was seriously out of line, hence the very high value for dichloro in this example. No reason for the discrepancy could be found, but we believe it was caused by occasional erratic behavior of the iustrument, due possibly to extreme line voltage fluctuation. Tahle I1 shows that analyses of triazine solutions run in duplicate do not on the average show much less variability than the difference between determinations of known samples and the true values. Thus, most of the uncertainty in the method appears to be hound up in the instrumental reproduction of the absorption curves and the translation of these data into absorbance values. Consequently the absolute error in the determination of a triazine by this method is about the same no matter how much of i t may be present in the sample.
The analytical bands fall in a region where there are relatively few strong interfering bands, which minimizes the possibility of spectral interference due to impurities when crude triazine mixturffi are analyzed. This possibility may he reduced still further by washing the mixtures with methanol, in which all four triazines are very sparingly soluble hut in which the likely contaminants such as nitriles and amides readily dissolve. By-products in the crude triazine mixtures may also be removed by passing carbon tetrachloride solutions through a short column of activated n e u t r a l d u m b . whichaermits the triazines to pass through diiectly, but .e more polar imp1 which adsorbs the aolar imvurities egree. to a significant degree. The a m o m t ofif an s-triazine mi mixture ._.l--l:~-l . results which gives optimum analytical by this method is a mere 2 to 3 mg. per ~~~~~~~
5 ml. of carbon disulfide solution. The smallest amount of any one triazine component in such a mixture which can be detected spectroscopicdly is about 40 to 60 pg. LITERATURE CITED
(1) Cook, A. H., Jones, D. G., J . Chem. Soe. 1941, pp. 276-62. (2) Eicner, P., Krafft, F., Bw. 25, 2263-9 (18921. (3) Heftmann, E., "Chromatography," p. 58, Reinhold, New Y o r k . 1961. ( 4 ) Meites, L., Thomas, H. C., "Advanced
Analytical Chemistry," Andvtical Chemistrv." McGrrtw-Hill. McGrrtw-Hill, New York, Toronto. New"York, Toronto, London, 1958. ,5) 5zi>liu, E. hl ., I(3po;~rt. I.., '..' l ' r i l i i w e m d ller!\,%tivve," C h p . 11, Iirwwisnrc, See. Yt.rk, 1!~5!1.
published. ((6) 6 ) Spencer, R. I)., to be yublished.
RECEIVED for review April 12, 1963. Accepted July 26, 1963. Presented a t the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 4-6.1963.
Temperatu re Programmed Capi1lary Columns in Gas Chromatography DAVID J. McEWEN . General Motors Research laboratories, Warren, Mich.
b An F 8 M Model 609 g a s chromatograph, with modified analyzer g a s controls and column oven heating system, has been used to temperature program capillary columns. This technique has been investigated for the analysis of dilute hydrocarbon g a s mixtures [99.870 Nz). For qualitative and quantitative analyses, the precision of the retention volume and peak area measurements have been determined.
F
OR TEE ANALYSIS of complex mistures, the capabilities of capillary columns and temperature programming have been amply demonstrated when used separately, but only recently have the two been combined. Teranishi, Nimmo, and Corse (6)and Boys (3) have described laboratory-constructed apparatus for temperature programming capillary columns, hut gave few details of their results. In the development of an improved method for analyzing automobile exhaust gas, this technique was investigated using dilute hydrocarbon gas mixtures. Rather than build a laboratory setup, a commercial gas chromatograph featuring flame ionization detection and column temperature pro+ gramming was modified to use capillary columns. Recently, a suitable commercial instrument has become available
(4). 1636
ANALYTICAL CHEMISTRY
Figure 1 . G a s chromatographic apparatus EXPERIMENTAL
Gas Chromatograph Modifications. Figure 1 shows t h e modified gas chromatograph (F & M Scientific Corp., Model 609) t h a t was used in this work. This instrument consists basically of the control cabinet, 1, and
t h e analyzer section, 7. T h e principal changes t h a t were made t o t h e apparatus include: modifying tho gas controls of the analyzer, addiug a gas sampling valve with a thermostatiug oven, rewinding the capillary colunp% and modifying the column oven heatmg system. The first three changes were
. . ...
....
