Serial Mode

Basic Speed Differential between Parallel and Serial Modes... 

In a serial mode (Fig. 36.1), one experimental step (in catalysis research this is usually the preparation of the ligand or the catalyst) is repeated n times before moving on to the next step. The only difference with traditional research is that the complete experiment (synfhesis/testing/analysis) is carried out for a set of catalysts rather than for an individual species. For example, a library of ligands from the same class can be assembled via traditional organic synthesis prior to its testing in catalysis. (A library of compounds is a rather large collection of different compounds with some common features and usually the same function, for example triarylphosphines or imidazolidinones.) Ideally, the compounds in the library can be structurally varied in at least two positions to ere-... 

In the serial mode, the digital word (number) is sent to the computer one bit at a time. Now a binary counter provides a parallel output since each of the output bits has its own data output channel and the value of each output bit is simultaneously available. To use a serial transmission scheme, this parallel output must be put into serial form. One way to accomplish this is to use a Universal Asynchronous Receiver Transmitter (UART). The detailed operation of the UART will not be given here as it is not germane to the subject of this book. It is sufficient to say that the heart of the UART is a shift register and the shift register is strobed by a signal from the computer that displaces the binary number, bit by bit, sequentially from the register to the computer. 

The parallel data transfer mode is simple to use and allows for greater flexibility than the serial mode. However, it requires numerous connections between the PIA and the A/D Converter, and is, therefore limited to those cases where the converter and computer are very close. This type of transmission is very popular in chromatographs which have a built-in dedicated computer. 

Automated sample preparation can be accomplished by using a batch or a serial approach. In the batch mode, multiple samples are prepared and then transferred to the analytical instrument for measurement. In the serial mode, samples are prepared one at a time and the SP device is connected (integrated) with the analytical instrument only. 

The direct measurement of the nonbound fraction is attractive because of its simplicity and since it, in principle, allows the derivation of binding energies. The measurements can here take place in a parallel or serial mode (Fig. 7.7). The... 

The Hewlett-Packard (HP) 7686 PrepStation System workstation allows you to write a program that will condition, load, rinse, and elute your SPE columns (Fig. 10.4, Table 10.4). A dedicated DOS-based ChemStation computer system by HP is required to run the instrument. The software uses a Menu Selectable Approach. The instrument operates in a serial mode and works with HP s disposable SPE cartridges. Individual flow rates for condition, load, rinse, and elute are selected. The workstation may be used to perform volumetric dilutions, sample mixing, bar-code reading, evaporation, and derivatization. When used with an HP 1050 HPLC or HP 5890 GC direct injections are possible. The instrument is also available in a stand-alone... 

There are a few ways of linking the techniques of LC-MS and LC-NMR. The most common method is in a parallel mode by splitting the flow, e.g. 50 1, so as to direct the majority of it to the NMR due to its relative insensitivity. This means that the analytes are detected simultaneously by both detectors and possibly also by UV, which may actually be used as the trigger to begin detection by the NMR and MS modules. Alternatively, the rapidly acquired MS data can be used to direct the NMR experiments or vice versa. A second method of interfacing the two techniques is to use the serial mode or stopped flow mode, which enables more sensitive NMR experiments to be carried out. A recent development in stopped flow NMR is the inclusion of in-line solid phase extraction (SPE) after the LC. The SPE acts as a fraction collector for individual compounds. This trapping/ washing step can improve sensitivity several fold. A third method is fraction collection, where samples from the LC are collected in a loop for analysis later, perhaps after certain data have been reviewed. 

It is the intention of this chapter to illustrate the progress made to date through fast to ultrafast HPLC in a serial mode and then the development and application of parallel HPLC analysis to both of these separation modalities. 

To achieve the best precision and accuracy in the determination a very reproducible procedure is necessary. This is best done if the system is computer controlled, including the handling of magnetic valves, temperature readings and reading of the coulometer. The UIC coulometer is equipped with both a parallel and serial (RS232) port and software to acquire the data in the serial mode is available from the manufacturer. 

Planar chromatography instruments possess incorporated microprocessors, allowing their own functioning and safeguarding of any instructions. The computer is very useful in the case of serial mode instruments use (Figure 8). 

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