V O L U M E 23, N O . 11, N O V E M B E R 1 9 5 1
1709
interfeiing substances. I n hemolytic serum in which there is a marked increase of iron ions, and in jaundice serum in which there is a marked increase in bile pigments-namely, bilirubin-these interfering substances (iron and bilirubin) cause a blurring of the sharp, distinct rnd point ordinarily obtained in titrating clear serun1s. ACKNOWLEDGMEYT
The authors wish to express their thanks t o 11. E. Gilwood for his s'@estions in this work' *I1 reagents were Obtained from W. €1. & L. D. Betz, Philadelphia, Pa.
LITERATURE CITED
J . -4m.Water W o r k s Assoc., 42, ( 1 ) Bets, J. D., and Noll. C. -I., 49-52 (1950). (2) Kramer, B., and Tisdall, T. F.,J . Bid. Chem.,47, 474 (1921). (3) Schwarzenbach, G., Helv. Chzrn. A c t a , 29, 1338 (1946). and Bangerter, F.. Ibid.. 29, (4) Schwarzenbach, G., Biedermann, W., 811 (1946). ( 5 ) Schwarsenbach, G., Kampetsch. E., and Steiner, R., Ihid., 28, 828 (1945). (6) , , Tisdall, T. F., J . Biol. Chrrn.. 56, 439 (1923). RECEIVED March 30, 1951. Presented a t t h e ~Ieeting-in-Miniature,S e w York Section, S ERICA AS CHE\IICIL SOCIETY. Brooklyn, X. Y . . March 17. 1930.
Microdetection of Sulfur LEONARD P. PEPKOWITZ AND EDWIN L . SHIRLEY Knolls Atomic Power Laboratory, General Electric Co., Schenectady, !V. Y .
HE usual microdetection of sulfide depends on the reaction rbetween iodine and azide, which is catalyzed by sulfide ( 2 ) . For organic materials and other solids this requires a fusion with sodium or potassium metal that often introduces errors caused by the sulfur content of the alkali metal. .-i method for the microdetection of sulfate, also described by Feigl ($), depends on the permanent coloration of barium sulfate precipitated in the presence of potassium permanganate. The sensitivity of the procedure is given as 2.5 micrograms of sulfuric acid (W), but this pioredure is rrbtricted to sulfate ion in solution in the absence of 1e:id sulfate.
i 'i
onstrated that arsenic, antimony, selenium, and tellurium do not interfere, as they are not converted t o volatile reducing compdunds by the reducing mixture. Sitrate interferes by oxidizing the evolved hydrogen sulfide to elemental sulfur in the condenser and must therefore be removed. APPARATUS
The apparat,us, simply constructed from a length of 6-mm. borosilicate glass tubing, is indicated in Figure 1. The upper bulb is cooled with an air jet and the solution heat,ed with a microflame. The combustion tube, which is used for certain organic materials such as thiophene, is also a length of 6-mm. tubing with a short copper oxide plug held in place by glass wool. The combustion tube, when used, is joined to the still by a short length of Tygon tubing. Rubber tubing will produce erroneous results because of the sulfur content of rubber. The copper oxide is heated to a dull red with a small Bunsen burner. REAGEPITS
-,&--
ABSORPTION TEST TUBE
TYGON
-
/
Nz
Reducing Mixture. AIix 100 nil. of 4770 hydriodic acid, 160 nil. of concentrated hydrochloric acid, and 40 ml. of 30% hypophosphorous acid; boil for 20 to 30 minutes t o remove any sulfur contamination; cool and store for use. Molybdate-Thiocyanate Solution. Dissolve separately 1.25 grams of ammonium molybdate in 50 nil. of water and 2.5 grams of potassium thiocyanate in 45 ml. of water. Acidify each solution with 5 ml. of concentrated hydrochloric acid. Store the solutions separately in dropping bottles. Mix 0.5 ml. of each solution in the absorption test tube before each determination. PROCEDURE
Icm
WOOL
H SCALE
