Anal. Chem. 1980, 52, 211-213
LITERATURE CITED H. E. Christensen, T. T. Luginbyhl, and B. S. Carroll, Eds., "Suspected Carcinogens. A Subfile of the NIOSH Toxic Substances List". USDHEW. Public Health Service. US. Government Printing Office, Washington, D.C., 1975. A. M. Amin. Chemist-Analyst, 44, 66 (1955). A. M. Amin and M. Y. Farah, Chemist-Analyst, 44, 62 (1955). E. H. Swift and E. A. Butler, Anal. Chem., 28, 146 (1956). A. M. Amin. Chemist-Analyst, 45, 95, 101 (1956). E. A. Butler, D. G. Peters, and E. H. Swift, Anal. Chem.. 30, 1379 (1958). E. H. Swift and F. C. Anson, Adv. Anal. Chem. Instrum., 1, 293 (1960). J. Jue and C. L. Huyck, J. Pharm. Sci., 51, 773 (1962). M. A. Ghafoor and C. L. Huyck, J . fharm. Sci., 51, 894 (1962). A. Cyganski, Talanfa, 23, 868 (1976). K. Lesz, H. Wieczorkiewicz, and T. Lipiec, Chem. Anal. Warsaw, 6 ,
21 1
(17) N. M. Trieff, V. M. Sadagopa Ramanujam. and G. Cantelli Forti, Talanta, 24, 108 (1977). (18) N. M. Trieff, V. M. Sadagopa Ramanujam, and G. Cantelli Forti, Microchem. J . , 22, 222 (1977). (19) D. S. Mahadevappa and N. M. M. Gowda, Tabnta, 22, 771 (1975). (20) N. M. M. Gowda and D. S. Mahadevappa, J. Indian Chem. Soc., 53,
705 (1976). (21) N. M. M. Gowda and D. S. Mahadevappa, Taalanta, 24, 470 (1977). (22) N. A. Lange and G. M. Forker, in "Handbook of Chemistry", Handbook Publishers, Sandusky. Ohio, 1956,p 952. (23) T. Higuchi, K. Ikeda, and A. Hussain, J. Chem. Soc. 8 , 546 (1967). (24) E. Bishop and V. J. Jennings. Tabnta, 8. 697 (1961). (25) E. Stenhagen, S. Abrahamsson, and F. W. McLafferty, Eds., "Atlas of Mass Spectral Data", Volume I, lnterscience Publishers, New York,
1969.
1033 (1961). A. Cbeys, H. Sion, A. Campe, and H. Thun, Bull. Soc. Chim. Belg., 7 0 ,
576 (1961). C. G.Ramachandran Nair, S. Geetha, and P. T. Joseph, Indian J. Appl. Chem., 30, 60 (1967). E. Bovalini and M. Piazzi, Ann. Chim. Roma, 49, 1067 (1959). M. K. Papay, K. Toth, V. Izvekov, and E. Pungor, Anal. Chim. Acta, 64,
409 (1973). T. P. Hadjiioannou and E. A. Piperaki, Anal. Chim. Acta, 90, 329 (1977).
RECEIVED for review June 15,1979. Accepted September 19, 1979. We are grateful to the Robert A. Welch Foundation (Grant No. H-416 to N.M.T.) and Electric Power Research Institute (Grant No. A-12022 to M.S.L.) for supporting the present work.
