Conversion of a Variable-Speed Strip-Chart Recorder to a Motor-Driven Syringe Robeit E. Gawleyl and Mlw F. Carison University of Miami, P.O. Box 2491 18. Coral Gables, FL 33124 In most laboratories. a motor-driven svrinee - (svrinee .pump) is a n unaffordahle luxury, in spite of the convenience they offer. In the U.S., asagemodel 341A syringe pump sells for $725 (Fisher Scientific). T o a synthetic chemist, slow additions of reagents are common, and the usual practice is to add a small portion "every few minutes", rather than continuously over a longer period. I t occurred to us that the gear box of a variahle-speed strip-chart recorder might offer the range of drive speeds necessarv for such a n annaratus. Most laboratories have old unused recorders on h i d , and ours was n o exception. We have converted a Hewlett-Packard model 7101B recorder, whose indicated chart speeds vary from 1i n . h to 2 in./s, into a variahle-speed syringe pump. T h e drive speed is variahle from ahout 40 s to over 3 days for 1in. of plunger displacement. The unit is outfitted with a moveable switch to shut off the drive motor a t the end of the discharge. The configuration we describe will accommodate any syringe whose harrel length is 3.5 in. or less. The largest syringe we have used is a Hamilton # 10.50 (gastight, 50-mL capacity). This particular model is 35 mm in diameter. and a l-in. disolacement corresponds to roughly 21 mL. We use a 12- or 24411. stainless steel needle (Aldrich Chemical Co.) with Luer huh. hent a t a 90° angle heiow the Luer huh, to transport the effluent to the reaction flask. Details of ihe Conversion 1) Remove from the recorder all components except the chart drive motor and eear box. ineludine,. the . olate coverine the too of the main cavity. The syringe drive mechanism is mounted on what was the inridesurfare of the rhart backup plaw.The H-l'7101H backup plate id hinged and should be moved so as to ~xpoaethis surface. 2) Mount a 131s-in.gear on the axle that held the chart drive gear. 3) On one end of a piece of '12-in. X 16 threaded rod, lo3/&. long, mount a 2%-in.gear, and on the other, drill aS/,e-in. hole. Mount this piece in place of the rod which served to hold the chart paper roll. This is a~.sorine-mounted bracket. which makes it conve" nient ro adjust the position of the plunger drive plate. However, ir is necessary to insert a in-in.-thickplate h~tweenthe springmounted bracket and the recorder ensing to prevent the force of the drive motor pressing on the syringe from stretching the spring and disengaging the gear. 4) Mount a third gear, 2%-in., to the end plate so as to engage the other two gears already in place. 5) Near the center of the backup plate, mount a 2-in.-wide Lshaped bracket having a 1Yz-in. hole cut in its vertical face. The vertical face should he roughly 5%-in. from the drive gears in order to have enough room for the syringe barrel and needle. Constructseveral 2-in. square face plates withcenter-cut holes of various sizes to aceommodate different syringes; these are mounted to the face of the L-bracket with two small screws cemented to the bracket and two knurled nuts for fastening. 6) Two 3/,-in. nuts, separated by about 2 in., ere placed on the threaded bar. An assemhlv consistine of the oluneer . .. drive olate and n mirroswireh is cemented to these nuts wthepoxy. 7 ) The motor in wirpd as illustrated in Figure 1. The "power on" nwiuh and the "chart drive startlrtop" switch are used a s the
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Author to whom correspondence should be addressed. No reDrints are available.
554
Journal of Chemical Education
"power an'* and "drive start" switches for the pump. The light between them is used as the "drive end indicator". 8) A small clamp is fashioned so as to provide an end-stop to trigger the microswitch which stops the drive motor when the syringe is fully discharged. The apparatus is pictured in Figure 2. Operation is as follows. T h e syringe (with plunger in full discharge position) is inserted into the L-bracket, and the drive plate is moved (manuallv) until it is touchine the svrinee With the . - nluneer. power on; the end-stop clampis moved to the right until the drive indicator light comes on. After securing the end-stop clamp, the plunger drive plate is hacked off to the desired position. The syringe is charged and remounted, and the desired discharge speed is selected. When the drive start switch is closed, the pump will discharge the syringe and stop automatically.
Figure 1. Diagram for wirlng of motor.
Figure 2. me assembled apparatus.
