New Color Test for Selenium SIR: Selenium and its compounds are notorious for their toxicity. As the industrial use of selenium and its derivatives has been mushrooming, the possibility of air contamination by these chemicals has suggested the necessity for a stable, sensitive, and specific test for selenium, which should be capable of adaptation to quantitative work. As elemental selenium, selenides, selenites, and selenates are readily converted to selenous acid by a n oxidizing agent such as nitric acid or hydrogen peroxide in the presence of concentrated hydrochloric acid, procedures for the detection or determination of seleneous acid can be applied to practically any inorganic selenium compound. Selenous acid can be detected by reaction with iodides in acid solution ( 7 ) , with thiourea in acid solution (2) through the formation of a red precipitate of selenium, or with asymmetric diphenylhydrazine (4). The hydrazine is oxidized to a mixture of compounds which have an unstable red-violet color. -4nother test for selenous acid involves oxidation of pyrrole in phosphoric acid solution to give a mixture of blue-green dyes of unknown constitution (9). The disadvantages of redox procedures for the detection and determination of selenium have been mentioned by Cheng (I). A brown mixture of compounds of uncertain structure is formed b y the reaction between selenites in acetic acid solution and 1,8naphthalenediamine (3). Hoste (5, 6) and Cheng ( I ) have also shown that 3,3'-diaminobenzidine reacts with selenous acid to form a light yellow 5,5'dipiaselenol. This nonredox reaction is Fpecific for selenous acid and has been used by these authors for the determination of selenium. The dipiaselenole has a n-ave length maximum a t 347 to 349 mp in aqueous solution. Although red, blue. or green colors are not too common in spot test malysis, a yellow color interferes in many organic reactions. Because so many organic compounds absorb in the ultraviolet and a fairly large number near 400 mp>a compound absorbing in this range would be more difFicult to determine because of the greater possibility of interference. The author has found that the colorless 4 dimethylamino - 1,2 - phenylenediamine and 4 - methylthio - 1,2phenylenediamine react with selenous acid to give stable bright red and blue-
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ANALYTICAL CHEMISTRY
purple colors, respectively, in appropriate media. The preparation of the diamine salts and their derived piaselenoles has been described (8). Both of the piaselenoles are stable, fairly insoluble in water, and very soluble in ether, alcohol, and benzene. The bright red color formed in the spot test for selenous acid with 4-dimethylamino1,2-phenylenediamine dihydrochloride is due to the following reaction:
, , ,A
substituted for 3,3'-diaminobenzidine, with minor modifications in the procedures of Hoste and Gillis (6) or Cheng (1) for the quantitative determination of selenium. EXPERIMENTAL
Ten microliters of the aqueous or alcoholic test solution containing selenous acid was mixed in a microtube with 20 p1. of a 0.5% aqueous solution of 4methylthio - 1,2 - phenylenediamine
449 mp
As this piaselenole has its wave length maximum at 449 nip in alcoholic solution and 503 mp in approximately 1 N hydrochloric acid solution, the latter medium is preferable for the detection or determination of selenium. On the other hand, the blue-purple color obtained in the reaction of selenous acid with 4 - methylthio 1,2 phenylenediamine hydrochloride is caused b y the presence of the quantitatively formed, stable, dicationic dye:
hydrochloride. If kept in the refrigerator, the latter solution is stable at least 2 weeks. The other diamine is also stable for 2 weeks. After the solutions mere mixed and allowed to stand for 5 minutes, the drop mas evaporated under a vacuum.
