Silica pressure gradient mode

N-alkyl silica-based stationary phases typically employed in HPLC separation of peptides and proteins have been investigated to a large extent in CEC mode. In most cases, gradient elution was required to optimize the resolution and analysis time. Tryptic digests maps of cytochrome c by pressurized CEC were better resolved than by pHPLC [93], The experiments were conducted at low pH in the presence of trifluoroacetic acid (TFA) to prevent tailing of basic peptides, on a column packed with 1,5-pm C18 silica particles. It has been... 

A 10% aliquot of the digestion mixture was analyzed on a Vydac C18 250 im ID fu silica cap aiy column connected on-line to ESI-MS (4). A linear gradient of 2% B to %% B in 45 minutes using solvent A (0.1% TFA) and solvent B (90% acetonitrile, 0.07% TFA) was used with a flow rate of 2 jul/min. Sample elution was monitored by UV detection at 200 nm. Mass spectra were recorded in the positive ion mode using a TSQ-700 triple quadrupole instrument (Fiimigan-MAT, San Jose, CA) with an electrospray ion source opo ating at atmospheric pressure. Scans were continuously acquired every three seconds between la/z 500 and 2(XX) in the centroid mode. 

Recently the separation of 10 anthraquinone aglycones and two glycosides from Rheum by capillary electrophoresis was described [88] and compared with an HPLC separation. Two of the investigated aglycones also occur in madder alizarin and purpurin. Because all of the anthraquinones can be charged by means of complexation with a borate buffer, capillary zone electrophoresis (CZE) was chosen as separation mode. The separations were carried out with a 90 cm x 75 pm fused silica capillary. The detection window was located at 80 cm. Dectection occurred at 260 nm. The voltage was 23 kV and the temperature 20°C. The injection was pressure controlled (1.2 sec at 200 mbar). The total run time was 39 min (compared to 63 min for gradient RP-HPLC for the same set of test substances). 

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