Steam Distillation Apparatus for Concentration of Trace Water Soluble Organics T. L. Peters Analytical Laboratories, The Do w Chemical Company, Midland, Michigan 48640
Direct injection of aqueous solution is widely used in the gas chromatographic analysis of water soluble organics. The technique is straightforward, rapid, and minimizes sample handling. However, samples containing dissolved solids can rapidly plug the injection port with salts. In addition, when organic concentrations are below the detection limits of the instrument, a preconcentration technique is needed. For many cases, an adsorption concentration technique is useful. In this procedure, an aqueous injection of up to 500 p L is made onto a Tenax GC precolumn a t ambient temperature. After venting off the water, the precolumn is rapidly heated to flash the organics onto an analytical column ( I ) . Another concentration technique currently being used is the volatile organic analysis system (2, 3 ) . Here the volatile organics are purged from a water sample with an inert gas onto an adsorbent trap. The trap is then thermally desorbed to drive the organics onto an analytical column. Static headspace analysis techniques offer another possibility for determining relatively volatile materials in the presence of water ( 4 ) . However, the described methods are generally not suitable for effective concentration of low-molecular-weight alcohols, nitriles, ketones, and aldehydes. These types of compounds, classified as volatile polar organics (VPOs), have previously been concentrated for determination by a distillation/ headspace/gas chromatographic analysis technique ( 5 ) . One hundred milliliters of sample was heated and the first 1.5 mL of distillate collected. This distillate was saturated with sodium sulfate and the static headspace sampled a t elevated temperature. Detection limits claimed were from 4 to 8 parts-per-billion for the VPOs in the original sample. For simplicity and versatility, an easier procedure is desired for concentration of VPOs, one that employs a minimum of equipment and sample handling. This work describes a small all-glass distillation-concentration system that is convenient 0003-2700/80/0352-0217$01.OO/O
to operate and fulfills the above requirements.
EXPERIMENTAL Distillation Apparatus. A diagram of the all-glass distillation-concentration system is shown in Figure 1. It consists of a distillation pot, condenser, a condensate collection (distillate) chamber, steam/water contact column, and an overflow return tube for a portion of the condensate to return to the pot. The system was built by the Dow Glass Fabrication Laboratory. Gas Chromatography. Gas-liquid chromatography was performed on a Varian Model 1400 gas chromatograph equipped with a flame ionization detector. The column used for the determination of acrolein and acrylonitrile was a 1.8 m X 2 mm i.d. glass column packed with 60/80 mesh Tenax GC adsorbent. The temperatures of the injection port and detector were 180 and 230 "C, respectively. The column temperature was maintained at 95 "C. The carrier gas was nitrogen at 15 mL/min flow rate. The sample size used was 2 pL. For the remainder of the components examined, the column was 1.8m X 2 mm i.d. glass packed with 0.1% SP 1000 over 80/100 mesh Carbopack C. The injector, column, and detector temperatures were the same as before. The nitrogen carrier gas flow rate was 30 mL/min. Procedure. For this study, 300 mL of sample was placed in the 500-mL round bottom flask. Several boiling stones were added and the sample was heated sufficiently for a distillation rate of 2 mL/min. After refluxing for an appropriate interval of time, 2 p L of the distillate from the top chamber was withdrawn and injected into the chromatograph using conditions suitable for the determination of compounds of interest. RESULTS AND DISCUSSION In practice, the VPOs will azeotropically distill into the distillate chamber and be preferentially retained there. Condensate overflow back to the pot is stripped by the rising steam and W O s are recycled back into the distillate chamber. Since such dilute solutions are being used, each component behaves independently of the others. This results in co-dis0 1979 American Chemical Society
212
ANALYTICAL CHEMISTRY, VOL. 52, NO. 1, JANUARY 1980 ---T
-
n
Flgure 1. All-glass distillation-concentration apparatus
,i1
O
90
i
2
4
6
8
Minutes Figure 3. Chromatogram of 0 010 ppm of acrolein (A) and acrylonitrile (C) after distilhtion/concentration Component B is an unknown impurity concentrated from the distilled water
loor I 90
--
- - --
1
-------I
70
01 0
1
5
10
I
15
20
,
25
J
30
301
!/
Distillation Time In Minutes
Flgure 2. Concentration profile of acrylonitrile (A) and acrolein (6) I
tillation of various azeotropes when mixtures are concentrated by this process. Owing to their inclusion on the Environmental Protection Agency (EPA) list of 129 "Priority Pollutants", initial investigations were with the determination of acrolein and acrylonitrile a t levels below 1part-per-million (ppm) in water. Water samples fortified with known amounts of these two chemicals were concentrated in the distillation apparatus. A plot of recovery vs. distillation time (Figure 2) indicates that 15 min is sufficient to reach an equilibrium. Linearity of sample component recovery between 0.01 and 1.0 ppm is excellent. Use of this distillation-concentrator increased the concentration of the compounds in water by a factor of nearly 300 in 15 min (Figure 3). Difficult to extract or purge from water, the lighter alcohols are easily concentrated by the distillation-concentrat.or. Figure 4 indicates that methanol is the slowest to reach equilibrium,
I 0
0
5 10
20
30
40
50
60
70
80
Distillation Time In Minutes Figure 4. Concentration profile of n-propanol (A), ethanol (B), and methanol (C)
requiring more than an hour. A t first this behavior seems strange since methanol has the lowest boiling point of the three alcohols. However, methanol does not azeotrope with water while the other alcohols do. T o demonstrate the usefulness of the azeotropic effect, concentration profiles were made of three glycol ethers with azeotropic boiling points near 100 "C.These materials and pertinent physical constants are listed in Table I. Although the 2-butoxyethanol boils nearly 47 "C higher than the 2methoxyethanol, the azeotropic boiling point is 1.1"Clower.
