Estimation of Trace and Maior Quantities of Lower Alcohols, Ethers, and Acetone in Aqueous Solutions By Gas Liquid Partition Chromatography S. J. BODNAR and S. J. MAYEUX Esso Standard Oil
Co.,
Baton Rouge, La.
,A rapid, simple, reasonably accurate method was needed for the analysis of large numbers of samples containing two or more of the following components: water, acetone, diethyl ether, diisopropyl ether, ethyl alcohol, and isopropyl alcohol. The difficulties involved in running oxygenated compounds on the mass spectrometer precluded its use. Distillations required a great deal of time, but yielded no acetone-ether splits. A gas liquid partition chromatographic procedure employing a triethylene glycol or a polyethylene glycol-400 substrate was developed and has been applied to aqueous solutions containing trace and major amounts of the components mentioned.
A
arose in this laboratory for a rapid, simple method ivhich Ivould give reasonably accurate results for the analyses of large numbers of samples containing two or more of the following components: water, acetone, diethyl ether, diisopropyl ether, ethyl alcohol, and isopropyl alcohol. The mass spectrometer load was such that inclusion of these samples would have upset the routine mass spectrometer setup. The difficulties involved in running oxygenated compounds on the mass spectrometer also precluded its use. Distillations would have sufficed for major components in the majority of cases, but the acetone-ether splits could not be obtained. HoweTer, distillations would have entailed a great deal of manpower, which was not available, and the time required was unfavorably long. A distillation for samples containing ether and acetone as well as alcohol required 8 hours. Therefore, it was decided to investigate the possibility of gas liquid partition chromatography. Terford advocated the use of a triethylene glycol column for the separation of lox boiling alcohols and ketones (3). A pilot column of this type was set up and a preliminary qualitative and quantitative calibration established. Under the conditions of operation (Table I) the pairs diethyl etherdiisopropyl ether and ethyl alcoholDEFINITE NEED
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0
ANALYTICAL CHEMISTRY
isopropyl alcohol could not be separated. In most of the samples to be run, the ethyl and isopropyl alcohols were not in combination. A total ether figure was deemed sufficient for samples containing diethyl ether and diisopropyl ether, because the relative ratio of the two ethers could be easily estimated on a tri-m-cresyl phosphate column. For quantitative estimation of individual components the internal standard method was chosen because results were rapidly and simply calculated, minor fluctuations of operating variables were compensated for, difficulties due to differences in thermal conductivity between components n-ere avoided, and simple, inexpensive equipment for sample injection was used (2). Methyl ethyl ketone was chosen as the internal standard because of its complete separation from and elution between the pairs diethyl ether-ethyl alcohol and acetone-isopropyl alcohol. Calibration standards were made up by pipetting known amounts of oxygenated compounds into volumetric flasks and diluting to the mark with water. The results desired were to be expressed in volume per cent based on the sample as received representing 100 volume %, water always being determined by difference. This would then obviate the necessity of taking into account the nonideality of the systems. The following observations mere made on the pilot column: Water was the last component eluted and did not interfere in any concentration, if the sample size did not exceed 0.10 ml. Elution order was diethyl ether and diisopropyl ethers, acetone, methyl ethyl ketone, ethyl alcohol and isopropyl alcohol, water. The retention times are listed below. The volume per cent component was directly proportional to the ratio of its peak height to that of the methyl ethyl ketone internal standard over the range investigated. At lower concentrations the curve passed through the origin. By choosing the conditions of flow rate and temperature a second sample could be run on the same column before water from the first sample mas eluted. Variations in sample size, sensitivity, and amount of internal standard used could handle any component from
0
il”
,L c
Figure 1. Schematic diagram of dual column chromatograph unit 1. 2.
3.
4. 5. 6. 7. 8. 9. 10. 1 1.
Helium cylinder and primary pressure regulator Molecular Sieve 1 3 X drier Helium manifold system with secondary pressure regulators Constant temperature air bath Preheater, 13-foot ‘/a-inch copper tubing (coiled) Gow-Mac thermal conductivity cell Serum bottle cap inlet system Chromatographic column, 7-foot 3/s-inch copper tubing coiled Double-pole-throw switch 6-volt storage battery 0.5-mv. recorder
traces to major component at the temperature and flow rate used. Calibrations would hold for the given range, regardless of the system in rvhich a component appeared. Based on the above considerations, a dual column chromatograph was built, which employed two similar triethylene glycol columns, housed in the same constant temperature air bath. Each column had a separate preheater, detector, sample inlet system, and pressure regulator but !vas switched into and out of a common recorder, power source, and sensitivity control by a two-way switch. A schematic diagram of the instrument is shown in Figure 1. Operating under the conditions enumerated in Table I, a sample could be run every 20 minutes in the following manner: 1 Inject sample A into column 1. 2. Inject sample B into column 1 1 minute after alcohol peak of sample A is eluted. 3. Because water is determined by difference, water peaks are not recorded.
