Anal. Chem. 1980, 52, 354-355
354
R. J. Day
RECEIVED for review September 10,1979. Accepted November
s*E- Unger
5 , 1979. This work was supported by the National Science
R* G'
Department of Chemistry Purdue University West Lafayette, Indiana 47907
Foundation, CHE 78-08728 and the MRL Program DMR 77-23798. R.J.D. thanks the Analytical Division of the American Chemical Society for a summer fellowship.
AIDS FOR ANALYTICAL CHEMISTS Modular Chemically Inert Mixer for Flow and Stopped-Flow Experiments F. J. Holler" and W. C. Mateyka Department of Chemistty, University of Kentucky, Lexington, Kentucky 40506
With the increased use of flow methods in recent years and, in particular, the development of analytical methods utilizing the stopped-flow technique (1) has come the need for a modular chemically inert mixing chamber that may be easily interfaced with a variety of flow systems. A number of efficient, well-characterized mixers have appeared in the literature, and these have been reviewed in detail elsewhere (1-3). Most mixers are designed for single-purpose mixing systems, and they are therefore not easily reconfigured for different mixing modes. The tangential-jet mixer developed and described by Gibson and Milnes ( 4 ) has received wide acceptance, and it is incorporated in a commercial stopped-flow mixing system (Durrum Instrument). The mixer is sandwiched between the syringe drive system and the observation cell of a stopped-flow module while maintaining leak-free operation. Repair or replacement of the mixer generally requires complete disassembly of the flow system, and use of the mixer with observation cells of unusual shape or design generally dictates a redesign of the mixer holder and the interconnection scheme for the various parts of the instrument. Berger and co-workers (5)have described a highly efficient mixer which provides extremely rapid mixing (200 p s ) making it useful for fundamental work with very rapid reactions, but it may not be easily incorporated into more conventional mixing modules, and very high pressures are required for its operation. Papadakis e t al. (6) have reported a quartz mixer which exhibits many of the characteristics which are desirable in analytical applications of rapid mixing including small size, high mixing efficiency, chemical inertness, and optical transparency, but its uses are somewhat limited by the fragile nature of the assembly, particularly its tendency to break at the junction between the tangent delivery tubes and the body of the mixer. Using the flow pattern of this mixer as a basis, we have substantially redesigned the mixer and have developed construction and assembly procedures which minimize breakage, enable rapid fabrication, and facilitate interfacing the mixer to a variety of different types of mixing experiments. In the following sections, these procedures are presented in some detail, and the use of the mixer is described.
are connected to the inlet streams via standard 1/4-28 tube end fittings for liquid chromatography and the unique connector block shown in the figure. The fittings mate with mixer a t the ground and polished flats on the surface of the mixer body. The outlet of the mixer may be connected to various observation cells in two different ways. As shown in Figure 1, a glass-to-tubing liquid chromatography connector is used to couple the outlet of the mixer to any desired module by simply drilling and tapping the module to mate to the male thread of the connector. A groove is ground in the mixer (see figure) to accommodate the connector. A Teflon washer is placed between the outlet of the mixer and the inlet of the observation cell, both to protect the mixer and to provide a seal a t the connection point. For situations in which it is desirable to have the mixer and observation cell form a single functional unit, the mixer may be sealed directly by glass-blowing to a cell made of the same material. This configuration is shown in the diagram of a UV-visible spectrophotometric observation cell of Figure 2. This mixer-observation cell is similar in some respects to the cell described by Papadakis et al. (6) but connections to it are made via the plastic connectors detailed in the previous paragraphs, and it is therefore much less susceptible to breakage. In fact, several mixer and mixer-observation cell units have been constructed and used in a variety of flow experiments, and none has been broken either while in service or during the assembly procedure. The robust nature of these mixing units is presumably due to the very short lengths of glass or quartz tubing used in their construction and the stability of the connection scheme. An added advantage of this mixer is the capability of mixing two, three, or four solutions in the same flow system by utilizing the proper combination of ports A, B, C, and D in the connector block shown in Figure 1. The usual dead time and mixing time experiments have been carried out (6, 7) utilizing a syringe drive module built in our laboratory (8). The dead time of the combined stopped-flow instrument was found to be 3-5 ms limited by the speed of the syringe drive module, and the mixing time was less than or equal to this value in all experiments.
