Anal. Chem. 1907, 59, 799-800
duction systems. Changes in both background and excitation conditions should be smaller when the ICP is used to detect eluents from supercritical fluid chromatography. The fluid flow rates will normally be lower for SFC and the solvent will be well separated from the analyte species. A number of improvements are now being made. These include automated peak area detection, simultaneous background subtraction using photodiode array and direct reading spectrometers, and automation of the sample injection. We are in the process of characterizing the spatial profiles (both lateral and vertical) of the emission signals from the injected samples. We are also determining optimum experimental conditions including flow rates and ICP power. Other supercritical fluids are also being tested including NzO, propane, and NH,, which are commonly used for supercritical fluid chromatography. Because of the low flow rates required, xenon is also a practical supercritical fluid. The effect of Xe on the plasma excitation conditions and supercritical fluid induced background should be much smaller than those resulting from COz. Xe has been shown to be a useful mobile phase for supercritical fluid chromatography (9).
ACKNOWLEDGMENT Donation of the ICP power supply by Perkin-Elmer is appreciated. Loan of the SIT vidicon detector and controller by Princeton Applied Research Corp. is gratefully recognized. Registry No. COz,124-38-9;Xe, 7440-63-3; NzO, 10024-97-2; NH3, 7664-41-7;propane, 74-98-6. LITERATURE CITED (1) Browner, R. F.; Boorn, A. W. Anal. Chem. 1984, 56, 786A. (2) Browner, R. F.; Boorn, A. W. Anal. Chem. 1984, 56, 875A.
799
(3) White, C. M.; Houck, R. K. HRC CC, J . High Resolut. Chromatogr.
Chromatogr. Commun. 1986, 9 4. (4) Olesik, J. W.; Bradley, K. R. Spectrochim. Acta, Part 8 , in press. (5) Boumans, P. W. J. M. Line Coincidence Tables for Inductively Coupled Plasma Emission Spectrometry. 2nd ed.; Pergamon: Oxford, 1980. (6) Richter, 8. E. HRC CC, J . High Resoiut. Chromatogr. Chromatogr. Commun. 1985, 8 , 297. (7) Blades, M. W.; Caughlin, B. L. Spectrochlm. Acta, Part8 1985, 406, 579. (8) Boorn, A. W.;%rowner, R. F. Anal. Chem. 1982, 5 4 , 1402. (9) French, S. B.; Novotny, M. Anal. Chem. 1986, 58, 164. ~
John W. Olesik* Department of Chemistry Venable and Kenan Laboratories 045A University of North Carolina Chapel Hill, North Carolina 27514
Susan V. Olesik Department of Chemistry The Ohio State University 140 West 18th Street Columbus, Ohio 43210 RECEIVED for review July 21, 1986. Accepted November 4, 1986. Funding was provided in part by BRSGS07 RR07072 awarded by the Biomedical Research Support Grant Program of the Division of Research Resources from the National Institutes of Health, a Du Pont Young Faculty Grant, the University of North Carolina Department of Chemistry, and the UNC University Research Council. Portions of this work were presented at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Atlantic City, NJ, March 1986, and the Federation of Analytical Chemistry and Spectroscopy Societies Meeting, St. Louis, MO, Sept 1986.
A I D S FOR ANALYTICAL CHEMISTS Rotary-Type Injector for Capillary Zone Electrophoresis Takao Tsuda* Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466, Japan
Toshihide Mizuno and Junichi Akiyama Shimadzu, Nishinokyo-kuwabara-cho,Nakagyo-ku, Kyoto 604, Japan In capillary zone electrophoresis, deficiencies are present in injection methods that use either electroosmotic flow (1, 2 ) or suction (1-4). In an electroosmotic method, introduction is carried out by applying an electrical field between a column inlet and a sample reservoir. Thus, sample components are introduced by both electroosmotic flow, u(osm), and mobility, u(mob). The latter is generally dependent on the number of charges on a solute and its molecular size. Thus, the total amount of each solute injected depends on the nature of the solute. When (u(mob)Iof a solute is larger than lu(osm)l and each sign is different, the solute cannot be introduced into the column. sampleintroduction with suction, the end of the column dipped in the sample solution should be lifted up for every injection (1-3). Injecting an accurate amount, repeatedly, is difficult due to constant Positioning ofthe level ofthe cohmn. Therefore, it is better to use an internal standard for cakulating the total amount injected (3, 4 ) . If we use a rotary type injector, which is commercially
available for liquid chromatography, bubbles are generated inside the injector, causing the electrical current to stop. This may be due to the electrochemical reaction at the metal surface inside the injector. A rotary type injector is more favorable for the injection of an absolute amount of solute than injection methods that use electroosmotic flow and suction. We have devised a new rotary injector which can be used under high electrical field conditions.