5 - Methylthio - 2,1,3 - benzoselenadiazole or 5-methylthiopiaselenole is yellow in 95y0 ethyl alcohol, A,, 390 mp. It forms a red monocationic 448 salt in 50% sulfuric acid, A,, mp. T o obtain the highly colored dicationic salt, sulfuric acid has to be the solvent. Either of the two reagents could probably be advantageously
sary, for then the solvent composition is readily controlled-for example, 5methylthiopiaselenole formed in one procedure is blue-purple in concentrated sulfuric acid (the dicationic salt) and red in 50y0 sulfuric acid (monocationic salt). If the test drop were not thoroughly dried, this solvent remainder could dilute the sulfuric acid enough to
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Drying in a vacuum is not necessary. but evaporation under a vacuum speeded up the operation. Drying of the sample was believed to be necee-
give a mixture of the mono- and dicationic salts.
o.2 ml. of concentrated sulfuric acid n.as added, a or less deep blue-purple color was formed, according to the amount of selenous acid present. The limit of identification was found to be 0.05 y of selenium; the concentration limit was 1 to 4,000,000. I n the use of 4-dimethylamino-1,2-
ACKNOWLEDGMENT
The author wishes to express his appreciation for the technical assistance provided by Robert R. Miller. LITERATURE CITED
(1) Cheng, K., Chemist Analyst 45, 67
( 5 ) Hoste, J., Anal. Chinz. Acta 2. 402 (1948). ’ ( 6 ) Hoste, J., Gillis, J., Zbid., 12, 158 (1955). ( 7 ) Poluekstoff, N., Mikrochemie 15, 32 (1934).
( 8 ) Sawicki, E . , Carr, A., J . Org. Chem., 22.503 (1957). J . Chem. SOC.Japan, Znd. (9) Sukdki, Id., C h e m Sect., 56, 323 (1953).
ECGESE SAWICKI
/InCC\ (LYOU].
(2) Denigks, G., Bull. SOC. pharm. Bordeaux 75, 197 (1937). (3) Feigl, F., “‘Q$itative Analysis by Spot Tests, 3rd ed., p. 266, Elsevier. New York. 1946. ~ ~ (4) Feigij’ F., Demant, V., ;Mikrochirn. Acta 1 , 322 (1937).
Robert A. Taft Sanitary Engineering Center U. S. Public Health Service Cincinnati 26, Ohio
fifth annual meeting of the ASThI Committee E-14 on Mass Spectrometry was held M a y 20 to 24 in Xew York. Abstrgtcts of the papers presented are given here.
I t is possible to change the design of the Mattauch instrument so that Caz is reduced to zero or Caa and C,32 are reduced to zero simultaneously, without substantial alteration of the distinguishing characteristics of this instrument.
for standardized input signals. Simultaneous oscillographic and digital recording of a mass spectrometer scan compare to +0.3%. The speed of the digitizer is well above present mass spectrometer peak scanning rates.
Two Time-of-Flight Mass Spectrometers. D. B. HARRISGTON, Bendix Aviation Research Laboratories, Detroit, Rlich.
A Proposal for a Sim le High Frequency Mass Spectrometer. FALK (Sew York University, New York, N. Y.) A N D F. S C HERIXG, ~ Technische Hochschule, Aachen, Germany.
Analog Computing Mass Spectrometer System. C. K. HINES,Consolidated Electrodynamics Corp., Pasadena, Calif.
phen>.lenedianiine dihydrochloride the procedure was the saine, except that 0.2 ml. of 1N hydrochloric acid was added instead of sulfuric acid. This color test was somewhat less sensitive.
I
RECEIVED for review February 1, 1957. Accepted May 27, 1957.
Mass Spectrometry THE
A description is given of two standard models of the Bendix time-of-flight mass spectrometer, both feat,uring oscilloscopic display of 10,000 complete spect’ra per second and clean separation of adjacent peaks well beyond mass 100. Accessories for pulse counting and/or current integration of any pair of selected peaks are available. The design of the vacuum system allow t,he choice of a variety of gasket material, cold trap, and diffusion pump coml)inations. The Model 12-100 is a basic instrument suitable for gas and liquid analysis, process monitoring, and identification of the Beparated components of a gas chromatograph. Side ports at the ion source are available for the study of evaporating solids and photoionization processes. The Model 14-100, while performing all the functions of the Model 12-100, is expressly designed to take advantage of the time-,of-flight principle for the study of fast reactions. The fast pumpout necessary for this application is achieved by arrangement of the leak a t the ionization chamber. which is an open structure with high transmission grids, and by the use of a large cold trap and diffusion pump.