CONSTRUCTION DETAILS
DESCRIPTION OF THE MIXER The most basic form of the mixer is illustrated in Figure 1, along with its simplest connection scheme. The inlets to the mixer consist of two to four jets drilled tangentially into the bore of a short length of quartz or pyrex tubing. The jets 0003-2700/80/0352-0354$01 .OO/O
All of the mixers and mixer-observation cells were fabricated from 7 mm 0.d. X 2 mm i.d. heavy wall quartz or Pyrex tubing. If a two-stage mixer is desired (Figure l),the first step in the construction is the drilling of the channels for the second stage
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1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 2, FEBRUARY 1980 FACE OF S E A L
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QUARTZ MIXER
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SIDE VIEW
The basic mixer. Connections to the tangential jets are made at ports A, B, C, or D in the multiple connector block. The mixer is connected to various observation cells by inserting the LC connector into a properly threaded hole Flgure 1.
mrn
Flgure 2. Spectrophotometricobservation cell. The mixer is essentially identical to that shown in Figure 1 except that there is only one stage. The cell is assembled from three pieces of quartz tubing and two optical quartz windows
with an Airbrasive Unit as described in Ref. 6. Following this, or as a first step in the construction of a single stage mixer, a 2-mm plug is sealed into the mixer end of the tube as shown in Figure 2. Depending on the number of solutions to be mixed, two to four flats are ground and polished on the sides of the tube, precisely at right angles to one another, in order to mate exactly with the multiple connector block shown in Figure 1. This step is accomplished quite easily with the grinding jig illustrated in Figure 3. T h e jig consists of a small stainless steel block through which is drilled a hole just large enough to pass the tubing. A slot is milled in the block which intersects the hole for the tube at a right angle and whose depth is such to make the bottom of the slot coplanar with the desired polished flat of the mixer tube. The tube is inserted into the jig and clamped in place with the plastic thumbscrew, A. The flat is then easily ground using an air turbine grinder (Starlight Industries, model 501005 or similar tool) and polished with #400 and then #SO0 emery papers. Relative positioning of the other flats is accomplished with the indexing ring arrangement shown in the figure. After each flat has been ground, thumbscrew A is loosened, and the tube is rotated through 90" as indicated by the carefully ruled indexing marks on the ring. The screw is then retightened, and the grinding and polishing of the next flat is carried out as before.
QUARTZ OR PYREX TUBING
Figure 3. Grinding and polishing jig for construction of the mixer from quartz or Pyrex tubing. See text for explanation of operation
The crucial step in the construction process is the drilling of the mixing jets from the flats to the bore of the tubing. This is done in much the same fashion as previously described (6) except that care must be taken to ensure that the entry point of each jet is exactly in the center of its corresponding face (see Figures 1 and 2). The final step in the construction of the basic mixer is the grinding of the slot a t the outlet to accommodate the LC connector shown in Figure 1. By placing the mixer in a lathe chuck and rotating it at medium speed, the slot may be cut using a diamond grinding bit mounted in a hand-held motor tool (Dremel). The multiple connector block may be easily machined from a small block of Delrin, any other rugged plastic, or metal, if desired. The proper combination of holes for the desired jet configuration are drilled and tapped to fit the '14-28 tube end fittings at locations A, B, C, and D as shown in Figure 1. A hole is then drilled to accommodate the mixer such that the jet entry points are centered in the holes at A, B, C, and D. This hole should fit the mixer very closely so as to provide support for it. Connection to the mixer is carried out by inserting the mixer into the connector block, tightening the end fittings gently with the fingers in the sequence A, C, B, D, and finally, tightening the fittings with a small wrench until leak-free operation is achieved. Manufacturers of the fittings suggest that glass-to-Teflon seals such as these are stable to 500 psi, a figure more than adequate for many flow and stopped-flow experiments. Several of these mixers have been constructed and used in our laboratory with a variety of observation cells over a period of about two years. They are easily and rapidly assembled into flow systems or reconfigured to suit the needs of the experimenter. These qualities should make them useful in a number of applications requiring modularity and simple connection to other flow system components.
LITERATURE CITED (1) Crouch, S. R.; Hdlec, F. J.; Notz, P. K.; Beckwfth, P. M. Appl. Spectrosc. Rev. 1977, 73, 165. (2) Eerger, R. L. Slophys. J . 1978, 2 4 , 2. (3) Chance, E. Tech. Chern. 1974, 6, 5. (4) Gibson, Q. H.; Mllnes, L. Biochern. J . 1964, 97, 161. (5) Berger, R. L.; Ealko, B.; Chapman, H.Rev Scl. Instrum. 1968, 39,493. (6) Papadakls, N.: Coolen, R. E.; Dye, J. L. Anal. Chern. 1975, 47, 1644. (7) Holler, F. J.; Crouch, S . R.; Enke, C. G. Anal. Chern. 1978, 48, 1429. (8) Holler, F. J., unpublished work.
RECEIVED for review September 10, 1979. Accepted October 12, 1979. Acknowledgment is made to the Donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research.