Switch power source, recorder, and sensitivity control to column 2 after alcohol peak from sample B is eluted from column 1. 4. Inject sample C into column 2. 5. Inject sample D into column 2 1 minute after alcohol peak from sample C is eluted. 6. Switch power source, recorder, and sensitivity control to column 1 after the alcohol peak from sample D is eluted on column 2 . By this time, the water from samples A and B has been eluted from column 1. 7. Sample E may now be injected into column 1 and the process repeated indefinitely. EXPERIMENTAL
Preparation of Chromatographic Column. Three hundred grams of 30-60 mesh Johns-Manville C-22 firebrick were weighed out. One hundred grams of polyethylene glycol-400 or triethylene glycol (Fisher Scientific G o . ) were weighed out a n d mixed with twice its volume of acetone. The mixture was poured over the firebrick in a large evaporating dish and stirred in the cold. The evaporating dish was placed on the steam bath with occasional stirring until dry. The impregnated brick was resieved and the 3060 mesh portion retained. This operation presented no difficulty. A loosely packed glass wool plug was inserted into one end of a 7-foot length of 3/8-in~h copper tubing. The plugged end was rested on a synchronous vibrator and the tubing was loosely clamped in a n upright position. A small glass funnel was attached to the top of the tubing with a small piece of Tygon tubing. The vibrator was turned on and the column packing was slowly poured into the funnel. After the column was full. about a n inch of packing was poured out and a loose glass wool plug mas inserted in the top end. The column was then coiled around a quart sample bottle 3.5 inches in diameter. Thermal Conductivity Cell. GOKM a c direct-pass thermal conductivity cells with MT/T filaments were operated at 138-ma. filament current. These cells were wired into a conventional bridge circuit. Sensitivity Control. A 10-turn 100ohm Helipot allowed 0 t o 100% sensitivity settings over the range 0 t o 5 mv. Figure 2 depicts the circuit diagram for the dual column control box. Constant Temperature Air Bath. Both columns, preheaters, sample chambers, and thermal conductivity cells were enclosed in a 9 X 12 X 18 inch constant temperature bath constructed of '/Finch Transite. Heat was supplied by two 330-watt heaters. Temperature was controlled by a laboratory Model 126 Thermocap relay and was easily controllable within ~k0.5' C. Gas Flow. Helium was delivered from t h e cylinder through t h e Molecular Sieve X-13 drier t o t h e manifold a t 20 p.s.i.g. This eliminated random drifts that were suspected as being due to trace amounts of water in some
~~~
Table 1.
~~
~
_ _ _ _ _ _ _ _ _ _ _
Comparison Peak Heights Ratios and Standard Deviations of Three Similar Columns
All columns 7 feet X 3/0 inch copper tubing (coiled). 30 g. triethylene glycol per 100 g. 30-60 mesh Johns Manville C-22 firebrick (unwashed). 110' f 0.5" C.; 6 p.8.i.g. helium inlet pressure (80 ml./min.); 0.01-ml. sample size; maximum sensitivity; 0-10 mv. recorder 20 inches/hr.; 5.00 ml. MEK per 100.00-ml. sample Pilot Column Column 1 Column 2 StandVol. Std. Av . Std. Av. Std. Av. ard Component dev. ratio dev. ratio dev. ratio 70 A Diisopropyl ether 0.08 0.11 2.50 5.0Ei 2.44 0.07 2.40 Acetone 1.00 0,280 0.008 0.286 0.008 0.302 0.007 Isopropyl alcohol 0.05 44.00 5.99 0.14 5.25 0.14 5.42 B Diisopropyl ether 7.50 3.68 0.10 3.67 0.04 0.17 3.78 Akcetone 0.50 0.146 0.006 0.129 0.006 0.129 0,009 Isopropyl alcohol 47.00 6.42 0.04 0.09 5.44 0.12 5.53 c Diisopropyl ether 3.00 1.49 0.08 1.38 0.04 1.46 0.04 Acetone 0.30 0.086 0.003 0.116 0.006 0.129 0.007 Isopropyl alcohol 55,OO 7.33 0.13 6.28 0.09 0.05 6.39 D Diisopropyl ether 1.00 0.50 0.03 0.49 0.08 0.47 0.02 Acetone 1.30 0,362 0.012 0.337 0.025 0.348 0.013 Isopropyl alcohol 40.00 5.48 0.11 0.21 4.72 0.04 4.89
B-Col
I
I
