Large-Bo re Cap iII a ry and Low- Pressure-Dro p Packed Columns ROY TERANlSHl and T. R. MON Western Regional Research laboratory,
b Large-bore capillary columns, 0.02inch i.d. and 0.03-inch i.d., 500 feet and 1000 feet long, respectively, have been made with theoretical plate values equal to or better than those obtained with 0.01 -inch i.d. columns 100 to 200 feet long. The capacity of the large-bore columns permits direct injection, nondestructive thermistor detectors permit the isolation of tenths of milligram quantities of pure material per run. Construction and performance of a low-pressuredrop packed column are discussed.
U. S.
Department of Agriculture, Albany, Culif.
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s POWERFUL as mass spectrometry
is, other spectral data are needed for establishing chemical structure with greater certainty. To obtain such information, milligram quantities of pure material must be isolated. To accomplish such preparations, largebore capillaries and low-pressure drop packed columns were investigated because of the interesting possibilities indicated (1-3, 6-7, 9 ) . EXPERIMENTAL
The air-bath oven with temperature control and programmer was purchased from Beckman Instruments, Inc., Fullerton, Calif.; and the microdetector, from Carle Instruments, Inc., Anaheim, Calif, The stainless steel tubing used for the columns was obtained from Superior Tube Co., Norristown, Pa., and from J. Bishop Co., Malvern, Pa. Dual capillary columns, 500 feet long, 0.0625-inch o.d., 0.02-inch i d . , and 1000 feet long, 0.0625-inch o.d., 0.03-inch i d . , were wound on a single spool as reported by McEwen (4). The lowpressure drop packed column,
Table I. Theoretical Plates (Thousands) at 125" C., 15 cm./sec.
1000 Feet,
0 03-inch 1.d.
Compound n-Hexanol n-Octanal n-Amyl acetate Limonene n-Decane
1490
SF 96-50 H:(&)
120 119 125
Carbowax 2031 41 73
500 Feet, 0.02-
inch i.d.,
SF 96-50
134 104 200
ANALYTICAL CHEMISTRY
1% 144
174
180
AVERAGE LINEAR VELOCITY ~ c r n / L e c ~
Figure 1 . HETP curves, SF 96-50 coating, 1 000-foot, 0.03-inch i.d. column 0
n-hexanal,
+ limonene
0
n-octanal,
A n-amyl ocetote,
120 feet long, 0.125-inch o.d., 0.10-inch i d . , was also wound on a spool. >ICEwen ( 4 ) has shown that spacing between column windings is necessary for good temperature control. The capillary columns were coated by injecting 5-ml. and 25-ml. portions of 10% (w./w.) solutions of stationary liquid in chloroform in the 0.02-inch i.d. and 0.03-inch i.d. columns, respectively. The lowpressure drop packed column was coated with 50-ml. portions of 1% (w./w.) solution. Three to four portions were pushed t'hrough with nitrogen a t 50-1 00 p.s.i. Flushing with nitrogen for several hours between each portion removed most of the chloroform. Measurement of material injected and excess stationary liquid b1on.n out with the flushing showed that after three such portions, no more stationary liquid was held in the column. Coating and flushing of the columns were done with the nitrogen flowing from the injector to the detector end. Conditioning of the columns was done with nitrogen flowing from t'he detector end to the injector end at' 50-100 1) temperature was 200"-225" C. for silicone oil SF 96-50 and Carbon-ax 2011. After several days at such conditions, excess stationary liquid and smaller molecules of the stationary liquid had been removed, and the columns could be used immediately after installation.
