Sample Cleanup Using Liquid Chromatography

Most environmental GC analyses involve a sample cleanup procedure. For example, Schomberg (11) recommends optimized sample cleanup by using liquid chromatography with size exclusion, ion... 

For method tryout, run a control sample and two fortifications from each site. One fortification should be done at the LOQ and the other at the highest expected residue level, perhaps 1000 x LOQ. If the recoveries are within the acceptable range of 70-120% and there are no interferences, proceed with the method validation. If interferences are present which prevent quantitation of the analyte, try additional cleanup steps with SPE or use a more selective detection method such as liquid chromatography/mass spectrometry (LC/MS). 

Residue analytical methods for neonicotinoids in crops, soil and water samples have been developed. The basic principle of these methods consists of the following steps extraction of the crop and/or soil samples with acetone or the other organic solvent, cleanup by liquid-liquid partition or column chromatography, and quantitative analysis by high-performance liquid chromatography with ultraviolet detection (HPLC/UV). Simple column cleanup procedures are used to improve the accuracy and sensitivity of these methods. 

Multidimensional liquid chromatography encompasses a variety of techniques used for seunple separation, cleanup and trace enrichment [12,279-289]. A characteristic feature of these methods is the use of two or more columns for the separation with either manual or automatic switching by a valve interface of fractions between columns. These techniques require only minor modification to existing equipment, and of equal importance, enable the sample preparation and separation procedures to be completely automated. 

SEC in combination with multidimensional liquid chromatography (LC-LC) may be used to carry out polymer/additive analysis. In this approach, the sample is dissolved before injection into the SEC system for prefractionation of the polymer fractions. High-MW components are separated from the additives. The additive fraction is collected, concentrated by evaporation, and injected to a multidimensional RPLC system consisting of two columns of different selectivity. The first column is used for sample prefractionation and cleanup, after which the additive fraction is transferred to the analytical column for the final separation. The total method (SEC, LC-LC) has been used for the analysis of the main phenolic compounds in complex pyrolysis oils with minimal sample preparation [974]. The identification is reliable because three analytical steps (SEC, RPLC and RPLC) with different selectivities are employed. The complexity of pyrolysis oils makes their analysis a demanding task, and careful sample preparation is typically required. 

Tanaka, M., Yamazaki, H. (1996). Direct determination of pantoprazole enantiomers in human serum by reverse-phase high-performance liquid chromatography using a cellulose-based chiral stationary phase and column-switching system as a sample cleanup procedure. Anal. Chem. 68, 1513-16. 

A rapid and simple method for PBDE and HBCD determinations in sediment and fish samples was used. The analytical method was based in selective pressurized liquid extraction (SPLE) [21] without further cleanup step and analysis by gas chromatography coupled to mass spectrometry (GC-MS), working with negative ion chemical ionization (NCI) [22, 23],... 

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. 

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). 

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. 

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. 

The primary sample extract is subsequently subjected to cleanup using several different approaches including conventional liquid-liquid partitioning, diphasic dialysis, solid-phase extraction, immunoaffinity chromatography, and... 

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. 

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