ANALYTICAL CHEMISTRY, VOL. 1 o o r
52, NO. 1, JANUARY 1980
Table I. Azeotropic Dataa
I
I
t 80
70
?-
8
&-
I-
501
&?
30 +
compound
bp, "C
2-methoxyethanol 2-ethoxyet hanol
124.5
2-butox yethano
azeo- % H,O in trope azeobp, " C trope 99.9 99.4 98.8
135.1 171.2
77.8 71.2
79.2
a Data taken from "Azeotropic Data", Advances in Chemistry Series N o . 6, 1952.
sot
a
213
40r , Epichlorohydrin
0
5 10
30 40 50 60 Distillation Time In Minutes
20
70
80
Flgure 5. Concentration profile of 2-bvtoxyethanol (A), Pethoxyethanol (B), and 2-methoxyethanol (C) 100
90 80 70 60
2 0
5
50
L 3
4
Figure 7. Chromatogram of concentrate representing 0.004 ppm epichlorohydrin in the original water sample
40
30 20 10
0
2
Minutes
a 8
1
1
I
10 15 20 25 30 Distillation Time In Minutes Figure 6. Concentration profile of 2-butanone (A) and acetone (B)
5
Figure 5 illustrates the great difference this small change makes. As the azeotropic boiling point approaches the boiling point of water, no concentration can take place. The point at which useful concentration factors can be gained would appear to be when the azeotrope formed has a boiling point of less than 99 "C. Compounds that do not azeotrope with water, such as methanol and acetone, can still be concentrated provided their boiling point is substantially less than 100 "C. However, the time required for equilibrium concentration in the distillate will generally be longer than that required for an azeotrope with an equivalent boiling point. As an example, note on Figure 6 that 2-butanone (azeotropic bp 73.4 "C) concentrates
somewhat more rapidly than acetone (bp 56 "C). Boiling a sample to achieve concentration can be a problem with fairly reactive materials. However, by buffering the sample to the appropriate pH, even species such as epichlorohydrin can be determined at trace levels. The peak in Figure 7 represents a concentration of 0.004 ppm in the original sample. For those organics that can be concentrated by this system, the absolute recovery in the upper distillate chamber is usually around 80%. The majority of the remaining 20% of a compound is found in the reflux condenser. By continually withdrawing the concentrate from the distillate chamber after equilibrium has been reached, virtually 100% recovery can be obtained.
LITERATURE CITED (1) Bowen, B. E. Anal. Chem. 1976, 4 8 , 1584. (2) Bellar, T. A,; Lichtenberg, J. J. J . Am. Water Works Assoc. 1974, 66,
739. (3) Bellar, T. A,: Lichtenberg, J. J.: Kroner, R. C. J . Am. Wafer Works Assoc. 1974, 66. 703. (4) McAullife, C. Chem. Techno/. 1971, ( I ) , 46. (5) Chian, E. S. K.; Kuo, P, P. K.; Cooper, W . J.; Cowen, W. F.; Fuentes, R. C. Environ. Sci. Techno/. 1977, 1 7 , 282.
RECEIVED for review June 1,1979. Accepted October 15,1979.