The packing for the low-pressure drop packed column, spring inside of spring, was made of #33, 0.007-inch diameter Xichrome wire. The inner spring was wound around a 0.02-inch diameter needle held and turned with a hand drill. l f t e r the inner one was formed, it was trimmed and insert,ed into a 0.0625-inch o.d., 0.04-inch i d . , notched tubing held and turned with another hand drill, and the outer spring was wound and then trimmed. Thus, a spring inside a spring was formed with one continuous wire These springs were dropped one by one into 0.125inch o.d., 0.10-inch i.d. tubing 20 feet long. The 20-foot sections were joined with Swagelok fittings and wound onto a spool. The pressure drop across 120 feet of such packing material was so low that it could not be measured with any accuracy with the equipment available. The flow rates were controlled by adjusting pressures to needle valves used as restrictors. Therefore, because of the low-pressure drop, much longer columns are esperimentally feasible, and the total number of theoretical plates available with packed columns can be easily increased. Theoretical plate values were determined with n-hexanol, n-octanal, n-amyl acetate, and in some cases, n-decane. The conditions used were similar to those \vith 0.01-inch i.d.
AVERAGE LINEAR VELOCITY
(Sm
/ILC
Figure 2. HETP curves, Carbowax 20M, 1 000-foot, 0.03-inch i.d. column 0 tote,
n-hexanol,
+ limonene
0 n-octanal, A n-amyl a c e -
Table (I. Column Efficiencies
Feet per Theoretical 100,000 plat,es t'heoretical per foot plates
Inside diameter, inches
1,000 250 100 (10")
0.01
0.02 0.03 0.10 0.10, packed a
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Figure 3. Comparison of retention times of compounds used in theoretical plate calculations with the two stationary liquids used
columns (8). The sample loads were 0.1 to 0.5 microliter, direct injectionsi.e., no stream splitting.
velocity, especially with n-hexanol. Also, if the sample load for a single component is over 0.2 to 0.3 milligram, an appreciable loss in efficiency is obseived. Similar curves were obtained with 500-footJ 0.02-inch i.d. capillary columns, and the results are summarized in Table I. Figure 3 shows chromatograms obtained with the mixture of compounds used in the calculation of theoretical plates with a 1000-foot, 0.03-inch i.d. capillary column. K i t h the dual
RESULTS
Figures 1 and 2 show HETP curves obtained with 1000-foot, 0.03-inch i.d. capillary columns coated with S F 96-50 and Carbowas 20N. I t can be readily seen from such results that, with these columns and the sample loads used, column efficiencies decrease considerably with the increase in linear
100
Estimated.
2ox I
m
1,000 (10,000=) 1,000
injector and dual column system, two columns with different stationary liquids are always available with one instrument without any exchange of columns. K i t h an adjustable-zero recorder, the direction of signal can be used to indicate which column is being used, as illustrated in Figure 3. With a recorder without a zero-adjust, polarity to the recorder must be reversed. Because different stationary liquids are necessary even with very &cient columns, the quick, easy availability to two similarly efficient columns with two different stationary liquids proves to be very convenient. Figure 4 shows an analysis of a 10-cc. sample of laboratory gas with a hydrogen flame ionization detector a t the end of a 1000-foot, 0.03-inch i.d. capillary column. For wch analybis, a smaller input resiytance to the electrometer tube is needed-Le., the chopping
32 Min.
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100 400
lox I
5OX
IOOX
2mox 2ooox
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40
I. 40
125"
150'
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J U W , I
'
16
2'4
50"
750
Figure 4. Chromatogram of laboratory gas, flame ionization detector
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56 150"
v
\
1000 c.
6$ 150'
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7 2 rnin. 150' C.
