Sealed, Inert, Gas Circulating Pump W. A. McAllister, W. V. Southerland, and G . B. Rouse, Jr. Department of Chemistry, East Carolina University, Greenville, M.C. 27834 IN A STUDY AT THIS LABORATORY involving the catalysis of the oxidation-reduction reaction between carbon monoxide and nitric oxide, an inert, leak-proof, gas circulating pump was needed. The gases are contained in a closed glass loop with the catalyst in a U-tube portion of the loop. The gases must be circulated slowly and continuously for days, and the rate of circulation must be reproducible, relative to gas pressure and impeller speed. A centrifugal design was adopted because of its inherent simplicity. The circular motions for such a design can be transmitted without mechanical connection using a magnetic stirrer, allowing the pump to be completely sealed. The other primary requirement is that the pump be unreactive and have no catalytic effect with respect to the gases studied. In this design, shown in Figure 1, the gases only contact glass, Teflon (DuPont), and Apiezon Wax (James G. Biddle Company, Plymouth Meeting, Pa.). The wax is used for a seal because it is inert and easily removable for cleaning the pump. Epoxy glue could be used for a permanent seal. For ease of construction, the pump was designed around the 7I8-inch “Roto-Stirrer” obtained from the Lab Apparatus Company (Catalog No. 2495). This seemed to be the least expensive of the several possibilities considered. The only critical construction details are to arrange the stirrer close to the top glass disk, and the tangential angle of the outlet. The perforated glass disk is not critical and can be replaced by a disk with a central 12-mm hole. This disk is fused in place but could be epoxied. The Teflon disk is simply a bearing surface. The result of this simple approach is a maximum gas circulation rate of about 10 ml per minute. Since this is not a positive displacement pump ( I , 2), it is difficult t o (1) C. J. Sterner. Rea. Sci. Iustrum., 31, 1159 (1960). (2) M. J. Hiza and A. G. Duncan, ibid.,40,513 (1969).
Figure 1. Sealed, inert, gas circulating pump
measure circulation rates L‘S. revolutions per minute. The approximate rate was determined by observing the movement of NOn in the system. The pump operates in a range of pressures from a vacuum to one atmosphere; of course, circulation rates also depend on pressure. ACKNOWLEDGMENT
Thanks are due Owen Kingsbury for his patience and glassblowing skill. RECEIVED for review March 6, 1972. Accepted June 21, 1972. We thank the Environmental Protection Agency and the North Carolina Board of Science and Technology for financial support.
Improved Ebullator for Solution Concentrator Morton Beroza, Malcolm C. Bowman, and Barbara A. Bier1 US.Department of Agriculture, Agricultural Research Sercice, Beltsaille, Md. 20705 and Tfton, Ga. 31 794 A DEVICE,particularly useful in pesticide residue for simultaneously concentrating many solutions in test tubes to small volumes ( I ) , is presently available in a much improved form from Kontes Glass Co. Concentration is rapid until the solution reaches a low level, at which point evaporation slows markedly because the last 0.5 to 1.0 ml is below the heating zone of the evaporator block. Thus, losses of pesticide resulting from inadvertent evaporation to dryness ( 2 ) are avoided, and very little attention of the analyst is required in overseeing this normally time-consuming operation. ~-
~
(1) M. Beroza and M. C. Bowman, ANAL.CHEM.. 39. 1200 (1967). (2) J. A. Burke. P. A. Mills, and D. C . Bostwick, J. Ass. Ofic: Ana/. Chem.. 49,999 (1966).
With this device, boiling of a solution is initiated by a n ebullator, which is a small glass rod bent so the open end of a n attached short length of tubing faces downward ( I ) ; the trapped pocket of air initiates and maintains ebullition. See K of Figure 1. The use of small-bore stainless steel needlestock tubing to direct a stream of micro-bubbles of nitrogen through the solution for ebullition has significant advantages over the glass ebullator used originally. As noted before ( I ) , benzene tends to bump and some shaking of the test (or other distilling) tube is necessary to start boiling with the original ebullator; with the stream of N B ,benzene is smoothly concentrated without bumping. If heating should be interrupted, as is sometimes necessary, the solution being concentrated fills the little air
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Table 1. Recoveries of 100-Nanogram Amounts of Pesticides from 10 Milliliters of Solution Subjected to Concentration for 2 Hours with a Stream of Nitrogen Micro-Bubbles and with a Glass Ebullator (gl. ebull.) ( I )
Recoverv ( % ) from solution of Hexane ___ with Benzene with NZstream gl. ebull. NZstream gl. ebull. 98.2 92.3a 96.6 90.8a 98.6 94. 2b 95.7 92.66 94.2 93.w 98.3
Pesticide Lindane Heptachlor Aldrin Heptachlor epoxide Dieldrin
100.0 100.6 100.7 101.2
p,p'-TDE p,p'-DDT
-
97.5 98. 9c 98.3c
96.2 96.2 94.9 97.6
97.0
-
97.6~
25-ng amount.
