Coupling instrumentation

This chapter will cover some of the more common accessory items for compressors such as the lubrication system, gears, coupling, instrumentation, vibration monitoring, and process control. The subject is broad and far-reaching. It is hoped that, for the first-time user, this discussion will be a good introduction and, for the veteran, it may offer another perspective on the subject. 

A major concern in the development of coupled instrumental methods is the interface that links the separation module to the detector. Many factors must be addressed, including adjustments of the experimental conditions to accommodate the flow rate of gas or liquid from the chromatographic column. The nature of the liquid eluents is also important in the operation of the detector. Thus, the design of new and improved interfaces has been the subject of a number of reports. 

Mass spectrometers coupled with gas and liquid chromatographs (GC-MS and LC-MS) result m versatile analytical instruments that combine the resolving power of the chromatographs with the exquisite specificity and sensitivity of a mass spectrometer. Such instruments are powerful analytical tools that are used by clinical labs to identify and quantify organic analytes. They provide structural and quantitative information in real time on individual analytes as they elute from a chromatographic column. These coupled techniques are very sensitive and only nanogram or picogram quantities of an analyte are required for analysis. Specific apphcations of these coupled instruments are found in Chapters 33 and 34. 

Additional features possible such as performing combinatorial synthesis or other reactions in the same device or a coupled instrument... 

The basic design of the gas chromatograph can be fitted with a range of specific injectors, columns and detectors to optimize the separation of components and aid their identification. Recent developments in computer control, the use of robotic autosamplers and the trend to couple instruments together for sequential procedures have lead to increased automation for routine analytical tasks performed by GCs in research, factory and quality control environments. 

However, in order to couple instruments successfully three requirements have to be fulfilled. First, the interface must be simple, inexpensive and must not degrade performance. Second, the time scale in which the instruments operate must be compatible. Third, the combination must offer some advantage over the use of the individual components. 

We have seen that NMR can provide detailed molecular structure information. It is possible to join together or couple an HPLC instrument with an NMR spectrometer. The HPLC performs the separation of a complex mixture and the NMR spectrometer takes a spectrum of each separated component to identify its structure. We now have a new instrument, an HPLC-NMR instmment. We call a coupled instrument like this a hyphenated instmment. The coupling of two instruments to make a new technique with more capabilities than either instmment alone provides results in a hyphenated technique or hybrid technique. HPLC-NMR is made possible with a specially designed flow probe instead of the standard static probe. For example, Bruker Instruments (www.bruker-biospin.com) has a flow probe for proton and C NMR with a cell volume of 120 p,L. Complex mixtures of unknown alkaloids extracted from plants have been separated and their stmctures completely characterized by HPLC-NMR using a variety of 2D NMR... 

FIGURE 9.5 AC-coupled instrumentation amplifier designs. The classical design using an RC high-pass filter at the inputs (a) and a high CMRR quasi-high-pass amplifier as proposed by C.C. Lu (b). 

Principles and Characteristics Simultaneous thermal analysis techniques, such as TG-DSC/DTA offer vital information on polymer structure based on heat flow behaviour and mass change [290], but little direct information on the composition of evolved gas products. A more complete thermal profile is provided when a thermal analyser is coupled to an identification tool. Henderson et al. [433] have recently described TG-DSC/DTA with evolved gas analysers (MS and FTIR). The skimmer coupling is the most advanced commercial way of combining a thermobalance or simultaneous TG-DSC/DTA instrument with a quadrupole mass spectrometer [338]. For descriptions of interface techniques in this coupled instrumentation, cfr. ref. [411]. Simultaneous TG-DSC-MS is capable of operation up to 2000°C [434]. 

In his book Philosophy of Sciences published in 1836, Andre Marie Ampere made use of the strange term cyber-netique, which in its modern concept denotes the multi-scient robot of self-organizing machine. It is reasonable to assume that computer-controlled cybermachines, such as the coupled instruments, will soon become essential tools in every modern analytical laboratory. 

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