different basic resins is shown in Figure 5 : an epichlorohydrin-bisphenol A epoxy resin, a phenol formaldehyde resin, and “Zytel 61” nylon. Effect of Change of Physical Properties on Pyrolysis Pattern. This work is still underway and no definite conclusions can presently be made. CONCLUSION
Both a filament pyrolyzer for flash pyrolysis as well as the furnace type ivere evaluated for use with the characterization of polyesters; the most reproducible results were obtained with the furnace. A simplified pyrolysis furnace was developed for use with a gas chromatograph. Pyrolysis, combined with gas chromatography, provides a rapid means
for the characterization of polyester resins. Gross differences in composition of polyesters can readily be detected. More subtle changes in composition can also be determined, but it is necessary to hold all experimental parameters within close limits. Thus a particular polyester composition can be fingerprinted. I n this preliminary study a correlation between physical properties and pyrolysis chromatograms was not found, Xlthough thermosetting resins were chosen for this work, the technique and instrumentation could probably be estended to all nonvolatile organic materials. The pyrolysis unit may also have an application to microcatalytic studies where the catalyst itself could be placed in the pyrolysis zone and the sample
passed through i t ; however, this was not investigated. LITERATURE CITED
(1) Davison. W.. Slanev. S.. Wrane. A.., Chem. I.%I n d . i956, 1356. ’ (2) Ettre, K., T‘eradi, P. F., ANAL. CHEM. 35, 69 (1963). \
,
00,
(3) Hewitt, G.. Whit,ham,, B.,, Analust ’ 8 6 . 643 (1961’). (4) Janak,‘ J., Gas Chromatography 185, 387 (1960). ( 5 ) Legate, C., Burnham, H., ANAL. CHEM.32, 1042 (1960). (6) Lehmann. F.. Brauer. G. M.. Ibid.. 33, 673 (1960).’ (7) Radell, E., Strutz, H., Ibid., 31, 1890 (1959). ~
RECEIVEDfor review April 18, 1963. Accepted Xovember 19, 1963. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., 1963.
Analysis of Corrosive Halogen Compounds by Gas Chromatography ROLAND A. LANTHEAUME D.A.M., 6 Avenue Sidoine Apollinaire, lyon (S),France
b Mixtures of hydrofluoric acid and chlorine trifluoride are analyzed by gas chromatography. A special sampling system permits one to vary the hydrofluoric acid concentration. Gas flow rates are controlled by means of a thermic microflowmeter. A corrosion-resistant thermal conductivity detector is used. The gas-introducing device is a nickel sliding valve with a piston and Teflon joints.
Phillips and Owens (6) worked with capillary columns using a flame ionization detector. More recently, other investigators (5) tested performances of various columns in separation of fluorine compounds, including HF and CIFp. A Teflon-lined thermal conductivity
G
analysis Of corrosive halogen compounds was first described by Ellis and Iveson (8) in 1958. The detector used was either a katharometer of conventional design with nickel resistances or a gas density balance. The only suitable materials were nickel, poly(tetrafluorethy1ene) (PTFE or Teflon), and poly(trifluoromonochlorethylene) (Kel-F). Columns were packed Jvith either Teflon or Kel-F, n-ith a Kel-F oil as the stationary phase. Ellis, Forrest, and Allen ( 2 ) proposed a quantitative method for the study of such components as HF, ClF, CL, CIF,, and UFe using a gas density balance of special design. The carrier gas used was argon; the retention times were reported for all these gases on two diff went columns. These results (3) were subsequently used by Iveson and Hamlin (4) in the design of equipment for the analysis of corrosive materials. AS CHROhlATOGRdPHIC
486
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ANALYTICAL CHEMISTRY
c3
It11 I ! +
b
L . 5mm
Figure 1 .
Thermal conductivity cell a.
b.
Nickel block Composite detector
cell equipped with hot filaments was used as the detector. The purpose of our work was to design and to test equipment for the analysis of corrosive materials. EXPERIMENTAL
Apparatus. Gas Chromatograph. Experiments were conducted with a “Chromodam corrosive gases” type chromatograph, manufactured by t h e D.A.M. Co., Lyon, France. The apparatus uses a nickel introduction device with Teflon joints and a thermal conductivity cell (1). The helium used as a carrier gas is purified prior to its introduction into the chromatograph in a precolumn provided with a 5 4 11olecular Sieve immersed in liquid nitrogen. The flow rate is 2 liters/hour. The sample volume is 10 ml. The chromatograph temperature is maintained a t 60’ R-ithin 0.1’ C. by a n electronic regulating device with proportional setting. The nickel “liquid gas” column, 2 meters long, 6 X 8 mm. in diameter, is packed with Voltalef 300 L D impregnated by Kel-F oil. [Products manufactured by Societe des Resines Fluor6es (S.R.F.), Pierre-Benite (Rhhne), France.] The particle sizes are between 250 and 315 microns. -1Graphispot recorder (Sefram, Paris) is used equipped with spot follower, graduated in 2.5-mv. increments with paper speed of 12 mm./minute. Detection. Each of t h e two detector components (shown i n Figure I ) incorporates a small heater oi
INLST
COW
ATMOOPUER
INLET WRRICR 6RS
\rlLET
CaRRlKS
I
6
Figure 2.
