A Very Expensive TLC Spotter Recently we were faced with the task of purifying a vitamin derivative by preparative thin-layer chromatography. We quickly discovered that spotting the sample manually yielded such irregular bands that isolation of the desired compound was unfeasible. The prohibitive expense of commercially available TLC spotters (about $1000) encouraged us to devise our own apparatus. Although the components of our apparatus are several times as expensive as a TLC spotter, they (or comparable equipment) are often already available in a well-equipped laboratory. The expensive components are a Moseley (Hewlett-Packard) 7030AM X-Y recorder and a Sage Model 341 syringe pump. The remainder of the apparatus is constructed as described below. A 2.5-cm segment of %gauge tubing was cut from a stainless steel syringe needle; the end was deburred and filed flat. The needle was then soldered to a Fahnestock clip in such a way that the flat end of the needle projected slightly below the recorder pen tip when the needle was attached to the pen by means of the clip. The other end of the needle was attached to 45 cm of 0.038crn LD. polyethylene tubing which was, in turn, attached to the 26-gauge needle of a 0.25-mlglass syringe. In a typical experiment, the Y-axis position of the recorder pen was set to approximately 1em above the rail and the X-axis was set t o 5 slcm sweep rate. An Analtech Avicel F 20 X 20 X 0.1 cm preparative TLC plate was placed on the recorder bed, and a 0.1-ml portion of aqueous solution containing the derivative was drawn into the syringe. The recorder scan was activated, and, as the needle contacted the plate coating, the syringe pump (which was set to deliver 0.02 mllmin) was activated. The pump was deactivated immediately after the scan in order to prevent erratic spotting during the baekscan. In this manner we were able to spot a plate in three passes; the result was equal t o that of commercial spotters a t only five times the cost!
Tom Lyons Fisher Juniata College Huntingdon. PA 16652
Volume 60
Number 11 November 1983
989
