Fused-core particle columns

It should be mentioned that there is another type of relatively new column that is made from the 2.7-pm fused-core silica particles, bonded with C18 alkyl chains, by fusing a 0.5-pm porous silica layer onto 1.7-pm non-porous silica cores. The selectivity of the fused-core particle columns is very similar to that of certain <2-pm C18 columns and has the advantage of a substantially lower back-pressure at much higher flow rates, which allows rapid separations to be performed even routinely on a conventional LC system without significant loss in efficiency or resolution. The fused-core columns are new to antibiotic analysis and may serve as good alternatives to <2-pm columns in the field. 

Chocholous, P., L. Kosarova, D. Satinsky et al. 2011. Enhance capabilities of separation in sequential injection chromatography—Fused-core particle column and its comparison with narrow-bore monolithic column. Talanta 85 1129-1134. 

As an alternative to wholly porous sub-2-pm particles, 1.7-pm fused-core particles surrounded by a 0.5-pm porous silica layer with 90 A pores, have emerged. In a comparative study, substantially lower back pressure was reported when the fused-core particles were used. This allowed for columns to be coupled in series, which increased the peak efficiency up to 92,750 plates (164). Wider-pore fused-core particles have an average pore diameter of 160 A. The wider-pore particles are particularly useful for increased sample loading and the rapid separation of peptides using volatile mobile phases (165). 

Of course, with <2 pm particles and/or 20 mm columns, fused core materials, high throughput columns and Chromolith HR, we have noticed tailing and peak broadening due to the instrumental dead volume, especially with the early peaks - even with modern equipment But for simple separations we can live with the loss of 20-40% efficiency, because whether a peak has a peak width of 3 or 4 s will, due to the narrow peak form and a satisfactory separation, not usually be registered from the user as a disadvantage - and then it is no problem. 

Fig. 4 High-pressure fast gradient separation of natural phenolic antioxidants, (a) Ascentis Express CIS column with fused core 2.7 Jtm CIS particles with a thin porous outer shell (0.5 p.m), 30 X 3.0 mm I.D. at 1.5 ml/min, 53 MPa. (b) Acquity BEH Phenyl column with totally porous particles in 1.7 Jtm particles at 1.5 ml/min, 74 MPa, UV detection, 254 nm. Sample 1, gallic acid 2, protocatechine 3, esculine 4, chlorogenic acid 5, caffeine 6, epicatechine 7, vanilline S, rutine 9, sinapic acid 10, hesper-idine 11,4-hydroxycoumarine 12, morine 13, quercetine 14, 7-hydroxyflavone.

The most recent approach in fast LC methodology for the analysis of pesticide residues in food has been presented. UHPLC, using either sub-2 am particle size column or fused-core column technologies, is becoming a reliable alternative to GC-MS methodologies for the analysis of pesticides, with sub-2 am columns being the most popular ones. 

Song, W, Pabbisetty, D., Groeber, E.A., Steenwyk, R.C., Past, D.M. (2009) Comparison of fused-core and conventional particle size columns by LC-MS/MS and UV apphcation to pharmacokinetic study. Journal of Pharmaceutical and Biomedical Analysis, 50,491-500. 

More recently, fused core columns from Supelco and core-shell columns from Phenomenex and Agilent have gained much interest in the field of fast chromatography. The particles used in these columns are made of a sub-1.2 to -2 pim solid core and a 0.35-0.5 p.m porous outer shell, with an overall particle size below 3 p-m, providing a compromise between high efficiency and modest operating pressures. Consequently, one can run these columns on conventional HPLC instruments to obtain very rapid separations. In UHPLC, however, smaller internal diameter columns can be used to reduce solvent consumption. Users can refer to several papers for advantages and applications of these two types of columns (22, 50-52). 

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