methylolphthalimide in order to achieve this level of sensitivity Several time-and-temperature conditions were studied for satisfactory regeneration of the aldehydes using either of the regenerants. Intervals of 1, 2, 5 , 10, and 60 minutes were studied a t temperatures of 250, 225, 200, 180, 100, 70 "C and room temperature. Two minutes at 200 "C was selected t o minimize the time required t o complete this reaction and yet minimize the amount of extraneous peaks o n the chromatogram. The results obtained in this investigation indicate that this procedure is suitable for quantitative or highly semiquantitative determination of saturated aldehydes u p t o CU. The applicability of this method to quantitative determination of
polyunsaturated or polyfunctional carbonyls or methyl ketones is being investigated. For example, the method may require modification in the case of acrolein (Table I) because this carbonyl presumably undergoes Claisen and Michael type condensations (21).
RECEIVED for review August 2, 1967. Resubmitted October 30, 1967. Accepted April 8, 1968. Work supported by the Division of Biology and Medicine, U. S. Atomic Energy Commission, under Contract No. AT(49-7)-2443. Trade names referred t o in this publication d o not imply endorsement of commercial products. ~~
(21) C . W. Smith, "Acrolein," Wiley, New York, 1962, pp 110-13.
Pyrolysis-Gas Chromatographic Determination of Organics in Aqueous Solutions Ihor Lysyj and Kurt H. Nelson Research Dicision, Rocketdyne, 6633 Canoga Acenue, Canoga Park, Calq. 91304
GASCHROMATOGRAPHY has been used for the determination of volatile organics in aqueous solutions o n numerous occasions. As early as 1960, attempts were made to remove or chemically change the water in a sample so as to reduce its effect on thermoconductivity detection. For example, drying towers were incorporated into gas chromatographic instrumentation in order to remove water ( I ) , and conversion of water to acetylene was investigated in a procedure for the determination of short chain alcohols, aldehydes, and esters (2). With the advent and wide commercial availability of hydrogen flame ionization detectors, it became possible to analyze directly any volatile organic species present in aqueous solutions. None of these techniques, however, is applicable to the analysis of nonvolatile organics dissolved in water. These organics constitute a group of materials important in industry and commerce-i.e., foods, drugs, polymers, etc. They also figure prominently in biological systems. The prior gas chromatographic approach to the determination of such materials is based principally on syntheses of higher vapor pressure derivatives, which can be analyzed in the vapor phase. One example of this approach is the esterification of amino acids followed by subsequent gas chromatographic analysis of the derivatives (3). Such indirect methods, however, are often tedious, and may require a number of complex procedural steps and relatively large samples. In this study, an effort was made to combine the direct pyrolysis of water samples containing organic matter with gas chromatography for separation of the pyrolytic fragments so as to permit qualitative and quantitative characterization of a n aqueous sample. Steam was used as the carrier gas. The addition of water vapor from the sample to the steam carrier has little or no effect on the performance of the hydro(1) I. R. Hunter, V. H. Ortegren, and J. W. Pence, ANAL.CHEM., 32,682 (1960). (2) J. T. Kung, J. E. Whitney, and J. C. Cavagnol, ibid.,33, 1505 (1961). (3) S. Makisumi and H. A. Saroff, J. Gas Cliromak~gr.,3,21 (1965).
gen flame ionization detector, and this permits the use of relatively large samples. Use of sample sizes as large as 0.25 cc permitted detection of dissolved organics at trace concentration levels. EXPERIMENTAL
Apparatus. The instrumental system consists of a sample injector, a pyrolytic unit, a carrier gas source, and a gas chromatograph with potentiometric readout. The sample injector is mounted horizontally and is connected through a Swagelok reducer t o the pyrolysis tube. It consists of a three-way valve, a glass syringe of appropriate size, and a sample intake tube. The pyrolytic unit consists of a Lindberg Hevi-Duty combustion furnace, and a 60-inch long by 3Il6-inch Monel pyrolysis tube filled with granular nickel which is retained by a small plug of quartz wool at each end. A check valve is connected to the carrier gas inlet of the pyrolysis tube to prevent pressure surges into the custom-built steam generator which is the source of carrier gas. The check valve, the carrier gas line, and the portion of the pyrolysis tube outside the furnace are maintained a t 125 "C with heating tapes to prevent condensation of the steam. An Aerograph Model 600-C gas chromatograph equipped with a hydrogen flame ionization detector is used for separation and measurement of the pyrolytic fragments. A potentiometric recorder with a I-mV full scale response completes the instrumentation. Procedure. The operating conditions of the instrumentation are 21 cc/min for the steam carrier gas, and 25 and 250 cc/min for the hydrogen and air, respectively. The temperatures are 700 "C for the pyrolysis tube and 120 "C for the gas chromatographic column. This column is a 6-foot long by 3/lG-in~h column with a filling of 20 per cent Carbowax 20M on 60 to 80 mesh Chromosorb W (AW-DMCS). The instrument is operated under standard conditions for at least 24 hours before the analysis of water samples is attempted. The sample sizes are from 0.1 to 0.25 cc. The injection technique consists of drawing the sample from a foil-closed flask into the syringe, turning the three-way valve, and injecting the measured quantity of sample into the pyrolysis tube. VOL. 40, NO. 8, JULY 1968
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1 INJECTION “CHES’”lN