Figure 2. Circuit d i a g r a m of dual column control box
1 ' 4 " Malleable Iran
1
Figure 3. Detail of sample injection point
cylinders of helium. The gas flowed from the manifold at 6 p.s.i.g., through the preheater into the reference side of the thermal conductivity cell, thence through the sample chamber into the column, from which it passed out through a rotameter. Flow was arbitrarily set with a rotameter to a preset value t h a t gave the desired time cycle. Sample Chamber. A l/r-inch tee was used as a sample chamber. This permitted t h e sample t o be injected through a serum bottle cap with a hypodermic syringe directly onto t h e t o p of t h e chromatographic column Dacking. This is illustrated in Figure 3. Table I lists and compares the peak height ratios of the individual components used in calibrations that were obtained on the "pilot" column and on
columns 1 and 2 of the dual chromatograph with a 1 to 20 ratio of internal standard t o sample. A single calibration for diisopropgl ether would have sufficed for all three columns, but individual curves were needed for isopropyl alcohol. I n this case, it is believed that minor differences in the amount of packing material used, ratio of organic substrate to inert material, packing variations, and ratio of internal standard to component were more critical for isopropyl alcohol than for diisopropyl ether. Isopropyl alcohol is very much more soluble in triethylene glycol than diisopropyl ether. Columns 1 and 2 of the dual chromatograph were packed with the same batch of packing material, while the pilot column was packed with a different batch, although the ratio of organic substrate to inert support was the same. This would account for the large difference between the isopropyl alcohol calibration curve of the pilot column and those of columns 1 and 2. The differences between columns 1 and 2 are due to the packing variable. When ratio of the internal standard to sample ratio was increased to ll2,to increase the slope of the isopropyl alcohol calibration curve, the situation was different, in that the use of one curve was justified for isopropyl alcohol but not for diisopropyl ether (Table 11). Unfortunately, the pilot column was used only to establish the qualitative aspects of the problem and the preliminary calibration of Table I. Therefore, no direct comparisons between the pilot column and columns 1 and 2 could be made for the internal standard-sample ratio 1 to 2. iilthough the mode of operation as described gave satisfactory results, a major drawback was that the columns lasted only about 2 months before triethylene glycol elution gave poor resolution and upset the time schedule, VOL. 30, NO. 8, AUGUST 1958
1385
Table II.
Comparison Peak Height Ratios and Standard Deviations of Two Similar Columns
Conditions same as in Table I except 50.00 ml. methyl ethyl ketone per 100.00-ml. sample Diisopropyl Ether Isopropyl Alcohol Column Vol. 70 Av. ratio Std. dev. Vol. o/o Av. ratio Std. dev. 1 1.00 0,048 0.004 40.00 0.494 0,005 2 1.00 0.054 0.009 0.506 0.002 40.00 1 3.00 0.136 0.006 44.00 0.539 0,008 2 3.00 0.155 0.007 44.00 0.546 0,007 1 5.00 0,249 0.006 47.00 0,582 0.007 2 5.00 0.266 0.005 47.00 0.589 0.007 1 7.50 0,336 0,005 55.00 0.672 0.010 2 7.50 0.376 0.007 55.00 0,672 0.007 Table 111. Ranges and Conditions of Application 7 feet X 3/s inch copper tubing (coiled); 30 g. polyethylene glycol-400 per 100 g. 30-60 mesh C-22 fire-brick; 100" st 0.5' C.; 6 p.5.i.g. Helium inlet (80 ml./min.); 0-5 mv. recorder 20 inches/hr. Methyl Ethyl Ketone, Component M1./100.00Sample 9% Range, Determined VOl. % M1. Sample Size, M1. Sensitivity Diethyl ether 0-2 100 1.00 0.05 1-10 25 20.00 0.02 Diisopropyl ether 0-2 0.05 100 1.00 1-8 0.02 25 50.00 Ethyl alcohol 0-5 100 1.00 0.05 3&42 25 20.00 0.02 Isopropyl alcohol 0-10 100 1.00 0.05 40-55 25 50.00 0.02 Acetone 0-4 100 1.00 0.05
Table IV.
