Table 1.
Replicate Determinations on a 1.034%
Slit image positions, mm. Reference Solution image image 0.000 9.882 0.114 9.996 0.149 10.037 0.181 10.069 0.181 10.065 0.199 10.089 0.144 10.027 0.121 10.002 0.202 10.086
Slit image difference, mm. 9.882 9.882 9.888 9.888 9.884 9.890 9.883 9.881 9.884
Sucrose Solution a t
30" C.
Remarks Room temp., C. 26 24 22.5 22.5 22 24 24 Same sample after 12 hours
Each value is an average of six consecutive readings. The error in reading is about ~ t 0 . 0 0 5mm.
on the ratio of the deflection and focal length of the primary lens, and the angle of the central prism. When this ratio is less than 1/100 and the central prism angle is 120°, linearity is theoretically correct within 0.3% (6). ACKNOWLEDGMENT
This ivork was supported in part by a research grant (RG-8264) from the United States Public Health Service. We thank George Unger, the university's glass blower, for his fine work in the construction of the new double cell. LITERATURE CITED
(1) Bates
The range of refractive index measurement is determined ( 2 ) b y the prism angle of the center cell, the optical path length, and the field of the filar micrometer (in our case 14 mm.). For our first cell we observed that a deflection of 1 mm. corresponded t o 2 X lo-' refractive index units. The unit was calibrated with sucrose solu-
tions ( 1 ) . The image deflection is measurable well within =kO.O1 mm., SO that one has a precision to about 2 X 10-6 refractive index unit. The maximum image deflection corresponds t o about 3 x 10-3 refractive index unit. T o the first order linearity between image deflection and refractive index difference is theoretically dependent
and associates, S a t . Bur. Std., Circular C 440 (1946). (2) . , Debve, P. P., J . i i p. p. l . Phvs. 17, 392 (1946 j. ' (3) Gill,.S. J., Hutson, J., Clopton, J. R., Downing, M.,J . Phys. C'hem. 6 5 , 1432, f\ -l F- -)-AI -l \ .
(4) Hadow, H. J., Sheffer, H., Hyde, J. C., Can. J . Research 27B, 791 (1949). ( 5 ) Korosy, F., Nature 174, 269 (1954). (6) Martin, D. B., 1I.S. t#hesis,UniversitJy of Colorado, 1962.
Gas Chromatographic Analysis of liquids Containing Nonvolatile Viscous Materials
L. J.
Myers, Humble Oil & Refining Co., Linden, N. J.
THE
GAS
CHROMATOGRAPHIST OCCB-
l sionally is required to analyze ma-
terials which contain high percentages of nonvolatile liquids for lorn percentages of volatile materials contained therein. Where temperatures high enough to volatilize the high-boiling components of such samples cannot be tolerated, because of thermal decomposition or other effects, ordinary gas chromatographic techniques are frequently unworkable; the nonvolatile components of the sample accumulate in the sample introduction sections of the equipment. Upon repeated analysis, such accumulation prevents the instantaneous volatilization of the lighter components when t h e sample is injected, with the result that the desired plug of gases is not delivered t o the column. Tailing of peaks can result and, in extreme cases, peak heights or areas will grow progressively smaller when the same sample is run repetitively. This effect is presumably due t o the retention of a portion of the volatiles dissolved in the accumulated nonvolatiles in the introduction system, with subsequent evolution so slow t h a t it merely raises the base line slightly. Such samples could be handled b y preliminary fractionation t o remove the nonvolatiles, but this leads t o other disadvantages. A simple device is described whereby such accumulation of nonvolatiles can
Figure 1. Assembly for cleaning sample introduction cell of gas chromatograph A. 8. C. D.
E. F. G.
H.
Carrier gas inlet Thermistor detector block Sample introduction cell with septum U-tube with tee Valve Four-way valve Gas chromatography column Exhaust
be cleaned from the system in a very short time without disassembly. I n the accompanying simplified diagram (Figure l), the C-tube, D, between the sample introduction cell, C, and the 4-way valve, F , is made of l/s-inch copper or stainless steel tubing, and is as short as possible. It is arranged so that it has a lob7 point, where a tee connection of the smallest possible volume is made with 'js-inch tubing using silver solder. The side arm of the tee is carried out of the case of the instrument where a valve, E , is connected in a convenient location. The side arm is arranged so that it has a continual downward slope. A sample containing nonvolatiles is injected with a syringe through the septum a t C in the usual manner with valve E closed. Sonvolatiles collect in the sample introduction cell and the nearby portion of the L?-tube. After all the desired volatiles h a r e been eluted from column G, valve E is opened and a relatively large volume of solvent (10 to 20 ml.) is injected through the septum with a large syringe. The carrier gas is allowed to continue flowing. The solvent selected should dissolve the nonvolatiles and have as low a retention time as possible on the column used. The solvent will be forced out valve E under the pressure of the carrier gas carrying the nonvolatiles with it. Solvent will be prevented from entering column G to any great extent because of the column's back pressure. After a few seconds, the solvent will be completely evaporated from the sample introduction cell and VOL. 35, NO. 1, JANUARY 1963
1 19
the U-tube, and valve E may be closed. Back-flushing the column, using the 4may valve, F,is optional. After a short wait, to stabilize the base line, a new sample may be injected. Thi- device has 15-orked quite satisfactorily in the determination of butanols and pentanols in a lubricating oil additive. Over 100 determinationc
n'ere made without any apparent chanqe in calibration factors, It is advisable to calibrate the chromatograph using kno\vvnmixtures of the volatiles in the nonvolatiles, rather than to use the pure volatiles. \Then small amounts of volatiles are to be measured in admixture with large amount< of viscous nonvolatiles, the
volatiles are apparently not completely evolved in the introduction cell, even in the firqt run, in some cases. Hon-ever. when calibration is performed with mi-itures similar in composition to the samples to be analyzed, and the .!-stem iq flushed as described after each run, accurate and reproducible rewlti can be expected.
