High-speed TLC

HSTLC microextraction High-speed TLC INADEQUATE analysis Homonuclear 7-correlated 13C... 

Dry column chromatography [528] provides several improvements over traditional column chromatography, such as better resolution and high speed. Another important characteristic is the near-quantitative applicability of TLC results in dry column analysis. Knowledge of the TLC characteristics of a sample is useful before column chromatography is employed. Careful control of the moisture content of the adsorbent is crucial to the dry column as well as other types of chromatography. 

The availability of new materials, methods, and instrumentation over the last 10 years has so greatly altered TLC, that the new form is now called high performance TLC (HPTLC). The HPTLC plates are far superior to the conventional type, having much smaller particles (2 to 7 pm) as well as a very narrow particle size distribution. This makes HPTLC faster, more reproducible, more sensitive, and more accurate for quantitative work. Its growth in drug applications has been greatly speeded by the use of automated sample application devices and accurate densitometers. A comparison of HPTLC and TLC is given below. 

The reversed-phase TLC system [stationary phase RP-18F254s mobile phase water-methanol-tetrahy-drofuran 5 2 3 (v/v/v) applied two times] was used in analysis of taxoids fractions obtained after high-speed countercurrent chromatography isolation and was suitable for paclitaxel and cephalomannine qualitative determination [6]. 

The alkaloids were extracted into ethanol and purified on a column chromatography of diatomaceous earth moistened with 2.5 H H2 SO. Non-alkaloidal materials were first eluted with ethylether, alkaloids were then eluted with CHCI3 saturated with aqueous ammonia. After evaporation of eluate, a solution of the residue in chloroform was submitted to TLC plates of silica gel 60 F-254 which developed in the solvent trichloroethane-diethylamine (9 1). After drying at 105 for 2 hours, the plates were sprayed with a solution of 4-dimethylaminobenzaldehyde in ethanol-4 M H2SO4 (1 1) and again dried at 105" for 60 minutes. Hyoscyamine and scopolamine spots were determined with the use of high-speed scanner at 495 nm. The calibration graph was rectilinear for 0.2 to 2.0 mg ml"1 of alkaloid, and the detection limit was 50 ng. The method was rapid and comparable with... 

This technique has other advantages compared with TLC and HPTLC, e.g. high-speed sample development, low consumption of eluant and reduced diffusion of analyte spots. Newman-Howells Associates and Supelco market horizontal sandwich chambers which are overpressurised in the latter system the chromatoplates can be eluted simultaneously from both ends, thus doubling sample throughput. 

The time required for most HPLC separations is less than thirty minutes and with some high speed HPLC separations which will be described later these times may be further reduced to less than two minutes. While GLC can often match this performance, neither TLC nor paper chromatography can provide resolution in a comparable time. Apart from the obvious advantage of time saving, relatively labile samples may be rapidly analysed by HPLC before any deterioration has occurred. The problem of sample lability may also be a problem in GLC where thermally labile compounds may be decomposed by the relatively high temperature used in GLC analyses. In contrast, most HPLC separations are carried out at room temperature. 

The test portion (50g) was extracted with 250 mL methanohwater (80+20) for 1.0 minute at high speed in a Waring blender. The mixture was gravity settled for 15 minutes and filtered through Whatman No. 4 filter paper. This common filtrate was used for all immunochemical and TLC analyses. 

The combination of preparative high-speed countercurrent chromatography with other separation methods, such as HPLC, and TLC, will enable chemists to isolate minor components of complex alkaloid mixtures more efficiently. This technique is not limited to alkaloid separations and, in theory, other complex mixtures of compounds having only minor differences in their partition coefficients should be efficiently separated by high-speed countercurrent chromatography. 

In the laboratories of the authors, simultaneous PIT/PIV measurements with TLCs are performed and a flow in a mini chaimel is investigated (Fig. 10). The illumination is done by two 250 W halogen cold light sources, and the images are acquired by a high-speed color CMOS camera with a long-distance microscope. With this measurement setup, measurements with a frequency... 

For N-RPC, M-RPC, U-RPC, and S-RPC separations, the preparative plates must be prepared by casting adsorbent on the plane parallel glass rotors. After the layers have dried, they are shaped by scraping with a special tool. Since these layers rotate at high speed, more binder has to be used than in conventional TLC insufficient binder results in layers which are very soft, loose, and powdery on the surface, with a tendency to crack. The slurry has to contain a certain amount of water to ensure regular flow very liquid slurries will not give an homogeneous layer whereas a thick slurry will not flow readily. 

The shape and size of the spot produced on chromatograms are decisively influenced by the amount of solute, the volume of the solution applied, the diameter of the spot at the start, and series of other factors. In an attempt to standardize the quantification in TLC, Mohammad and Tiwari (141) and 0. Shadrin et al. (143) have established a linear relationship between the size of the spot and the amount of inorganic anions. A representative plot is given (Fig. 6). A. Timeibaev et al. (164) have determined Ti in sulfite-cellulose liquor and high speed steel by visual colorimetry or by planimetry using a calibration graph. 

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