might he present in complex gas mixtures, be titrated by bromine, and be emumusly reported as sulfur. Reduction to H2S rather than oxidation to SO2 has the added advantage of providing a four-fold increase in sensitivity because of the greater electron change required for the bromine oxidatiou of H2S. Although the need for individual calihration for each compound favors the use of a furnace between the chromtograph column and the detector, it complicates the analytical system and thus may not be suitable for process control analysis under mill conditions.
Air P o U u i h Conirol Aasw. 8, 338
UTEFATURE CITED
(1) Adam, D.
F., Koppe, R. K., Tuttle,
W. N., J. Air Pollution Control Assoc.
15, 31 (1965). (2) Altshuller, A. P.,
BeUar, T. A,, Clemons, C. A,, Vander Zanden, E., Intern. J. Air Water PoUuticn 8, 29 I1 Qfi4)~ \_"_.,_
(3) Coulson, D. M., Cavanagh, L. A,, U. S. Patent 3,032,493 (May 1, 1962). (4) Fredericks, E. M., Harlow, G. A,,
ANAL.CHEM.36, 263 (1964). (5) Jacobs, M. B., Braveman, M. M., Hochheiser, S., Ibid., 29,1349 (1957). (6) Klaas, P. J., Zbid., 33, 1851 (1961).
(7) Martin, R. L., Grant, J. A,, Ibid., 37, 644 (1965).
(8) McKee, H. C., Rolliwitz,
W. L., J.
(1959). (9) Nader, J. S., Dolphin, J. L., Ibid., 8 , 336 (1959).
(10) Ruus, L., Waste Water Laboratory,
Stockholm, private
communication,
1964. (11) Thomas, E. W., Toppi 47, 587 (1964). (12) Wright, R. H., Schoening, M. A,, Hayward, A. M., Zbid., 34,289 (1951).
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pGovement. Air ~Poll&ion Symposium, 150th Meeting, ACS, Atlantic City, September 1965.
Evaporation Manifold for Septum-Sealed Vials Gerald J. Litt' and Norman Adler,' Merck Chemical Manufacturing Division, Mcrck & Co., Inc., Rahway, N. J.
c
hy evaporation is quite often a requisite step in the analysis of trace components. Typically, micro amounts of the component must be recovered quantitatively from tens to hundreds of milliliters of solution. The evaporation of such large volumes is often done in stages, starting with a container of large surface area to hasten the evaporation. The residual contents are then transferred after each stage to a container of progressively smaller volume until the final micro container is reaxhed. It is readily apparent that a one-step evaporationi.e., directly into the final containerwould not only be more convenient but would avoid the risk of loss of sample associated with multiple transfer steps. The suitability of septum-sealed pharmaceutical vials for the convenient yet quantitative preparation and sampling of micro solutions for analysis by gas-liquid chromatography, infrared spectrometry, and other techniques has recently been described ( 1 ) . The viab would thus be of considerahle value as the final container for the evaporation process. It is the object here to describe an evaporation manifold designed expressly to permit controlled, one-step evaporation of solutions directly into this type of container. The apparatus is shown in Figure 1. The receiver, 8 3-ml. vial (Wheaton Glass Co., New York, N.Y.) designed to accept a septum closure and reshaped to a conical form, is plugged into the body of the evaporation manifold through a tightly fitting rubber grommet ('7/,,inch 0.d. X 0.5-inch i.d., No. HHS-2186, Federated PurONCENTRATION
' Prment address, New England Nuclear Gorp., Boston, Mass. 'Present address, Artbur D. Little, Inc., Cambridge, Mass. 1096
ANALYTICAL CHEMISTRY
chaser, Springfield, N.J.). The solution to be evaporated is fed from the separatory funnel to the vial via a 0.047inch i.d. tube made of Teflon which is fitted onto a ring seal extension of the inlet from the standard taper joint. This tube terminates about 1 em. from the bottom of the vial. The rate of
Figure 1.
