ated a t high inlet pressure and low input to outlet pressure ratios also permits separations to be carried out in significantly shorter time. For instance, the analysis of a mixture such as that shown in Figure 2 required about 43 minutes of instrument running time, using the conventional instrumental conditions given in Table I. By employing the high pressure technique, i t has been possible t o carry out the same analysis in 27 minutes. This increased speed of analysis was also attended by a 35% improvement in column efficiency, resulting in better separation of the various components. The reduction in analysis time is the result of the ability to use much higher carrier gas flow rates without the usual decrease in column efficiency found with columns operated a t higher input to output pressure ratios. The effect of column packing size and inlet to outlet pressure ratios on column
efficiency a t various linear gas velocities is shown in Figure 3. REFERENCES
(1) Anon., Instruction Sheet on Diaeald, Aldrich Chemical Co., Inc., 3747 N. Booth St., Milwaukee, 12, Wis. ( 2 ) Bayer, E., Preprint Papers Second Symposium on Gas Chromatography, p. 231, Amsterdam, May 1958, Butterworths, London, 1958. (3) Bohemen, J., Purnell, J. H., Zbid., p. 6: (4) Dal N’ogare, S., Bennett, C. E;; Harden, J . C., “Gas Chromatography, p. 117 (V. J. Coates, H. J. Noebels, I. S. Fagerson, Eds.), Academic Press, New York, 1958. ( 5 ) Desty, D. H. (Ed.), “Vapor Phase Chromatography,” p. siii, Academic Press, New York, 1957. (6) Dimbat, M., Porter, P. E., Stross, F. H., ANAL.CHEM.28, 290 (1956). (7) Gardner, K., Overton, K. C., Anal. Chim. Acta 23,271 (1960). ( 8 ) Zbid., 23, 337 (1960).
(9) Insull, W., James, A. T.,Divisions of Analytical and Petroleum Chemistry, Symposium On Advances in Gas Chromatography, 132nd meeting, ACS, N’ew York, N’.Y., September 1957. (10) James, A. T., Martin, A. J. P., Bzochem.’J. 5 0 , 679 (1952). (11) Ibid., 63, 144 (1956). 112) Keulemons. A. J. M.. Kwantes. A.. Rijnders, G. k. A., Anal. Chim. hctu 16, 29 (1957). (13) Kirkland, J. J., “Gas Chroniatography,” p. 203 (V. J. Coates, H. J. Noebels, I. S. Fagerson, Eds.), Academic Press, New York, 1958. (14) hletcalfe, L. D., Schmitz, A. A., ANAL.CHEM.33,363 (1961). (15) Quin, L. D., Hobbs, M. E., Zbid., 30, 1400 (1958). (16) Scott, R. P., W.,Preprint Papers Second Symposium on Gas Chromatography, p. 189, Amsterdam, May 1958, Butterworths, London, 1958. (17) Stoffel, W.,Chu, F., Ahrens, E. H., Jr., ~ A L CHEM. . 31, 307 (1959). RECEIVEDfor review February 9, 1961. Accepted July 19, 1961. Delaware Science Symposium, N’ewark, Del., February 1959. ~
Determination of Impurities in Nonionic Detergents by Gas Chromatography TOSHIO NAKAGAWA, HIDE0 INOUE, and KAORU KURIYAMA Research laboratory, Shionogi & Co., lid., Amagasaki, Japan
b In this paper it i s shown that longchain alcohols and low molecular weight polyethylene glycols can be detected and determined quantitatively by gas chromatography. Impurities usually included in nonionic detergents are thus determinable b y the simultaneous application of gas chromatography and conventional methods. In lower members of polyethylene glycol or its mono- or dimethyl ether, the logarithm of retention volume increases linearly against the number of oxyethylene units.
