Detection systems conductivity type

Fibre optic-based flow-through optical biosensors The dramatic advances in fibre optic development in die last decade have promoted construction of sensors where radiation, whether emitted, transmitted or reflected, is conducted fi-om the sample to the detection system. The wide variety of available optical waveguide types (solid rods, hollow cylinders, micro-planar geometries) has been used with varying success in sensor development. 

Passive types of leak detection such as observation wells and collection sumps where product is collected and analyzed directly should work effectively with methanol. Active leak detection systems that rely on thermal conductivity and electrical resistivity sensors will not work with methanol because its properties are so different from gasoline. Another type of active leak detection system that will work with methanol or any other type of fuel relies on changes in impedance in a sensor wire as it becomes wetted with the fuel [4.5]. These leak detection systems also have the advantage that they can pinpoint the location of the leak along the length of the sensor wire. 

While the parameters listed in Section 3.3.4.1 that determine the retention are fundamental in character, the parameters concerning the eluent discussed below depend on the detection system being used. This particularly applies to conductivity detection, which is possible directly or in combination with a suppressor system. These two modes of conductivity detection are fundamentally different and require eluents that not only differ with regard to their type but also to their concentrations and pH values, respectively. Therefore, the influence of these parameters on both modes is discussed separately for the most important detection system. 

Through the choice of stationary phase and eluent composition, the selectivity can be modulated, but the eluent must meet the requirements of the detection system. Although the conductivity detector is still the most popular, other types of detection can be applied for different analytes. These include electrochemical (amperometric, pulsed and integrated amperometric, potentiometric), photometric (UV-Vis, indirect photometric following post column derivatisation, chemiluminescence, refractive index), and fluorescence. 

Postcolumn derivatization with absorbance spectroscopy Postcolumn derivatization reactions involve the chemical reaction of the analyte with a chromophore, after the analyte has passed through the column, followed by the detection of the analyte by UV-Vis absorbance spectroscopy. This type of detection system is typically used for transition and lanthanide metal cations due to the incompatibilities between the transition metal complexing eluent and the conductivity supressor. The properties of the postcolumn derivatization species should include high molar absorptivity of complexes, reactivity with most metals, formation of stable metal com-... 

ED imposes certain restrictions on the type of chromatography that is employed and the mobile phase that is used. The detecting system requires a conducting mobile phase and thus must contain water. Therefore, the majority of normal phase systems are not usable. Reversed-phase high performance liquid chromatography (RP-HPLC), however, is ideally suited to ED. Nevertheless, certain precautions must be taken for its effective use. 

Detector—The detector shall be a thermal conductivity type or its equivalent in sensitivity and stability. The system shall be capable of detecting 0.1 % concentration of any component of interest. For calculation techniques utilizing a recorder, the signal for the concentration diall be at least 5 chart divisions above the noise level on a 0 to 1(X) scale chart. Noise level must be restricted to a maximum of 1 chart diviaon. When electronic integration is employed the signal for 0.1 % concentration must be at least twice the noise level. 

In Phase III, the final dosage formulation has been established and the pivotal clinical trials are being conducted. Degradation products have been identified, so the method selectivity should be reevaluated to ensure that all degradants can be detected and quantitated. The analytical methods are completely validated, and appropriate for routine quality assurance and control purposes. The type and frequency of system suitable testing (SST) should be determined, and an excellent publication on SST for chromatography systems is available [47],... 

---