EXPERIMENTAL SECTION A schematic diagram of the injector is shown in Figure 1. A (load position) and B (injection position) in Figure 1 show cross-sectional views of the rotary injector. C shows a rotary injector viewed from the left side of A. The injector consists of one robr, two stators, a d one central pin made from fine ceramic (Kyocera Co., Kyoto, Japan). The plates and Screws were made by using a tetrafluoroethylene resin. The rotor and stators have two flow passages. After one passage is filled with a sample solution (A in Figure l),the rotor is rotated 90' by hand (B in
0003-2700/87/0359-0799$01.50/0 0 1987 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 59, NO. 5, MARCH 1, 1987
A
B
3 2 1 2 3
C
H
2min Flgure 3. Reproducibility of injection.
/
Table I. Reproducibility of Injection n
aniline
solute Figure 1. Schematic diagram of rotary injector made of fine ceramics: 1, rotor; 2, stator: 3, plate for setting rotor and stators; 4, central pin; 5, supplemental tubing between injector and reservoir; 6, tubing for sample introduction; 7, capillary column; 8, knob made by stainless steel covered with a silicone tube. Positions a and b are load and injection, respectively. injector
L
-
detector
--
-a & ____L A
dc power supply
Figure 2. Schematic diagram of instrument for capillary zone electrophoresis: 1, capillary column: 2 and 3, supplemental tubing: 4, reservoir: 5, terminal.
Figure 1). The passage containing a sample solution comes in line with a column head. The flow passage in the rotor had a 0.3 mm i.d. and a length of 5 mm (inner volume, 0.35 wL). A schematic diagram of the instrument for capillary zone electrophoresis is shown in Figure 2. Injections were performed under high voltages of up to 15 kV. W and fluorescence detectors (UV-2and FR-530, respectively, Shimadzu, Kyoto, Japan) were used. Other instruments were the same as those previous reported (2, 3).
Reproducibility of injection is shown in Figure 3. The experimental conditions of Figure 3 were as follows: sample, 0.5% aniline solution; injection amount, 0.35 fiL; column, FEP tubing (0.2 X 195 mm); applied voltage, 12.9 kV (32-42 PA);sensitivity of UV detector, 0.64 OD at full scale; column medium, 0.001 M phosphate buffer (pH 7 ) with 0.5% ethylene glycol.
RESULTS AND DISCUSSION The presence of bubbles, due to a metal surface, can be eliminated by using the present injector whose component parts are made from fine ceramic and tetrafluoroethylene resins. The reproducibilities of the present injector are shown in Table I and Figure 3. In Figure 3, four replicate injections are shown. Under these experimental conditions, aniline was neutral and was carried only by electroosmotic flow from injection to detector via the column. The peaks in Figure 3
no. of injection mean of peak area
std dev coeff of variation, 70
5 353 7.8 2.2
dansylated spermidine 4 526 8.0
1.5
show no tailing. In the estimation of the coefficient of variation for replicate injections, both processes of the injection and of the development in the column were included. The coefficients of variation, shown in Table I, averaged about 1.9%. Figure 3 and Table I show that the present method demonstrates good reproducibility. The present injector has the following advantages: (1)The injection amount is accurate. Therefore, the determination of the absolute amount of solute is possible. (2) It is easy to exchange sample solution by refilling a passage (6 in Figure 1)with a microsyringe. (3) Successive injections are possible by setting a microsyringe in line with the above passage. (4) Injection is possible while a high electrical field is applied. However, there are also the following disadvantages: (1) Although the injection amount (0.35 pL) is very small, a few microliters of sample solution is necessary to fill up the passage (6 in Figure 1). (2) For safety reasons, it is necessary for the injector to be operated automatically. (3) Since the sample solution is kept under a high electrical field, there is a possibility that unstable components may decompose if kept in the flow passage for long periods of time (6 in Figure 1). Although the present rotary injector has some disadvantages, it is more reliable for quantitative determination and is easy to operate when compared with either electroosmosis or suction injection methods.
LITERATURE CITED (1) Jorgenson, J. W.; Lukas, K. D. Anal. Chern. 1981, 53, 1298-1302. (2) Tsuda, T.; Nomura, K.; Nakagawa, G. J . Chrornatogr. 1983, 264, 385-392. (3) Tsuda, T.; Nakagawa, G.; Sato, M.; Yagi, K. J . Appl. Biochern. 1983. 5 , 330-336. (4) Fujiwara, S.;Honda.
S.Anal. Chern. 1986. 5 8 , 1811-1814.
RECEIVED for review May 16,1986. Accepted November 24, 1986. This work was supported by Grant-in-Aid for Cancer Research from the Ministry of Education, Science and Culture (No. 61010038).
