Computer, control chromatograph

Overall, the technical complexity of the Deans switch system is considerably greater than that of a mechanical switching valve and it is accepted that reliability and ease of use is reduced as the system complexity increases. For many compound types, however, the completely non-intrusive nature of the Deans method offers sufficient advantages to justify its application. However, the use of modern electronic pressure and flow controls integrated into the overall computer control of the chromatographic system does now make the operation of Deans switches significantly easier or more reliable than has been reported in its earlier applications. 

Each solvent passes from its reservoir directly to a pump and from the pump to a mixing manifold. After mixing, the solvents pass to the sample valve and column. The pumps control the actual program and are usually driven by stepping motors. The volume delivery of each solvent is controlled by the speed of the respective pump. In turn, the speed of each motor is precisely determined by the frequency of its power supply which can be either generated by external oscillators or, if the chromatograph is computer controlled, directly from the computer itself. 

The manifold also receives and mixes solvents from each of the programmed valves. The valves are electrically operated and programmed to open and close for different periods of time by adjusting the frequency and wave form of the supply. Thus, a predetermined amount of each solvent is allowed to flow into the manifold. The valves can be driven by oscillators contained in a separate electronic programmer or if the chromatograph is computer controlled, the controlling waveform and frequency can be provided directly from the computer. 

The mass spectrometry employed electrospray ionization and each metabolite gave an [M + H]+ ion which was then used as a precursor ion for a product-ion MS-MS scan. For subsequent MS" experiments, the base peak of the previous MS-MS experiment was chosen under computer control and this allowed all analytes to be studied in a single chromatographic separation. 

As with most aspects of downstream processing, the operation of chromatographic systems is highly automated and is usually computer controlled. Whereas medium-sized process-scale chromatographic columns (e.g. 5-151 capacity) are manufactured from toughened glass or plastic, larger... 

Two potential disadvantages of temperature programming are the inevitable delay between consecutive chromatographic runs whilst the oven is cooled down and a stable starting temperature re-established, and the possible decomposition of thermally-labile compounds at the higher temperatures. Computer-controlled systems have improved the reproducibility of temperature programming, and automated forced cooling of the oven... 

Today s gas chromatograph is a modern, computer-controlled instrument, consisting of an integrated inlet, column oven and detector, with electronically controlled pneumatics and temperature zones. It has an inlet capable of both the split and splitless-injection techniques and it has a highly sensitive (detection limit in the pictogram range) detector... 

Note As is often the case, the HPLC system will be under computer control, which is likely to be part of a data-handling system. Since the data generated from the OQ hardware tests typically require chromatographic data handling, the data-handling software should be validated beforehand. The data-handlingfLC control software installation and IQ/OQ implementation, which are not addressed in this chapter, may take a considerable amount of time. This is often the case since this process typically involves an initial client/server implementation. 

It is beyond the scope of this chapter to discuss and explain how the requirements can be implemented in analytical laboratories. This has been described in a six-article series published in Biopharm [16-21]. We elaborate here on the validation aspect of the rule. Part 11 requires that computer systems used to acquire, evaluate, transmit, and store electronic records should be validated. This is not new, as processes and steps to validate such systems were described earlier in the chapter. FDA s expectations for validation have been described in the Part 11 draft guidance on validation [4]. This guidance makes it very clear that functions as required by Part 11 should be validated in addition to functions that are required to perform an application such as chromatographic instrument control, data acquisition, and evaluation. Specific functions as required by Part 11 are as follows ... 

The use of small columns such as microbore liquid chromatographic columns, requiring smaller sample size, and computer-controlled solvent delivery and collection systems should lead to the development of fully integrated and automated cleanup systems. Small sample sizes facilitate miniaturization of sample preparation procedures, which in turn brings several benefits including reduced solvent and reagent consumption, reduced processing time, less demand for bench space, and ease of automation. 

Processor or computer control of all or at least some of the chromatograph s parameters. 

In 1990, Bushey and Jorgenson developed the first automated system that coupled HPLC with CZE (19). This orthogonal separation technique used differences in hydrophobicity in the first dimension and molecular charge in the second dimension for the analysis of peptide mixtures. The LC separation employed a gradient at 20 (xL/min volumetric flow rate, with a column of 1.0 mm ID. The effluent from the chromatographic column filled a 10 pU loop on a computer-controlled, six-port micro valve. At fixed intervals, the loop material was flushed over the anode end of the CZE capillary, allowing electrokinetic injections to be made into the second dimension from the first. 

Static headspace extraction is also known as equilibrium headspace extraction or simply as headspace. It is one of the most common techniques for the quantitative and qualitative analysis of volatile organic compounds from a variety of matrices. This technique has been available for over 30 years [9], so the instrumentation is both mature and reliable. With the current availability of computer-controlled instrumentation, automated analysis with accurate control of all instrument parameters has become routine. The method of extraction is straightforward A sample, either solid or liquid, is placed in a headspace autosampler (HSAS) vial, typically 10 or 20 mL, and the volatile analytes diffuse into the headspace of the vial as shown in Figure 4.1. Once the concentration of the analyte in the headspace of the vial reaches equilibrium with the concentration in the sample matrix, a portion of the headspace is swept into a gas chromatograph for analysis. This can be done by either manual injection as shown in Figure 4.1 or by use of an autosampler. 

The computer controlled experimental equipment consists of a feeding system, a gradientless reactor, a gas chromatograph for the analysis of the reaction mixture as well as data processing and control unit consisting of two PCs. A detailed description of the experimental setup can be found in reference [1],... 

The depressurization system acts as an interface between the supercritical conditions in the extraction cell and the atmospheric conditions to which the extract is eventually subjected when the extractor is not connected on-line to a chromatographic system for the individual separation of extracted species with a view to their subsequent detection. A wide variety of commercially available devices for this purpose exists that range from straightforward glass capillaries — the end of which can be readily cut off in the event of clogging — to hand-operated restrictors to computer-controlled units. This is one of the characteristic components of commercial SF extractors (one that can differ markedly among manufacturers). 

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