Figure 1 . Apparatus for Xiicrodetection of Sulfiir The method described in this paper, while somewhat less sensitivr than the azide-iodine test, is applicable to sulfur in any form iiicludiiig sulfate, sulfide, or elemental sulfur. The procedure is I r : r d on the use of the reducing misture originally described tiy 1,uke (3)and used as the basis of a quantitative microprocedure by Pepkowitz (4,5). The reducing misture (HCI HI II.,POz)converts the sulfur in most materials directly to hydrogeri sulfide on gentle heating. This includes such substances as eleniental wlfur, barium sulfate, lead sulfatr, and a number of organic materials. Some organic substances, notably thiophene, niwt be pyrolyzed before reduction. The evolved hydrogen sulfide i j absorbed in an acidic ammonium molybdate-potassium thiocyanate solution ( I ). The niolyhdate is reduced and red molybdenum thiocyanate is formed. L-nder the conditions of the present test the procedure is sensitive t o 0.5 microgram of sulfur. Neither acetylene, nor sulfur dioxide produces the red coloration, hut the reducing misture will if allo\vrd to boil over into the receiver. I t u-as esperimentally dem-
+
+
hpprosimately 2 ml. of the reducing mixture are introduced into the still a t A and washed in with a drop of concentrated hydrochloric acid. This is easily done by tipping the still slightly. The nitrogen line is connected a t A and the gas is allowed to bubble through the still a t a slow rate so as not to carry over any of the reducing misture. The air jet is turned on and the reducing mixture is boiled gently with a microflame for 2 to 3 minutes t o remove any sulfur contamination. The absorption tube is not in position during this step in the procedure. The still is allowed to cool with the gas stream flowing while the absorbent is being prepared. When cool, the gas line is removed and the sample is introduced at A . Solid samples can be placed in A and washed into the still with a drop of concentrated hydrochloric acid or they can he introduced in a small glass capillary which is pushed into the tube and broken off a t the bend. Liquids are introduced by the same procedure. The gas line is replaced and the apparatus assembled with the distillation tube dipping into the absorbing solution. The gas flow is adjusted so as not to spatter the absorbent and the reducing solution is heated gently with a microflame to a gentle reflux. I n a feu- seconds the absorbent will turn red if any sulfur is present. For the more refractory organic materials, the reducing misture is intrcduced and the still assembled, including the combustion t,ube. The reducing mixture is purged as before and cooled with the gas flowing. When cool, t'he absorber is placed
ANALYTICAL CHEMISTRY
1710 111 position and the sample introduced into the combustion tube 2 to 3 cm. from the copper oxide either as a solid or liquid, directly or in a capillary. The gaa line is connected and the reducing mixture and copper oxide are heated. The sample is then pyrolyzed with the same burner used to heat the copper oxide.
Among the samples which have been conveniently handled in this way are lubricating oils, sulfur-containing dyes, penicillin, and thiophene. LITERATURE ClTED
L. hl., and Kichols, XI. L., “Gas Analysis,” S e w Tork, 1Iacniillan Co., 1929.
(1) Dennis,
(2) Feigl, F., “Laboratory Manual of Spot Tests,” New York,
Academic Press, 1943. (3) Luke, C. L.,ANAL.CHEM.,15,602 (1943). (4) Pepkowitz, L. P., included in hlanhattan Project Claaaified Report LA416 (1945). (5) Rodden, C. J., et al., “Analytical Chemistry of the Manhattan Project,” New York, McGraw-Hill Book Co., 1950. RECElrhD March 14, 1951. Presented a t the Pittsburgh Conference o n Analytical Chemistry and Applied Spectroscopy, Pitmburgh, Pa., January 1951. T h e Knolls Atomic Power Laboratory is operated by the General Electric Research Laboratory for the Atomic Energy Commission. The work reported here was carried out under contract No. W-31-109 Eng-52.
Application of Auxiliary Methods of Analysis to Mass Spectrometry J . N. PITTS,
JR.’, J. G. CALVERT2, AND F. E. BLACET University of California, Lms Angeles, Calif.