I 1/2 INCH/WIN
Figure 1. Chromatogram of pyrolytic fragments from aqueous starch solution RESULTS AND DISCUSSION
Three classes of organic materials were selected for this study-carbohydrates, polypeptides, and lipids. The selection was influenced by the fact that these materials figure prominently in all biological systems and constitute the majority of natural organics dissolved in unpolluted waters (4). They are also of considerable commercial importance. To represent these classes of organic materials, model compounds were selected-potato starch, gelatin, and heptanoic acid. A concentrated effort was made to evaluate potentially promising gas chromatographic columns for separation of the fragments produced by the pyrolysis of such materials. The evaluation was based on the resolution of the pyrolytic fragments from each organic class, the stability of the column in the temperature range 100 to 200 “C, and the extent of column bleeding at elevated temperatures. In this initial investigation, Carbowax 20M, Silicone Oil 710, m-phenylether ( 5 ring), and SE-30 were studied. Porous glass, 60 to 80 mesh, was used as the support for SE-30 at a loading of 10 per cent. The other substrates were coated at a liquid phase loading of 20 percent on 60 to 80 mesh Chromosorb W, which had been acid washed and treated with dimethyldichlorosilane to minimize peak tailing. The chromatograms obtained with SE-30 on porous glass afforded poor reproducibility. The silicone oil exhibited only moderate temperature stability under steam carrier gas. Although this column resolved gelatin fragments fairly well, neither heptanoic acid nor starch fragments were notably separated. Carbowax 20M and m-phenylether substrates exhibited very good temperature stability and ability for separation of the pyrolytic fragments. To complete the column (4) E. A. Birge and C . Juday, Ecological Monographs, 4 (4), 440 (1934). 1366
ANALYTICAL CHEMISTRY
2 INCHES/HlN
Figure 2. Chromatogram of pyrolytic fragments from aqueous gelatin solution evaluation, three additional substrates were investigatedethylene glycol adipate, diethylene glycol malonate, and Apiezon L. Examination of the chromatograms obtained at 600 and 800 “C for starch, gelatin, and heptanoic acid did not show these substrates to be superior to Carbowax 20M, which was used in subsequent investigations. The temperature conditions for pyrolysis were also studied. The chromatograms for aqueous solutions of gelatin, starch, and heptanoic acid were obtained at 500,600, 700, and 800 “C as indicated by the pyrometer on the combustion furnace. Chromatograms of greater complexity in the number of peaks and also better in terms of resolution were obtained in all cases at higher pyrolysis temperatures. To illustrate the differences in the pyrolytic patterns, chromatograms were obtained at 700 “C for starch, gelatin, and heptanoic acid in aqueous solutions. The concentrations were 100 ppm for the starch and gelatin, and 10 ppm for the heptanoic acid. The pyrolytic fragments from 0.1-cc injections were separated on the Carbowax 20M column at 120 “C with steam as the carrier gas at 21 cc/min. The chromatograms presented in Figures 1 through 3 show the similarities and differences obtained for materials of different molecular structure. Examination of the chromatograms revealed a total of fourteen peaks which would be discernible in the pyrolysis of a water sample containing all three materials. The retention times and heights of these peaks are presented in Table I for ease of comparison. As can be seen in Table I, all three materials would contribute to most of the major peaks. However, there would also be some distinctive peaks which would originate from only one of the materials. As examination of Table I reveals, starch produces distinctive peaks at retention times of 0.38 and 0.54 minutes. Gelatin is fully characterized by a group of distinctive peaks with retention times of 0.60, 0.70, 0.90, 1.24, and 5.34 minutes.
Table I. Separation of Pyrolytic Fragments on Carbowax 20M Column
Peak 1 2 3 4 5 6
7 8 9 10 11 12 13 14
2
Retention time, min 0.22 0.30 0.34 0.38 0.40 0.46 0.50 0.54 0.60 0.70 0.90 1.24 4.10 5.34
Peak heights, mm Hep tanoic Starch Gelatin acid 168 14
254+ 189 29
254+ 117 46
67 33
4
156 5
61 3 13 53 42 20 6
3 5
7
t 1
INjECTlON
2 INCHES/MlN
Figure 3. Chromatogram of pyrolytic fragments from aqueous heptanoic acid solution Heptanoic acid has a distinctive peak at a retention time of 0.50 minute. These specific peaks can be used for quantitative and qualitative (through calibration) characterization of aqueous solutions containing the materials discussed in this presentation. It has been demonstrated that direct pyrolysis of water samples containing organic matter, when combined with gas
chromatographic separation of the produced fragments, can be used for qualitative and quantitative characterization of aqueous solutions. Pyrolysis-gas chromatographic peaks specific t o a given compound can be used for qualitative identification. After calibration with standard solutions, such peaks can also be used for quantitative determination in a manner similar to conventional techniques used in spectroscopic analysis. In the case of interpretation of very complex mixtures, or mixtures of closely related compounds, the concentrations of the organic components can be calculated with the help of mathematical models, which relate all pyrolysisgas chromatographic peaks t o the concentration of each component. With the application of least squares technique in a matrix form, the possibility of interpretation of very complex pyrograms exists.
RECEIVED for review February 21, 1968. Accepted April 25, 1968. This work was supported by Contract No. 14-01-0001965, Office of Saline Water, U. S. Department of Interior.
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