Anal. Chem. 1986, 58, 2348-2350
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0.5
I
6
that can detect air bubbles, as previously described ( 4 ) . Ammonia determinations were made with both manifolds. With the LED/LDR colorimeter a calibration curve linear through 0.7 Kg-mL-’ with a correlation coefficient of 0.9996 was obtained. A detection limit of 5 ng.mL-’ was estimated from the blank standard deviation measurements a t 99% confidence. Reproducibility is better than 1%and a negligible carry-over exists between samples, as shown in Figure 2. Another aspect of the system proposed in this work is that it can effectively provide for coupling the technique of MCFA with that of FIA. One application could be when the chemistry required for a determination envolves a slow reaction followed by a rapid one. In this case, the slow reaction would proceed in a MCFA manifold (taking advantage of its low sample dispersion for long residence time) while the second reaction could take place with the resampled volume by introducing it in a carrier reagent fluid (single-lineFIA manifold) or in an inert carrier fluid that merges with the reagent, passing through an incubation coil and then through the flow cell.
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ACKNOWLEDGMENT The author is grateful to C. H. Collins for manuscript re-
10 mln
10 mln
Figure 2. (A) calibration run for ammonia determinatton with manifold B. The numbers over the peaks are the ammonia concentrations in MpmL-’. All measurements were made in triplicate. (B) Signals obtained using the same manifold after 2 h showing the stability and absence of carrysver between blanks and 0.5 MgmL-’ ammonia standard solution.
mentis used. On the other hand, the second valve of manifold B (VJ can easily be placed near the detector and there are no difficulties with synchronism. Additionally, the operation of manifold B can be fully automated by automating the second valve operation. This can be achieved by using a circuit
vision and critical comments. Registry No. NH,,7664-41-7.
LITERATURE CITED (1) Pasquini, C.; de Oliveira, W. A. Anal. Chem. 1985, 57, 2575-2579. (2) Pasqulnl, C.; Ralmundo, I . M., Jr. Q u h . Nova 1984, 7 , 24-28. (3) Ruricka, J.; Hansen, R. H. Now Inledion Analysis; Wlley: New York, 1981. (4) Patton, C. J.; Rabb, M.; Crouch, S. R. Anal. Chem. 1982, 5 4 , 1113-1 118.
RECEIVED for review January 7,1986. Accepted April 24,1986.
Multtfunctlon Valve for Flow Injection Analysis Jun-ichi Toei* and Nobuyuki Baba Development Department, Scientific Instrument Division, Toyo Soda Manufacturing Company, Ltd., 2743-1 Hayakawa, Ayase-shi, Kanagawa 252, Japan The reproducible introduction of a precisely measured volume of sample into a moving carrier or reagent stream is one of the basic factors that must be fulfilled in order to ensure the successful performance of any flow injection analpis (FIA) system (1,2).Numerous devices for introduction of samples have been proposed (3-5) and now hexagonal valves such as the Rheodyne 7125 are popular for the purpose. Though they have brought precise introduction of samples, the trouble is that they have only that function. As Ruzicka had already pointed out, a parallel introduction of sample and reagent is very important in FIA. Mindegaard and Bergamin have proposed injectors that have those two functions (6,7). They have reduced consumption of expensive reagents and obtained good success with the valves. But they still have a disadvantage in that introduction of samples could not be performed without a separate operation. In a previous paper (8) we have reported a new-type valve by which sample injection and flow change-over of a stream could be performed at the same time. Now we have designed and fabricated a simple and new type of injector that has two functions, that is, introduction of sample or sample and reagent (9). 0003-2700/86/0358-2348$0 1.50/0
