Trapping column

H. G. J. Mol, H.-G. Janssen and C. A. Cramers, Use of open-tubular trapping columns for on-line extr action-capillar y gas cliromatography of aqueous samples , 7. High Resolut. Chromatogr. 16 413-418 (1993). 

An alternative way of eliminating water in the RPLC eluent is to introduce an SPE trapping column after the LC column (88, 99). After a post-column addition of water (to prevent breakthrough of the less retained compounds), the fraction that elutes from the RPLC column is trapped on to a short-column which is usually packed with polymeric sorbent. This system can use mobile phases containing salts, buffers or ion-pair reagents which can not be introduced directly into the GC unit. This system has been successfully applied, for example, to the analysis of polycyclic aromatic hydrocarbons (PAHs) in water samples (99). 

The IEX—Dual Trap RP system configuration (Fig. 13.2) directs first-dimension IEX effluent to two alternating reversed-phase trap columns (typically 2.1 x 10 mm... 

FIGURE 13.2 Schematic of a comprehensive 2DLC (IEX/RP) configuration with alternating sampling of first-dimension IEX eluent by two RP trap columns, and a single downstream analytical RP column. A salt diversion valve is present to divert salts from the IEX dimension to waste, and prevent contamination of downstream collected fractions or mass analyzer. 

Achiral-chiral LC-LC is most often used to separate the desired analyte from interfering components, such as matrix components, metabolites, excess derivatiza-tion reagent, or other impurities. Separating such interferents from the analyte allows for better analyte quantification or enantiomeric ratio determination. Also, achiral columns are seen as a way to protect the more expensive chiral columns from matrix components that might become irreversibly retained and deteriorate column performance. Short achiral columns (trap columns) are sometimes used to reconcentrate the chiral analyte after a previous separation (either chiral or achiral) as a type of online enrichment. Configurations that combine an achiral column for increased selectivity and trap column(s) for online enrichment are relatively common, though this type of configuration requires more columns and increases complexity. 

Additionally, the inj ected matrix must also be miscible with the solvents used in the separations. For normal phase mode separations, all water must be removed from the injected matrix. Since many of the complex matrixes, such as plasma, urine, and other biological fluids contain a large amount of water, this requires more time consuming sample preparation. However, water can be injected into a polar organic or reverse phase mode separation. Even within the same mode, mobile phases that are very different can cause large disturbances in the baseline. Oda et al., (1991) solved this problem by inserting a dilution tube followed by a trap column in order to dilute the mobile phase used on the achiral column. Following the dilution tube, a trap column was used to reconcentrate the analyte of interest before the enantiomeric separation. 

Figure 5.20. a Chromatogram of stibine, methylstibine, and dimethylstibine as separated by the OV-3 trap/column with the quartz furnace/AA detector. The stibines were prepared by the NaBH4 reduction of 2 ng Sb each as Sb (III), methylstibonic, and dimethylstibonic acid, b Analysis of a sample of seawater (100 ml) from the open Gulf of Mexico (Station SN4-3-1, 12 March 1981)... 

The planar acetyl groups lie close to planes perpendicular to the helix axis, and project at angles of 120° apart. This allows the chains to hydrogen-bond side by side in a variety of trigonal and hexagonal arrangements, invariably trapping columns of water molecules. The... 

Hopfgartner et al. (2002) compared ternary column online SPE LC/MS and TFC with offline 96-well plate SPE LC/MS to quantitate three drug candidates in human plasma. A protein precipitation step was performed before the SPE LC/MS. Dual trapping columns (YMS AQ, 10 x 2.0 mm, 5 /tm) were used with an analytical column (Intertsil Phenyl, 50 x 2.1 mm, 5 /tm). The run cycle was 3 min calibration range was 0.2 to 250 ng/mL. The run cycle was 2 min with a calibration range of 5 to 1000 ng/mL for TFC. Offline SPE LC/MS achieved the same calibration range with a run time of 2 min. 

Step 1 Condition autosampler sample loop and liquid transfer line with water from pump 1. Condition trap column 1 and analytical column with 95 to 100% water delivered from pumps 3 and 4 during equilibration. Switching valve A = off switching valve B = off. 

Step 2 Sample injection from autosampler into trap column 1 for 3 to 5 min using 100% pump 1. Sample is focused, filtered, and concentrated in trap column 1. Condition pumps 3 and 4 to 95% water in composition. Switching valve A = on switching valve B = on. 

FIGURE 14.12 Fully automated nano HPLC-MS with autosampler injection of large sample volume using two parallel online sample trapping, concentrating, desalting, and filtering columns. Pumps 1 and 2 transfer sample from loop of the autosampler into trap column 1 while pumps 3 and 4 elute sample in trap column 2 into the analytical column then to MS. 

Step 4 Clean autosampler sample loop and trap column 1 using 90% organic solvent from pumps 1 and 2 and then condition trap column 1 and sample loop with 100% water from pump 1. Continue to run gradient elution of sample from trap column 2 and analytical column using pumps 3 and 4 until the end. Switching valve A = on switching valve B = on. 

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