Standard Deviation of 14 Determinations
Blind sample by three operators" on dual column chromatograph. Conditions same as in Table I11 Volume Per Cent Column 1 Column 2 Diiso ropy1 Isopropyl Diisopropyl Isopropyl Detn. etRer alcohol ether alcohol 1 4.7 47.3 5.5 46.9 2 46.8 4.6 47.1 5.4 3 4.7 47.1 46.5 5.5 4 47.7 47.0 4.3 5.3 5 47.6 47.5 4.4 5.0 6 5.3 48.2 5.7 47.5 7 5.3 47.8 5.8 47.6 Av . 4.8 47.5 5.5 47.3 Std. dev. 0.4 0.4 0.3 0.5 a Operators had very little experience during time of test. Table V.
Typical Results by Distillation and Dual Chromatograph
All results in volume per cent Dual Chromatograph Component Column 1 Column 2 Distillation" Diisopropyl ether 4.2 4.3 4.2 Isopropyl alcohol 49.6 49.8 50.4 233 Diisopropyl ether 3.8 4.2 4.4 Isopropyl alcohol 50.2 50.2 51.2 238 Diisopropyl ether 4.0 4.2 4.3 Isopropyl alcohol 48.7 48.0 49.2 240 Diisopropyl ether 5.1 5.0 6.0b Acetone 0.63 0.52 ... Isopropyl alcohol 50.2 51.3 51.0 247 Diisopropyl ether 3.3 3.3 3.8 Isopropyl alcohol 51.2 51.6 53.6 a Average of two results whose difference generally ran 1.0-1.5 for isopropyl alcohol. Summation of acetone and diisopropyl ether. Cannot separate by distillation. Sample No. 232
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ANALYTICAL CHEMISTRY
This necessitated keeping two precalibrated and precoiled columns ready to replace the exhausted columns. Changing columns and recalibrating two points for curves not through the origin and one point for curves through the origin could be done in 2 days. Adlard pointed out that polyethylene glycol400 was best suited of the polyethylene glycols for hydrocarbon work (1). For the systems discussed here this was highly successful, as the five observations listed for the triethylene glycol held for polyethylene glycol-400. However, the resolution was slightly better for the polyethylene glycol-400, as a partial separation could be obtained between the pairs diethyl ether-diisopropyl ether and ethyl alcohol-isopropyl alcohol. Polyethylene glycol-400 columns have been in daily service for over 6 months with no sign of deterioration. The retention values for the compounds involved under the conditions listed in Tables I and I11 are:
Compound Diethyl ether Diisopropyl ether Acetone Methyl ethyl ketone Isopropyl alcohol Ethyl alcohol Water
Retention Time. Seconds from Air TriPolyethylene ethylene glycol glycol-400 (conditions (conditions Table I ) Table 111) 60 90 60 336
126 432
487 786 786 3,680
677 978 1,020 3,240
RESULTS
Table I11 summarizes the ranges and conditions under which the dual chromatograph has found routine application. Table IV shows the standard deviations obtained on each column of the dual chromatograph for multiple determinations of a single sample. This indicates the total error of the method and included errors associated with three different operators, bottling of individual samples from master batch, addition of internal standard, sample injection, and calculation of results. This standard deviation was determined after minimum instruction of the operators; it will be reevaluated after the method has been in use for one year and an improvement is expected. After these determinations vere made, the standard deviation indicated an error in the diisopropyl ether calibration for one of the columns. This was rectified when the column 1 calibration for diisopropyl ether was found to be in error. Table V compares some typical results obtained by distillation and gas liquid partition chromatography. Table VI lists the calibration data used to deter-
Table VI.
Calibration Data for Estimation of Low Concentrations of Diethyl Ether, Diisopropyl Alcohol, and Acetone
Conditions same as in Table I11 Volume % isopropyl alcohol = diethyl ether = acetone = 1.00 Weight Yo isopropyl alcohol = acetone = 0.79 diethyl ether = 0.73 Peak Height Ratios Column 1 Column 2 Isopropyl Diethyl Isopropyl Diethyl alcohol ether Acetone alcohol ether Acetone
Av. Std. dev.