6
Figure 3. 300-Foot capillary column received (left) and rewound (right)
CIS
made to adapt the instrument to gas analysis using capillary columns, whereas the fourth was made to improve performance. Gas Controls. A schematic flow diagram for t h e modified analyzer is shown in Figure 2. The heavier lines represent t h e carrier gas; t h e lighter lines, the hydrogen, nitrogen diluent, and air. The added panel, 14 (refer also to Figure l), has a four-way valve for using either nitrogen or hydrogen as the carrier gas, and toggle and needle valves for setting the various gas flows t h a t are measured with t h e rotameters on panels 11 and 13. The rotameter for the carrier gas was originally between the flow controller, 15, and the injection block, 10. It was moved upstream of the flow controller, as shown, to be independent of varying columninlet pressure. Regardless of what column is used or the variation in the column inlet pressure during temperature programming, the carrier gas pressure upstream of the flow controller is set the same for all experiments and only one flow calibration curve is required. The pressure gauge, 8, (Marsh Equipment Co., type 220) was added between two toggle valves, 9, for measuring either the rotameter or column inlet pressure. The flow controller can be bypassed by opening both toggle valves, if column operation a t constant inlet pressure is desired. For easier adjustment of the carrier gas flow, the original valve that was attached to the flow controller a t the rear of the analyzer was replaced with a vernier needle valve, 12, (Ideal Aerosmith Inc., Model V-52-2-14) and attached to the rotameter panel, 11. Gas Sampling Valve. The gas samplig valve, 17, (Greenbrier Instruments Inc., type D) has been described (6). It is pnenmatically op-
erated by the solenoid valve, 16 (Ross Operating Valve Co., PAL type), and thermostated in the oven, 6 (Blue M Electric Co., Model OV-SA). The connections to the sample gas inlet and outlet ports of the valve are made a t the top of the oven a t 5. Capillary Columns. The capillary column, 18, was obtained from the Perkin-Elmer Corp. in the form shown on the left in Figure 3. This form, however, was m u i t a b l e for temperature programming because of slow heat
transfer to the inner layers of tubing. To avoid this limitation, the tubing was rewound with spaces between the layers of tubing for rapid air circulation as shown on the right. To coil the tubing in this form,,metal spacers were placed abont 1.5 mches apart around the periphery of a mandrel and held with rubber bauds. The spacers were made by cutting a perforated steel sheet ('/Isinch holes a t '/&uch staggered centers) along the centers of adjacent rows of holes. While slowly rotating the mandrel in 8 lathe chuck, the tubing was guided into the U-notches of the spacers. After completing the coiling operation, the tnbiug was held in place with wire ties a t the ends of the spacers. The coil was slid off the mandrel and the inner row of
220
200
I80
9
160
5
$
2e 5> 0
140
Figure 4. Column oven temperature lag
IM
100
80
60
-1"
0
5
10
15
20
25
30
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TIME, MINUTES
VOL. 35, NO. 1 1 , OCTOBER 1963
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spacers removed. For the 150-foot columns, each was coiled a different diameter so that two or three columns could be connected in series.
Table 1.
Instrument Conditions for Chromatographic Experiments
Figure Sample
5 Liquid hydrocarbons 12 x 10-6 10 12s
Sample volume, ml. Electrometer, range attenuation Columna 1 column temperature, 25 to 90
OC
50
70
30
'-
MINUTES
s c2 to Ca
hydrocarbons 0.17
hydrocarbons olefins 0.086toO 80 0.18
as noted
)64 to 400 2 23
IO
-so
1
128 2 0 to 50
Inlet pressure, p.5.i.g. 37 35 4s 58 Air, ml./minute 620 620 260'' 630 Hp, ml./minute 35 35 20 55 Carrier, ml./minute 4 6 Sr 4 . 4 x2 7 . 1 €I, 4.1 1;2 Auxiliary K2, 30 30 27 30 ml. /minute a Column 1 is a 150-foot capillary tube coated with silicone oil, column 2 is a 300-foot capillary tube coated with Ucon LB-550-X. * .I, Perkin-Elmer flame ionization detector was used for this experiment.
23
4
7
c1 to cs
1
c.
TEMP.
6
c1 to c4
2
Figure 5. Programmed separation of hydrocarbon mixture See Table II for the peak identification
gram after the foliowing changes n e w made to the oyen heating system. The portion of the perforated shield above the fan \\as nrapped with aluniinum foil t o force the air more directly over the heater wires. The original fan motor n a s replaced with one (Bodine Electric Co., Model B2190) run at 7400 r.p.m. The speed of the motor can he adjusted between 3000 and 9000 r.p.m. with the variable transformer, 2 (Figure 1). The controller thermo0.72
0.28
0.80
3.086
0.14
ML.
I
v)
z
W
I
iii
I
I
.-
I
I
-
L
1
3.3
I
2.6
2.2
26
3.0
2.2
-
Figure 6. carbons
ANALYTICAL CHEMISTRY
A
1
2.b
L..J--.-L-
2.2
L.-LL1_1
3.0
2.6
2.2
1.3
2.6
2.2
MINUTES
Figure 7. Effect of gas sample size on component separation
Low-temperature separation of light hydro-
Column Oven Heating System. Initial chromatographic experiments using temperature programming indicated large temperature differences between the column and the controller thermocouple. T o compare the ternperatures of the thermocouple and the air around the column, a thermometer, 4 (Figure l), was inserted through a hollow bolt in the oven cover, 3, so that the mercury bulb was close t o the column. The controller was set t o start a t 45" C., increase at a nominal heating rate of 9" C. per minute, and hold the temperature a t 206" C. Curve 1 of Figure 4 shows the indicated thermocouple temperature for this heating program. Curve 2 represents the thermometer temperature and illustrates the large temperature difference between the thermocouple and the air around the column. Even after holding the controller a t a thermocouple temperature of 206" C. for 41 minutes, the oven temperature only reached 146" C. Curve 3 represents the thermometer temperature for the same heating pro-
l
3.0
Y. I U T E S
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