Specifications detector linear range

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 ... 

Several kinds of detection systems have been applied to CE [1,2,43]. Based on their specificity, they can be divided into bulk property and specific property detectors [43]. Bulk-property detectors measure the difference in a physical property of a solute relative to the background. Examples of such detectors are conductivity, refractive index, indirect methods, etc. The specific-property detectors measure a physico-chemical property, which is inherent to the solutes, e.g. UV absorption, fluorescence emission, mass spectrum, electrochemical, etc. These detectors usually minimize background signals, have wider linear ranges and are more sensitive. In Table 17.3, a general overview is given of the detection methods that are employed in CE with their detection limits (absolute and relative). 

The model immunoassay is the enzyme-linked immunosorbent assay (ELISA) in which a non-specific capture antibody is bound to a surface, such as a multi-well plate or small tube [13]. In the basic form of ELISA, a second antibody tagged with an enzyme interacts specifically with the analyte. The enzyme assay produces a colored product that is read with a spectrophotometer. There are many variations on the basic immunoassay format that serve to increase sensitivity, specificity, linear range, and speed. Many commercial instruments have been developed to take advantage of various technologies for reporter molecules. The immunoassay may be coupled to an electronic sensor and transducer, such as a surface acoustical wave (SAW) sensor. Electrochemiluminescence (ECL) is a method in which the detector antibody is tagged with a ruthenium-containing chelate [13-15]. When the tag is... 

Efficiency Separation Factor (a) Specificity (Detector) Retention Quantitative Time Reproducibility Reproducibility Sensitivity Linearity Dynamic Range Throughput (Preparative) Speed Baseline Stability Total... 

Detector linearity is probably the most important specification for any detector that is to be used for quantitative analysis. It is defined as the concentration range over which the detector response is linearly related to the concentration of solute passing through it. 

This again emphasizes the need for an improved procedure for defining detector specifications. The linear dynamic range of the electron capture detector is again ill-defined by many manufacturers. In the DC mode the linear dynamic range is usually relatively small, perhaps two orders of magnitude, with the response index lying... 

Following the establishment of specificity, the method(s) should be validated to allow for use in release and stability testing. Such validation is typically less stringent than for final methods (sec Chapter 12), but should demonstrate specificity, linearity, range, accuracy, and analysis repeatability for the API. For related substances, specificity should be demonstrated and the limit of detection (LOD) and limit of quantitation (LOQ) should be established for the API to serve as surrogate values for the LOD and LOQ of impurities for which authentic substances are not available. To achieve a sufficient LOD and simultaneously keep the API in the linear dynamic range of the detector, it may be necessary to use different sample concentrations for the analyses of the API and related substances. It is additionally beneficial to repeat the separation on new columns from different batches to ascertain that the separation obtained can be maintained column to column. 

This is the classical ion chromatography detector and measures the eluate conductivity, which is proportional to ionic sample concentration (provided that the cell is suitably constructed). Its sensitivity decreases as the specific conductivity of the mobile phase increases. The active cell volume of 2 gl is very small. Good conductivity detectors have automatic temperature compensation (conductivity is highly temperature-dependent) and electronic background conductivity suppression. The linear range is not large. 

Refractive index is very sensitive to temperature and pressure. For that reason the reference and the measurement cell are close since the difference in temperature between them is critical. Specifications of a RI detector are refractive index range, linearity range, cell volume, maximum pressure in cell, temperamre control. " ... 

Linear range concentration range over which a detector has a constant and therefore linear response, >rf, to a specific compound. 

Among the detectors discussed thus far, ICP-MS is certainly not the cheapest one. The advantage of ICP-MS lies in its multielement capabilities, excellent detection limits, and wide linear range. Moreover, low detection limits are not restricted to the hydride-forming arsenic compounds. The application of ICP-MS as an element-specific detector changed the knowledge about arsenic compounds... 

Detector specifications have been discussed in chapter 5. They reveal the accuracy and precision attainable in quantitative analysis and also the lower concentration levels that are possible in trace analysis. As in GC, the five specifications of prime importance are detector response, detector noise level, detector sensitivity, or minimum detectable concentration, detector linearity and linear dynamic range [1], The detector response, detector woAe level and the detector are relevant to trace... 

Once the installation qualification is complete, the instrument is then tested against operational specifications. This often includes testing each component individually. For example, the pump is tested for the accuracy and precision of flow rate a UV-visible detector has its wavelength settings calibrated, and the linear range, accuracy, and precision are verified (the last three often in conjunction with a test of the injector and pump). These test results are compared against the manufacturer s specifications using qualified standards and test components. 

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