film above the solution interface. The interferences from 1 mg. of nickel(I1) were entirely removed by washing the extract with IN hydrochloric acid and 1N sodium hydroxide. Palladium formed a violet-red complex with 2-nitroso-1-naphthol. The colored extract showed a minimum transmittance a t a wave length of 540 mp. Preliminary addition of 1 ml. of lOyo sodium thiosulfate solution completely prevented the formation of a nitroso-naphtholate complex with 1 mg. of palladium( 11). Platinum was not added in test solutions to examine its interference effects. However, zero sample blanks, which TI ere consistently found, showed no interference by possible traces of platinum introduced during fusions in platinum crucibles. Tin(II), as SnC12.2H20, imparted a deep Burgundy-red color to the acetate extract. Treating the test solution with bromine \-der and sodium thiosulfate eliminated all interference from 1 nig. of tin(I1) in the deterniination of 1 y of standard cobalt. Stability. All reagent solutions, prepared as directed, remained stable a t room temperature. T h e standard cobalt solution gave t h e same absorbance
for 1-ml. volumes throughout a period of 6 months. The 0.04% 2-nitroso-lnaphthol reagent retained full strength during tests of 3 weeks. Isoaniyl acetate extracts of the cobalt2-nitroso-1-naphtholate complex shoFed excellent color stability. Tf'hen kept in stoppered cuvettes, extracts from standard solutions and from soil and rock sample solutions retained their original color absorbances for 2 weeks. Recovery of added cobalt confirmed the reliability of this colorimetric nitrosonaphthol procedure. Results in Table I1 show that 1- and 2-7 amounts of added cobalt LT ere fully recovered from soil and rock sample solutions. For the 18 samples listed, the average recol ery difference was computed to be 0.02 y of cobalt per 1.00 y of added cobalt. A standard sample of ingot iron, NBS 55b, was found by this colorimetric method to contain 56 y of cobalt per gram (0.005670 cobalt). This result agrees favorably 11ith the Kational Bureau of Standards certificate ai-erage value of 0.006% cobalt. The sensitivity and concentration range of the method are indicated by the calibration curve (Figure 2). Extracts from 10-nil. solutions containing
0.1 y of standard cobalt gave average readings of 99.0% transmittance, equivalent to an absorbance of 0.004. Reproducible determinations are thus obtainable for 0.1 y of cobalt in 10 ml. of solution, a value equal to 0.01 y of cobalt per ml. LITERATURE CITED
Almond, H., ANAL.&EX.
2 5 , 166-i
(1953).
Almond, H., Bloom, H., U. S. Geol. Survey, Circ. 125 (1951). Baron, H., 2. anal. Chem. 140, 17384 (1953).
Bogland, E., Analyst 71, 230-1 (1946).
Claamen, A , , Daamen, A , , Anal. Chim. Acta 12, 547-53 (1955).
Clark, L. J., Axley, J. H., ANAL. CHEW27, 2000-3 (1955).
Feigl, F., "Chemistry of Specific, Selective and Sensitive Reactions,,' p. 254, Academic Press, New York, 1949.
(8) Ilinski, RI., Ber. deut. chem. Ges. 17, 2581-93 (1884).
(9)
Jungblut, F., Chim. anal. 38, 49-54 (1956).
(IO) Pontet, S L , Zbid., 37, 372-4 (1955). (11) Yoe, J. H., Barton, C. J., IKD.ENG. CHEILI., ANAL. ED. 12, 405-9 (1940).
RECEIVEDfor review May 14, 1957. Accepted January 22, 1958.
Amino Acid Analysis by Reactor-Gas Chromatography SIR: -4new approach to the analysis of compounds of biological significance presented in this report makes use of a special reactor-gas chromatographic unit. An amino acid solution is injected into a continuously hydrogen-flowing system, m-here a series of reactions and operations takes place. The amino acids first reach a microreactor containing 30% ninhydrin on a diatomaceous earth at 130' C. Oxidation occurs instantly to volatile aldehydes and the latter flow t o a chromatographic column containing silicone oil on Celite, where separation takes place. As each aldehyde emerges from the column, it is hydrocracked in a microreactor containing a nickel-kieselguhr catalyst at 425' C. This is based on a technique developed by Zlatkis and Ridgway ( 2 ) . The methane and water produced then pass through a Drierite column, so that only methane is allowed to enter a thermal conductivity cell where analysis takes place. 3lixtures containing alanine, a-amino-n-butyric acid, valine, norvaline, leucine, isoleucine, and norleucine have been analyzed by this technique. 1 156
0
ANALYTICAL CHEMISTRY
The use of a microreactor for hydrocracking the chromatographically separated products is significant. Primarily, it solves the problem created by the presence of water in any aqueous solution to be analyzed by gas chromatography. As no convenient method for drying aldehydes following a chromatographic separation is available, conversion of the aldehydes to methane and n a t r r , n hich can be dried, would obviate this difficulty. Further, it enhances the srnsitivity of the method, as the thermal conductivity cell is detecting methane only and the cell may be operated a t ambient temperatures where it is very sensitive. The necessity for calibrations due to differences in the thermal conductivities of aldehydes is eliminated by having each peak on the chromatogram come from the same compound, methane. Only differences due to the carbon number of thc individual aldehydes need be considered. Quantitative results obtained from a limited number of samples appear promising, and 1 y of an amino acid can be detected. With the development of new detector cells (1) i t should be possible to increase the sensitivity of
this procedure to detect as little- as 0.001 y. The method is limited to amino acids which can be oxidized to volatile aldehydes. Glycine cannot be used here, because of the polymerization of formaldehyde formed in the oxidation reaction. The reactor-gas chromatographic technique is simple and rapid, requiring but one operation and giving analytical results in less than 30 minutes. An extension of this procedure to other amino acids, protein hydrolyzates, and amino acid mixtures from synthesis'_is now in progress. LITERATURE CITED
McKilliam, I. G., Devar, R. h., il'atwe 181, 760 (1958). ( 2 ) Zlatkis, A , , Ridgway, J. A,, manuscript in preparation.
(1)
*ILBERT ZLATKIS JOHN F. OR&
Department of Chemistry University of Houston Houston, Tex. RECEIVEDfor review April 21, 1958. Accepted April 30,1958. Work supported in part from a grant from the Robert ii. Kelch Foundation to J. F. 0.
