Post-extraction cleanup

Trace analysis of soil samples often requires post-extraction cleanup to remove coextracted matrix interferences. There are several difficulties that may arise during chromatographic analysis due to interferences present in sample extracts. To avoid these and other issues, one or more of the following cleanup techniques are often used. 

HPLC/MS and HPLC/MS/MS analyses are susceptible to matrix effects, either signal enhancement or suppression, and are often encountered when the cleanup process is not sufficient. To assess whether matrix effects influence the recovery of analytes, a post-extraction fortified sample (fortified extract of control sample that is purified and prepared in the same manner as with the other samples) should be included in each analytical set. The response of the post-extraction fortified sample is assessed against that of standards and samples. Matrix effects can be reduced or corrected for by dilution of samples, additional cleanup, or using calibration standards in the sample matrix for quantitation. 

The systems described thus far addressed only a portion of the individual tasks required to elucidate DNA sequence. A more efficient process would fully integrate the tasks of DNA extraction, purification, template preparation, and amplification with sequencing reaction chemistry, post reaction cleanup, separation, and detection [152]. Several groups have explored partially integrated systems intended to streamline various steps in this process [152-156],... 

The rest of the examples in this report involve liquid chromatography and either pre- or post-column sample treatment. Table I will give the reader some idea of the analyses which can be done and what kinds of treatment and detectors are in use. Pre-column treatment, for example, may include cleanup by dialysis, by chromatography, by extraction, by distillation, or by precipitation of protein. Pre-column concentration may be done by chromatographic column or by evaporation. And pre-column derivatization may involve digestion or simpler reactions. At the other end of the table, post-column derivatives have been made for use with both fluorescent and colorimetric detectors. 

Crop Extraction and Cleanup (OPA-MERC). GLYPH and AMPA were extracted and cleaned up prior to post-column fluorogenic labeling HPLC determination in exactly the same manner as for the FM0CC1 procedure with the exception that the concentrated highly acidic fractions from the 50W - X8 columns were adjusted with 10 M KOH to pH 3-8. This was necessary in order to prevent adverse shifting of the HPLC mobile phase pH and subsequent shifts in retention and deterioration of peak shape. 

FI liquid-liquid extraction systems may be coupled to gas and liquid chromatographs in all the three modes presented in Sec. 3.4.6. The objectives for the separation may involve sample cleanup or/and preconcentration for gas and liquid chromatography, but also post-column derivatization for the latter, in fact most applications in the latter field belong to this category. 

Immunoaffinitv assay The Irnmunoaffinity assay which Involves the use of an antibody column that traps the mycotoxins has been used for AFBl, AFMl and OTA (8, 9, 13, 36, 83,84). The toxin can be then eluted from the column for subsequent analysis or adsorbed In a solid-phase to which the fluorescence Is then read directly. Thus, the affinity column serves as a specific cleanup and concentration tool for the analysis. Recent advances In Improvement of Instrumentation of fluorescence detection and post-column derlvatlzatlon have led to a wider application of this method for AF detection. An AOAC collaborative study showing good result has been completed (85). In such an assay, AF extracted from the sample Is first diluted with buffer at pH 7.0 and then subjected to a disposable affinity column containing antl-AF antibody Sepharose gel. After washing, AF Is removed from the column with methanol, subjected to treatment with Iodine solution, and the fluorescence determined. Nevertheless, this method cannot be used for mycotoxins, such as TCTCs, which do not have high fluorescence or a chromophore. 

Zhang, X. H. and Chen, J. M. 2005. HPLC analysis of alfatoxins in medicinal herb extracts by immunoaffinity column cleanup and post-column bromination. J. Chiru Mat. Med. 30 182-186. 

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