Functional Group Analysis in Gas Chromatography Treatment of Vapors with Selective Reagents
SIR: The developnient of highly sensitive detector systems in the field of gas liquid chromatography has made possible the analysis of extremely small amounts of volatile compounds. These detectors have found extensive application in t h e gas chromatographic separation of compounds of an homologous series or of mixtures of compounds of uniform functionality. But the usefulness of their high sen-itivity has been limited when dealing with mixtures of unknown compounds representing a variety of functional group classes because of difficulties msociated with establishing the identity of compounds present in submicrogram amounts. We developed a technique for qualitative analysis of functional groups of compounds present in vapor form a t concentrations of i o + to lo-* gram per milliliter. The technique i. easentially an extension of the prechromatographic reaction technique of Ba-qette,
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Figure 1 . GLC functional group analysis of a vapor mixture A.
Untreated sample (2 ml.1 Sample ( 2 ml.) with concentrated H&Oa min. C. Sample (2 ml.) with Na(m)-3 min. D. Sample ( 1 mi.) with Na(m)-3 min. f azane ( 1 ml. in oxygen)-3 min. E. S a m,d e (.1 ml.1. with Na(m1-3 min. 4Ozone (1ml. in oxygen)-3 mi;. NH~OH,HCI (20%'0)-3 min. 1 . Acetaldehyde. 2. ethyl vinyl ether. 3. methyl acetate. 4. methanal. 5. methacrolein. 6. n-butyraldehyde. 7. n-heptane. 8. 2-butanone. 9. 3-heptene. 10. propianaldehyde. 1 1 . formaldehyde. 12. ethyl farmate
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ANALYTICAL CHEMISTRY
Ozeris, and Whitnah ( 1 , 2). I t is simple, fast, and highly sensitive. Interpretation of the chromatograms is relatively easy and, since sample manipulation by extraction and /or concentration is often not required, qualitative and quantitative alterations of sample components can be avoided. This technique should compliment other methods (3-9) for the identification of components of complex mixtures of organic compounds separated by gaq chromatography. EXPERIMENTAL
T'apor Yampleq are treated at room temperature with chemical reagents in a hypodermic syringe for 2 to 5 minutes before injection into a gas chromatograph equipped with a flame ionization detector. Reagents are chosen to remove belectively components of certain functional groups or to alter them chemically to yield new peaks on the chromatogram. Two or more treatments mar be given to the same vapor sample by transfer of the vapor from one syringe to another. Liquid reagents ( 5 PI.) are applied near the open end of a 2-ml. hypodermic syringe and distributed evenly on the syringe wall by a rotary and downward movement of the plunger. Barrels with ground glass surfaces are essential for even distribution of the liquid. Treatment with metallic codium is accomplished by making a thin slice of the metal adhere to the end of the plunger. A wide 10-ml. Yyringe used to the 2-ml. mark is preferred for this treatment to eupoqe the largest powible surface area of metal and to minimize the diffusion path. Ozonolysis is obtained by introducing 1 ml. of the sample into the syringe, then filling i t to the 2-ml. mark with a miyture of ozone and oxygen. Hydrogenation is accompliqhed by introducing a. small amount of Adam's catalyst, PtOz, into the bottom end of the barrel of the syringe and then adding 1 ml. of .ample vapor and 1 ml. of hydrogen. If heat is required to accelerate a reaction, a' for saturation of the aromatic ring, the syringe is made gas tight and the plunger is locked in position with an O-ring seal. At the same time, the needle end of the syringe is closed with a Luer-lok two-way valve. This arrangement allows pressure to build up inside the syringe during heating without loss of -ample. .I miyture of nine known compounds (acetaldehyde, ethyl vinyl ether, methyl acetate, methanol, methacrolein, nbutyraldehyde, n-heptane, 2-butanone, and 3-heptene) a t concentrations of approsimatelp lo-' gram per milliliter in argon gas was subjected to analysis bv the new technique (Figures 1 and 2). The trmted vapor sample5 were injected
into a gas chromatograph (Researc,li Specialties Co., Richmond, Calif.) equippedwith a flameionizationdetector. The column, 6 ft. X '/4 inch stainleas steel packed with 15% "Ucon" T o n Polar, L B 1715 on Chromosorb W. m a operated at 50' C. with a nitrogen gas flow rate of 60 ml. per min. The untreated sample gave a c h i matogram with a series of peaks which were only partially resolved (Figure 1.1 i. Concentrated sulfuric acid removed all compounds except the saturated hydrocarbon n-heptane (Figure 1B). Treatment with metallic sodium resulkd in the elimination of all compounds esrept hydrocarbons, saturated and unwturated, and ether (Figure 1C). The unsaturated compounds were deteckd by further treatment with ozone. Ozonide decomposition product's-formaldeh>-de. propionaldehyde, butyraldehyde. and ethyl formate (Figure ID)-gave evidence of t,he position of the double bonds in ethyl vinyl ether and 3-heptene. Additional treatment with hydroxylamine identified the carbonyl functions of the aldehydes (Figure 1E). E-ter function of methyl acetate was detected by treatment with sodium h>-droside (Figure 2B), and carbonyl functions of acetaldehyde. niethacrolein, n-butyraldehyde, and 2-hut~anone with sodium borohydride (Figure 2C). Reduction products, which are primary and secondary alcohols of these coinpound.;! appeared as new peaks n-lien the column was operated at a higlirr
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Figure 2.
