Spotting devices

When applying samples to a TLC plate, it is best not to touch the layer with the applicator. If this is necessary, it should be done carefully in order to prevent the dislodge-ment of some of the layer particles which may lead to spotting error. This is especially true of home-made plates which do not contain a binder. It is best, therefore, to touch only the drop on the end of the applicator to the surface of the layer. 

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The introduction of the sample into the adsorbent layer is a critical process in HPTLC. For most quantitative work a platinum-iridium capillary of fixed volume (100 or 200 nL), sealed into a glass support capillary of larger bore, provides a convenient spotting device. The capillary tip is polished to provide a smooth, planar surface of small area (ca 0.05 mm2), which when used with a mechanical applicator minimises damage to the surface of the plate spotting by manual procedures invariably damages the surface. 

PATR 3064 E.L. Miller, "Development of XM66E2 Electric Detonator for Use in Type 19 Spotting Device" (March 1963)... 

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... 

Carefully apply 1 pi of a sample solution onto the starting point (origin) of five Chromarods using an appropriate spotting device. Spot another sample or one concentration of the standard solution onto another five Chromarods. 

Fig. 21.3. Visual proteomics require samples to be prepared by a microfluidic circuit. Cells grown in microreactors are released and sorted to reach a device that lyses them. Various well-known separation circuits are used in series for generating suitable fractions of the lysate. Importantly, a spotting device akin to those used for DNA array production produces 10 pL droplets that are deposited on an EM grid. One cell will provide enough material to cover 1 to a few grids, when one droplet is deposited per grid square...

This problem is minimized by the use of an automatic spotter designed by Getz (35). This spotting device, allowing complete control of the initial spot size of both sample and standard by the appropriate choice of solvents and air flow, is an improvement over an earlier design by Beroza et al. (6). 

An automatic sample-spotting device has been developed, which uses a flexible fused silica capillary tube as the applicator and a motor-driven syringe to suck up and deposits onto the layer sample volumes in the range of 100 nL to 20 pL as spots or bands.Controlled by a microprocessor, it can be programmed to select samples from a rack of vials and deposit fixed volumes of the samples to selected positions on the plates. The applicator can spot a whole plate with various samples and standards without operator intervention. Moreover, the applicator automatically rinses itself between two sample apphcation sequences to eliminate carryover of samples. 

S.6), or by use of commercial spotting devices. Application of smaller initial zones increases the concentration of analyte at the origin, which allows the weight of applied sample to be reduced to avoid overloading and to improve resolution, while maintaining detection intensity. Application of initial spots in the 1-2 mm range or lower is now common, especially for high-performance TLC. 

Preadsorbent zones This is a thin-layer plate designed with an area below the silica or bonded silica sorbent that is made up of diatomaceous earth or a wide pore silica gel. The purpose of this preadsorbent area is to allow fast sample application even with a crude spotting device with no absorption or separation of the sample components. After drying, when the development begins, the sample dissolves and concentrates onto itself to form a narrow band before it moves onto the active sorbent for separation. These sample bands improve the resulting separation compared to spots placed on the active layer, as streaking the sample does on any TLC plate. These plates are particularly well suited for dirty or biological samples where this area acts to preclean the sample, rather like an initial filtration. 

Figure t. Microcapillary spotting device for TLC a) Capillary tube b) Septum c) Support tube d) Rubber bulb... 

The simplest technique to apply samples spotwise is to use a fixed volume pipette that fills by capillary action and delivers its content when it touches the layer. In order to ensure that the layer is not damaged and the spots are precisely positioned, it is advisable to guide the pipette with respect to the lateral position and with reproducible constant pressure. This is possible with a Nanomat " (Fig. 2), a mechanized spotting device. 

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