A Simple Alternative to Separatory Funnels for Chemical Extractions Ragnar Bye University of Oslo, Department of Pharmacy, P.O. Box 1068, 0316 Oslo, Norway Extraction methods are employed widely in many fields of chemistry, especially in organic or analytic chemistry. s carried out in order to seoarate the Extraction s t e ~ are compound in question from the sample solution and/or for preconcentration purposes. So far, separatory funnels have been the predominant vehicle in such operations. However, there are several well-known disadvantages associated with the use of separatory funnels making them unattractive to chemists in general, and not a~preciated .. for use in training laboratory courses:
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If carried out manually, the reproducibility of the extraction is strongly dependent on the shaking intensity, which depends on the person shaking it. T h e r e always is a risk of leakage due to pressure that can (and can even rebuild UD during - the shaking- Drocess sult in explosions). The shaking process is time-consuming,especially when repeated extractions are required. It is difficult to treat the sample solution prior to extraction; far instance, heating is impossible unless this is carried out in another vessel. Weighing of the sample directly into the separatory funnel is not possible; instead, it has to he transferred from a weighing boat into the separatory funnel afterwards. In order to circumvent the mentioned disadvantages associated with the use of separatory funnels, we have developed a novel magnetic bar-stirred extraction method using conventional conical flasks (Erlenmeyers) ( I ) . Additional necessary equipment are a constant-rate magnetic stirrer and a specially designed h u t easy-to-make, glass a d a p t o r mounted in the opening joint of the flask. (See figure.)
General Procedure for Any Magnetic Bar Extraction Method Transfer the actual amount of sample to the conical flask either by weighing (directly into the flask) or by means of a pipet. Add a Teflon-coated magnetic bar, the predescribed volumes of reagent solutions, and the extraction solvent. Mount the glass adaptor in the opening joint of the flask and be sure that the flask has been placed in the center of the stirrer. Turn this on and let stir a t a given rotation speed for a definite time. Let the contents rest for about 5 min in order to separate the phases. Turn the flask carefullv u~side-down(in order to minimize mixing of the two open the stopcock, and drain the 1owe;layer. Proceed a s described in the procedure in question.
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Journal of Chemical Education
If the remaining phase is to be extracted once more, add the required volume of extraction solvent (and of reagents, if any) and repeat the operation. If. an the other hand. the lower laver is to be extracted once agam, dram this mto another conical flask, replace the adaptor, and repeat the process. Discussion of the Method Three well-established melhods were tested by using the proposed technique: a nonaqueous, perehlaric acid titration (assay) of amphetamin sulfate after extraction of the base into chloroform (a pharmacope method); a speotrophotometrie method for the determination of phosphate with molybdenum aeid/asearhic acid as complexing agent and extraction into n-hexanal; a flame atomic absorption spectrometric method far the determination of copper in a biological sample (with an established concentration of copper) after dry ashing, complexation with ammonium pyrrolidine dithiaearbamate (APDC) and extraction into methyl isohutyl ketone (MIBK).
The results for all the three methods were in excellent agreement with those obtained when the analyses were carried out in the established way; i.e., after manual extraction using separatory funnels. For optimization of any stirring-bar extraction method a signavtime curve should he established in order to assess the extraction time necessary for the method in question. The minimum time is indicated where the curve begins to flatten out. Anv constant-rate mametic stirrer can be used. but a "multipoint stirring-plate" capable of stirring a number of flasks simultaneouslv a t a constant and res selected s ~ e e d that can he varied insteps will he even more convenient. The glass adaptor should he easy to make for a glassblower. It should, however, be noticed that the length of the tube leading into the flask should be such that the opening is never in contact with the solution, neither during the extraction nor the emptying stage. The tube allows the entrance of air during extraction, thus avoiding any built-up pressure and for a n easy drain of the solution after having turned the flask upside-down.
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Conclusions The novel extraction technique described in this article should offer pronounced advantages relatlve to the conventional separatory funnel technique. For more detailed information on the procedures and the results of the test analyses and for a more thorough discussion of the technique reference 1should be consulted. (Reprints are available from the author) Literature Cited 1. Bye, R.;Agasostel T.;krheirn,A Freaenkiu. J. A n d Chem. 1993,345,411
