Guard column switching

Classical sample preparation procedures such as filtration centrifugation, liquid-liquid extraction, and SPE are effective against blocking by the sample. The most important technology, however, is the guard column switching. The different variants are described in Section 2.7.1.3.5. 

Guard Column Switching and Sample Loading Strat es... 

An online filter was also used to protect the analytical column. A guard column was used before the T to prevent breakthrough. A restrictor was used to balance the pressure before, during, and after the valve switches. After sample transfer, the valve was switched back. With this method, both water-insoluble retinoids and water-soluble retinoic acid were extracted simultaneously. Because of the minimal light exposure of these light-sensitive analytes during the procedure, an extraction recovery of 97 to 100% was achieved with a quantitation range of 100 fmol to 3 nmol. 

Kaiser [3U used on-line sample preparation to determine trace anions in solvents, including isopropanol, acetone and Af-methylpyrrolidone. A large solvent injection can interfere with both the ion exchange separation and the conductivity detection by causing large disturbances in the baseline. In this application the anions were concentrated on a AG9-HC guard column and then the solvent was sent to waste before it could enter the analytical column. After the solvent was cleared from the AG9-HC concentrator column, the AG9-HC concentrator was switched in line with the AS9-HC analytical column for the separation. The method detection limits for chloride, sulfate, phosphate and nitrate are reported in the sub pg/1 range. 

In another method, creams and ointments of a developmental corticosteroid are simply dissolved in tetrahydrofuran-isopropanol (30 60), clarified by centrifugation, and injected directly onto the HPLC column [331]. The automated switching valves direct the analytes plus an internal standard through the guard column to the reversed-phase analytical column,... 

Boppana V, Miller-Stein C, Schaefer WH (1996) Direct plasma liquid chromatographic-tandem mass spectrometric analysis of granisetron and its 7-hydroxy metabolite utilizing internal surface reversed-phase guard columns and automated column switching devices. J Chromatogr B 678 227-236... 

The analysis is started with the guard column and separation column in series. After about 3 min, the valves, controlled by the detector programme, switch over such that the eluent flows past the guard column, direct to the separation column. The columns are switched at a point when the components to be determined, but not the interfering matrix, have reached the separation column. After about 35... 

Figure 4 LC/MS/MS of a mixture of gabapentin and naproxen using polarity switching. Micromass Quattro II, electrospray ionization rat plasma sample prepared by protein precipitation/extraction using a MetaChem 4.6 X 30-mm Polaris column with 3- Xm packing with a MetaChem 2000-MG2 guard column. Flow rate = 2.0 mL/min split 1 10 to MS. Injection volume 10 uL step gradient 100% 0.1% acetic acid, 0—1.0 min 70/30 0.1% acetic acid/acetoni-trile, 1.0—1.5 min 100% acetonitrile, 1.5—2.0 min. (Courtesy of Laura F. Polchinski, Ion Ebright, and Scott T. Fountain, personal communication.)...

Boppana, V.K. Miller-Stein, C. Schaefer, W.H. Direct Plasma Liquid Chromatographic-Tandem Mass Spectrometric Analysis of Ganisetron and its 7-Hydroxy Metabolite Utilizing Internal Surface Reversed-Phase Guard Columns and Automated Column-switching Devices, J. Chromatogr. B. 678, 227-236 (1996). 

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