the microscale laboratory Inexpensive Reagent Dispenser H. Brouwer
Redeemer College Ancaster, ON Canada L9K 1J4 With the movement toward microscale experiments in chemistry, disposable syringes are finding wide use as convenient and inexpensive devices for measuring small volumes of liquids. Unless syringes are well-labeled and kept away from other solutions, however, there is the danger that a solution may become accidentallycontaminated. Reagent bottle dispensers are a better and more convenient alternative, but the high cost of commercial units make their widespread use in most chemistry labs prohibitive. This article describes an inexpensive reagent dispenser constructed with a disposable syringe and three-way valve, as shown in the accompanying diagram. The Luer thread on the side-arm of a three-way stopcock (Cole-Parmer Cat. No. M-06464-75) is removed with a sharp knife and a glass delivery tube (4 mm 0.d.) with tapered end is attached with suitable sized tubing. For small volumes (5 mL),the stopcock is attached to a hypodermic needle (#IS) inserted through a rubber stopper; for larger volumes, the stopcock should be connected to a piece of tubing (the resistance to flow of the needle makes the transfer too slow for volumes >5 mL). In both cases, additional tubing reaching the bottom of the bottle is required as well as a second hole or slit in the rubber stopper to allow air into the bottle. A syringe of appropriate volume (1-100 mL) is attached to the top of the stopcock to complete the dispenser. The device is operated by positioning the stopcock so that the desired volume of liquid can be drawn from the reagent bottle into the syringe, after which the stopcock is
rotated 90" and the plunger is depressed to transfer the liquid into the receiving - flask. The process is repeated as needed. This dispenser also may be used to fill a buret. By connecting it to a buret with a side filling tube and using a 30or 50-mL syringe, the titrant may be transferred directly fmm the reagent bottle into the buret.
Macrostyle Microscale Equipment Joseph Casanova and Gary S. Coyne CaliforniaState University, Los Angeles Los Angeles, CA 90032
The use of microscale equipment for the organic laboratory continues to gain momentum. Persuasive arguments of improved safety, ease of chemical waste disposal, and economy of size have been advanced and are valid. The conversion to smaller scale also minimizes exposure to solvents and other chemicals, decreases laboratow bench clutter, and reduces the time required to complete experiments (1).Improvement in air quality in the laboratory has been documented (2).The move to microscale is taking hold internationally, with reports of the change over ap. pearing recently from PRC (3) and fmm the UK (4). Reviews have appeared (3. Statistics are reported for the conversion of a general organic chemistry laboratory fmm conventional to microscale (6). A variety of new experiments have been stimulated by conversion to smaller apparatus (7). Despite the advantages of microscale techniques, criticism often is voiced that efforts directed toward use of small quantities of startine materials reauire the abandonment of some conventi&al techniques necessary for the successful preparation of larger amounts of material. We sought to find a compromise between milligram scale experiments and the traditional macroscale approach. Microscale operations sometimes can fail to demonstrate techniques that students will need later in preparative organic chemistry in undergraduate or gradu&'research or in industry. We have designed and prepared our own glassware, so i s to have available equipment that can beused more like the larger scale equivalent and to save on startup cost. In situations where a skilled glassblower is in residence (8).but where limited financial resources are available, it can make senseto construct glaxqware on site. The only direct cost is that of the glass joints and s.yringe. An aluminum block to Drovide smwth-heatine ~ ~ (9)-is - --. &sn .- ~ ---provided to students. Grcbased in bulk the materials for one kit, not including the aluminum heating block, cost $55.10 (late 1992). This price included an institutional discount. D e ~ e n d i n eon soecific details. commercial microscale kits rangefrom about $150 to $300 each. We chose to minimize the number of parts in the kit. and to stress multiple use for as many as possible. 'l'he figure is a scale drawing of the parts and some common assemblies. Our experience with this apparatus in the beginning organic laboratory has been satisfactory, and permits us to take advantage of small scale without abandoning teehniaues for lame scale preparation and with modest s t a r t u ~ cost. A typicai beginningstudent can achieve excellent result for a classical fractional distillation ex~eriment.' It compares fully to our previous experience using macroscale equipment and to results reported usine microscale equiim&nt(10). Scale drawingsbf the apparatus and a parts list are available on request fmm the authors. ~
Three-way Stopcock Rubber Stopper
-Reagent Bottle
Diagram of reagent dispenser. A148
Journal of Chemical Education
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