Drummond MICROCAPS

Spotting device 1-p.l disposable micropipet (e.g., Drummond Microcap), I-pi microsyringe, or (semi)automatic sample spotter Constant humidity chamber containing a cup of saturated NaCl solution 100°C oven... 

The method used for application of sample solutions is determined by whether HPTLC, TLC, or preparative layer chromatography (PLC) and qualitative or quantitative analysis are being performed. Sample volumes of 0.5-5 pi for TLC and 0.1-1 pi for HPTLC are applied manually to the layer origin as spots using fixed volume glass micropipets, such as Drummond Microcaps or selectable volume 10 or 25 pi digital microdispensers. In addition, many manual and automated instruments are available for sample application, especially for quantitative HPTLC. 

The easiest way to prepare a bell is to use a commercial micropipette, such as a IO-/1L Drummond "microcap." These are available in vials of 50 or 100 microcaps and are inexpensive. To prepare the bell, cut the microcap in half with a file or scorer and then seal one end by inserting it a small distance into a flame, turning it on its axis until the opening closes. 

A series of standard solutions of cholesterol were prepared by serial dilution. Equal volumes (2 pi) of a solution of known concentration of the sample and of each of the standard solutions were spotted on to the adsorbent alternatively. For high accuracy a micrometer syringe should be used, but also, a capillary pipette (Drummond Microcap), could be used. 

Apply 10 pi of each of the three standard aspirin and caffeine mixtures and 10 pi of sample solution in duplicate by streaking onto preadsorbent areas of adjacent channels using Drummond microcaps. 

Figure 4 Application of initial zones to a glass-backed 20 x 20 cm channeled preadsorbent silica gel plate using a Drummond Microcap micropipet. (Photograph supplied by Analtech.)...

Accurate and consistent application of samples and standards to the plate in small, equally sized zones is critical for successful densitometry [79], This is best accomplished manually using Drummond disposable microcap micropipets [80] (Fig. 

Drummond Disposable Microcaps are available from Thomas Scientific, P.O. Box 99, Swedes-boro, NJ 08085 and Sargent-Welch Scientific Co., aVWR company, P.O. Box 1026, Skokie, IL 60097. 

In the recommended experiment, either 1, 5, or 10 il of dye is applied as a spot or a streak to the origin of a TLC plate or sheet. The origin is set at 2 cm from the bottom of the plate. Each spot or streak is applied 2-3 cm apart. Application of spots or streaks is made with 1-, 5-, or lO-pl Microcap micropipets or with a lO-pl digital microdispenser (Drummond Scientific Co.). For applications of 5 or 10 pi, solvent is dried during sample application with the aid of a hair dryer. The solvent front line is drawn lightly with pencil on each plate or sheet, 10 cm from the origin. Two different commercially precoated plates may be used... 

Apply 1, 5, and 10 pi of the 18-4A standard to the origin of the plate using 1-, 5-, and 10-pl Microcap micropipets or a Drummond digital microdispenser. Locate the origin 2.5 cm from the bottom of the plate. Draw the solvent front line... 

Draw an origin line 2 cm from the bottom plate. Draw a solvent front line 10 cm from the origin. With Microcap micropipets or a Drummond digital microdispenser, apply 5 and 10 pi of each standard to separate origins as a 1-cm streak (Chapter 5). 

Draw an origin line 2 cm from the bottom of the plate. Draw a predip line (see Experiment 7) 2.3 cm from the bottom of the plate. Draw a solvent front line 10 cm from the origin. Predip the plate in 5% ethanolic PMA to the 2.3-cm mark as described in Experiment 5. After the plate has dried, apply 1-, 2-, 3-, 4-, and 5- J.l spots of standard to the origin line with Microcap micropipets or a Drummond 10 pi microdispenser. 

Apply 5 pi (15 pg) of each standard to the preadsorbent zones of the plate with either a Microcap micropipet or a Drummond digital microdispenser. 

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