Extraction clogging

Fluidised beds have been used previously for the industrial-scale recovery of the antibiotics streptomycin and novobiocin.30 However, more recently, considerable interest has been shown in the use of fluidised beds for the direct extraction of proteins from whole fermentation broths.31 In a packed bed, the adsorbent particles are packed within the contactor. The voidage, that is, the inter-particle space, is minimal and thus feedstock clarification is mandatory to avoid clogging of the bed. In a fluidised/expanded bed, the adsorbent bed is allowed to expand by irrigation with feedstock. Bed voidage is increased, allowing the passage of particulates in the feed. The diameters of the adsorbent beads are exaggerated for illustrative clarity. 

Until this point, the sample preparation techniques under discussion have relied upon differences in polarity to separate the analyte and the sample matrix in contrast, ultraflltration and on-line dialysis rely upon differences in molecular size between the analyte and matrix components to effect a separation. In ultrafiltration, a centrifugal force is applied across a membrane filter which has a molecular weight cut-off intended to isolate the analyte from larger matrix components. Furusawa incorporated an ultrafiltration step into his separation of sulfadimethoxine from chicken tissue extracts. Some cleanup of the sample extract may be necessary prior to ultrafiltration, or the ultrafiltration membranes can become clogged and ineffective. Also, one must ensure that the choice of membrane filter for ultrafiltration is appropriate in terms of both the molecular weight cut-off and compatibility with the extraction solvent used. 

On-line dialysis also separates the analyte from tissue matrix based upon molecular size, but in this case, the sample extract is passed over a membrane filter through which the analyte (and other low molecular weight compounds) is diffused into a second solvent on the other side of the membrane filter. Usually, the second solvent is then concentrated on to an SPE column to minimize the dilution effect that is caused by the dialysis process. Agasoester used on-line dialysis to separate oxytetracycline from muscle, liver, milk, and egg tissue matrix components. A problem encountered with on-line dialysis is the inability of analyte molecules that are bound to proteins in the sample extract to pass through the membrane filter. Problems with membrane clogging are reduced with on-line dialysis compared with ultrafiltration because no external force is being applied to bring the analyte across the membrane filter. 

Both GC and HPLC columns are expensive, so it is important not to clog them during analysis. GC columns will be clogged by nonvolatile compounds. For these materials, it is important to use HPLC. Samples must also be free of suspended particles that will clog the finely packed HPLC columns. Filtering samples, especially soil extracts, before injection is essential. 

At this point the checkers filtered the mixture through a pad of 30 g of Cellte to remove the green precipitate. This filtration reduces the problem of emulsions and clogging of the separatory funnel during subsequent extractions. 

Excellent separations of corticosteroids can be achieved on an ODS column with a suitable ratio of methanol/water as an eluent. In this assay hydrocortisone is quantified using betamethasone as an internal standard. The structure of betamethasone is close to that of hydrocortisone but since it is more lipophilic it elutes from the ODS column after hydrocortisone (Fig. 12.12). The assay is a modification of the BP assay for hydrocortisone cream. In the assay described here the internal standard is added at the first extraction step rather than after extraction has been carried out in order to ensure that any losses in the course of sample preparation are fully compensated for. Extraction is necessary in the case of a cream because the large amount of oily excipients in the basis of the cream would soon clog up the column if no attempt was made to remove them. The corticosteroids are sufficiently polar to remain in the methanol/water layer as they have a low solubility in hexane, while the oily excipients are removed by extraction into hexane. The sodium chloride (NaCl) is included in the sample extraction solution to prevent the formation of an emulsion when the extract is shaken with hexane. Solution 2, where the internal standard is omitted, is prepared in order to check that there are no excipients in the sample which would interfere with the peak due to the internal standard. 

ISCOR technology is most applicable to aquifers with hydraulic conductivities greater than 10 " cm/sec. Vertical and horizontal heterogeneities within the aquifer will affect the oxidant s path and distribution rate through the aquifer. Heavy rainfall can back up water in the injection wells or trip the leak detectors and shut down the ISCOR system. Suspended solids from the precipitation of manganese(IV) oxide, undissolved oxidant, or other sources can cause clogging in the injection and extraction wells and uneven distribution of the oxidant. 

In some designs, a glass fiber filter is supported above the extraction disc to prefilter samples containing particulates without clogging the extraction disc. Because of the rigid disc design, frits to support the extraction disc are not necessary. The polyethylene frits used in conventional SPEi columns may be a source of contamination (90) and have a large surface area and void volume. 

Assemble an apparatus (see Fig. 61). Place the dry beads into a porcelain or quartz tube and perform chlorination at 750-800 °C during one hour. Ghromium(III) chloride can sublime, therefore see that the tube outlet is not clogged by the product. Cool the apparatus in a stream of chlorine. Extract the beads from the tube and mechanically separate the chromium chloride formed on their surface from the unreacted charcoal. In what other ways can anhydrous chromium(III) chloride be obtained ... 

The crude extract needs to be further purified for HPLC analysis. Direct injection of the crude extract into the HPLC would clog the frit and analytical column with precipitated impurities (i.e., proteins). 

The sample homogenization with an MeCN THF mixture was used for the simultaneous determination of SMM, miloxacin, and oxolinic acid. The supernatant was filtered and injected directly into the ion-pair chromatographic system using a shielded hydrophobic phase. This method did not require time-consuming and complex extraction procedures moreover, the use of a restricted-access-material column prevented both column clogging and peak broadening throughout the analysis. On the other hand, no preconcentration of the sample affected the LOD... 

The introduction of commercial instrumentation in this automated area has been too slow and too disappointing to meet the need for routine analysis of numerous samples. The options have been the extraction of one sample at a time or individual samples in parallel. Either of these options make the repetitive analysis of the same sample or the sequential analysis of different samples exceptionally time consuming. Parallel analysis, proposed by one manufacturer, is susceptible to cross-contamination and across the board sample loss with clogging of one extraction vessel. In order to move supercritical fluid extraction into the realm of routine operations for residue analysis, rapid analysis of multiple samples needed to be addressed. 

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