Anal. Chem. 1987, 59, 687-688
dotherm. An extremely intractable case is that involving compound l b (cf. Figure a), which requires a combination of He and reduced heating rate to bring about base line resolution. A 50% reduction in the heating rate or sample mass alone failed in this case. The idea that peak resolution in DSC may be enhanced with the use of a high thermal conductivity purge gas is not entirely new (cf. ref 4). However, this idea has not been verified previously by experiments and computer simulations. Furthermore, earlier claims (4)as to the negative influence of He on analytical sensitivity need not be universally true. It has been shown herein how the thermal characteristics of the sample itself play an important role in this regard.
ACKNOWLEDGMENT The authors thank the Du Pont Co.Jor instrumental sup-
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port and Kenneth L. Brown for gifts of the cobalt samples.
Registry No. He, 7440-59-7. LITERATURE CITED (1) Jang, 0.-W.; Rajeshwar, K. Anal. Chem. 1988, 58, 416. (2) Jang, G.-W.; Rajeshwar, K., manuscript in preparation. (3) Morgan, S.L.; Deming S. N. J . Chrometogr. 1975, 112, 267. (4) Baxter, R. A. In ThermalAna&s/s; Schwenker, R. F., Jr., Garn, P. D., Eds.; Academic: New York, 1969; Voi. 1; p 65.
RECEIVED for review August 11, 1986. Accepted October 6, 1986. This research was supported by the Texas Advanced Technology and Research Program and the Strategic Defense Initiative Office, Innovative Science and Technology Branch, through the Defense Nuclear Agency, Contract No. DNA 001-85-6-0181.
Automated Ion-Exchange Column System for Biological Sample Fractionation Y. T. Kim and Christiaan Glerum* Ontario Tree Improvement and Forest Biomass Institute. Ontario Ministry of Natural Resources, Maple, Ontario, Canada LOJ 1EO Ion-exchange resins are widely used in chemical laboratories for separation of many organic compounds. In our laboratory we have been extracting amino acids and sugars from tree tissues and separating the various fractions by passing them through cation- and anion-exchange columns prior to separating them on thin-layer chromatographic plates (1). Ionexchange columns are needed not only for separation of compounds but also for increasing the concentration of samples as well as for purifying the samples (2). When tree tissues are extracted for various compounds, the ion-exchange columns are a neccessity prior to chromatographic analyses (1, 3-5). When ion-exchange resin columns are used, the flow rate has to be carefully controlled and the solution level on top of the resin should not be allowed to go below the top of the resin because air bubbles in the resin will decrease the resin's efficiency, which would be a serious source of error. Furthermore, only a few columns (about four) could be run manually a t one time. To avoid the time-consuming work of watching the meniscus in the columns from not getting past the top of the resin, a device was developed that automatically stops the solution flow at the desired level in the column. With this system one can operate many columns a t any one time. We now operate 10 columns concurrently in our laboratory. The construction of this device is described below.
DESCRIPTION OF APPARATUS The device consists of three components: (1)power supply, (2) solenoid, and (3) detector control. The electronic circuit diagram with the materials used is shown in Figure 1, while the assembled circuit is shown in Figure 2. Because we operate 10 columns with this system, the power supply has to provide the voltages for 10 integrated circuits (IC) and 10 solenoids. The 23 V dc is regulated by the IC LM317 voltage regulator for the IC LM1830 and the 25 V dc for the solenoids is directly connected to the bridge rectifier. Two platinum wires are inserted as probes through the glass wall of each chromatography column, 19 cm above the Teflon stopcock and about 1cm above the ion-exchange resin. The column is 25.0 cm high and 1.05 cm i.d. with a 200-mL reservoir on the top. The resin bed is 15 cm high. Silicon rubber tubing is attached to the delivery tip and passed through a 24-V solenoid, which controh the flow by opening and closing the silicon 0003-2700/87/0359-0667$01.50/0
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Flgure 1. Electronic circuit diagram and materials used: 1, LM1830 (10); 2, 2N5195 (10): 3, 2N3904 (10): 4, 1N645 (10): 5, 100-V 4-A bridge rectifier (1): 6, power transformer, 115 V, 60 Hz in, 24 V dc, 3 A (1); 7, LM317 voltage regulator (1); 8, capacitor, 4000 pF 75 V dc (1); 9, 50 pF 50 V dc (1); 10, 0.05 pF 100 V (10); 11, 0.001 pF (10); 12, vector board (1); 13, neon indicator (1): 14, fuse holder (1): 15, toggle switch (2); 16, resistor 2.7 K (20): 17, resistor 7.5 K (10): 18, capacitor, 100 p 25 V dc (10); 19, wnnector (1); 20, case (1). The numbers in the diagram are matched with the numbers of the materials.
The numbers in parentheses are the number of parts needed for a
complete circuit. tubing. The control signal from the platinum probes is generated by the IC LM1830 and sent to the solenoid via a current-boosting transistor. This IC works as an oscillator and as a threshold detector, which generates about 7-kHz ac signal that goes through the probes and solution. It has an internal reference register (nominal 13 kR) of 10-kRthreshold resistance, 680-mV threshold 0 1987 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 59. NO. 4. FEBRUARY 15. 1987
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IC LM183O overcomes this residual current. Commercial solenoids need modification on their tips. The device is simple in design and inexpensive to set up. The cost of all the components together was less than $200. It allowed us to incresse our efficiency significantly by enabling us to handle a greater number of columns a t any one time. We increased the number of columns from four to ten, and in addition, we can expand the system to 24 columns or more if needed. The device has a simple purpose, which to our knowledge is not being used in any other laboratory for ionexchange columns or column chromatography. It can a h be used in gel filtration.
1
ACKNOWLEDGMENT The authors are greatly indebted to B. K. Lee, for designing and assembling dl of the electronic circuitry and for his many valuable suggestions.
Figure 2. Assembled ctcuI1.
LITERATURE CITED voltage, and 500-#A threshold current. Since the signal used is ac, the ac ripple cumponent should be minimized before the signal reaches the solenoid driver stage; therefore a filter capacitor was connected between pin 9 of IC LM1830 and common ground. DISCUSSION The IC L M l W prevents the deposits of electrolytes or any charged organic compounds on the platinum probes because of the ac current. When a strong electrolytic solution is used, traces of the solution on the walls act as a conductor, but the
(1) Glaun. C.: 8.htb22. J. J. Urn. J. Bo(. 1980 58. 40-54. (2) ZwebJ. 0.; Yarma. J. &n&c& of Unmetogaphy; CRC Rsrs: Cleveland. OH. 1972 Vd. 2. D 70. (3) zweb. 0.; shsnna. J. 01 ~ ( o g s p h y CRC ; ~ssa: CIevelaBnd. OH. 1972 Vd. 2. pp 195-254. (4) Blackbum. S. H a of Chromatcqaphy: Amho Adds and Amims: Zwsh?. G.. Slwma. J.. E*.: CRC Pres% Boca Raton. FL.
HanaDorr
1983: VoI. 1.
6 201.
(5) Dickson. R. E. phyrlol. mnt. 1979. 45, 400-400.
RECEIVED for review August 25,1986. Accepted October 27, 1986.
CORRECTION
Elemental Characterization of t h e National Bureau of S t a n d a r d s Milk Powder Standard Reference Material by Instrumental and Radiochemical Neutron Activation Analysis Robert R. Greenberg (Anal. Chem. 1986,58, 1986). An error was introduced into this paper in the final stages of the production cycle, after author review of the galley proof. On page 2511 the correct spelling of the name of the author is Robert R. Greenberg.
