Specifications detector linearity

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 ... 

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 method for defining detector linearity is perfectly satisfactory and ensures a minimum linearity from the detector and consequently an acceptable quantitative accuracy. However, the specification is significantly looser than that given above and there is no means of correcting for any non-linearity that may exist as there is no correction factor given that is equivalent to the response index. It is strongly advised that the response index of all detectors (CiC and LC)... 

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... 

Stockton and Irgolic developed a low-cost automated interface for the Hitachi Zeeman GF-AA which makes possible the use of this instrument as an element-specific detector for HPLC. The interface consists of an Altex slider injection valve with pneumatic actuators and a 40-/rl sample loop, a linear actuator and a sequence control circuit. 

As a result of the imperfections inherent in all electromechanical and electrical devices, true linearity is a hypothetical concept, and practical detectors can only approach this ideal response. Consequently, it is essential for the analyst to have some measure of detector linearity that can be given in numerical terms. Such a specification would allow quantitative comparison between detectors and indicate how close the response of the detector was to true linearity. Fowlis and Scott [1] proposed a simple method for measuring detector linearity. They assumed that for an approximately linear detector, the response can be described by the power function... 

No single HPLC detector has all the characteristics of a good detector, which include sensitivity, specificity, detectability, linearity, repeatability, and dependability. Detection by UV/vis is widely used for the analysis of lipids it is simple, concentration sensitive, and nondestructive. However, the analyte to be monitored by UV/vis absorption must contain a chromo-phore, and because many fat molecules do not contain a chromophore, this detection system cannot be used in many cases. Fortunately, in cases where no chromophore is present in the molecule, a chromophore can be introduced through derivatization. If the derivatization is done before the analyte enters the column, it is called precolumn derivatization, whereas if it is done after the elution of analyte, it is called postcolumn derivatization. 

In this step of the validation it is investigated whether the matrix influences the signal of the detector. The study concerns either an extract or a digest this new matrix may influence parameters defined in the previous step. All the conclusions obtained in the first step have to be verified (calibration, linearity, chromatographic conditions and performance, internal standard etc.). For the determination of trace organic contaminants this step is of great importance as it has to assure that no interfering compounds remain because quantification is often performed with non specific detectors (e.g. ECD, FID,... 

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... 

Temperature-programmed desorption (TPD) can be described as the measurement of the rate of desorption of preadsorbed molecules as a function of temperature. It involves heating of sample while contained in a sample holder—as the temperature rises, certain absorbed species will have enough energy to desorb and will be detected simultaneously by means of specific detector (for example, mass spectrometer). In TPD experiments, temperature increases linearly and the concentration of desorbed gas is recorded as a function of temperature. Therefore, TPD profile is traced as desorption rate versus time (or temperature). If detector signal is properly calibrated, concentration of desorbed gas can be plotted as a function of temperature. 

Detector—A sulfur selective detector is used and shall meet or exceed the follovring specifications (a) linearity of 10, b) 5 pg sulfur/s minimum detectability, (c) approximate equimolar response on a sulfur basis, d) no interference or quenching from co-eluting hydrocarbons at the GC sampling volumes used. 

The final part of a gas chromatograph is the detector. The ideal detector has several desirable features, including low detection limits, a linear response over a wide range of solute concentrations (which makes quantitative work easier), responsiveness to all solutes or selectivity for a specific class of solutes, and an insensitivity to changes in flow rate or temperature. 

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