* 50-ng amount.
300-ng amount.
8. Figure 1. Gas-stream ebullator for solution concentrator A , Distilling tube. B , 28-cm
length of needlestock tubing. C, Heater block. D,Distillation column (wrapped with aluminum foil). E, Alligator clip holds needlestock tubing B at proper height. F, Teflon tubing. G, Needlestock tubing. H,Rubber stopper. I , Copper bushing. J , Copper tubing leading to air or gas supply. K is the original glass ebullator
pocket of the original ebullator and bumping ensues when heating of the solution is resumed. This difficulty does not occur with the Np-stream ebullator. Also, rinsing off adhering solution after concentration is more convenient and efficient from the stainless steel tubing than from the glass ebullator. EXPERIMENTAL Apparatus. The gas-stream ebullator is illustrated in part in Figure 1. The Kontes Tube Heater C, No. K720000, from Kontes Glass Co., Vineland, N.J., was used with their 12-ml distilling tubes A (No. K-288250) and distillation columns D (No. K-569251) wrapped with aluminum foil ( I ) . The Kontes Tube Heater has a n advantage over the 2412
original evaporator ( I ) in having a fully proportioned heater control allowing quick heat-up and 1 0 . 5 "C temperature maintenance of the heating block. A temperature suitable for evaporating a given solvent can be noted on the block temperature control dial and reset a t this point for evaporating that solvent at any future time. Nitrogen is led t o the 9 heating tubes from a cylinder or other source of compressed gas in the following order: a pressure gauge set a t 5 psig, a needle valve, a short length of copper tubing Jsoldered to a 1/4-in.to l/p-in.0.d. copper bushing I (Harry Alter Co., Chicago, Ill., Bushing No. 11449) having a rubber stopper H i n its distal (l/*-in.) end penetrated by nine 2.0-cm lengths of 24-gauge (0.022-in. 0.d.) needlestock tubing G (Vita Needle Co., Needham, Mass.), each of which is connected via a 60-cm length of 24-gauge Teflon (Du Pont) tubing F to a 28-cm length of 24-gauge stainless steel tubing B (Vita Needle) that is set in distilling tube A . Before use, the tips from which the N? emerges are immersed in a beaker of hexane, and the needle valve is adjusted t o give as slow a flow rate as possible (about 10-20 bubbles per second) while maintaining flow from every tip. During concentration of solutions, each gas exit is held about 1.7 cm from the bottom of its distilling tube (or a t any other desired height) by clipping the tubing with a n alligator clamp E a t the top of the distilling column. Gas exits not being used may be closed by pushing them into a cork or rubber stopper. Procedure. With the apparatus in a hood, the heating block is operated at the desired temperature (110 "C in this study). Tips of the tubing were set below the heating zone at a level coinciding approximately with the 0.5-ml graduation of the distilling tube. For comparative purposes, the evaporation rate was also determined with the original ebullator, the open ends of which were at the 1.0-ml level. Pesticide solutions (100 ng of each of 7 pesticides in 10 ml of 1 drop of mineral oil keeper) were benzene or hexane analyzed after concentration and dilution to 1 ml by electroncapture gas chromatography essentially as previously described ( I ) .
+
RESULTS AND DISCUSSION
Table I gives the recoveries of the pesticides in hexane and benzene solutions deliberately left in the apparatus for 2 horns with the nitrogen stream used to induce and maintain ebullition. The hexane solutions required less than 45 minutes and about 1 hour for concentration with the nitrogen-stream and the original ebullator, respectively. The benzene solution required about an hour for concentration with the nitrogen stream. The Tube Heater concentrates the solutions as
ANALYTICAL CHEMISTRY, VOL. 44, NO. 14, DECEMBER 1972
rapidly or more rapidly than the original apparatus and recoveries after concentration with the nitrogen stream are as good as those reported previously with the glass ebullator (I). Thus, the gas-stream ebullator does not cause appreciable loss of the pesticides. The gas-stream ebullator may be particularly helpful when an inert or reducing atmosphere is needed during evaporation, since the appropriate gas can be used for ebullition. Unlike the original glass ebullator, the new ebullators are not easily broken, but they do have the disadvantage of requiring a source of gas supply. In a modification of the gas-stream ebullator that seemed to provide an added convenience, a stainless steel rod was silver-
soldered alongside the tip with its end extending about 1.7 cm beyond the gas exit. With this arrangement, the rod was allowed to rest on the bottom of the distilling tube, holding the gas exit 1.7 cm from the tube bottom. The need for adjusting each gas exit level by clipping the tubing to the column was thus eliminated.
