1946).
No.
Detection and Estimation of Microquantities of Cyanide A. 0. GETTLER AND L. GOLDBAUM New York University, New York, .V. Y . OST of the color-producing tests employed for the detection of cyanide possess sensitivity but lack specificity. Only the Prussian blue test and the thiocyanate test are specific for the detection of cyanide, but as ordinarily performed, they are not sufficiently sensitive for the quantitative microdetermination of cyanide. The sensitivity of the Prussian blue test may be enhanced by conducting the hydrogen cyanide, derived from a nitrogen- or cyanide-containing substance, through a piece of filter paper previously impregnated with ferrous sulfate and sodium hydroxide. The test paper is supported in position in a specially designed glass apparatus by a pair of identical glass flanges having finely ground surfaces. PREPARATION OF TEST PAPER
Five grams of hydrated ferrous sulfate are dissolved in 50 ml. of distilled water and any insoluble residue is removed by filtra-
tion. .?. single sheet of filter paper (Whatman KO.50 smooth glazed, acid- and alkali-treated) is immersed in this solution for 5 minutes, then removed from the ferrous sulfate solution, suspended by means of a clamp, and allon-ed to dry in the air. The dried piece of filter paper is then dipped into a 20% sodium hydroxide solution. When the paper is thoroughly wetted, it is removed and again allowed to dry in the air. Circular pieces of the paper, having exactly the same diameter as the ground-glass flanges, are cut out. These test papers will retain their usefulness for several weeks if stored in a cool dark place. GROUND-GLASS FLAXGE CONNECTIONS
The apparatus consists of a twin pair of plane ground-glass flanges of circular cross section. Each flange i s continuous with a length of glass tubing and is fitted with two glass hooks. The glass tubing guides the aerated gases to the test paper, which is tightly held between the two flanges. The glass hooks on each flange are connected t o corresponding hooks on the other flange by means of a stout rubber band n-hich serves t o keep the flanges in close planar contact.
V O L U M E 19, NO. 4, A P R I L 1 9 4 7
271
By aerating a solution containing.hydrogen cyanide and conducting the gas through a specially prepared test paper, secured by a pair of ground-glass flange connections, the sensitivity of the Prussian blue test has been increased to detect and estimate as little as 0.2 microgram of cyanide. The method may also be used to detect nitrogen in one crystal of an organic compound.
The apparatus, which is illustrated in Figure 1, may be purchased a t Machlett and Son, Kew York, IT.Y., or a t Eck and Krebs, New York, N. Y. METHOD IN DETAIL
Two milliliters of the solution to be analyzed (or 2 ml. of blood or 2 grams of finely macerated tissue) are placed in a 50-ml. aeration tube and 3 ml. of water are added. Blood samples are acidified with 20% trichloroacetic acid in order to precipitate proteins and thus prevent foaming during the process of aeration. Other materials are acidified with dilute sulfuric acid. The exit tube of the aeration tube is attached to one end of the pair of assembled flanges by means of rubber tubing. The other end of the apparatus is connected to a water aspirator. The aeration tube is placed in a beaker containing hot water (90" C.). The surface of the water in the beaker should be no higher than the surface of the liquid in the tube. Suction is now applied a t a maximum rate for 5 minutes. Experiments have d e k i t e l y established that during this period of time, all the hydrogen cyanide is aerated out of the solution, absorbed by the alkaline test paper, and converted to the Prussian blue pigment.
the determination of progressively larger concentrations of cyanide: For a concentration of cyanide ranging from 0.2 to 1.0 microgram an orifice of 4 mm. was found to be ideal, for concentrations ranging from 1 to 5 micrograms a diameter of 10 mm. was used, while a diameter of 15 mm. was suitable for a concentration range of 5 to 20 micrograms. Table I presents a series of results obtained by the method described.
Table I. Tissue Used, 2 Grams Liver Blood Liver Blood Liver Brain Blood Brain Blood
Determination of Hydrogen Cyanide H C S Added, Micrograms Csing 4-Mm. Flange 0.2 0.2 0 4
0.3 0.5 0.5
Using 10-Mm. Flange 1.0 1.0 2 0 2 0 3 0 3 0
1.0 1.0 2.0 3.0 3.0 5.0 5,O
Figure 1. Diagram of Apparatus
The test paper is now removed from the flanges and placed in a dilute solution of hydrochloric acid (1 to 4). This acid treatment dissolves the iron hydroxides which tend t o mask the blue color of the test. The paper is then washed with distilled water and dried. A blue stain remaining on the paper indicates the presence of cyanide and the intensity of the stain is proportional to the quantity of cyanide present in the test solution. The limiting sensitivity of the test is 0.1 microgram of hydrogen cyanide. I t is specific for cyanide and no other substances interfere with the test. Standard Prussian blue stains are prepared for comparison purposes by applying the above method to solutions containing definitely known amounts of cyanide within any desired concentration range. The quantity of cyanide in the solution of an unknown is determined by comparing the unknown stain with a series of standard stains, which may be preserved indefinitely if they are mounted between glass plates. Experiments indicate that best results are obtained when flange orifices of progressively larger diameters are employed for
0.4
0.6 0 6 0.8 0.8
2.0
Upper. Side view (two units assembled) Lower left. End view of single unit Lower right. Oblique view of single unit
0.2 0.2
0 4
5 0 5 0
Liver
H C N Estimated by Comparison with Standard Stains, Micrograms
0.I 0.8 1.0 1.0 2.0 2.0 3.0 2.0 5.0 4.0 1.0 1.0 2.0 2.0 3.0 2.0 4.0 5.0
This method may be extended to the detection of nitrogen in organic compounds by use of the following procedure.
A crystal of the organic compound is embedded in a small portion of metallic sodium which is placed in a small piece of Pyrex tubing sealed a t one end. The solid material in the tube is then heated by a direct flame until fusion occurs, and while still red hot, is dropped into a test tube containing 2 ml. of distilled water. The glass tubing shatters and the contents dissolve in the water. Any nitrogen present in the compound will exist as sodium cyanide. The solution is now subjected to the treatment described above for the detection of cyanide. In organic crystals containing both nitrogen and sulfur a little thiocyanate is formed during the fusion with sodium. With an excess of sodium, acting on a small crystal of an organic compound, practically no thiocyanate is formed; the greatest part of the nitrogen is converted to cyanide and hence its detection by the method described never fails. The authors made no quantitative determination of nitrogen in oiganic crystals, and did not weigh the crystals. In a series of nitrogen-containing compounds they were able to detect the nitrogcn by the blue stain produced by the cyanide which was formed from the nitrogen, hydrogen, and carbon in the compound. The quantitative estimation is recommended for cyanide-containing materials only.
