Interfaces, coupled instruments

Similar work was performed by Shaw et al.3 in 1999 when they used FT-Raman, equipped with a charge coupled device (CCD) detector (for rapid measurements) as an on-line monitor for the yeast biotransformation of glucose to ethanol. An ATR (attenuated total reflectance) cell was used to interface the instrument to the fermentation tank. An Nd YAG laser (1064 nm) was used to lower fluorescence interference and a holographic notch filter was employed to reduce Rayleigh scatter interference. Various chemometric approaches were explored and are explained in detail in their paper. The solution was pumped continuously through a bypass, used as a window in which measurements were taken. 

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. 

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. 

Capillary Electrophoresis Chips. Some of the first microchip-CE separations have been performed on glass chips that used on-chip miniaturized pneumatic nebulizers, or on-chip or off-chip liquid junction interfaces coupled to a subatmospheric ESI ion trap instrument. - High-efficiency ( 31,000 plates/chip or 300,000 plates/m) separations on 11 cm long channels, or fast separations on 4.5 cm channels, of peptide/protein samples were achieved (Figure 53.17). Some of these chips were also tested for performing transient isotachophoretic sample preconcentration. ... 

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]. 

The control of the airborne sound location system, the coupling monitor and the real-time evaluation of all signals, including the echo indications from the ultrasonic instrument, is carried out on two additional boards in the PC. The graphic user interface (under Windows 95), including online help, enables an easy operation of the system. The evaluation program links all echo indications in real time with the probe position and displays them in a graphic repre-... 

Instrumental Interfaces. The basic objective for any coupling between a gas chromatograph (gc) and a mass spectrometer (ms) is to reduce the atmospheric operating pressure of the gc effluent to the operating pressure in the ms which is about 10 kPa (10 torr). Essential interface features include the capability to transmit the maximum amount of sample from the gc without losses from condensation or active sites promoting decomposition no restrictions or compromises placed on either the ms or the gc with regard to resolution of the components and reliability. The interface should also be mechanically simple and as low in cost as possible. 

One of the attractive features of SFE with CO2 as the extracting fluid is the ability to directly couple the extraction method with subsequent analytical methods (both chromatographic and spectroscopic). Various modes of on-line analyses have been reported, and include continuous monitoring of the total SFE effluent by MS [6,7], SFE-GC [8-11], SFE-HPLC [12,13], SFE-SFC [14,15] and SFE-TLC [16]. However, interfacing of SFE with other techniques is not without problems. The required purity of the CO2 for extraction depends entirely on the analytical technique used. In the off-line mode SFE takes place as a separate and isolated process to chromatography extracted solutes are trapped or collected, often in a suitable solvent for later injection on to chromatographic instrumentation. Off-line SFE is inherently simpler to perform, since only the extraction parameters need to be understood, and several analyses can be performed on a single extract. Off-line SFE still dominates over on-line determinations of additives-an... 

Satisfactory performance of the SFE-SFC-HRMS instrumentation (resolution 1200) was only possible after optimisation (temperatures, restrictor and quartz tube positions, flow characteristics and sample transfer conditions). Mass spectra obtained for Irganox 1010/1076/1330 and Irgafos 168/P-EPQ by SFC-HRMS were identical with those obtained by use of DIP [431]. However, the sensitivity of the SFE-SFC-MS interface is low (at best 4 % of that obtained with sample introduction via DIP). An enormous amount of sample is lost in all parts of the coupling system (SFE, SFC and... 

LC-PB-MS is especially suited to NPLC systems. RPLC-PB-MS is limited to low-MW (<500 Da) additives. For higher masses, LC-API-MS (combined with tandem MS and the development of a specific mass library) is necessary. Coupling of LC via the particle-beam interface to QMS, QITMS and magnetic-sector instruments has been reported. In spite of the compatibility of PB-MS with conventional-size LC, microbore column (i.d. 1-2 mm) LC-PB-MS has also been developed. A well-optimised PB interface can provide a detection limit in the ng range for a full scan mode, and may be improved to pg for SIM analyses. 

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