Specifications detector flow sensitivity

A similar specification, the flow sensitivity should also be defined in terms of that flow change which will provide a signal equivalent to twice the noise level. The value of the flow sensitivity is also important in the design of the pump to be used with the detector. 

Solute property detectors, such as spectroscopic andj electrochemical detectors, respond to a physical or chemical] property characteristic of the solute which, ideally, is] independent of the mobile phase. Althou this criterion is rarely met in practice, the signal discrimination is usually sufficient to permit operation with solvent changes (e.g., flow programming, gradient elution, etc.) and to provide high sensitivity with aj wide linear response range. Table 5.4. Solute-specific detectors complement ulk property detectors as they provide high ... 

Important performance characteristics of UV/Vis detectors are sensitivity, linearity, and band dispersion. These are controlled by design of the optics and the flow cell—more specifically by spectral bandpass, stray light characteristics, and the volume and path length of the flow cell. 

Manufacturers publish their product s performance characteristics as specifications, which are often used by the customer for comparison during the selection process. Table 1 shows the specifications of an Agilent 1100 Series Quaternary Pump, which is quite representative of other high-end analytical pumps. Note pulsation is particularly detrimental to the performance of flow-sensitive detectors (e.g., mass spectrometer, refractive index detector). Differences in dwell volumes and composition accuracy between HPLC systems might cause problems during method transfers. 

The determination of the different forms (e. g. compounds or complexes) in which an element occurs (often referred to as the speciation of an element and speciation analysis, respectively [28]) is in most cases performed by hyphenated techniques. These are the combination of a high-performance separation technique such as gas or liquid chromatography, or electrophoresis, and an element- or compound-specific detector [29]. While the former provides the separation of the different elemental species prevalent in the sample, the latter brings selective and sensitive detection. In the case of AAS, only the hyphenation with gas and Hquid chromatography, respectively, has gained importance. The combination of atomic absorption spectrometry and electrophoresis has never proven successfiil, obviously due to the incompatibility of the extremely low flow rates of electrophoretic separations with the aspiration volumes of flame atomisers and the difficulties of interfacing the two techniques. 

A very elegant analytical technique for the lead alkyls is that of Ballinger and Whittemore. They combined pressure programming with use of an atomic absorption spectrophotometer as a specific detector to produce a rapid, precise, and sensitive analytical technique. A 10 foot column packed with 20% 1,2,3,-tris-(cyanoethoxy)-propane on 60/80 mesh Chromosorb P coated with 1% potassium hydroxide was operated at 85°C. Flow rates were programmed from 10—00 ml/min., (Figure 159). Analysis of the five lead alkyls was completed in less than one and a half minutes. The amount of lead was determined by the absorption of the lead 2833 S. emission line. The method could detect as little as 20 nanograms of lead as lead alkyl. The application of atomic absorption spectroscopy to the determination of lead alkyls separated chromatography has also been discussed by... 

A radioactivity detector is used to measure radioactivity in the HPLC eluent, using a flow cell. The detection principle is based on liquid scintillation technology to detect phosphors caused by radiation, though a solid-state scintillator is often used around the flow cell [17,31]. This detector is very specific and can be extremely sensitive. It is often used for conducting experiments using tritium or C-14 radiolabeled compounds in toxicological, metabolic, or degradation studies. 

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