Evaporation manifold
flow, regulated by the Tenon SWPCOCK, is preferably adjusted to prevent the liquid level from reaching this tube, yet to maintain a definite liquid phase during the evaporation. In practice each unit requires an occasional inspection after the initial adjustments to ensure optimum conditions. The low wettability of Teflon minimizes the spread of solution up the out.side of this tube. A stream of air or an inert gas, iutroduced via the other Teflon tube, sweeps the vapors from the vial. The opening of this tube is directed against the side of the vial, rather than straight down, to avoid excessive sweeping action. A third port in the manifold serves as the exit line and permits simultaneous application of vacuum. When air is used as the sweeping gns, the flow rate may be conveniently and reproducibly regulated by using hypodermic needles of various sizes as vents. In this case, the needle is first connected to a drying and filtering tube to prevent entrance of water or dirt. I n general, the optimum combination of the degree of vacuum and the flow rate of the sweeping gas is dependent upon the solvent being removed and the vapor pressure and physical state of the residue. Wide variations in operating parameters may be tolerated, however, and only a few trials are necessary to select settings that provide a reasonably rapid evaporation rate while minimizing the risk of blowing the dried sample out of the vial. The system may also be heated to accelerate evaporation. For solvents boiling helow 75' C., the bottom half of the receiver vial is immersed in a water bath of appropriate temperature. If necessary, the upper chamber of the manifold may be heated simultaneously with a hot air blower or an infrared lamp. For solvents with
boiling points around 100" C., the entire evaporation apparatus is suspended in a tall form beaker over boiling water. Thp reflux action of the water warms the entire unit, and minimizes condensation of solvent in the upper chamber of the manifold. Other refluxing solvents may be used to give different temperature ranges, providing they are compatible with the grommet material. For volatile or thermolabile solutes, the apparatus van be used in a freeze drying mode, but a t the cost of longei evaporation times. After the evaporation is completed and the system brought back to atmospheric pressuie, the vial is removed and sealed with a ieptum. The vial may be weighed before and after the evaporation, to prrmit determining the net weight of the reciduo. The apparatus was tested by evaporating 0.3- to 3-mg. quantities of m-
phenetidine (either as the free base or as the hydrochloride salt) dissolved in 25 ml. of solvent. Methylene chloride was used as the solvent for the base and was evaporated in about 30 minutes. Aqueous 0.5N HC1 was used for the salt, and was evaporated in about 2 to 2.5 hours. Recoveries were determined by measurement of ultraviolet absorption. Low recoveries (less than 90%) were obtained when both types of samples were taken to complete dryness. The losses may be due to volatility of the base (b.p. 254" C.), but are attributed principally to entrainment of micro particles in the gas and vapor stream for the hydrochloride salt. Evaporation to incipient dryness-i.e., to the point where about 250 PI. of solution remains-consistently gave recoveries within the 95-1OOojO range for the salt. Recoveries for the free base under
these conditions, although significantly improved, were still somewhat low, Although higher recoveries could be obtained by using milder conditions for the evaporation (i.e., slower air flow), it was more expedient to evaporate the base onto a small quantity (40-60 mg.) of powdered sodium bisulfate added to the receiver. By thus forming a nonvolatile salt in a difficultly entrainable form, quantitative recoveries (well within +5% of target) could be obtained reproducibly and rapidly over the 0.3- to 3-my. range. ACKNOWLEDGMENT
The assistance of Peter Dockery in the glassblowing is gratefully acknowledged. LITERATURE CITED
(1) Adler, N., ANAL. CHEM. 36, 2291 (1964).
Automatic Vapor Sampling for Gas Chromatographic Analysis G. Szhkely, G. R&z, and G. Traply, Department of Physical Chemistry, Technical University of Budapest, Budapest, Hungary
sampling method for A vapor mixtures condensing a t high temperatures has been developed; it COYTISUOUB
eliminates mechanically moving parts of construction. The arrangement is especially suitable for drawing samples from reactors or other flow systems. In industrial and laboratory practice it frequently is necessary to analyze vapor mixtures condensing at relatively high temperatures by a continuous sampling technique and to effect precise analyses using small samples. The main problem is to withdraw the sample, because the sample must be maintained above the condensing temperature. Sampling equipment for this purpose dcwibed in the literature is made of Teflon or metal, and construction involves moving parts. Handling this equipment is, therefore, not easy; moreover, methods do not lend themsel\es t o automation and can only be used to a temperature limit.
a pressure drop should be maintained at the end of the system to keep Hz flowing through the column. At the same time, air necessary for the operation of the flame ionization detector is drawn through. A sample for analysis is obtained by closing the mercury valve for a few seconds by the timer. This causes the vapor to be sampled to pass capillary 10 toward the chromatographic column via the sampling pipe, 11. After a short time the mercury valve is opened again to let in the carrier gas which carries the sample through the column. Because in one
44.
cycle the timer switches only once, resetting is performed by the switching valve, 3, filled with an electrolytee.g., [NH4]&04 solution-and having electrodes in its vessels. When the liquid level is the same in both sides, only one contact closes. After closing the mercury valve the increasing pressure in the system before the valve drives the liquid levels apart in the manometer, thereby activating the reswitching circuit. To control the duration of the closing phase of the mercury trap, the height of the contact can be adjusted in the side of the manometer
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-
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1 5.
air 7 vu6uum
6 9.
EXPERIMENTAL
Flow Design. We have solved the problem by the arrangement shown in Figure 1. I n the sampling part, 11, the pressure is slightly above atmospheric. There is excess pressure ahead of the chromatographic column, 6, when the mercury trap is open. This causes a small portion of the carrier gas to enter connection 11 via the capillary choke. As the chromatographic column has much higher flow resistance than the capillary tube,
6.
2 4 e Figure 1. 7. 2. 3. 4.
5. 6.
Apparatus for automatic vapor sampling
Container for carrier gas Differential manometer Switching manometer Timer Mercury valve Chromatographic column
Hl
7. 8.
9. 70. 7 7.
Flame ionization dector Differential manometer [for air stream) Hydrostatic pressure control Capillary as pneumatic choke Sampling connection to reactor
VOL. 38, NO. 8, JULY 1966
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