Field-flow fractionation retention time

The group of flow FEE is the most improved separation technique within the FEE family. Particularly the asymmetrical flow field-flow fractionation (AF4) provides a broad range of application possibilities. In this case, the separation is caused by different diffusion coefficients (D) by inducing a flow field with a perpendicular liquid flow. A permeable wall (porous frit covered with an ultrafiltration membrane see Fig. 4.10b) allows the cross flow to act as force field. The retention time (t) is given by the following equation ... 

Ftg- 2 Elemental size distributions of the colloidal material in a freshwater sample as given from an FLFFF coupled to ICPMS. A UV detector is placed on line prior to the ICPMS and the UV size distribution is included. The signals are plotted as a function of retention time, hydrodynamic diameter (from FFF theory), and molecular weight (from standardization with PSS standards). Source From Determination of continuous size and trace element distribution of colloidal material in natural water by on-line coupling of flow field-flow fractionation with ICMPS, in Anal. Chem. J... 

Kassalainen and Williams [135] coupled thermal field flow fractionation (ThFFF) and matrix-assisted laser desorption/ionisation time-of-flight mass spectroscopy (MALDI-ToF-MS) to yield a powerful combination of techniques for the analysis of polydisperse PS. ThFFF high selectivity and sensitivity to chemical composition were used to separate polydisperse polymers and polymer mixtures into the narrow polydispersity and homogeneous chemical composition fractions essential for MAT.DT-ToF-MS analyses. On the other hand, because it is possible to measure directly using MALDI-ToF-MS, it alleviates the need for polymer standards for ThFFF. Kassalainen and Williams [135] address the coupling of ThFFF and MALDI-ToF-MS and identify compatibility issues. Optimum conditions were determined and developed to maximise the capabilities of the combined technique. Depending on the polymer and the method of matrix-assisted laser desorption/ionisation (MALDI) sample deposition, fractions from 1-10 ThFFF runs were combined for MALDI-ToF-MS analysis. Binary solvents are used to enhance ThFFF retention and resolution of low (<15 kDa) polymers, and methods developed to allow routine MALDI-ToF-MS analyses of PS polymers up to 575 kDa. Overall, the compatibility of the two techniques was extended from several kilodaltons to several hundred kDa. Polymer... 

Clinical tests of perfluorochemical oxygen carriers revealed three major problems (1) insufficient stability evidenced by coarsening of the emulsion, (2) toxicity, and (3) unsatisfactory retention time of the fluorochemical in blood and in organs. The toxicity and stability are to some extent related. The biocompatibility of perfluorochemical emulsions is impaired by an increase in particle size [35]. The coarsening of fluorochemical emulsions has been attributed the progressive increase in particle size to Ostwald ripening [94-99]. The diameter profiles for the emulsified perfiuorocarbon droplets in Fluosol-DA and Fluosol 43 have been determined by sedimentation field-flow fractionation [96]. 

Retention In field-flow fractionation The retention ratio is generally defined as ratio of the average sample velocity v and the average solvent velocity (v(x)). Equal expressions are obtained by using the dead time to and the retention time of the sample Ir or the corresponding volumes Vo and Vr ... 

In flow FFF, sqraration is driver by a cross-flow field (Rgure 12.8(b)) and yields a Stokes diWeter, a diffusion coefficient, >, and a friction coefficient. Density does not affect the retention time. The measuremoit is fast (1-10 min) and simple. FF Fractionation, Inc. markets an instmment, the F-1000, that is based on this principle. It covers a very wide size range from 0.004 to 80 pm. The upper limit is not restricted by the method, but by the size of the tubing connecting the components, and hertce, can easily be modified to extend the range even further. 

For this study, a bi-phasic bioreactor design was utilized, operating in a semi-continuous flow process, having a hydraulic retention time of four days. Groundwater, with contaminant concentrations as high as 7000 ppm creosote, was treated on-site. This demonstration achieved a removal efficiency of greater than 99% for total polynuclear aromatic hydrocarbons (PAHs). This includes a removal rate of 98% for the most recalcitrant, and most hazardous fraction of the PAHs, and 88% for PCP. The field test proved that biotechnology application for hazardous waste remediation can be effective at an actual waste site. 

---