EXPERIMENTAL SECTION Injector. Figure 1shows the cross sectional view of the injector, in which 1 is a stator of a circular plate shape and 2 is a rotor. The rotor is made of Teflon and the stator is made of Kel-F which is surrounded by a stainless steel frame in order to stand the high pressure. This valve can operate satisfactorily under 50 kg/cm2. This valve has three positions and we can select each position with ease by use of a pulse motor that makes the rotor rotate clockwise or counterclockwise. The precise positioning can be performed by use of photosensors as a position indicator. Figure 2 shows the shapes on the surface of the stator and the rotor. The small openings a to j and the grooves a’, a”, a”’, f’, f”, and f”’ are at the stator and the grooves A to G are at the rotor. In the stator the small opening a is connected to a pump and f is connected to reaction tubing. The small openings b,e and g j are connected to a sample and a reagent loop, respectively. The small openings c,d and h,i are also connected to a circuit of sample and reagent charge. Arrangement. Figure 3 shows the arrangements of the flow formed by the stator and the rotor, (a) is the load position, (b) is the sample injection position, and (c) is the reagent and sample injection position (after this we call the position “reagent injection position”). In load position, a solution flows f-F”’-A-a”’-a and a sample and a reagent are charged into the loops, respectively. 0 1986 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 11, SEPTEMBER 1986 f
a
3
to a &im
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thim
t
4
’
\ 5
Figure 1. Structure of the valve: 1, stator; 2, rotor; 3, rotor seal; 4, spring; 5, connector.
a
b
to a reaction t h i n g
t
T
fmnapnp C
to a reaction t h i n g
Figure 2. (a) Structure of the stator: a-f small openings connected to tubing; a-a’, a-a”, a-a”’, f-f’, f-f”, f-f“’, grooves. (b) Structure of the rotor: A-G grooves.
Table I. Reproducibility of Injection flow rate, mL/min
type of injection
0.5
sample reagent
1.0
sample reagent
measurement peak height peak area peak height peak area peak height peak area peak height peak area
re1 std dev (%, n = 7) 0.61 1.10 0.46 1.38
0.46 0.68 1.09 1.38
In sample injection position, to which the rotor is rotated clockwise from the load position, the solution flows f-f’-E-e-sample loop-b-C-a”-a and another path is stopped at j. In reagent injection position, to which the rotor is rotated counterclockwise from the load position, the solution flows f-f”-D-e-sample loop-b-B-a”-a and also f-f”-g reagent loop-j-Gat’-a. So a
fmnapnp
Flgure 3. (a) Arrangement of the Row In load position. (b) Arrangement of the flow in sample injection position. (c) Arrangement of the flow in reagent injection position.
sample and a reagent are injected into the flow as a parallel plug flow at the same time. Precision Testing. The testing was run using a CCPM pump (metal free Toyo Soda), reaction tubing (0.4 mm i.d. X 50 cm), and a UV-Vis spectrophotomeric detector UV-8OOO (Toyo Soda). Results were recorded on a CP-8000 data station (Toyo Soda). The sample loop and the reagent loop were Teflon tubes (0.4 mm i.d. X 79.6 cm) with 1OO-wL volume. Flow rate in all tests reported here was 1 or 0.5 mL/min and the absorbance was monitored at 254 nm. The testing solution for injection was 0.1% aqueous acetone solution and deionized
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Anal. Chem. 1988,58,2350-2352
I
0.032 0.0.
C
I
injected into the flow. Though the loop volume and the diameter of the both loops were the same in case (A) and (B), the peak shapes of the two were not in agreement. It could be due to the differences in the shape of grooves and connectors at the rotor or the stator. We are currently investigating the problem. When flow rate was 0.5 or 1mL/min, the reproducibilities of the sample injection and the reagent injection were investigated and the results are shown in Table I. The reproducibility of a sample injection only was slightly worse than that with six-port injection valves. In the case of the sample and the reagent injection, the reproducibility was almost twice as bad as that in the case of an only sample injection. The reproducibility may depend upon the number of loops. As the timing of the slide of the rotor was slightly long (about 1s), we investigated the reproducibility of the injections at a flow rate of 0.5-1 mL/min. But under these conditions the results were almost the same. So in conclusion, under low pressure (about 1-3 kg/cm2), which usual FIA is performed, the timing would not affect the injection.
c+
CONCLUSION
2 mn.