1 000-foot, 0.03-inch i.d., SF 96-50 column, 1 0-cc. sample, hydrogen
VOL. 36, NO. 8, JULY 1964
1491
Figure 5. Chromatogram of kerosine, 1 20-foot, 0.1 0-inch i.d., 0.1 25-inch o.d., SF 5-microliter sample, thermistor detector
off the tops of the first two peaks indicated that the control-grid voltage had exceeded the linear response rangebut direct vapor analyses possibilities are illustrated. Figure 5 shows a chromatogram of kerosine with a 120-foot low-pressure drop packed column, programmed temperature. The temperature of the column and time of elution of terpenes and terpenoids from this 120-foot lowpressure drop packed column is comparable with a 75-footJ 0.01-inch i.d. capillary column. HETP curves were obtained with the low-pressure-drop packed column, and the optimum column efficiency was established a t approximately 5 cm. per second. S o appreciable loss in efficiency was observed with several tenths of milligram loads. Data are sum-
marized and compared in Table 11. Because of the efficiency and capacity of the low-pressure drop packed column, highly efficient columns can now be built to prepare milligram quantities of pure material heretofore very difficult to obtain. ACKNOWLEDGMENT
The authors thank H. S. McDonald for his suggestions, D. C. Patterson for his help, and R. S. Souza for assistance in construction and assembly of the equipment. LITERATURE CITED
(1) Ettre, L. S., Cieplinski, E. W., Averill, W., J . Gas Chromatog. 1, 7 (1963). (2) Halasz, I., Horvath, C., ANAL.CHEM. 35, 499 (1963).
96-50 low-pressure drop packed column,
(3) Jentzach,
D., Hoverman, IT., J . Chromatog. 11, 440 (1963). (4) McEwen, D. J., ANAL. CHEM.35,
1636 (1963).
( 5 ) Quiram, E. R., Ibid., p. 593.
(6) Schwartz, R. D., Brasaeaux, D. J., Shoemake, G. R., J . Gas Chromatog. 1, 32 (1963). ( 7 ) Sternberg, J. C., Poulson, R. E., ANAL. CHEM.36, 58 (1964). (8) Teranishi, R., Buttery, R. G., McFadden, W.H., Mon. T. R.,Wasaerman, J.,Ibid., p. 1509. (9) Zlatkis, A., Kaufman. H. R.. S u t u r e 184, 2010 (1959). RECEIVEDfor review March 26, 1964. Accepted April 29, 1964. 2nd International Symposium on advances in Gas Chromatography, University of Houston, Houston, Texas, March 23-26, 1964. Reference t o a company or product name does not imply approval or recommendation of the product by the L-. S. Department of Agriculture to the exclusion of others that may be suitable.
Partic le-to-Co Iumn Diameter Ratio Effect on Band Spreading J. C. STERNBERG and R. E. POULSON' Beckman Instruments, lnc., Fullerton, Calif.
b Packed columns conventionally in use employ particlesfrom '/8 to ' / b o of the column diameter. Recent studies have suggested a departure from the generally accepted proportionality between observed plate height and particle diameter in columns packed with particles larger than '/8 the column diameter; plate heights smaller than a particle diameter have even been reported in one instance. A systematic study of the effect of column-toparticle diameter ratio on the spreading of unretained component peaks has been carried out and has revealed some heretofore unrecognized relationships. Special experimental methods employed are described and their 1492
ANALYTICAL CHEMISTRY
validity demonstrated. The possibility of obtaining plate heights for unretained components smaller than the particle diameter has been verified, and the performance expressed in terms of the product of plates per unit pressure drop and plates per unit time has been found to b e optimal for particles l/* to '/3 of the column diameter. The performance of packed columns over the entire range of particle-to-column diameter ratios i s compared with open tubular columns. New data are also presented on the effects of pressure drop and of very high linear velocities on column performance, and a suggested effect of incipient turbulence i s indicated.
T
in packed columns have been obtained using very small packing particles, and it is generally accepted t'hat a direct proportionality exists between plate height and particle diameter (4,8). For retained components the plate height is about 3 to 5 times the particle diameter, while for unretained components the plate height is 2 to 3 times the particle diameter (3) ; in every case plate heights greater than the particle diameter are expected. -1recent' paper by Giddings and Robison ( I I ) , however, reported HE BEST PLATE VALUES
1 Present address, C . S.Department of Interior, Bureau of Mines, Petroleum Research Center, Laramie, Wyo.