I
N APPLYIXG a nonionic detergent to industry, much care should be paid t o the physicochemical properties of the detergent, especially the critical micelle concentration, micellar weight, solubilizing power, and cloud point in its aqueous solution. These properties are affected considerably by the species and quantities of impurities as well as by the molecular weight distribution. Accordingly, it is advisable to determine the impurities before practical use of the detergent. Polyethylene glycols (PEG), longchain alcohols, and fatty acids are frequently included as impurities in nonionic detergents which have a polyoxyethy!ene chain as a hydrophilic
1524
ANALYTICAL CHEMISTRY
group and a long-chain hydrocarbon as a lipophilic group. Among these impurities fatty acids can be determined by a n acid value test. P E G of higher molecular weight can be evaluated by paper chromatography sprayed with modified Dragendorff’s reagent (3, 7 ) . Long-chain alcohols and P E G of lower molecular weight are not easily detected by paper Chromatography, because a n appropriate dyeing reagent is yet unknown. These impurities, however, can be determined easily by gas chromatography a t relatively high temperatures. By the simultaneous application of these methods, the impurities ordinarily involved in nonionic detergents are detected and determined without difficulty. The logarithm of retention volumes of homologous fatty alcohols, acids, or esters increases linearly with the increase in the number of carbon atoms (2, 6, 9). A similar relationship has been observed between the logarithm of retention volume and the number of oxyethylene units in the homologous series of P E G or its mono- or dimethyl ether. EXPERIMENTAL
Apparatus. A Shimadzu GC-1Atype gas chromatograph equipped with a thermal conductivity detector
was used. T h e U-shaped column consisted of stainless steel tubing, 6 m m . in inside diameter, 3 meters long. and packed n i t h silicone 550 (30 parts) on firebrick (20- to 42-mesh, 70 parts). In the case of monornethyl ethers of PEG, Shimadzu Thermol 2 (a silicone oil suited for higher temperatures) was employed instead of silicone ,550. Silicone 550 and Thermol 2 gave the same relative retention volume for ethylene glycol monomethyl ether and also for diethylene glycol monomethyl ether. Materials. Nonionic detergents used are methoxydodecaoxyethylene decyl ether (MPd-12), methoxydodecaoxyethylene dodecyl ether (MP1-12), Brij 30, Brij 35 (Atlas Powder Co.), and Sikkol BL-4.2 ( N k k o Shokai Co.). MPI-12 was synthesized from molecularly distilled methoxypolyethylene glycol (MPEG) and dodecyl bromide (8). The elimination of volatile impurities by passing the sample through a molecular distillation apparatus was omitted intentionally. MPd-12 was synthesized from hIPEG and decyl chloride through a similar course (8). Ethylene glycol monododecyl ether was synthesized from the potassium alcoholate of ldodecanol and ethylene chlorohydrin, didodecyl ether was synthesized from the potassium alcoholate of dodecanol and dodecyl bromide, triethylene glycol monomethyl ether from the potassium alcoholate of diethylene giycol monomethyl ether and ethylene bromohy-
a : AIR b : WATER c : PHORONE d 1-DODECANOL C
d
a b
I
0
5
IO
I5
w
0
5
10
15
cr:
1
W
Therefore the peak is probably ascribable t o the coexisting dodecanol. Quantitative analysis is also possible if the peak area of dodecanol is assumed to h proportional to its content. Suppose that b grams of dodecanol is added to a grams of the sample, and w grams of this mixture is chromatographed. The total dodecanol content
w
z
0
a
r/)
cc w
n
a
0 W ui
a
13’
R
dodecanol content in 1 gram of the original sample. When the peak area is plotted per gram, A/w,against weight fraction of added dodecanol, x = b/ (a b), a linear relation should be obtained because
+
5
0
15
10
.4/w
= c
aa + b (m) = c ((1- z i a + z J = ca
n h
5
0
15
10
RETENTION TIME FROM INJECTION, MINUTES
Figure 1. 1.
2.
3. 4.
Gas chromatograms
MPI-12 MPI-12 1 -dodecanol MPI-12 phorone Thoroughly purifled M P I - 1 2
drin, and tetraethylene glycol monomethyl ether from the potassium alcoholate of diethylene glycol and methoxydiethylen glycol chloride. Other samples listed in Table I are of extra pure grade. Procedure. -4fter setting t h e column b a t h a t 200’ C., 0.0042 ml. of test material was inserted into sample chamber by a striped capillary tube. T h e carrier gas (hydrogen) was sent a t a rate of 100 cc. per minute. T h e retention time was calculated from the distance between the summits of the sample and air peaks. Retention volume is defined as the product of the retention time and the flow rate of the carrier gas. Relative retention volume (R.R.V.) is given by the retention volume of the sample divided by that of
Table I.
+ +
ldodecanol. Peak area was obtained as the peak height multiplied by the half-value width. RESULTS A N D DISCUSSION
MP1-12. T h e gas chromatogram of MP1-12, which was decolored with active charcoal, is reproduced in Figure 1. There are four peaks, t h e first two of which are obviously those of air a n d water. T h e last peak has t h e same retention volume as t h a t of dodecanol, and becomes larger \Then dodecanol is added deliberately. All other expected impurities which may exist in the sample have R.R.V.’s considerably apart from 1 (Table I).
