Off-line coupling

Off-line coupling of HPLC with FD-MS has been used by several authors [118-121] for the determination of oligomers, oligomeric antioxidants (such as poly-TMDQ), ozonation and vulcanisation products. Pausch [122] reported on rubbers, cyclic polyurethane oligomers, as well as on the determination of the molecular weight distribution (up to 5300 Da) and oligomer analysis of polystyrene. Also the components of an aniline-acetone resin were deduced from FD-MS molecular weights [122]. 

In off-line coupling of LC and MS for the analysis of surfactants in water samples, the suitability of desorption techniques such as Fast Atom Bombardment (FAB) and Desorption Chemical Ionisation was well established early on. In rapid succession, new interfaces like Atmospheric Pressure Chemical Ionisation (APCI) and Electrospray Ionisation (ESI) were applied successfully to solve a large number of analytical problems with these substance classes. In order to perform structure analysis on the metabolites and to improve sensitivity for the detection of the various surfactants and their metabolites in the environment, the use of various MS-MS techniques has also proven very useful, if not necessary, and in some cases even high-resolution MS is required. 

M.A. Hawryt and E. Soczewinski, Separation of some flavonoids using RP-HPLC - NP-TLC off-line coupled system. Chromatographia 52 (2000) 175-178. 

Popp, P., C. Bauer, M. Moder, and A. Paschke. 2000. Determination of polycyclic aromatic hydrocarbons in waste water by off-line coupling of solid-phase microextraction with column liquid chromatography. J. Chromatogr. A 897 153-159. 

Delgado-Zamarreno, M.M. Bustamante-Rangel, M. Garcia-Jimenez, M. Sanchez-Perez, A. Carabias-Martinez, R. 2006. Off-line coupling of pressurized liquid extraction and LC/ED for the determination of retinyl acetate and tocopherols in infant formulas. Talanta 70 1094 1099. 

Off-line coupling of leaching to subsequent steps of the analytical process... 

Introduction - Integrated Systems On-line and Off-line Coupling of Meteorological and Air Quality Models, Advantages and Disadvantages... 

However, the on-line approach is not always the best way of the model integration. For some specific tasks (e.g., for emergency preparedness, when NWP data are available) the off-line coupling is more efficient way. 

The communication between off-line coupled meteorological and AQ models is often a problem of underestimated importance. The variety of modelling systems previously introduced give rise to different approaches and methods implemented within interface modules. Tasks covered by interfaces are minimized in coupled systems relying on surface fluxes, turbulence and dispersion parameters (i.e. eddy... 

The Working Group 2 of COST-728 compiled a survey of the multiple and diverse coupled meteorological and air quality modelling systems developed and applied covering mainly European countries. The attention was focused on off-line coupled modelling systems, which are by far the more numerous, even if the number of... 

Off-Line Coupling of Meteorological and Chemical Transport Models... 

For consistent calculation of boundary layer parameters in off-line coupling the land-use classes in the meteorological model should ideally match the land-use classes presented in EMEP (Table 13.2). In the coupling with HIRLAM, where only... 

Feedbacks with the Off-Line Coupled Modelling Systems... 

The Atmospheric Chemistry Transport modelling system used is based on the off-line coupled CAMx and HIRLAM models has been developed to simulate particulate and gas-phase air pollution on different scales. It has been used to simulate short and longterm releases of different chemical species and air pollution episodes. At present it is run in a pre-operational mode 4 times per day based on 3D meteorological fields produced by the HIRLAM NWP model. Currently this modelling system is setup to perform chemical weather forecasts for a series of chemical species (such as O3, NO, NO2, CO and SO2) and forecasted 2D fields at surface are available for each model as well as an ensemble of models (based on 12 European regional air quality models). The simulated output is publicly available and it is placed at the ECMWF website (http //gems.ecmwf.int/d/products/raq/forecasts/) of the EC FP6 GEMS project. 

There is a clear difference in needs for the on-line coupling of chemistry transport models and the off-line coupling. For the off-line coupled models it would advantageous to improve the quality of meteorological outputs, especially for fair weather conditions (including calm conditions and a focus on extreme situations). Parameters that can be used directly in off-line coupled models and that are important for processes like rainout should also be readily available. (It is important to remember that the couplings can be done in two directions not only from NWP to atmospheric CTM, but also from atmospheric CTM to NWP, see above). 

On-line and off-line coupling of meteorological and air quality models... 

Simplest off-line coupling The chemical composition fields from atmospheric... 

In conclusion, it is worth recognizing that the advantages and disadvantages of the on-line and off-line coupling of the meteorological and chemical transport models can depend on the specific task and objective of the applications. Diversity and specifics of the tasks and objectives, in their turn, will require the existence of both approaches for the foreseeable future. 

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