Pneuma.ic introduction valve with Teflon joints
fixed output in the form of a helical filament connected to thermosensitive elements. These elements constituted by two thermistors are incorporated inside the filament. They are designed t o control thermal gradients created by the source. This somewhat intricate rtssembly is embedded into a silicone elastomer; it then appears as a cylinder of 1.7 mm. in diameter and a few millimeters long inserted into a thin-walled metal tube. This casing is placed axially into a cylindrical chamber drilled through a n isothermal block (Figure 1). The sample gas circL lates through the annular space comprised between the tube and the chamber wall. The above assemblv, which ensures the mechanical strength of the system, protects also the detector against corrosion; proper choice of elements, their relative locationf,, and dimensions made the detector highly sensitive. The isothermal bhck incorporates also two chambers in which are circulating, respectively, tl- e carrier gas and the gas issued from the separating columns. The four thermistors in the system are connected togethcr in the Wheatstone bridge arrangements (two thermistors located in the same chamber form two opposite sides of the bridge). The isothermal block is placed in a cylindrical casing mace of brass which protects outgoing wires of the chamber elements and also plays the role of a thermal screen againrrt radiation and convection currents. Introduction Valve. The introduction device, shown in Figure 2, is a multiway sliding v d v e , inside of which moves a piston. The piston assembly is made of nickel, its tightness ensured by T e l o n joints. An automatic take-up device utilizes the creep of Teflon. The sample gas (IIF C1F3) is
+
Table 1.
1
2
95.6 4.3
86.8 13.1
...
...
3
4
s
6
a
7
Chromatogram
9
10
of HF and
ClF3
either permanently sweeping the introduction volume or a bypass a t the moment of introduction. The sample gas circuit comprises the inlet and outlet chambers of the carrier gas. h leak of corrosive gas into the valve introduces it into the carrier gas circuit. This will disturb the zero calibration only, without damaging any of the chromatographic components. The two circuits-carrier gas and sample gas-are entirely independent and are never stopped during analysis. A manually operated electric valve controls the cock. Sampling. Two bottles of pure products (hydrofluoric acid and chlorine trifluoride) were sufficient to produce mixtures of various H F concentration in ClF3. Measurement and Control of Flows. Flows were measured by means of a thermal micro-flowmeter (Model U 60 built by the D.A.M. Co.) operating as follows: A straight, thin-walled nickel tube placed horizontally is swept by the gas to be analyzed. On its outer side are wound symmetrically resistances with a high temperature factor. These resistances, coupled as a Wheatstone bridge, are supplied under constant voltage. Under a no-flow condition, the temperature distribution is symmetrical, and the bridge is equilibrated. Gas flow in any direction introduces thermal and electric unbalance producing volt-
Run KO. ClF3, % HF, 70 ClF, 70
P
Figure 3.
ages measurable with a millivoltmeter, read directly or recorded. The nickel tube is located inside a protective isothermal block to reduce the influence of external temperature. A metal casing encloses this assembly, the regulation and compensation devices, and 1 he electrical connections. The externa I appearance of the unit is a cylinder prci Tided with two axial outlets. RESULTS
Pure hydrofluoric acid was used in the experiments. Chlorine trifluoride had the following composition: ClF3, 98.5 %; ClF, 1.4 %; Cl?, 0.15 %. The qualitative analytical results (Figure 3) are satisfactory with respect ClF), to the separation of ( H F Cln, and ClF,, but better results might be expected with a smaller volume of gas. The quantitative analysis was performed as follows: Peak area (8)is computed by multiplying the height by the width (measured a t middle-height). -4reaction factor, K , is chosen for each component. (ClF, K = 2; HF, K = 0.75; ClF,, K = 1; Cla, K = 0.75.) These factors are relative and depend on the operating conditions such as temperature, sample volume, etc. The peaks are normalized ( K X S),
+
Experimental Results
3
4
84
74
15.9
25.9
...
...
5
6
7
8
71.2 28.7
63.3 36.6
59.2 41.7
98.5 0 1.4
...
...
...
VOL. 36, NO. 3, MARCH 1964
487
and the percentages of each component are computed, taking into account the impurities (C1F and ClJ which may be present in the chlorine trifluoride. The esperimental results obtained are presented in Table I. CONCLUSION
Satisfactory results were obtained with the equipment used. Qualitative and quantitative analysis of corrosive mixtures of gases such as HF, Cl,, ClF3, or even TFa, may be successfully performed using the assembly described above. The system is extremely simple, and requires little care from the operator.