Control of Second-Order Aberrations in a Mattauch-Type Mass Spectrometer. Consolidated ElectrodyC. F. ROBIKSON, namics Corp., Pasadena, Calif. In a Mattauch-type mass spectrometer, the Cqi2 (second-order angular) aberration coefficient can be reduced to zero by a particular choice of parameters, as is well known. The COZ (second-order energy) aberration coefficient is not usually substantial, but the Cas (cross-product) coefficient is substantial, and its influence is aggravated by the impossibility of controlling the angular divergence and the energr spread of the ion beam separate1 in mass spectrometers of the Mattaucg type.
8.
The focusing properties of a cylinder condenser suggest the construction of a mass spectrometer depending upon a resonance method. The ions of a beam with a certain energy vibrate in a static electrical field of cylindrical shape with frequencies depending upon their mass. An alternating field superimposed upon the static field can be used to diminish the ion rurrent by resonance filtering. Improved Mass Spectrum Digitizer.
W.H KING,JR, Esso Research and EnD Al. gineering Co., Linden, N. J., A ~ G. SLOCOJIB, Consolidated Electrodynamics, Corp., Pasadena, Calif
Sandiford and King at the ASTRI E-14 meeting in May 1956 described a mass spectrum digitizer embodying the deflection of galvanometers for digital conversion. The galvanometer beam scans across a grating which produces a number of light pulses pro ortional to the maximum deflection of &e galvanometer. The accuracy of this digitizer is limited by its resolution of 1 part in 200 at full scale and 1 part in 60 at the point of Eensitivity crossover. Statistical data obtained with one of these units of Esso Research and Engineering Co. indicate that its accuracy is essentially equal to the resolution limit. A different version of the digitizer was developed to improve accuracy. This instrument is also a true peak-measuring device and does not require determination of the moment that the Eignal passes through its peak value. Simultaneous digital presentation of mass number is again provided. Full scale output of the digitizer has been increased to 1000 counts. The range of an improved automatic attenuation circuit has been extended to include a X100 multiplier as well as the former X1, X3, X10, and X 3 0 ranges. Accuracy of the digitizer is within itO.l?Z0
A cycloidal-focusing mass spectrometer, an analog computing peak selector, and an automatic constant pressure sampling manifold are being used as a system to determine the fuel-air ratio in a jet engine test burner. Ratios taken during the traversing cycle of a servo-driven sampling probe provide a plot of the fuel-air profile in the burner. Reference Samples of Isotope AbunAND V. H. DIBELER, dance. F. L. MOHLER Kational Bureau of Standards, Washington, D. C. A few additions have been made to the list of reference samples and an effort has been made to collect data on isotope abundance measurements made on these saniples.
Identification of Organic Compounds J. H. BEYKOK, Dvestuffs Division Imperial Chemical Ind;stries, Ltd., Manchester, England. by Mass Spectrometry.
Identification of organic compounds by mass spectrometry depends largely for its success on the ability of a mass spectrometer to distinguish between ions of the same nominal mass, such as C2H4+, Nz+, and CO+, on the basis of their accurate masses. Commercial single-focusingmass spectrometers of resolving poiver of the order of 1000 enable empirical formulas of organic compounds to be determined by measurement of the mass of the parent ion coupled with measurement of the relative abundance of the heavy isotopes. I n some cases, this information, combined with information on the physical and chemical properties, is sufficient to identify an unknoxvn substance. Examples of identifirations based on the parent peak and the infrared spectrum, and on the parent and fragment ions of the mass spectrum are given. VOL. 2 9 , NO. 9, SEPTEMBER 1957
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