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Anal. Chem. 1982, 54, 1909-1910
Figure 1.
Circuit dlagram of temperature monitor. A f15 V power supply, not shown, is required. Underlined resistor values are f5%; ail others
are *I%. on the drift tube. Because ion mobilities on which the instrument's tunable selective capabilities are based are temperature dependent, accurate monitoring of detector temperature is imperative. An inexpensive dual channel temperature monitoring circuit has been designed to measure the temperature of the ion mobility spectrometer and a heated transfer line connecting the instrument to a gas chromatograph. The circuit employs platinum resistance temperature elements (0.062 in. (0.16 cm) diameter X 1in. (2.5 cm) Ilong) and is capable of resolving 0.02 OC. Due to the small size of the elements and accuracy of the electronics, a wide variety of applicationsi is possible.
EXPERIMENTAL SECTION Two matched Model 78-0012-0120 platinum resistance temperature elements (Rosemount, Inc., Minneapolis, MN) are used as temperature sensors. A four-pole double throw toggle switch selects which sensor is in use. The sensors are supplied by a constant current source. Changes in temperature which cause linear variations in resistance result in linear variations in voltage across the sensor. This voltage is scaled and offset so that the temperature can be directly read from the display of a low cost digital panel meter (PCIM 176 f 200 mV DPM Module, Printed Circuits International, Inc., Sunnyvale, CA, or equivalent). A circuit diagram is provided in Figure 1. CIRCUIT DISCUSSION The monitor's simplicity is due to the temperature characteristics of the platinum resistance elements. Changes in resistance are directly pro,portional to temperature over a wide range (-50 to +250 "C). An integrated circuit (IC-1) and its
associated components maintain a stable 1 mA current through the selected sensor. The AD581 10-V reference and the voltage divider constructed from R1 and R2 provide a precise 1.000 V reference for IC-1. IC-2, IC-3, and their components scale and offset the voltage across the sensor for use by the DPM, such that the temperature can be directly read on the display. IC-2, a medium grade instrumentation amplifier configured for a gain of -20, has a high common mode rejection ratio which is used to cancel out any 6 0 - H ~ ac noise induced on the long sensor wires. Trim pots R18 and R12 are adjusted to set 0 and 100 "C, respectively. The final result is sent to the DPM with a full scale of 200 mV. It should be noted that the sensor detection wires are separate from the current supply leads. This avoids errors due to the variations in voltages on the supply leads which change resistance with temperature. When the monitor is used below 0 "C, the current source should be adjusted below 1mA to lower current heating in the sensor. Multiple sensors can be used as long as they have matched temperature-resistance characteristics. Any good, low-cost FET input OP-AMP can be substituted for the LH0042C's (such as LF411). The circuit can resolve 0.02 OC although it is currently limited to 0.1 "C by the DPM. Construction cost, approximately $95 for parts, could be lowered if less precise performance is required.
LITERATURE CITED (1) Baim, M. A,; Hill, H. H., Jr. Anal. Chern. 1982, 5 4 , 38-43
RECEIVED for review March 15,1982. Accepted April 16,1982.
Modified Soxhlet IExtractor for Room-Temperature Extraction Henryk Matuslewicz Department of Analytical Chemistry, Institute of General Chemistry, Technical University of Poznafi, 60-965 Poznaii, Poland
Most continuous extraction procedures for solids utilize the Soxhlet extractor, an efficient and widely used laboratory tool. For characterization of einvironmental particles such as coal fly ash, spent oil shale, atmospheric and urban particulates, 0003-2700/82/0354-1909$01.25/0
etc. by leaching procedure it is important to obtain quantitative information about the nature and amounts of potentially toxic elements leached from these materials. As a consequence, it is intended to establish a laboratory-based system 0 1982 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 54,
NO. 11, SEPTEMBER t982
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Figure 1. Detall of the modified Soxhlet extractor: (1) Soxhlet extractor; (2) side arm; (3) glass support for thimble; (4) thimble; (5) coil condenser; (6) ball joint; (7) clip: (8)double surface condenser having a coil; (9) Inlet tube; (10) three-necked flask; (11) long glass tube, with a glass fiber heating band; (12) Thermowell.
for preparation of leachate material likely to be representative of that produced under different, natural environmental conditions. One alternative process is standard Soxhlet extraction with water using reduced internal pressure of the system to lower and/or control the leaching temperature. An intrinsically different leachate is prepared by this method since the solid is always being leached with fresh distilled water. This process is useful for establishing the extent and time dependence of solubility of individual species under conditions where solid-solution equilibria have no influence. A disadvantage of this technique is that it cannot easily be operated
at temperatures much below 50 "C, for example, if one would want certain extractions to be conducted a t room temperatures. T o meet that requirement I modified a classical Soxhlet extractor which may be used for extraction of solids at room temperature. This apparatus was assembled from standard items of Quickfit glassware (1) and was used for characterization of pollutants from coal combustion and from coal and oil shale conversion processes by leaching study (2). Figure 1 shows a schematic diagram of extractor unit together with conventional boiling flask, Soxhlet extractor, and reflux condensers. The modifications are as follows. First, an additional condenser is mounted between the boiling flask and Soxhlet extractor. The condenser prevents hot solvent vapors from ascending around the thimble chamber in the standard extractor, so the extraction takes place at room temperature. Second, the insulated and heated long glass tube, mounted between the flask and an outlet of the upper condenser, allows the solvent vapors to pass directly to the condenser and drop as a cool liquid onto the sample. Because the dimensions of the heated bypass tube are quite critical, especially the length, a flexible Teflon connector can be included to eliminate tensions between components of glass assemblies and would greatly increase glass blowing tolerances. Third, the main part of the apparatus has a small glass tube built in the Soxhlet extractor body. This side arm serves for taking aliquots of emerging leachate for subsequent analysis. On the other hand, in this tube one can install an appropriate detector for continuous monitoring of the leachate pH, conductance, temperature, etc. The Soxhlet extractor has a small support for the extraction thimble which allows taking the leachate and measuring the above mentioned parameters. In addition, since the apparatus is quite long, it should be supported by a ball joint for stress-free connections. The volume of the solvent flask is easily varied, usually depending on whether the extracted material or the extract is of interest. The solvent is heated by a Thermowell (Pilz-Heraeus, West Germany), and the glass tube is insulated and heated by a glass fiber heating band (Pilz-Heraeus). The apparatus is easily taken apart for cleaning. The extraction under nitrogen, if necessary, poses no difficulties. The application of the described extractor is not for routine experiments but the unsual type of extraction, which calls for room temperature.
ACKNOWLEDGMENT The author thanks David F. S. Natusch, Colorado State University, Fort Collins, CO, for suggesting this study and for his continued encouragement and interest. LITERATURE CITED (1) Catalog, Jobling Laboratory Division, England, 1972. (2) Natusch, D.F. S.; Bauer, C. F.; Matuslewlcz, H.; Evans, C. A.; Baker, J.; Loh, A,; Linton, R. W.; Hopke, P. K. International Conference on Heavy Metals in the Envlronment, Toronto, 1975, pp 553-576.
RECEIVED for review February 16,1982. Accepted May 6,1982.
