Reversed Phase Silicas

Sixteen solid-phase materials were tested on a laboratory scale and the antho-cyanin and sugar content of collected fractions were determined. Among these, reverse-phase silica gels and macroreticular non-ionic acrylic polymer adsorbents such as Serdolit PAD IV or Amberlite XAD-7 turned out to be most suitable. SPE was used to investigate these materials on an enlarged scale, improving elution gradient and column purification. Amberlite XAD-7 was successfully applied in a middle-scale separation. ... 

Reversed-phase silica gel column Place a cotton wool plug at the bottom of a glass chromatography column. Pack 5 g of reversed-phase silica gel slurried with a solvent mixture of n-hexane-benzene-methanol (80 20 0.4, v/v/v) into the glass column. Place an anhydrous sodium sulfate layer about 1 -cm thick above and below the silica gel bed Bell jar-type filtering apparatus Buchner funnel, 11-cm i.d. 

Reversed-phase silica gel, silica gel ODS-Q3,75A, 30-50-p.m (Wako Pure Chemical Industries, Ltd)... 

Reversed-phased silica gel column chromatography cleanup... 

Dissolve the crop residue samples from Section 6.3 in 0.5 mL of dichloromethane. Transfer this solution to the top of the reversed-phased silica gel column with... 

A PRP -1 (Hamilton Reno, NV) reversed phase column was coated with cetylpyridinium and eluted with tetramethylammonium salicylate acetoni-trile water.89 The separation was comparable to that observed on conventional ion exchange. Coated phases were also used to separate oxalate complexes of manganese, cobalt, copper, and zinc.90 Reversed phase silica supports were coated with poly(N-ethyl-4-vinylpyridinium bromide), poly(dimethydiallylammonium chloride), poly(hexamethyleneguanidinium... 

Albert, K. 1988. Correlation between chromatographic and physicochemical properties of stationary phases in HPLC C30 bonded reversed-phase silica. Trends Anal. Chem. 17 648-658. 

Curran DP (2002) Fluorous Reverse Phase Silica Gel. A New Tool For Preparative Separations in Synthetic Organic and Organofluorine Chemistry. Syn-lett 1488-1496... 

Curran DP, Luo ZY (1999) Fluorous Synthesis with Fewer Fluorines (Light Flu-orous Synthesis) Separation of Tagged from Untagged Products by Solid-Phase Extraction with Fluorous Reverse-Phase Silica Gel. J Am Chem Soc 121 9069-9072... 

Figure 3. Solid phase extraction over fluorous reverse phase silica...

P. W. Schmidt, D. Avnir, D. Levy, A. Hohr, M. Steiner and A. Roll, Small-angle x-ray scattering from the surfaces of reversed-phase silicas Power-law scattering exponents of magnitudes greater than four, J. Chem. Phys., 1991, 94, 1474. 

Reversed phase Silica with long C chain 3-15 C-18... 

A mixture of rhodium II) acetate (228 mg, 0.516 mmol), the imidazolidinone (1.70 g, 6.15 mmol), and dry chlorobenzene (20 mL) is heated under reflux for 18 h in a flask fitted with a Soxhlet extraction apparatus into which a thimble is placed containing an oven-dried mixture of sodium carbonate and sand (2 1, 5 g). The progress of the ligand-exchange reaction can be monitored by HPLC (p-Bondapak-CN column, methanol). The resulting blue solution is concentrated under reduced pressure, and the residue is purified by column chromatography (reversed phase silica, Bakerbond Cyano 40 mm prep. LC packing, methanol). 

Few reports exist on the l.c. separation of such cationic carbohydrate oligomers as those resulting from partial hydrolysis of chitosan. The neutral, A -acetylated analogs from chitin hydrolyses are, however, well separated on columns of aminopropyl silica gel and reversed-phase silica gel. ... 

Although a reductase was not actually applied, separation of 26 from (S)/(R)-20 was accomplished by use of reversed-phase silica as the column material and methanol/ water as the eluant. In view of the observed dependence of the g factor on concentration, aggregation in this protic medium was excluded. In the HPLC setup, the mixture was fully separated within less than 1.5 min. By use of the JASCO-CD-1595 instrument in conjunction with a robotic autosampler, it was possible to perform about 700—900 rather exact ee determinations per day (111). 

In the case of amines the type of interaction shown in Figure 15.9 may occur. The shorter the alkyl chain length on the silica gel surface the more likely it is that adsorption also plays a part in the extraction. It is possible to buy highly endcapped reverse-phase silica gels where most of the residual silanols have been blocked but it may be better to take advantage of the mixed lipophilic and adsorptive properties of reverse phases which have not been endcapped. 

The packing material first described for direct injection of biological samples was prepared by simply saturating the accessible adsorption sites of a Cis reversed-phase silica with human plasma proteins (105). After saturation, the human plasma proteins were denatured at the external surface, and their native conformation was destroyed. With this treatment, the proteins formed a hydrophilic layer with weak ion-exchange properties, which provided protection from contact with the sample proteins, whereas the alkyl ligands inside the pores remained unchanged and thus served for analyte retention. The retention behavior of the saturated phase did not alter with this treatment, but the efficiency was reduced dramatically. Such protein-coated columns have shown a lifetime of several months (106). 

Comparable to the other protein-coated supports are the Ultrabiosep and the BioTrap phases. The former are composed of C4, Cg, or Cis reversed-phase silica supports covered with a biological polymer which is not described in the literature (135). The latter are commercially available as Bio Trap Acid or Biotrap Amine precolumns (136). They are Cis-modified silica supports covered with -1-acid glycoprotein as a biocompatible layer. Due to the immobilized protein, this type of reversed-phase material also possesses weak ion-exchange properties. 

---