HE development oi the analytical mass spectrometer has made possible the identification and determination of micro amounts of isomers which would be extremely difficult, if not impossible, to identify by conventional microchemical methods. However, even the mass spectrometric approach to isomer identification may fail where the characteristic portion of the mass spectrum of an isomer is hopelessly obscured by contributions from other constituents of the sample. The authors were able to solve an analytical problem of this type by developing a method, possibly of general application, in which the identity of the compound in question was elucidated by determining through an auxiliary means the relative intensity of the parent mass peak. The value for the relative int,ensity of the peak from the unknown sample was then compared with data obtained for the relative intensities of the several pure isomers and the unknown isomer readily identified. If this method is to be successful, the isomers in question must show appreciably different tendencies toward ionization to form the parent ions, and one must be able to determine the total number of moles of the isomer in the sample. The latter quantity can be determined by any auxiliary means suitable for the misture a t hand, The relative intensity of the isomer in the sample is obtained by dividing the intensity of the ion current of the parent peak by the total number of moles of isomer present. The authors have found this method of anal?-sis particularly useful in identifying micro amounts of n-propyl and isopropyl iodides produced in the gas phase photolysis of mixtures of eit’her n-butyraldehyde or isobutyraldehyde with iodine vapor ( 1 ). The composition of the sample containing the iodide to be identified was such that the mzm spectrum resulting from the alkyl group of the iodide was completely obscured by contributions from other materials present in the sample. As the only significant differences between the mam spectra of these two isomeric iodides occur as a result of contributions of the respective alkyl fragments, i t was impossible to determine bj- the usual mass spectrometric methods which particular isomer was present in the sample. However, by utilizing the differences of the relative parent peak intensities of the primary and secondary isomeric iodides it was possible to analyze a large number of these samples and conclusively prove that in one series of photolyses the iodide produced was solely the n-propyl isomer, and in the other case it was the isopropyl isomer. The procedure utilized the careful determination of the m/e 170 peak of the sample, the recondensation of the sample, and the determination of total iodide by microchemical analysis based upon a modification of the Viebock method (2-4, 6, 7 ) . The 1 Present address, Department of Cheniistry, Northwestern University Evanston, 111. 2 Present address, Department of Chemistry, Ohio State University, Columbus, Ohio.
relative intenvity of the unknowi C3-iodide was then calculated by dividing the m / e 170 ion current (in units of volts developed acrops the 20,000-megohm input grid resistor of the FP54 amplifier tube) by the total number of moles of iodide present. This value for the relative intensity of the iodide in the sample was then compared with values for pure n-propyl and pure isopropyl iodides obtained under exactly the same operating conditions of ?he mass spectrometer. The following experimental values for relative intensities of the C3-alkyl iodides were obtained with a West,inghouse Type LV mass spect’rometer operating under the following conditions: ionizing electron current, 10.0 microamperes; electron accelerating voltage, 60.0 volts; ion draw out. voltage, 3.0 volts; t.emperature of ionization chamber, 200’ C. ; main magnet current, about 76 ma. Purc ti-propyl and isopropyl iodides were found to have relative intensities of 1.96 i 0.08 and 1.02 i 0.03 (volts per mole), respec.tivel;\. I n several photolyses of n-but\-ialdeh!-de-iodine mixtures ( I ) the value for the relative intensity of the C8-alkyl iodide present among the products was 1.93=0.2. Clearly, the compound was the primary iodide. The CI-iodide from two isobutyraldehyde-iodine photolyses )\-as found to have a relative intensity of 1.00 i0.03, and the conipound was thud identified as the secondary iodide. To date the only extensive application of this method of niicroanalysis of isomers has been upon samples containing either one or the other of the propyl iodides (1). On the basis of some preliminary work on samples containing methyl and ethyl iodides along with a Ct-alkyl iodide ( 5 )it seems reasonable to expect that the C3 isomer can be identified and that relative amounts of the three iodides present can be elucidated from a knowledge of the m/e 170, 156, and 142 peaks of the sample and t~ microdetermination of the total iodide present. The m / e 112 and 156 peaks enable one to calculate the amount,s of the methyl and ethyl iodides present, and from this result one can calculate the relative intensity of the C3-iodide and establish its identity. LITERATURE CITED
(1) Blacet, F. E., and Calrert, J. G., J . Am. C h m . Soc., 73, 667 (1951) .
(2) Elek, A., IND.ENQ.CHEM.,ASAL.ED.,11, 174 (1939). (3) Niederl, J. B., and Niederl, V.,“Micro Methods of Quantitative Organic Analysis,” 2nd ed., Tea- York, John Wiley & Sons, 1942. (4) Pitts, J. N., Jr., doctoral dissertation, University of California, Los Angeles, July 1949. (5) Pitts, J. N., and Blacet, F. E., J . Am. Chem. Soc., 72, 2810
(1950). (6) Siggia, S., “Quantitative Organic Analysis via Functional Groups,” New York, John Wiley & Sons, 1949. (7) Viebock, F.,and Brecher, C , Em., 63B,3207 (1930). RECEIVED November 3, 1950. lzIass spectrometric d a t a for these iodides on microfilm or photocopies are available for $0.50 in Document 2932A from American Documentation Institute, l i 1 9 S St., N.W., Washington 6, D. C.