Circulating Pump and Cell for Electrochemical Studies of Gases Paul
E. Toren,
Central Research Laboratories, Minnesota Mining & Manufacturing Co., St. Paul, Minn.
a study of the reaction- of D some n e d y synthesized compounds, it was necessary to measure the elecURISG
trochemical oxidation-reduction properties of a number of gases in solution. Because only small amounts of material were available for these experiments, i t was not possible to work with a solution saturated by a continuous flow of sample gas. Consequently a closed system requiring only a small amount of sample was devised, enabling measurements to be made using only a fenmilliliters of gas a t pressures as low aq 50 mm. By using a knon-n amount of gas sample in a closed system, it was also possible to make coulometric measurements by recirculating the sample through the electrolysis cell until i t was quantitatively o-iidized or reduced. The cell is illustrated in Figure 1. The standard-taper joint a t the top of the cell is fitted with a n ASCO stirring gland, which will accommodate either the conventional dropping mercury electrode capillary, or 6-mm. glass tubing containing a solid electrode. The bottom connection allows the use of a mercury pool electrode, which may be stirred magnetically or by a mechanical stirrer passed through the opening in the stirring gland. For ex-
12-MM. BALLJOINTS
d
120
I
I
1
ANALYTICAL CHEMISTRY
f
f
lZP5M.
.
BALL J O ~ N T ,
ALL
SLIGHTLY ENLARGED
i TusE
JOINT
SAMPLE BULB
TO bE
(APPROY
CLOSE SLIDINGfir
5
HL
)
FOR P I S T O N
'' 11
,CD
(APPROX
IZMM.ODIA)
\
TEFLON STIRRING
BAR
1 (TURNED DOWN
TO
'
T
-I-*') \
STOPCOCK
CYLlNDER8-9MM DlA)
I -i
'
J
1
. 6/A : M J ; ; N T
'-A5 ClRCJLAllNG P U 3 2
I.
P\
's io/3c
JO.NT
!%MM.
BAL; JOIN~ A M D L Eb u - 3
Figure 2. Gas-circulating pump and sample bulb
ploratory work, it is usually convenient to stir magnetically and use the top opening for the dropping mercury electrode, so that current-voltage curves can be recorded periodically during a coulometric oxidation or reduction. The construction of the circulating pump and the sample bulb is illustrated in Figure 2. The all-Teflon and glass pump has only one moving part and no mechanical valves, yet it provides positive circulation of gas through the liquid in the clectrolysis cell. The fit of the piston, its rate of travel in the pump cylinder, and the leakage of gas past the piston are such that a pressure difference of about 1 inch of mater is established during the pump stroke. -1s the piston rises, about 1 inch of liquid is drawn into the lower pumii connection, preventing entry of gas from belon while the cylinder is filling with gas leaking around the piston from above. On the downstroke, the positive pressure below the piston is enough to displace the liquid from the lower connection and force the gas
from the pump cylinder through the liquid in the cell. Since the operating pressure equals only about 1 inch of water, the liquid level in the electrolysis cell should not be more than half a n inch above the lower pump connection. The piston is raised and lowered by an external permanent magnet suspended from the rim of a wheel rotated a t 10 r.p.m. by a small motor., I n use, the apparatus is assembled as sho~vnin Figure 3, with the sample in the sample bulb and the desired electrodes and electrolyte solution in the cell. The system is deaerated by passing nitrogen into the system through the upper stopcock, through the pump cylinder and the solution, and out the lower stopcock. Then the sample is introduced by turning the loner stopcock. Sitrogen is supplied through the upper stopcock to bring the internal pressure of the system to 1 atm. (when the sample is introduced at reduced pressure) before the upper stopcock is turned to complete the circulation loop. The desired electrochemical 011erations can then be carried out in the closed system.
Gns CIRCULATION ELECTROLYSIS CELL i
Figure 3.
Gas-circulating system