0,755 0.744 0.741 0.747 0.007
2.45 2 45 2.56 2.49 0.05
1.37 1.39 1.41 1.39 0.02
0.714 0.713 0,726 0.718 0.008
2.56 2.54 2.38 2.49 0.08
Sample
tones, but a specific acetone determination mas desired in each case. In addition to the routine applications, the dual chromatograph has been invaluable in trouble shooting large number of samples rapidly, special pilot plant studies, and “what is it?” samples. ACKNOWLEDGMENT
The authors wish to thank the Esso Standard Oil Co. for permission t o publish this paper. Special thanks are due to P. ITr.Boudreaux and E. A. Koel,
Acetone, Weight % GLPC Chemicala
TiR TiOH T 49 T 45 T 40 T 23 P FI 40 WA
1.39 1.41 1.40 1.40 0.01
peak height component/peak height methyl ethyl ketone Rt. % (vol. yo)component = I I lV1 peak height component in standard sample/peak height methyl ethyl ketone, M = , weight 7’ (or volume 7 0 ) component in standard sample mine low concentrations of isopropyl alcohol, diethyl ether, and acetone. It was found that either weight or volume per cent could be calculated directly, because at low concentrations the specific gravity of the samples was very close t o 1.00. Table VI1 compares the results obtained by gas liquid partition chromatography and chemical method for acetone. The chemical method determines total carbonyl b y hydroxylamine hydrochloride, which is calculated as acetone. It was known that some of these samples contained traces of numerous aldehydes and ke-
Table VII. Estimatian of Acetone by Gas Liquid Partition Chromatography and Chemical Analyses
0.24 0.27
0.41 0.38
0.56 0.39
0.64 0.86
1.50 4.52
1.10 4.35
1.66 1.67
1.97 1.93
0.41
0.19
Total carbonyl by hydroxylamine hydrochloride calculated as acetone. a
who ran the majority of analyses on which this study was based. LITERATURE CITED
(1) Adlard, E. R., Vapour Phase Chro-
matography Symposium, London, England, May 30 to June I,1956. (2) Hausdorff, H. H., “Vapor Fraq; tometry (Gas Chromatography), Perkin-Elmer Corp., Norwalk, Conn. (3) Terford, H. C., Regional Meeting, Southwest Section, ACS, Houston, Tex., December 1958. RECEIVEDfor review August 29, 1957. Accepted April 9, 1958.
Determination of Surface Area Adsorption Measurements by a Continuous Flow Method F.
M. NELSEN and F.f.
EGGERTSEN
Shell Development Co., Emeryville, Calif.
b A promising new approach to the measurement of surface area by the adsorption of nitrogen is presented. Nitrogen is adsorbed by the sample a t liquid nitrogen temperature from a gas stream of nitrogen and helium and eluted upon warming the sample. The nitrogen liberated is measured b y thermal conductivity. Good agreement was obtained with the conventional volumetric method. The new method does not involve vacuum techniques and is therefore free of concomitant maintenance problems, gives a permanent record automatically, is faster and simpler for routine application, and requires less skill. It can probably b e extended to a lower range of areas, because of the high sensitivity of the thermal conductivity detection.
T
most widely used method for determining surface area involves measuring the amount of gas adsorbed on a solid surface at a temperature close t o the boiling point of the gas. Nitrogen is most commonly used as the adsorbate. If the adsorption is measured a t several gas pressures, the BrunauerEmmett-Teller (BET) equation (1) can be used to calculate the amount of adsorbate required to form a monolayer. This value, multiplied by the proper factor for area covered per unit amount of nitrogen, gives the surface area. I n this method the amount of adsorbed gas is usually determined by measuring pressure differences in a calibrated highvacuum apparatus, which is fragile and complex. Recently, Loebenstein and Deitz (4) proposed a scheme for reducing the vacuum requirements by HE
using a mixture of the adsorbate and a n inert gas such as nitrogen with helium. However, they made no basic changes in the method of adsorption measurements. The method described is also based on gas adsorption and use of the BET equation, but the adsorption measurements are entirely different. The amount of adsorbed gas is determined by concentration measurements in a continuous flow system rather than by pressure-volume measurements in a static system. The procedure is rapid and is applicable over a wide range of surface areas. Results of some exploratory tests are given to demonstrate the feasibility of the method. More extensive studies are in progress t o establish the scope and precision. VOL. 30, NO. 8, AUGUST 1 9 5 8
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