Liquid-solid chromatography sample cleanup

Removal of interferences is a critical step before analyses of trace level contaminants such as PCDDs and related compounds [111]. Co extractives can occur at much high levels than studied compounds and can complicate identification and quantitation. Extensive sample cleanup techniques which include bulk matrix removal and liquid-solid chromatography are needed to remove coextractives that can interfere with analysis by causing false positives and raising detection limits. 

Using mentioned extraction/deproteinization procedures, the obtained aqueous or organic extracts often represent very dilute solutions of the analyte(s). These extracts may also contain coextractives that, if not efficiently separated prior to analysis of the final extract, will increase the background noise of the detector making it impossible to determine the analyte(s) at the trace residue levels likely to occur in the analyzed samples. Hence, to reduce potential interferences and concentrate the analyte(s), the primary sample extracts are often subjected to some kind of additional sample cleanup such as liquid-liquid partitioning, solid-phase extraction, or online trace enrichment and liquid chromatography. In many instances, more than one of these cleanup procedures may be applied in combination to allow higher purification of the analyte(s). 

Tire aqueous or organic extract obtained at this point may be a very dilute solution containing interfering compounds and making it difficult to determine trace level concentrations of the analyte(s) of interest. To reduce interferences and concentrate the analyte(s), the primary sample extract is furiher subjected to various types of sample cleanup procedures such as conventional liquid-liquid partitioning, solid-phase extraction, matrix solid-phase dispersion, online trace enrichment, liquid chromatography, online dialysis and subsequent trace enrichment, and supercritical fluid extraction. In most cases some of Urese procedures are used in combination to obtain highly purified extracts. 

SIMPLICITY. No complicated equipment is needed for the implementation of solid adsorbents to accumulate organic compounds from water. The procedure is identical to gravity flow adsorption chromatography used for decades by many chemists to remove extraneous material from liquid samples in a process called sample cleanup. The simplicity of this procedure with the reduced sample manipulations minimizes solute losses and sample contamination. 

Solid-phase extraction (SPE) (Fig. 6) is a miniature version of the liquid chromatography experiment. It was commercialized and introduced in the late 1970s. With the availability of prepacked cartridges, SPE first became popular in the mid-1980s [19]. It has been widely applied to sample cleanup in the drug discovery... 

Lagana, A. et al., Sample preparation for determination of macrocyclic lactone myco-toxins in fish tissue, based on on-line matrix solid-phase dispersion and solid-phase extraction cleanup followed by liquid chromatography/tandem mass spectrometry, J. AOACInt., 86(4), 729, 2003. 

Simple dissolving or liquid-liquid extraction with immiscible solvents and pH control is often sufficient. For more complex samples, cleanup of extracts by column adsorption chromatography or a more modem method such as solid phase extraction, supercritical fluid extraction, or solid phase microextraction is usually applied. Cleanup is not as important in TLC because strongly sorbed matrix components that could irreversibly destroy a high-performance liquid chromatography column or carryover and be detected in later samples can be applied onto the plate if the subsequent development and detection of the analyte are not adversely affected. 

A cleanup procedure is usually carried out to remove co-extracted matrix components that may interfere in the chromatographic analysis or be detrimental to the analytical instrument. The cleanup procedure is dependent on the nature of the analyte, the type of sample to be analyzed, and the selectivity and sensitivity of the analytical instrument used in the analysis. Preliminary purification of the sample extracts prior to chromatographic separation involves liquid-liquid partitioning and/or solid-phase extraction (SPE) using charcoal/Celite, Elorisil, carbon black, silica, or aminopropyl-silica based adsorbents or gel permeation chromatography (GPC). 

Crop material is homogenized with acetonitrile-water (9 1, v/v). The crop extract is centrifuged and an aliquot is rotary evaporated to a small volume. The sample is subjected to a Cig solid-phase extraction (SPE) cleanup procedure. The concentrated eluate is subjected to liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis. 

For reliable identification of a residue, detailed information about the molecular structure of the analyte is essential. The total information about the molecular structure of the analyte is the sum of the information derived from each individual analytical step of tire method. Frequently used selective analytical steps based on chromatography or immunoaffinity, provide more or less general indirect information. For example, solid-phase extraction (SPE) cleanup followed by liquid chromatography/ultraviolet detection (LC/UV) has been suggested for screening and quantification of ivermectin residues in liver, but presumptive positive samples can be confirmed by derivatizing an aliquot of the SPE eluate and reanalyzing the fluorescent derivative of ivermectin in an LC-fluorescence system (17). 

Following initial sample extraction, the primary extract must frequently be subjected to some kind of further cleanup including liquid-liquid partitioning, diphasic dialysis, solid-phase extraction, matrix solid-phase dispersion, immunoaffinity chromatography cleanup, liquid chromatography cleanup, or online trace enrichment. In some instances, some of these procedures are used in combination in order to attain higher purification levels. 

Following the primary sample extraction, the crude extract can be further subjected to various types of cleanup procedures including conventional liquid-liquid partitioning, solid-phase extraction, and liquid chromatography cleanup. In some instances, more than one of these cleanup procedures may be used in combination to obtain highly purified extracts. 

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