GLC functional group analy-
sis of a vapor mixture A. Sample ( 2 ml.) with H20-3 min. B . Sample ( 2 ml.) with N a O H (20%70)-3min. min. C. Sample ( 2 ml.) with NaBH4 (1 5%1-3 D. Sample (2 ml.) with concentrated KMnOl-3 min. Peak numbers identify compounds (see Figure 1 ).
temperature. Differentiation betn-een aldehydes and ketone, waq pos;sihle with potassium permanganate. This rcagent removed aldehydes and unqat,urated compounds whde ketone Ira; not, affect'ed (Figure 2 0 ) . In addition to the treatments illustrated in Figures 1 and 2, we found use for acetic anhydride as an esterifying agent, acetic anhydride and ferric chloride as ether c1ea;age reagents. and alcohol dehydrogenase and diphosphopyridine nucleotide (DPX I for removal of primary al(~oho1s;.Extension of the scope of the new technique to
detect functional group; juch as carboxylic acids, phenolr, amines. and mercaptans appears feasible. -1 detailed account of this work nil1 he reported later. LITERATURE CITED
Bassette, R., Ozeris, S., \l-hitnah. C. H., ANAL.CHEW 34, 1540 1962,. ( 3 ) Bassette, R., Khitnah. C. H , Ibid.,
(1)
32. 1098 11960).
(3) Casu, B., Cavallotti, L.,
I n ( ( ] . . 34,
1514 (1962).
( 4 ) Dorseg, J. A , , Hunt, R . H.. O'Teal, 11. J., Ibzd., 35, 5 1 1 (19631. ( 5 ) Selson, K. H., Hinee, IT. J.,Grinlet.
11. P., ,+niitli. D. E.. l h z d . , 32, 1110 11960). ( 6 ) Rovan, R., Jr.. Ibzd.. 33, 6% (1961). ( 7 ) Pporek, I and the greenish yellon cake recrystallized twice from methanol and twice from ethanol. The final material was dried 3 hours at 110" C. giving a light yellow product that appeared somewhat brittle and lumpy when hot but hecame uniformly soft and lump-free on vooling. Yield: 13.7 grams (257,). Evap-
oration of filtrates and recr!-dlizatioii of residues allow recovery in excess of 90%. Chloride Analysic : Four ianiples. ranging in size from about 0.15 t,o 0.22 gram were analyzed for chloride according to usual gravimetric procedures ( 2 ) , except that coagulation of silver chloride \vas allowed t o take place overnight at room temperat'ure rather than by heating, the latter procedure causing formation of hydrous ferric oxide. Csing a density of 1.5 grams per cc. for the complex (estiniabed from density relative to carbon t'etrachloridehexane mixtures), a value of 52.195, C1 viith standard deviation of 0.6 p.p.t. was found. Calculated for C,H;?XFeCl4: 52.17y0. ( T h k material was used in the standardizations except as noted.) Using the hydrated salt as a starting material, 54 grams (0.20 mole) of ferric chloride hexahydrate (J. T. Baker Reagent Grade) was melted on a steam bath and 22 grams (0.20 mole) of tetramethylammonium chloride stirred in. Enough hot ethanol to take up the product was added (about 500 ml.), the solution was filtered and chilled and the product recrystallized twice from ethanol. Chloride Analysis: 52.16yc
