Linearity, detector

Detector Linearity Linear Dynamic Range Detector Noise Level... 

True detector linearity is, in fact, a theoretical concept, and despite the claims by many manufacturers, LC detectors can only tend to exhibit this ideal response. As the linearity of the detector will determine the accuracy of the analysis, it is important to have some method for measuring detector linearity that can describe it in numerical terms. A method for linearity measurement was proposed by Scott and Fowlis (3), who assumed that for a nearly linear detector the response of the detector could be expressed by the following equation. 

Absorbance detectors are also commonly used in combination with postcolumn reactors. Here, most issues of detector linearity and detection limit have to do with optimization of the performance of the reactor. In a typical application, organophosphorus compounds with weak optical absorbances have been separated, photolyzed to orthophosphate, and reacted with molybdic acid, with measurement being performed by optical absorbance.58... 

A second source of error may be in the detector. Detector linearity is an idealization useful over a certain concentration range. While UV detectors are usually linear from a few milliabsorbance units (MAU) to 1 or 2 absorbance units (AU), permitting quantitation in the parts per thousand level, many detectors are linear over only one or two decades of operation. One approach in extending the effective linear range of a detector is high-low injection.58 In this approach, an accurate dilution of a stock sample solution is prepared. The area of the major peak is estimated with the dilution, and the area of the minor peak is estimated with the concentrated stock. This method, of course, relies on linear recovery from the column. Another detector-related source of error that is a particular source of frustration in communicating... 

Experimental problems signaknoise, detector linearity Ha/X 6678 is typically about 100), calibration, reddening. 

Regarding OQ validation, if one has only an isocratic pump available, it is recommended that one does not perform a detector linearity test at this time. However, this test can be subsequently performed as part of either the PQ validation or individual method validation, both of which typically test the performance of the system as a whole (holistically). 

Blank Pump Accuracy and Detector Linearity -Water Blank 1 1 Pump Composition 1 ... 

The wavelength accuracy and detector linearity and detector noise have the same effect on laser-induced fluorescence, as those of a UV absorbance detector. 

For a conductivity detector the parameters that need to be considered are cell response, detector linearity, detector sensitivity, and the effect of the detector s internal thermistor. 

Linearity problem Broken optical fiber Wavelength accuracy Detector linearity Noise... 

Detector linearity would normally be tested as part of an overall holistic test that examines the linearity of the complete instrument, the injector, as well as the detector. The test would normally be designed to cover the range up to 2 absorbance units (AU). 

Detector Nonlinearity Assessment. Detector linearity is implicitly assumed when conventional chromatogram Interpretation is accomplished. This assumption must be checked by plotting the the area under a narrow chrcmatogram versus concentration for various concentrations and fitting the data with a polynomicil to see if Beer s law holds. That is, the polynomial ... 

Nonlinear regression enables broad molecular weight distribution standards to be used for SBC calibration and permits simultaneous resolution correction euid calibration. Furthermore, it greatly increases the variety of equations 4iich can be fit to calibration curves, detector linearity data and chromatogreun shapes. 

Pump flow rate accuracy and gradient accuracy Detector linearity of response, noise, drift, and wavelength accuracy Injector precision, linearity, and carryover Column heater temperature accuracy... 

Detector linearity of response, noise, drift, and wavelength accuracy... 

A steady pressure should be maintained within the flow cell when performing the detector linearity test. Filling the flow cell with the test solution manually with a syringe sometimes leads to pressure fluctuations and hence unstable readings. An alternative is to use the pump to deliver test solution to the flow cell. However, this option requires a large volume of test solution. 

The test sample to use in qualification should be a small molecule that is soluble in water, has a strong UV chromophore, and possesses a charge at the intended separation pH value. A nonvolatile compound is also desirable, especially when used for assessing peak area reproducibility during the detector linearity test. Some examples of test samples that can be used are benzoic acid, 4-hydroxyphenylacetic acid, 4-hydroxybenzoic acid, and 4-hydroxyacetophenone. 

To measure detector linearity, increasing concentrations of a sample are injected and analyzed using a preconditioned capillary prepared as described in Section 12.3.2. The linearity of the detector is measured over the concentration range of... 

Preamplifier Linear charge pulse from detector Linear tail pulse... 

Kamble and Venkatachalam [23] reported a gas chromatography (GC) method for the determination of clopidogrel in tablet dosage forms. This method used a DB-17 capillary column of 30 m length and 0.25 mm internal diameter, equilibrated at an oven temperature of maintained at 250 °C. Dioctyl phthalate was used as an internal standard, and clopidogrel was detected at 4.1 min by means of a flame ionization detector. Linearity in the method ranged from 0.5 to 5.0 mg/ml, with a recovery of 99.89%. 

The following may serve as an example to illustrate the point. We may inject 5 pi of a sample solution into a column with an inner diameter of 5 mm. If we inject the same amount of sample into a column with a diameter of 1 mm, then (eqn.7.19) the sensitivity would be increased by a factor of 25. However, the sample loading (Qs) would be increased by the same factor and the result may be increased peak broadening, necessarily combined with loss of detector linearity. 

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. 

Beacause of the imperfections in mechanical and electrical devices, true linearity is a hypothetical concept and practical detectors can only approach this ideal response. It is therefore important that the analyst has some measure of linearity that is specified in numerical terms so that comparisons can be made between detectors and the proximity of the detector to true linearity understood. Fowlis and Scott [4] proposed a method of measuring detector linearity. They assumed that for a closely linear detector the response could be described by the... 

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)... 

It is seen that there is a clear difference between the peaks, and the error involved is quite considerable, as discussed in chapter 2 where detector linearity is discussed in detail. It follows that in order to... 

Electronic Position Sensitive Detectors, linear and area detectors, make the collection of the information contained in diffraction or scattering patterns highly efficient. 

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