Columns carbon loading

Even if chain length is the key parameter, the ligand bonding density (usually above 2.5 umol/m ) may be very influential in determining overall stationary phase hydrophobicity. When the monolayer capacity, theoretically estimated by [L]j, increases as a result of increased bonding density, adsorption competitions are less operative and enhanced retention is expected. It should be noted that ligand bonding density can be calculated on the basis of the column carbon load and the total surface area of the column. 

Figures 10 and 11 show the structure of the hindered phenolic antioxidant Irganox 1010 (Ciba) and its negative ion APCI mass spectra, respectively. Separation was achieved under the following LC conditions Column Aqua Cl 8 (Phenomenex) 3 pm, 150x2.00 mm, 15% carbon loading, proprietary end capping. Column Temp 50°C. Injection volume 5 pi.

A similar study has been carried out in order to test the capacity of RP-HPLC for the authenticity test of chilli powders on the basis of pigment composition. Carotenoid pigments were extracted by shaking 3 g of chilli powder with 10 ml of acetone for 30 min. The supernatant was decanted and the procedure was repeated as the solid rest was nearly colourless. The collected organic phases were evaporated and redissolved in the mobile phase. Separations were performed on a narrow-bore ODS column (150 X 2 mm i.d., carbon loading, 9.5 per cent). Eluents A and B were methanol-ACN (80 20, v/v) and bidistilled water, respectively. Gradient elution was initiated by 15 per cent A increased to 80 per cent A in 25 min, held for 10 min, increased to 90 per cent A in 10 min, held for 10 min, increased to 97 per cent A in 3 min and held for 62 min. Each step of gradient elution was linear. Measurements were... 

Figure 3.11 Comparison of the retention of toluene to decylbenzene as a measure of hydrophobicity of different octadecyl-bonded silica gels with different carbon loadings. Columns , LOC-ODS-E O, LOC-ODS-NE O, HIC-ODS-E A, HIC-ODS-NE eluent, 80% aqueous acetonitrile at 30 °C. Compounds. 1, toluene 2, nonylbenzene.

The most widely used support substance for the manufacture of packing materials in analytical HPLC columns is silica. Silica can be treated with organochlorosilanes or similar reagents to produce siloxane linkages of any derived polarity similar to what is done for GC columns (stationary phases). The most popular materials are octadecyl silane (ODS), which contains a carbon loading of CIS groups and octyl, which contains C8 groups materials such C2, C6, and C22 are also available. 

Column Particle size ( lm) Length (mm) ID (mm) Pore size (A) Surface area (mVg) Carbon load (%) End capping pH range... 

Solid supports for RP-HPLC are, in most cases, silica gel derivatized with cyano, C4, C8, Q8, or diphenyl groups and, therefore, have limited stability at pH values <2.0 or >8.0. Less commonly used supports are polymer based that will withstand high pH. Besides their carbon load, silica gel particles can be of different sizes, shapes, and with pore sizes ranging from 80 to 500 A. Literally hundreds of different columns are available.147 48 A commonly used particle is spherical, 5 pm in diameter, and with 300-A pore size. Whereas C4 and C8 columns are preferred for proteins or very hydrophobic peptides, C18 is most commonly used for a wide variety of peptides. 

The column, filled with 100 mg of octadecyl silane (ODS-3,10.5% carbon load, end capped), is preconditioned with 1 ml of methanol and 2 ml of water. The SPE column is washed with 500 pi of a solution of 5 mM potassium dihydrogenphosphate, 10% (v/v) of methanol. Analytes are eluted with 300 pi of methanol and centrifuged at... 

Studies on solid supports have shown that tlie pore size of the silica-based sorbents is of little importance in MSPD, but it should be considered as could vary with the sample. Particle size is of greater importance since particles as small as 3-20 m can lead to extended solvent elution times and plugged MSPD columns. However, 40 m particles with 60 Angstrom pores have been used extensively and successfully. Sorbents that have a blended range of particle size such as 40-100 m work equally well and can be used in most applications (101, 103). These materials also tend to be less expensive. Depending on the application, analysts can also use non-end-capped materials and materials with a range of carbon loading. Different applications may benefit, suffer, or be unaffected by these parameters, but workers should consider them to obtain the best extraction efficiency and the cleanest sample. 

Cl 8, 5 m, end-capped with 20% carbon load, analytical and guard column... 

The importance of the amount of carbon load on the column, which varies widely between columns from different manufacturers, has been discussed for a long time. The differences in chromatographic retention and selectivity are a result of the utilization of different silica materials as supports and a variety of reagents and procedures to produce the bonded phases. Several studies have shown that the capacity factor, k, generally increases with increasing carbon content (12). However, sometimes the results show that k values are not always correlated with the differences in carbon content. This may be explained, as Unger (13) illustrates, by the fact that the carbon content alone is often misleading in the comparison of columns because of differences... 

Table 3 Capacity Factors for the C12 0, C18 3, and C20 4 Derivatives on Columns with Differing Percentages of Carbon Load...

Barbiturates Barbital, phenobarbital Separated on a C-18 high carbon loaded silica column mobile phase methanol-water detected by UV at 254 nm... 

The dominant stationary phase in HPLC is modified silica and, to be more specific, octadecyl silica (ODS). It should be pointed out that there could be great differences between various types of ODS materials or even between different batches of the same material. Carbon load, free silanol content, endcapping, type of silica, and coupling chemistry to the Cig moiety, not to mention the several physical characteristics of the packing material all involve the behavior of an ODS column. However, a rather safe generalization is that, in such material, hydrophobic interactions are a dominant mechanism of separation [3-7]. 

The cesium-enriched concentrate will be passed through columns containing a zeolite such as Linde (Union Carbide Corp.) AW-500 (chabazite) where the cesium will be absorbed. Two columns are used in tandem to increase efficiency when the first column is loaded with cesium, the flow will be diverted to the second column, and a fresh column will replace the first column. The spent sodium carbonate will be recycled back to the feed. The zeolite containing the cesium will go to the solidification plant. 

The discrepancies with the HPLC method are probably due to the imperfect nature of the C18-silica columns. Some of the new-generation reverse-phase materials, such as C18-alumina, polymeric C18, ultra-high carbon-loaded CT8, and porous graphitic carbon may overcome these problems. A recent development is an immobilized artificial membrane (lAM) column, which should more closely model the biological membranes. 

The influence of inlet concentration of MTBE on the performance of an activated carbon adsorption column was studied in three references [27,34,55]. The authors found that the influent concentration of MTBE shows a strong correlation with capacity, a higher concentration resulting in a higher carbon loading [27,34]. The carbon usage rate was found to increase with the inlet concentration [34,55]. 

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