F@ro 4. Typlcei peak shapes of the standard sample with the valve: (A) sample lnjectlm in reegent Injection position; (B) reagent in)ecuon in reagent WcUm pos#kn; (C) sample and reagent hjectkn in reagent injection position; sample volume 100 pL, reagent volume 100 pL.
water was used as a solution of the flow stream. Deionized water was used throughout the testing and acetone was analytical reagent grade and used without further purification.
RESULTS AND DISCUSSION A typical peak shape when only a sample solution was injected into the flow in reagent injection position (the reagent loop was filled with the deionised water) is shown (A) in Figure 4. Another typical peak shape when only a reagent solution was injected into the flow (the sample loop was filled with deionized water) is shown (B)in Figure 4. Peak C in Figure 4 is a peak shape when the both the reagent and the sample loops were filled with the solution and the solutions were
We designed and assembled a multifunction valve for flow injection analysis and investigated the properties. On the whole it would be one of the suitable injection devices for flow injection analysis.
LITERATURE CITED (1) Ruzicka, J.; Hansen, H. Now Injectbn Analysis; Wiley: New York, 1981. (2) Tyson, J. F. Ana&st(London) 1985. 170. 419. (3) Rocks, 8. F.; Sherwood, R. A.; Riley, C. Ciln. Chem. ( Whston-Salem, N . C . ) 1982, 28, 440. (4) Attiyat, A. S.; Christian, 0.D. Anal. Chsm. 1984, 56, 439. (5) Ruzicka, J.; Hansen, H. Anal. Chlm. Acta 1983, 745, 1. (6) Mindegeard, J. Anal. Chim. Acta 1979, 104, 185. (7) Bergamin, H. F.; Zagatto, G.; Krug, F.; Reis, F. An8l. Chim. Acta 1978, 101, 17. (8) Toei, J.; Baba, N. Bun&/ Kag8ku 1988, 35, 411. (9) Toei, J.; Baba, N., Japan patent pending, 1986.
RECEIVED for review March 18,1986. Accepted May 12,1986.
RapW Headspace Analysis in Sealed Drug Vials by Multichannel Raman Spectrometry Laura Porter Powell*' American Cyanamid Company, Chemical Research Division, 1937 West Main Street, Stamford, Connecticut 06904
Alan Campion Department of Chemistry, University of Texas, Austin, Texas 78712 Many pharmaceuticals slowly decompose when stored in the presence of oxygen and are therefore packaged in a nitrogen atmosphere. Gas chromatography is frequently used to verify the nitrogen gas purge and check for oxygen leaks. Raman spectrometry can potentially perform this determination more rapidly, reliably, and nondestructively. Previously reported Raman spectrometric headspace analyses have employed conventional scanning spectrometer systems (1,2).Residual oxygen content in sealed vials was determined nondestructively by using the nitrogen purge gas as an internal standard. The laser beam was focused inside the sealed vial and the internal Raman scattering was imaged Current address: American Cyanamid Co., Medical Research Division, Lederle Laboratories, Pearl River, NY 10965. 0003-2700/86/0358-2350$01.50/0
and measured. Both the pure rotational and the pure vibrational Raman peaks have been used; the rotational cross sections are approximately 10-fold larger than the vibrational cross sections (1,2).The time required for one scan was a t least 10 min, plus sample alignment and data analysis time. These techniques are not rapid enough for routine pharmaceutical quality control use. The well-known analysis speed of multichannel optical detection systems has been demonstrated for Raman spectrometry applications (3). This speed advantage was realized by Hug and Surbeck for gas-phase rotational Raman spectra of oxygen and nitrogen, each at atmospheric pressure. The authors suggest that pharmaceutical headspace analyses might be performed if specular reflections from the walls of the sample vials could be reduced by an iodine filter cell (4). 0 1988 American Chemlcai Society
