Detectors parameters

Expansion of Module 3 to include rules for selection of detectors and detector parameters. The rules will handle optical absorbance and fluorescence (including pre- and post-column deri-vatization) and electrochemical detection. 

The efficiency of the detection system is based on both detector and sample parameters. Detector parameters include the intrinsic detector efficiency, the geometric relation of detector to sample, scattering by the sample support and nearby material, and attenuation between the sample and the detector. Sample parameters include material stopping power based on composition, mass, diameter and thickness type and amount of sample cover and backing and radiation type, energy, decay fraction, and decay rate. 

In order to accurately describe narrow peaks and not cause peak distortion in fast HPLC, detector parameters such as sampling rate and digital filtering must... 

The pressure sensitivity of a detector is extremely important as it is one of the detector parameters that determines both the long term noise and the drift. As it influences long term noise, it will also have a direct impact on detector sensitivity or minimum detectable concentration together with those other characteristics that depend on detector sensitivity. Certain detectors are more sensitive to changes in pressure than others. The katherometer detector, which is used frequently for the detection of permanent gases in GC, can be very pressure sensitive as can the LC refractive index detector. Careful design can minimize the effect of pressure but all bulk property detectors will tend to be pressure sensitive. 

The pulse shape depends strongly on the detector parameters like the anode diameter and the applied voltage. 

When a chemiluminometer detector is used in the HPLC technique, it is necessary to take into account several instrumental parameters, such as reagent and eluent flows and concentrations, because many of these are not controlled (e.g., detector geometry and volume, pump pulsation, the mixing of the reagent and eluent flows, or background emission).216 Because increases in detector volume increase the chemiluminescent signal, the detector parameters must be correlated with the HPLC parameters to obtain the best reliability. 

Air samples from soil are usually withdrawn directly with syringes having airtight stopcocks through stainless steel or nylon tubes installed into the soils or headspace inside the closed chambers, as described in the previous section. Methane, one of the target gases, can be analyzed within 6 h of collection by GC-FID. The column and detector parameters are very similar to those set for the analyses of major air components in the atmosphere. Experiments have been conducted by individual teams at different geological locations to measure how soil consumes atmospheric methane, and how soil moisture and temperature control the consumption and production of CH4 and CO2 in it. ... 

The automated FIA system classed as a Type 6 analyser can be regarded as completely automatic in spite of the fact that the detector parameters are manually controlled, which does not really Involve human Intervention in the analytical process provided that the same type of sample and analyte(s) is dealt with throughout. 

The choice of detector is often dictated by the properties of the solutes and/or the sensitivity required from the analysis. The more important detector parameters governing the choice are listed below. 

The results given below are believed to be representative of the particular detectors or groups of detectors described. However, detector parameters may vary for different specimens of the same type, and will depend on possible changes in the manufacturing process. This is especially the case with parameters that depend on the gain, such as maximum count rate and afterpulsing probability. 

It is to be stressed again that the measuring cell of the detector must be very small. Otherwise, the sample zones that leave the column are extensively broadened. Together with the applicability, sensitivity - and price - this detector parameter also should be considered. The volume of the common flow-through measm-ing cells is just 10 pL. 

Equation (4.15) is the general relationship between Df and detector parameters it applies to both photovoltaic and photoconductive detectors. 

These are the second and third conditions on the material and design of an infrared photon detector they are partly interrelated insofar as they involve common parameters. When conditions 1-3 are satisfied the only detector parameter on which Z)J depends is q. One generally also wants to achieve the highest possible value of DJ (BLIP) by having the quantum efficiency near its maximum possible value i.e.,... 

Achievement of a very high at the desired is usually the primary demand on a photon detector, but other detector performance parameters can be important also. Listed in Table 4.2 are the various detector parameters and the requirements generally placed on them by the most advanced systems. 

Infrared detector applications often require arrays of many detector elements. The use of arrays has several ramifications. It requires minimum electrical power dissipation in each detector element, so that the entire array can be cooled efficiently. It also requires reasonable uniformity of detector parameters among the elements of an array [4.6]. Another consequence of the increasing sophistication of array technology is the need for lower cost per detector element, so that the cost of a large array not become excessive thus cost per element can be a sort of economic detector parameter just as important as the technical detector performance parameters. There is also a trend toward... 

For simplicity, we have lumped a number of detector parameters and operating conditions into the receiver effective temperature 7 cff Of particular interest in... 

The flow analyzer involves simple apparatus such as samplers, liquid drivers (peristaltic pumps, piston pumps, solenoid pumps), injection devices (rotary valves, injector-commutators), reactors and flow lines (usually narrow bore tubing), mixing chambers, and flow-through detectors. As a rule, these devices are readily available in most laboratories devoted to chemical analysis. Regarding detection, almost all analytical techniques have been used in flow analysis a small flow cell volume and a short response time that is compatible with system dynamics are important detector parameters. 

Detector parameters are taken from F. Suekane, Status of the KamLAND Experiment , Talk presented at Europhysics Neutrino Oscillation Workshop, (Now 98) 7-9 September 1998, Amsterdam, the Netherlands. 

For a simple estimate of the sensitivity and its dependence on the detector parameters, such as the heat capacitance and thermal losses, we shall consider the following model [4.99]. Assume that the fraction p of the incident radiation power P is absorbed by a thermal detector with heat capacity H, which is connected to a heat sink at constant temperature (Fig. 4.73a). When G is the thermal conductivity of the link between the detector and the heat sink, the temperature T of the detector under illumination can be obtained from... 

Table 4.2. Infrared detection systems requirements on detector performance parameters Detector parameters and properties System requirements...

Response factors in the thermionic detector are directly related to experimental conditions and vary for the nitrogen and phosphorous modes as well as the nature of the compound containing the heteroatom. Selectivities typical of the ratio of nitrogen to carbon range from 10 to 10 gN/gC. For phosphorons to carbon the range is 10" to 5 x 10 gP/gC. The linear dynamic range varies from 10 to 10 and differs for each compound examined. Using the appropriate column and detector parameters, traces of herbicides of 0.5 ng, for example, can be easily determined. 

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