Relative Retention Volumes of Various Related Compounds (The retention volume of sample divided by that of 1-dodecanol) Compound R.R.V. Compound R.R.V. Glycols Glycol dimethyl ethers Ethylene 0.078 Ethylene 0.048 Diethylene 0.22 Diethylene 0.14 Triethylene Triethylene 0.63 0.46 Tetraethylene Tetraethylene 1.78 1.35 1,4-Dioxane 0.070 1-Decanol 0.47 Glycol monomethyl ethers 1-Dodecanol 1.00 Ethylene 0.064 1-Tetradecanol 2.05 Diethylene 0.18 1-Dodecyl bromide 1.38 Triethylene 0.53 Ethylene glycol monododecyl ether 2.40 Tetraethylene 1 . 5 5 Didodecyl ether Undetectable Glycol monoethyl ethers Mesityl oxide 0.088 Ethylene 0.069 Phorone 0.31 Diethylene 0.21 1,3,5-Trimethylbenzene 0.18
+ c(l - a)z
(1)
where c is a constant. Extrapolating the straight line, the intercept on abscissa gives - a / ( 1- a ) , Once the calibration curve is obtained, the dodecanol content in any sample can be determined with ease. Suppose a sample whose peak area per gram is Al/wl. When this value is plotted on the calibration curve, a perpendicular line is drawn across this point, and the intercept on abscissa is read as 21; then the gram weight of dodecanol per gram of the sample is given by A,/w,c = a
+ xl(l - a )
(2)
The same procedure is applicable for any impurity whose peak area is proportional to its content. This assumption of proportionality has been verified in the cases of dodecanol and phorone. Straight lines crossing the orib’ rln ere obtained by the increasing addition of them into thoroughly purified MP1-12. The weight of test material, w, may be chosen at nill, but the use of a constant weight is more convenient. In this case a plot of A (instead of A/w) gives the same result. Throughout our experiment, 0.0042 ml. of each test material was chromatographed. This does not introduce a significant error, because the densities of all the test materials were nearly constant. The results shown in Table I1 m r e obtained by adding various amounts of dodecanol to the original MP1-12 sam-
Table II. Peak Area of Dodecanol Added to the Original M P l - 1 2
Weight Fraction of Added Dodecanol, 2,
X
0.00 4.64 8.96
15.56 20.05
Peak Area, A , Sq. Mm. 42.0
129.6 213.9 337.6 423.5
’401. 33, NO. 1 1 , OCTOBER 1961
Recovery Calcd. by Eq. 3, X lo-* 0.00
4.60 9 03 15.53 20.04
1525
ple which contained some dodecanol. The plot of A (sq. mm.) against z gave a straight line. By applying the least square method, a n empirical Equation 3 was derived. A = 42.1
+ 19.0 X 1 0 2 x
(3)
Recovery was calculated by putting the respective peak area into Equation 3. Satisfactory coincidence is observed between the first and third columns in Table 11. By comparing Equations 1 and 3, we get a 42.1 -1 - a - 19.0 x 102 The dodecanol content in the original sample is thus estimated to 2.17%. Mesityl oxide and phorone are possibly produced in the decolorization process of MP1-12. The solvent, acetone, may be polymerized by the catalytic action of hydrogen chloride ( I ) , which is probably included in active charcoal. The third peak in the chromatogram had the same R.R.V. as that of phorone, and became larger with the addition of phorone. The phorone content was estimated t o l.43To by a calibration curve. Both of the dodecanol and phorone peaks disappeared when the sample was allowed t o flow down in a thin film through a molecular distillation apparatus under high evacuation. This sample seems to be quite pure, because no impurity was detected by paper and gas chromatography. Peak areas of phorone added to thus purified sample are listed in Table 111. The A-x relation can be expressed by A = -1.3 19.95 X 10% (4)
+
Equation 4 practically passes through the origin. The deviation is within the limit of expeiimental error. The recovery is quantitative, as shown in the third column. MPd-12. Raw MPd-12 showed a peak corresponding to 1-decanol. After the flow-down through a molecular distillation apparatus, howeve;, xo impurities were detected either by paper chromatography or b y gas chromatography.