It may readily be adapted to programmed schedule of introduction. The inlet valve proved to have the necessary precision characteristics, tightness, and corrosion resistance. The detection cell has a high sensitivity and a stable signal all the time. The sensitive components, being protected from the gaseous flow, are not likely to have varying characteristics. ACKNOWLEDGMENT
Our appreciation is extended to Jacques P. Robin, Sational Institute of Applied Sciences, ISSX, for his technical help and guidance during this study.
LITERATURE CITED
(1) Chandenson, P. (to Ugine Society), U. S. Patent 3,007,333(July 11, 1961). ( 2 ) Ellis, J. F., Forrest, C. W., iillen, P. L., Anal. Chim. Acta 22, 27-33 (1960). (3) Ellis, J. F., I v e y , G., “Gas Chromatography 1958, D. H. Desty, ed., pp. 300-9, Butterworths, London, 1959. (4) Iveson, G., Hamlin, A. G., “Gas Chromatography 1960,” R. P. W. Scott, ed., pp. 333-43, Butterworths, London, 1961. (5) Lysyj, Ihor, h’ewton, Peter, ANAL. CHEM.35, 90-2 (1963). (6) Phillips, T. R., Owens, D. R., “Gas Chromatography 1960”, R. P. W. Scott, ed. , pp. 308-15, Butterworths, London, 1961. RECEIVEDfor review August 1, 1963. Accepted Xovember 4, 1963.
Determination of Organic Compounds in Dilute Aqueous Solution by Gas Liquid Chromatography JOSEPH J. CINCOTTA and RAYMOND FEINLAND Central Research Division, American Cyanamid Co., Stamford, Conn.
b The determination of organic compounds in dilute aqueous solution by gas chromatography has been a difficult problem when these compounds elute immediately after the crest of the water peak. A study has been made indicating that many such compounds can be determined with satisfactory precision and accuracy if a flame ionization detector is employed. Compounds studied include ketones, esters, and alcohols that elute in less than 1 to 7 minutes after the crest of the water peak. The relative responses of these compounds when present in nonaqueous solution and in dilute aqueous solution, in concentrations of less than 0.1% are compared. As a typical example, a rapid and direct quantitative method for determining ethyl acrylate monomer in aqueous polymeric emulsions is described.
M
have gas chromatographically analyzed organic compounds in aqueous solution using thermal conductivity detectors. One technique frequently employed is to choose a column that allows water to elute after or well ahead of the compounds to be determined (1, 7 , IO). This procedure, however, is not useful when the substances elute immediately after mater because the large tailing water peak partially or completely masks them. To circumvent this problem, Kung, Tl‘hitney, and Cavagnol (4) employed a heated precolumn of 488
A X Y AUTHORS
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ANALYTICAL CHEMISTRY
calcium carbide ahead of their chromatographic column and thermal conductivity detector. When aqueous mixtures of alcohols, aldehydes, and esters containing up to 90% water mere injected, quantitative results were obtained because the water was converted to acetylene before entering the column. Swoboda (8) reported that alcohols in aqueous solution can be quantitatively determined if a n argon ionization detector and a dual column system are employed. He found that while such a detector gives practically no response for water, a one-column system was not suitable because the water in the argon passing through the detector greatly reduced its sensitivity to alcohols. Using a dual-column system he retained the mater on the first column and back flushed it to the atmosphere while separating the alcohol components on the second column. Emery and Koerner ( 2 ) determined lower carboxylic acids that elute after water in dilute aqueous solution employing one column and a flame ionization detector. They found, however, that compounds that elute very close to water could not be determined because the elution of large quantities of water extinguished their hydrogen flame for about two minutes. X’elsen, Eggertsen, and Holst (6) have reported a method for determining total volatile hydrocarbons in aqueous polymeric emulsions. They avoided water interference by oxidizing all the organic compounds that eluted from their column to carbon dioxide and
water. The water was then removed b a calcium sulfate tube ahead of t h thermal conductivity detector used to measure the carbon dioxide formed. A similar technique was described by Hunter, Ortegren, and Pence (3) for determining carboxylic acids in aqueous solution. Two other methods for determining residual monomers in latexes have recently appeared in the literature. Tweet and Niller (9) devised a procedure, by combining distillation and gas chromatography, for monomers that can be extracted readily from water. The monomer was first separated from the aqueous emulsion by a n extractive distillation in the presence of a suitable organic solvent. The organic fraction containing the residual monomer was then gas chromatographically analyzed. Shapras and Claver (6) detected some monomers in aqueous emulsions of interpolymers directly using flame ionization detection but discussed the quantitative aspects of the determination only briefly. Our objective was to explore further the possibility of using a one-column gas chromatographic system and a flame ionization detector to quantitatively determine organic compounds in dilute aqueous solution when they elute immediately after water. I n this paper, the results of our study using two such systems, one incorporating a nonpolar silicone grease column and the other a polar polyethylene glycol column are given. -1rapid and direct quantitative method for determining ethyl acrylate
