Particle size analysis silica compounds

As with other types of solutes, chromatographers have attempted to improve the speed and efficiency of analysis of bases by fhe use of smaller particle (e.g., sub-2 p,m) or monolithic columns. Small particle columns have not yet been fully evaluated for the analysis of bases, to determine whether they give equivalent selectivity, and reduction in plate height commensurate with the reduction in particle size, as has been demonstrated for neutral compounds. Commercial silica monolith columns give reasonable performance for the analysis of bases at low pH, but show evidence of... 

Polynuclear aromatic hydrocarbons at trace concentrations may be analyzed by HPLC, GC and GC/MS by US EPA Methods 610, 8100, 8270 and 8320 (US EPA 1997). GC techniques involve the use of a flame ionization detector and a fused silica capillary column or a packed column such as 3% OV-17 on Chromosorb W-AW or equivalent. Certain PAH compounds may coelute on a GC column. This problem does not occur in the reversed phase HPLC analysis using UV and fluorescence detectors. A column such as HC-ODS Sil-X or equivalent having a 5-/Lim particle size is suitable for separating PAH mixtures. GC/MS is a confirmative method to identify individual compounds although some of the compounds produce the same characteristic masses. The compounds should be identified from fheir characferisfics mass ions and refenfion times. Various analytical methods and the characteristic mass ions of some... 

The separation characteristics of a considerable variety of other TLC supports were also tested using different dye mixtures (magnesia, polyamide, silylated silica, octadecyl-bonded silica, carboxymethyl cellulose, zeolite, etc.) however, these supports have not been frequently applied in practical TLC of this class of compounds. Optimization procedures such as the prisma and the simplex methods have also found application in the TLC analysis of synthetic dyes. It was established that six red synthetic dyes (C.I. 15580 C.I. 15585 C.I. 15630 C.I. 15800 C.I. 15880 C.I. 15865) can be fully separated on silica high-performance TLC (HPTLC) layers in a three-solvent system calculated by the optimization models. The theoretical plate number and the consequent separation capacity of traditional TLC can be considerably enhanced by using supports of lower particle size (about 5 fim) and a narrower particle size distribution. The application of these HPTLC layers for the analysis of basic and cationic synthetic dyes has also been reviewed. The advantages of overpressured (or forced flow) TLC include improved separation efficiency, lower detection limit, and lower solvent consumption, and they have also been exploited in the analysis of synthetic dyes. 

The columns are generally packed with silica gel. For the separation to be successful, the size of the silica gel particles should be 40-63 pm. A concentrated solution of the sample is prepared. The sample solution is applied at the top of the column, and the walls of the column are washed with a few milliliters of eluent. Solvent is added to the column, and air pressure is applied at a flow rate of 2 in./min to rapidly elute the desired impurity and/or degradant. Separation is based upon the differential interactions between the solute molecules and the adsorbent surface of the silica gel. Fractions are continuously collected and monitored by chromatographic techniques (HPLC with UV detection, GC, or TLC). The fractions containing the compound of interest are combined and evaporated to dryness. The isolated material is cleaned (post isolation cleanup, such as small-scale column or analytical HPLC reinjection, is essential) and submitted for LC-MS and NMR analysis. 

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