Polyphenyl Ether and Carbowax Mixture as Substrate for Gas Liquid Chromatographic Analysis of Glycol Mixtures SIR: With the ever-increasing use of plasticizers, such as glycerol (G), ethylene glycol (EG), diethylene glycol (DEG), and triethylene glycol (TEG), rapid methods for the determination of mixtures of these compounds are necessary. Ethylene glycol has been determined in D E G by differential oxidation procedure using potassium chromate (1). Mixtures of E G and glycerol have been determined using periodic acid. Ethylene glycol, DEG, and T E G have been determined by gas liquid chromatography employing an Apiezon column (g). This column did not differentiate between glycerol (b.p. 290' C.) and TEG (b.p. 290' C.). Recently, Nadeau and Oaks (3) have used tribenzylsilylbiphenyl as the liquid substrate to separate glycerol and TEG. The quantitative potentialities of this column were not discussed with respect to the separation of glycerol and TEG. A review of the literature afforded no other information on the separation of glycerol and T E G by gas liquid chromatography. Work carried on in this laboratory has been concerned with the qualitative and quantitative gas chromatographic determination of mixtures containing glycerol, EG, DEG, and TEG. Substrates, such as Carbowax 2014, Ucon greases, silicone oils, and Igepol, which are commonly used for alcohols and glycols, did not distinguish between glycerol and T E G ; to make this distinction, it was necessary to trap and identify the unknown by infrared spectroscopy. This was cumbersome and time-consuming. A column, used in this laboratory for qualitative and quantitative determination of mixtures containing EG, DEG, TEG, and glycerol, employs a mixed liquid substrate, polyphenyl ether and Carbowax. Separation is complete,
A
v)
w 60-
A
v)
Retentipn time, min.
5.8 6.05 7.2 7.7
9.1
9.3 9.4
9.6 10.6
11.4
11.5 15.1
i
B
l
40-
0
-
0
g
Compound PG or EG 2.3-Butanediol 2;CPentanediol 1,3-Propanediol 2,5-Hexanediol 1,S-Butenediol 2-Butene-1,Cdiol DEG lJ5-Pentanediol G l,6-"exanediol TEG
Retention Times
-
a a
Table 1.
1
U
w
The proposed column may be used for the analysis of other glycol systemsLe., other than the EG-DEG-G-TEG combination. The relative retention times for a number of glycols are listed in Table I. A drawing of a chromatogram of a mixture composed of nine. glycols is shown in Figure 2. The column may also be used to advantage in the analysis of the Cello-. solves. However, since the lower m e a bers of the Cellosolve family have relatively low boiling points, a 6-foot column is recommended. The resolution of a mixture containing nine Cellosolves by the 6-foot column is shown in Figure 3. Of all the materials investigated, polyphenyl ether (PPE) is the only sub-
Apparatus and Reagents. An F and M linear programmed gas chromatograph, Model 500, was used, equipped with a 4-foot, 1/4-inch outside diameter stainless steel column packed with 10% polyphenyl ether and 2% Carbowax on Fluoropak 80. The column is conditioned by programming the temperature up to 250' C. and maintaining a t this limit from 1 t o 2 hours, until a level base line is obtained. If time is not a factor, .. a t 230' C. is longer- conditioning more desirable. Operating Conditions. Initial column temperature, 75' C.; detector block, 270' C.; injection port, 290' C.; detector cell, 300" C.; program rate, 15' Der minute: temDerature limit, 200°AC.; bridge power, 100 ma.: helium flow, 60 ml. per minute through the column and 20 ml. per minute through the reference side; chart speed, 4 minutes per inch. Procedure. Glycol solutions are analyzed by the normal gas Fhromatographic procedure-Le., injection of the liquid sample into the instrument by means of a microsyringe. The components are identified by measuring their respective retention times. Quantitative analysis is made by measuring either the areas under the curves or their peak heights. The more convenient peak height measure-
w 80-
a
DISCUSSION AND RESULTS
EXPERIMENTAL
C
loor
ments are used in these laboratories. A drawing of a typical chromatogram of the EG-DEG-G-TEG mixture is shown in Figure 1.
with minimum tailing, so that as little a s 1% of any one compound can be determined in the presence of the other three. Unfortunately, this column cannot separate E G and propylene glycol, but either can be determined in the absence of the other.
20-
-
0
I-
\
\
TIME
Figure 1.
/
I \ I
\
- MINUTES
Chromatogram of EG-DEG-G-TEG mixture A. 6. C. D.
Ethylene glycol Diethylene glycol Glycerol Triethylene glycol
Figure 2.
