Column packing balanced density

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. 

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. 

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. 

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

A gas chromatographic method using a gas density balance detector has been described407 for the determination of chlorinated phenylchlorosilanes using a column packed with Celite 545 supporting 10% of Lukopren G 1000 (a silicone elastomer), with nitrogen as carrier gas. 

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... 

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. 

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]. 

The distribution of the solute between the mobile and the stationary phases is continuous. A differential equation that describes the travel of a zone along the column is composed. Then the band profile is calculated by the integration of the differential mass balance equation under proper initial and boundary conditions. Throughout this chapter, we assume that both the chemistry and the packing density of the stationary phase are radially homogeneous. Thus, the mobile and stationary phase concentrations as well as the flow velocities are radially uniform, and a one-dimensional mass balance equation can be considered. 

Sie et al. [601—603] analysed silicon and tin in different alloys and steel samples. A sample of the material (1-50 mg) was heated at 600-900° C in a quartz tube, which was then washed with chlorine. Chlorides were trapped in a colum packed with 15% of Kel-F 40 on Haloport F and analysed on the same column at 75°C. With the use of a gas-density balance and PTFE-coated filaments a sensitivity of 50 ppm was obtained for silicon. The analysis time of 15—20 min can be reduced to 10 min. 

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