Chemical Education Today
Letters Stopper with Interchangeable Septa for SPME When developing a method for the analysis of volatile organic compounds in natural waters by solid-phase microextraction (SPME) followed by GC–MS, we were confronted with the problem of the vessels to use for the extraction. The commercially available vials were too small and not suitable for our needs. For that reason we decided to use round- and flat-bottom flasks with sizes ranging from 10 to 100 mL with standard (14/23) taper-ground stoppers. Some of the plastic stoppers are hollow and have a cap on the top that can easily be removed. It is easy to drill a hole at the narrow end of the plastic stopper, or the whole bottom can be cut off. An 11 mm diameter GC septum forced into the opening makes an excellent seal (Figure 1). We call the modified stopper a stoppum. Alternatively, a hollow glass stopper can be cut at the ends and fitted with a septum although a diamond grinder is needed, which is not always readily available. The SPME can be performed from the solvent or headspace (Figure 2) and the flask can be thermostatted by conventional means. Larger flasks with volumes of 250 and 500 mL can also be used with a standard reducing adapter. Supporting JCE Online Material http://www.jce.divched.org/Journal/Issues/2009/Aug/abs924_2.html Keywords; Full text (HTML and PDF)
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Figure 1. The modified stopper.
1 cm
Figure 2. SPME performed from the headspace using the adapter.
Zoran Zdravkovski* and Jordan Cavdarov Institute of Chemistry Faculty of Natural Sciences and Mathematics Saints Cyril and Methodius University Skopje, Republic of Macedonia *
[email protected] Journal of Chemical Education • Vol. 86 No. 8 August 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