Chromatogram of glycol mixture
I
9 components
A. B. C. D.
E. F. G.
Ethylene glycol and 2,3-butanediol 1,3-Propanediol and 2,4-pentanediol 2J-Hexanediol Diethylene glycol 1,5-Pentanediol Glycerol Triethylene glycol
VOL 34, NO. 13, DECEMBER 1 9 6 2
1847
lOOr
Table II.
Run
EG
Precision of Method
Peak height DEG TEG
G
71.3 72 0 73.9 72.1 72.4
55.1 55 4 54.3 53 9 56.8
49.0 48 ~- 2 48.1 46.6 48 5
63.7
Av . 72.9 Std. dev. f l . 1
55.1
48.1
62.4
A1.l
A0 9
i~l.4
1 2 3 4 5
~
62 9 .~ .
60 5 61.3 63 6
40-
G
Lz
0
B Lz
20-
-
n. 5
IO TIME
Figure 3.
strate that separated glycerol and TEG. A 10% P P E on Fluoropak was also capable of resolving the composite mixture. EG-DEG-TEG-G, but there was some overlapping between the glycerol and DEG. This was eliminated by using a column containing 10% PPE and 2% Carbowax 20111. This mixture gave a well-defined separation of D E G and glycerol. with no effect on the glycerol and T E G separation (Figure 1). An estimation of the preci4on of the method is shonn in the data listed in Table 11, obtained by analyzing a compo4te mixture of glycol in methanol. The composition of the mixture on a weight to volume basis \vas: 2.067, EG, 2.23% DEG, 5.13% TEG. 5.47% G. The sample size used in the injection n a s 20 11. ‘Ihe glycerol peak is not
15
20
25
- MINUTES
Chromatogram of mixture of Cellosolves A. 6. C. D.
E.
F. G.
H. 1.
Monoglyme Diglyme Butyl Cellosolve Methyl Carbitol Glycerol a-monomethyl ether Butyl Carbitol Phenyl Cellosolve Benzyl Cellosolve m-Ethoxyphenol
as reproducible as the other three, but is still satisfactory for most applications. The column life appears to be indefinite, as, after approximately 500 analyses over 3 mont.hs, there was no apparent change in resolution. ACKNOWLEDGMENT
The authors express their gratitude to F. Gardiner Pearson and Lyle H. Phifer for many valuable suggestions a,nd to Virginia S. Schukraft for her
technical assistance in carrying out this program. LITERATURE CITED
(1) Cordone, M. J., Compton, J. W., ANAL. CHEX. 2 5 . 1869-74 (1953). ( 2 ) Ginsburg, L., Z&d.,31, 1822-4 (1959). (3) Nadeau, H. G., Oaks, D. M., Zbid., 3 2 , 1760-2 (1960).
IBRAHIM GHANAYEXI m I L L I A M B. S W A S N American Viscose Corp. Marcus Hook, Pa.
Absorption Flame Photometry SIR: Dr. J. TI7. Robinson of Esso Research and Engineering Co., Linden, I% J., . has been kind enough to call my attention to several erroneous statements in my review “Absorption Flame Photometry,” rrhich appeared in XKAL. CHEX. 34, s o . 5, 210R-20R (1962). These statements were largely based on my interpretation of his lecture (ref. 93 of the review). I should like to sup1)lythe corrected information herewith. Robinson prepared hollow-cathode lamps from many other metals besides tantaluni and tungsten (page 211 R, column 2. paragraph 3). The burner :idapter (page 212R, column 1, paragraph 2) was tried on only three metals, an insufficient number to permit judging its success. Rohinson’s new burner
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ANALYTICAL CHEMISTRY
(following paragraph) had not been used a t the time for emission flame photometry under the conditions described, but it was used for emission and absorption as described in his later paper [Robinson, J. TV., Harris, R. J., Anal. Chim. Acta 26, 439-45 (1962) 1. Neither was this burner (page 212 R, column 2, center) tried with oxyacetylene. Robinson did in fact detect vanadium by absorption in oxycyanogen (page 216 R , column 2, paragraph 4) a t a concentration of 300 p.p.m., but, as he points out, this is hardly useful for the determination of vanadium in petroleum. He was able to confirm David’s results for molybdenum (same column, paragraph 7 ) although, using an oxyacetylene flame, he was not able to
attain David’s sensitivity. The high sensitivity reported for platinum (page 216 R, column 3, bottom) was obtained by means of the adapter mentioned above; without the adapter the sensitivity was one tenth as great. Lastly (page 219 R, column 1. end of paragraph l ) , Robinson disclaims having worked with the sputtering technique. I apologize for these misinterpretations which could have been avoided by correspondence with Dr. Robinson before publication. It should be added that the data in Table I (11. 214 R) are in px. not 7’ as stated in the caption. PAUL T. GILBERT,JR. Beckman Instruments, Inc. Fullerton, Calif.
