Continuous-flow cleanup

In some instances, microdialysis sampling can be coupled on-line with mass spectrometry without prior separation or cleanup with techniques such as GC or LC. Continuous flow fast atom bombardment (cfFAB) has been used for the ionization of microdialysis samples without prior sample preparation. Coupling micro-dialysis directly to mass spectrometry via FAB was more feasible with cfFAB because it provided for a more robust, efficient ionization and prevented source fouling. 

Concentration using aCi8 SPE Continuous-flow (methanol), high-temperature (65°C), sonicated extraction system to isolate APEO metabolites from sediment samples (low-power ultrasonic energy) sediment extraction was complete after 7 min with a total solvent consumption of 3.5 ml/sample two-step cleanup, normal-phase SPE, reversed-phase... 

March 11,2011, Fukushima, Japan. A near-record earthquake with a 9.0 magnitude occurred off the northeast coast of Japan. It produced a nearly 50-foot high tsunami that flowed over protective walls, killed more than 19,000 people and destroyed or collapsed more than one million buildings. The nuclear reactors at Fukushima withstood the earthquake, but not the tsunami. Within three days, three reactor cores had melted. Within a few months, the plant lost other parts also. The event cause a release of large amounts of radiation. Officials evacuated more than 100,000 people from their homes to prevent radiation sickness. The cleanup continued for many months. 

In order to keep the impurity levels in the reactor water low, a continuous flow of the water is passed to the reactor water cleanup system, which in most of the plants is equipped with precoat filters with powdered ion exchange resins. 

An automatic method for the separation and determination of RF vitamin in food samples (chicken liver, tablet, and powder milk) is proposed by Zougagh and Rios [2], The method is based on the online coupling of supercritical fluid extraction (SFE) with a continuous flow-CE system with guided optical fiber fluorometric detection (CE-CE-ED). The whole SFE-CF-CE-FD arrangement allowed the automatic treatment of food samples (cleanup of the sample followed by the extraction of the analytes), and the direct introduction of a small volume of the extracted material to the CE-ED system for the determination of RF vitamins. Fluorescence detection introduced an acceptable sensitivity and contributed to avoidance of interferences by nonfluorescent polar compounds coming from the matrix samples in the extracted material. Electrophoretic responses were linear within the 0.05-1 pg/g range, whereas the detection limits of RE vitamins were in the 0.036-0.042 pg/g range. 

There are two general types of multidimensional chromatography separation schemes those in which the effluent from one column flows directly on to a second column at some time during the experiment, and those in which some type of trap exists between the two columns to decouple them (off-line mode). The purpose of a trap is often to allow collection of a fixed eluate volume to reconcentrate the analyte zone prior to the second separation step, or to allow a changeover from one solvent system to another. The use of offline multidimensional techniques (conventional sample cleanup) with incompatible mobile phases, is common in the literature, and replacing these procedures with automated on-line multidimensional separations will require continuous development efforts. 

The columns are generally packed with silica gel. For the separation to be successful, the size of the silica gel particles should be 40-63 pm. A concentrated solution of the sample is prepared. The sample solution is applied at the top of the column, and the walls of the column are washed with a few milliliters of eluent. Solvent is added to the column, and air pressure is applied at a flow rate of 2 in./min to rapidly elute the desired impurity and/or degradant. Separation is based upon the differential interactions between the solute molecules and the adsorbent surface of the silica gel. Fractions are continuously collected and monitored by chromatographic techniques (HPLC with UV detection, GC, or TLC). The fractions containing the compound of interest are combined and evaporated to dryness. The isolated material is cleaned (post isolation cleanup, such as small-scale column or analytical HPLC reinjection, is essential) and submitted for LC-MS and NMR analysis. 

Audunsson [29] reported on a sandwich-type extraction module equipped with liquid membranes, prepared by immersing hydrophobic microporous membranes (e.g. PTFE membranes) in organic solvents for about 15 min. The inert men ranes then act as supports for the immobilized solvent. When an aqueous sample passes by the membrane, non-ionic components in the sample are extracted into the hydrophobic liquid film and transferred into an appropriate acceptor solution on the other side of the membrane. When the acceptor remains stagnant while the sample flows continuous ) for a defined period, a preconcentration is effected in the acceptor solution, which is subsequently transferred to the detector. The procedure is equivalent to extraction and back-extraction in a single step. More details on such a system used for sample cleanup in gas-liquid chromatography is presented in Sec. 3.7. 

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