Slurry packing balanced

Columns consisting of particles of less than 30-50 jum in diameter are prepared most efAciently by slurry packing. Balanced-density slurry packing [11,12] is the most successful of such methods. In this technique, a supporting liquid is used which has the same density as that of the particles. This eliminates sedimentation problems. A typical balanced-density slurry-packing apparatus is shown in Fig.3.42. For the preparation of a... 

Slurry packing techniques are required for the preparation of efficient columns with rigid particles of less than 20 micrometers in diameter. The same general packing apparatus. Figure 4.8, can be used to pack columns by the balanced-density slurry, liquid slurry, or the viscous slurry techniques. Down-fill slurry packing is the method of choice for small bore columns and packed capillary columns. 

The two main methods of packing columns for HPLC are dry packing, which is suitable for particles of diameter > 30 jim, and balanced-density slurry packing which is best for small particles of diameter 5-30 jum. 

Fig. 3.42. Balanced-density slurry-packing apparatus. A, Whitey ball valve B, stainless-steel tubing (0.25 in. O.D. X 0.094 in. I.D.), the lower portion of which is machined to allow it to fit through the body of the Swagelok tee C, small hole in the side of B to allow access of eluting solvent ...

Balanced slurry packing a slurry of the solid support in a liquid with a density identical with that of the solid support is pumped into the column. As a result of the very stable slurry, a homogeneous dense column packing is then... 

Slurry packing is suitable for all types of column for all instances in which the pressure resistance of the column tube is sufficient. The balanced slurry technique, however, needs such high pressure drops in order to obtain reasonable fluid velocities with the rather viscous slurry that in most instances only metal columns can be used. 

Because the halogenated hydrocarbons that have to be used for this are both toxic and expensive, the use of balanced density slurries for packing columns is declining. 

Chromatography. I. Packing of columns Balanced density slurry method was employed and the quality of packed columns was tested chromatographically in methylene chloride. Benzene was injected as testing solute. Columns which gave satisfactory results [l.e., symmetrical elution curve, relative band broadening of 50 ym at linear velocity of 5 mm/sec, and permeability better than 1.10 -9 cm 2] were used for further experiments. 

An HPLC (39) method was developed for determination of the drug and its metabolites in human and rat bile. A stainless-steel column (15 cm X 4.6 mm I.D.) packed with UChrosorb RP-8 (Pore size 5pm) or Nucleasil Ci8 (pore size 5pm) was used. The columns were packed by means of a balanced density slurry method specially developed for the ammonia elution system. Gradient elution was performed with water (0.005 M ammonia) to which methanol was added, according to the desired programme. The final elution was usually effected with 100% methanol. Flow rate was Iml/min. A wavelength of 235 nm was found suitable for the detection of drug and its metabolites. 

Find et al. [25] developed a nickel-based catalyst for methane steam reforming. As material for the microstructured plates, AluchromY steel, which is an FeCrAl alloy, was applied. This alloy forms a thin layer of alumina on its surface, which is less than 1 tm thick. This layer was used as an adhesion interface for the catalyst, a method which is also used in automotive exhaust systems based on metallic monoliths. Its formation was achieved by thermal treatment of microstructured plates for 4h at 1000 °C. The catalyst itself was based on a nickel spinel (NiAl204), which stabUizes the catalyst structure. The sol-gel technique was then used to coat the plates with the catalyst slurry. Good catalyst adhesion was proven by mechanical stress and thermal shock tests. Catalyst testing was performed in packed beds at a S/C ratio of 3 and reaction temperatures between 527 and 750 °C. The feed was composed of 12.5 vol.% methane and 37.5 vol.% steam balance argon. At a reaction temperature of 700°C and 32 h space velocity, conversion dose to the thermodynamic equilibrium could be achieved. During 96 h of operation the catalyst showed no detectable deactivation, which was not the case for a commercial nickel catalyst serving as a base for comparison. 

All analytical HPLC columns with particles < 20 pm (usually 5 or 10 pm) are packed by the slurry technique [19], which can be further classified into the high-viscosity technique and the balanced-density technique. In the latter, the particles are suspended in a fluid that has a density similar to theirs, so particle segregation by sedimentation decreases. In both techniques, the suspending fluid must be chosen in such a way that particle dispersion is maintained without aggregation and particle agglomeration is avoided by proper selection of the polarity of the sluiTy [19], [24]. 

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