RECEIVED for review June 30, 1972. Accepted July 31, 1972. Mention of a proprietary product is for identification only and does not constitute an endorsement of this product by the U.S. Department of Agriculture.
Advantages of Dual Electrode Mounts in Spark Source Mass Spectrometry Using Electrical Detection C. W. Magee, D. L. Donohue, and W. W. Harrison Department of Chemistry, University of Virginia, Charlottesville, Va. 22903
THECONVENTIONAL ANALYSIS technique in spark source mass spectrometry (SSMS) has involved photographic readout and the use of a single internal standard against which concentrations of the other elements in the sample are calculated. Relative sensitivity factors may be used to improve accuracy, but the general quantitative capabilities (120-30x) of the overall SSMS method did not warrent the use of multiple external standards, considering the large numbers of elements often determined. External standards were shown to be useful when considering a smaller number of elements (I, 2) particularly with careful parameter control (3). The recently developed electrical detection readout ( 4 , 5 ) has greatly increased the precision and accuracy of SSMS to a point where external standards are now necessary to fully utilize the peak switching integration mode, where a precision of better than 5 can be reached. However, slight changes in sparking parameters or source conditions may create significant effects on the integration readout value. Therefore, when in the usual manner one takes a series of integrations on elements in the standard electrodes, followed by breaking vacuum and loading the analytical samples for similar integrations, it is with the assumption that all conditions are similar over what may be a quite protracted period of time. It would obviously be more ideal to be able to switch between standard and analyte pairs more rapidly and, beyond that, to be able to come back to check the relative response of the two several times, if desired, over the period of the analysis. This investigation concerns the use of dual electrode mounts to study the advantages of using standard and analyte electrode pairs in the source at the same time. Data are presented for several different types of samples. (1) J. Kai and M. Miki, Mitsubishi Denki Lab. Rep., 5, 175 (1964); as described in “Mass Spectrometric Analysis of Solids,” A. J. Ahearn, Ed., Elsevier, London, 1966, p 105. (2) J. Franzen and K. D. Schuy, Z . Anal. Chem., 225,295 (1967). (3) W. W. Harrison and G. G. Clemena, ANAL.CHEW,44, 940 (1972). (4) C. A. Evans, R. J. Guidoboni, and F. D. Leipziger. Appl. Sprctrosc., 24, 85 (1970). (5) R . A. Bingham and R. M. Elliott, ANAL.CHEM., 43,43 (1971).
EXPERIMENTAL
Apparatus. The basic mass spectrometer and experimental parameters have been previously described (6). The standard AEI electrical detection system ( 5 ) has been added and used in the peak switch integration mode for all data in this study. Appropriate magnet current, acceleration voltage, electron multiplier voltage, and sensitivity settings were determined for each isotope measured. Modifications or additions to the standard system include : A spark gap monitor pickup coil mounted externally in a source port feeds an R F voltage to a Tektronix Model R564-B oscilloscope for display. This is used in conjunction with the AEI Autospark manual control to maintain a constant spark gap. A modification of a Kennicott telescope mount (7) is used with a 30 x optical system, cross-hairs, and calibrated reticle to carefully align the electrodes on the ion beam axis and to view the discharge during sparking. Rack and pinion focusing of the shallow depth of field optical system allows measurement of spark-to-No. 1-slit distance on a calibrated scale. Glass ports are used both above and below the spark discharge with a light source in each to allow lineup of the standard and analyte electrodes. The standard spark shield has been modified to provide an additional small light entrance from the top (for the overhead light source) and a 1-inch square front viewing window. The latter allows full view of both electrode pairs and is covered with a replaceable glass plate held in place by tabs cut into the spark shield. A continuously variable (0-0.012-inch) V-shaped collector slit is substituted for the standard two-position slit. Digital integration readout is accomplished with a Heath Model EU-805 Universal Digital Instrument which allows voltage to frequency conversion and subsequent counting in the Events Counting mode. Electrode Materials. Copper samples are from JohnsonMatthey, steels and orchard leaves from NBS. USP grade graphite (Ultra-Carbon Corporation) was used to form electrodes with the orchard leaves ash residue. (6) J. P. Yuracheck, G. G. Clemena. and W. W. Harrison, rbid., 41, 1666 (1969). , (7) P. R. Kennicott, General Electric Corporation, Schenectady, N.Y., personal communication, 1972.
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