General detector

Select the detector. To acquire molecular weight distribution data, use a general detector such as a refractive index detector. To acquire structural or compositional information, employ a more selective detector such as an ultraviolet (UV) or infrared (IR) detector. Viscometric and light-scattering detectors facilitate more accurate molecular weight measurement when appropriate standards are not available. 

This classification is concerned with whether the detector responds to a specific feature of the analyte of interest or whether it will respond to a large number of analytes, irrespective of their structural properties. In terms of the previous classification, it may be considered that solute detectors are also usually selective detectors, while solvent detectors are general detectors. 

The most widely used HPLC detector methodology is, arguably, UV absorption, and this has capabilities as both a specific or general detector, depending upon the way it is used. 

It is usually recognized that general detectors are less sensitive than specific detectors, have a lower dynamic range (see below) and do not give the best results when gradient elution is used. 

Like the UV detector, the mass spectrometer may be employed as either a general detector, when full-scan mass spectra are acquired, or as a specific detector, when selected-ion monitoring (see Section 3.5.2.1) or tandem mass spectrometry (MS-MS) (see Section 3.4.2) are being used. 

General detector A (chromatographic) detector which responds to all compounds reaching it. 

Universal detector An alternative term for a general detector. 

The use of a volatile solvent, e.g., pentane, was not explored because of inherent limitations. Concentration of such extracts was not possible because of the volatility of the sample components. Therefore the maximum concentration factor that could have been achieved was limited by the partition coefficients of the compounds into the solvent used in the extraction. For most compounds this factor was estimated to be about 10 1. Furthermore, with CRMS and other general detectors, the solvent masking problem would still preclude observation of many compounds. Therefore, the method would be limited to detectors that are not responsive to the solvent used in the extraction. Recent work (3.4,5) has indicated that extraction with a volatile solvent is a viable approach for the analysis of a small set of compounds, e.g., the trihalomethanes, with an electron capture detector in drinking water samples where concentration factors of 10 1 or less are acceptable. 

The successful combination of mass spectrometry with gas chromatography (GC-MS) and, subsequently, with liquid chromatography (HPLC-MS) allowed not only the determination of urea pesticides in food but also the identification of their residues at trace level. Mass spectrometry is a technique that can be used as a general detector, with cyclic scanning. The selectivity and sensibility of analysis can be enhanced using characteristic ions of the molecule, with selected ion monitoring (SIM). Urea pesticides have been determined by HPLC-MS directly (175-180), without the thermal instability problems of GC analysis. 

Inclosure 29 depicts the general detector plan for the Tooele plant with a combination of bubblers and chemical alarms located in all work areas, air locks, and stacks. 

In general, detectors in CE have to cope with problems of three types small mass (picogram levels) of analytes injected (due to the limitations in the volumes), which can be loaded into the capillary, limited peak volumes, and inadequately separated peaks. 

Apparently, the sole disadvantage of the FID as a general detector is that it normally requires three separate gas supplies, together with their precision flow regulators. The need for three gas supplies is a decided inconvenience but is readily tolerated in order to take advantage of the many other attributes of the FID. The detector is normally thermostatted in a separate oven ... 

The sensitivity of the katharometer is only about 10 g/mL (probably the least sensitive of all GC detectors) and has a linear dynamic range of about 500 (the response index lying between 0.98 and 1.02). It is, however, a general detector and will sense all permanent... 

Often background shot noise limited Generally detector noise limited... 

Functional groups, such as cai bonyl, alcohol, halogen, and amine, yield fewer ions or none at all in a flame. In addition, the detector is insensitive toward noncombustible gases such as H2O, CO2, SO2, and NOf These properties make the flame ionization detector a most useful general detector for the analysis of most organic samples, including those that are contaminated with water and the oxides of nitrogen and sulfur. 

General and Selective Detectors Detectors can be classified either as general or selective. A general detector will respond to all or most of the ions that pass through the detector cell. A conductometric detector is classified as a general detector because... 

Generally, detectors are used for continuous monitoring and can be placed directly at the point(s) of interest. Physical monitors detect such parameters as particle count, pressure, temperature, and light intensity, whereas biological and chemical identification systems detect the presence of specific biological and chemical analytes. 

Absorption in the infrared region can be used both as a general and as a specific detector. For use as a general detector a stopped-flow technique must be used. In... 

Thermal conductivity detectors aie very general detectors, but not very sensitive. 

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