Recent advances in column switching high-performance liquid chromatography for bioanalysis

Online restricted access molecularly imprinted solid-phase extraction coupled with liquid chromatography-mass spectrometry for the selective determination of serum bile acids

“…Moreover, the backflush mode led to a more stable system, reducing the possibility of void volume formations restoring its initial particles distribution by backwashing the extraction column in every cycle. 26,27…”

“…Moreover, the backflush mode led to a more stable system, reducing the possibility of void volume formations restoring its initial particles distribution by backwashing the extraction column in every cycle. 26,27 The composition of the mobile phase was tested changing the organic proportion from 80% to 95% of methanol. Flow rate was evaluated from 0.2 to 0.6 mL min −1 .…”

A Review of Advances in Bioanalytical Methods for the Detection and Quantification of Olanzapine and Its Metabolites in Complex Biological Matrices

“…Using the column-switching approach, the SPE sample preparation technique can be easily combined with a chromatography instrument to provide such an on-line system. This system consists of two high-pressure pumps, an automatic six-port valve, a pre-concentration column, and an analytical column [ 96 ]. On-line SPE cartridges are commonly called pre-columns because the first cartridges used were the same pre-columns used in HPLC to protect analytical columns [ 97 ].…”

“…Then, using a six-port valve, the flow direction of the mobile phase is changed to the analytical column, where the chromatographic separation of the analyzed compounds takes place. Elution can be carried out in two different ways, as shown in Figure 11 [ 96 , 100 , 101 ]. In the straight-flush mode, the mobile phase flows in the same direction as in the purge step [ 93 ], while in the back-flush mode, the mobile phase flows in the opposite direction to the purge step [ 91 , 92 , 93 , 95 ].…”

“…In the straight-flush mode, the mobile phase flows in the same direction as in the purge step [93], while in the back-flush mode, the mobile phase flows in the opposite direction to the purge step [91][92][93]95]. In practice, the back-flush mode is more often chosen because, in this configuration, the endogenous components absorbed at the beginning of the purification column are directed to the waste, thus minimizing the matrix effect, and highly retained analytes are easily transferred to the analytical column in the elution step [96]. In addition, as an alternative to the column-switching approach, there are also several fully automated on-line SPE devices on the market, such as the ASPEC XL (Gilson, Middleton, WI, USA) used by the team of O. V. Olesen (2001), which in this instance allowed direct connection to the HPLC-UV system [102].…”