Table 111. Peak Area of Phorone Added to the Purified MPl -1 2
Weight Fraction of Added Phorone, x, X
lo-’
0.00
1,745 4.37 6.51 10.29
1526
Peak Area, A , S q . Mm. 0.0
32.0 85.5 129.2 204.0
Recovery Calcd. by Eq. 4, x 10-2 0.06 1.67 4.35 6.54 10 29
ANALYTICAL CHEMISTRY
Commercial Nonionic Detergents. A peak corresponding to dodecanol was observed in t h e gas chromatogram of a commercial nonionic detergent, Brij 30, whose composition is polyoxyethylene dodecyl ether and average oxyethylene number is about 3 [H.L.B. = 9.5; H.L.B. stands for Hydrophilic Lipophilic Balance proposed by Griffin ( 5 ) ] . The calibration curve for dodecanol was linear and gave a dodecanol content of 8.9%. When mono-, di-, tri-, or tetraethylene glycol was added to Brij 30, a peak appeared at the respective R.R.V. None of these peaks was observed on the original chromatogram of Brij 30. Accordingly, the absence of mono- to tetraethylene glycols is concluded. On the other hand, the paper chromatogram showed that Brij 30 contained some PEG’S of higher molecular weight. I n the gas chromatogram of Brij 30 appeared another peak whose R.R.V. was 2.4. This peak was ascribed to ethylene glycol monododecyl ether by its intentional addition. The gas and paper chromatograms of Brij 30 have thus revealed that it contained dodecanol, ethylene glycol monododecyl ether, and P E G containing more than four oxyethylene units. A similar gas chromatogram of Brij 35, which contains 17 oxyethylene units on the average (H.L.B. = 16.9), has proved the absence of long-chain alcohols and P E G having one to four oxyethylene units. P E G of higher molecular weight was detected on the paper chromatogram. Kikkol BL-4.2 (polyoxyethylene dodecyl ether having two oxyethylene units on the average) has shown similar patterns to those of Brij 30 on both the gas and paper chromatograms. Dodecanoi content was estimated to 9.8%. I n all of the above three detergents, mono- to tetraethylene glycols mere not found, whereas higher PEG’S were detected. These detergents are synthesized by blowing ethylene oxide into dodecanol, and polyethylene glycol can form along with the detergent if water is present during synthesis. The absence of the lower homologs may be due to the higher reactivities of water and PEG than those of dodecanol and its oxyethylene derivatives, or to any purification process which eliminates these lon-er homologs. Retention Volumes of Lower P E G and Its Derivatives. There is a linear relationship between the number of carbon atoms and the logarithm of retention volume in each homologous series of fatty alcohols, acids, and esters (9, 6, 9). The retention times of mono- to triethylene glycols have been reported to increase with the number of oxyethylene units (4). In order to examine the quantitative relation between the retention volume and the
number of oxyethylene unita in PEG, the logarithms of R.R.V.’s of mono-, di-, tri-, and tetraethylene glycols listed in Table I were plotted against their oxyethylene numbers. The graph shows a linear relation. The same relationship is found also in mono- and dimethyl ethers of PEG. Comparing these three homologous series at the same oxyethylene number, the R.R.V.’s decrease in the order P E G > monomethyl ether > dimethyl ether. This order is concordant with that of boiling point. Substitution of OH group by OCH, decreases R.R.V., but its effect becomes smaller with the length of oxyethylene chain as evidenced by the approach of three lines. ACKNOWLEDGMENT
The authors acknowledge the suggestions and discussion of Eric Hutchinson and Ichiro Ishizuka. LITERATURE CITED
(1) Claisen, L., Ann. Chem. Liebigs 180. 1 (1875). (2) Cropper, F. R.,Heywood, A,, “Symposium on Vapour Phase Chromatography,” Institute of Petroleum, London, May/June 1956. (3) Ginn, M. E., Church, C. L., Harris, J. C., ANAL.CHEM.33, 143 (1961). (4) Ginsburg, L., Ibid., 31, 1822 (1959). ( 5 ) Griffin. W. C.. J . Soc. Cosmetic Chem‘ ists 1, 311 (1949); Am. Perfumer Essent. Oil Rev. 6 5 , No. 5, 26 (1955). (6) James, A. T., Martin, A. J. P., Biochem. J . 50, 679 (1952). (7) Nakagawa, T., Nakata, I., J Chem. SOC.Javan. Ind. Chem. Sect. 59. 709 (1956). (8) Nakagawa, T., Tori, K., Kolloid-2. 168. ~-~ 132 (1960). ( 9 ) Ray, N. H . , J . A p p l . Chem (London) 4 , 21 (1954). .
-.
I
\ - - - - , -
RECEIVEDfor review March 30. 1961. Accepted J u n e 16, 1961.
Correction Water Analysis In this article by M. W. Skougstad and M. J. Fishman [ANALCHEM.33, 138R (1961)], on page 155R, column 1, last paragraph, the method summarized is that of J. P. Riley, Anal. Chim. Acta 9, 575 (1953). The method of Crowther and Large does not involve heating, nor does i t incorporate manganous sulfate. On page 155R, column 2, lines 1 and 2 should be changed to “The absorbance is directly proportional to nitrogen content u p t o 4 pg. per ml.” On page 163R, column 2, reference (3P), IGO BM/S-07 should be changed to IGO TM/S-07.
