Selectivity of detectors

A number of alarm systems suffer from repeated false alarms. This may be due to the poor design and selection of detectors, inadequate standards of installation or preventative maintenance, and faulty operation of the system by key holders. Recurrent false calls will quickly discredit any system and may result in the withdrawal of police response to any alarm activation. 

The following rules serve as guides for the selection of detectors in the authors laboratory. 

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. 

To increase resolution of recorded data effectively by using deconvolution, appropriately high signal-to-noise ratios are necessary. Depending on the spectral region involved, a factor that usually dominates the selection of detectors used, very different situations regarding signal-to-noise ratios may prevail. 

G. l.c.—Most reports have concerned the analysis of pesticides and efforts to increase the sensitivity and selectivity of detectors. The gas-chromatographic physical behaviour of bis(2-ethylhexyl) phosphate has also been studied. ... 

Figure 3.41 Agilent 1200 Series LCMS selection of detectors - ion trap, triple quadrupole and TOF with multimode source ( Copyright 2006, Agilent Technologies, Inc. Reproduced with permission).

The required IRF width, stability, and spectral range put some constraints on the selection of detectors for DOT. 

Selection of detector type and size should be controlled by its application, both immediate and long-term. In addition to cost, important performance characteristics of a semiconductor detector for gamma-ray spectrometry are the resolution, efficiency and peak-to-Compton ratio. 

The detector shall be a thermal conductivity type with high sensitivity and stability. The selection of detector temperature depends on sample composition, but temperatures of 10-50 °C above analysis colunm temperature have been found to provide adequate sensitivity. Regular checks on detector hnearity are essential in order to detect signs of filament ageing. The detector should be brought up to temperature and the current switched on several hours before analysis runs to ensure stability. Periodic cleaning, once every six months with srritable non corrosive solvent is recormnended to further ensure detector stability. 

When searching for the correct separation of the peaks, it is important to consider the selection of detectors. Notably, the most commonly used for identification of the components is the mass spectrometer (MS), while for the quantification of its simplicity and specificity toward organic compounds is the flame ionization detector (FID). 

The largest item driving cost is the SNR requirement. Wide selections of detectors are available from a host of companies. There are literally thousands of photomultiplier mbe types, array detectors (line and 2-D array), and semiconductor light sensors and thermal infrared detectors covering a spectral range from 150 nm to more than 40 pm. The wavelength range often determines the choice of detector type. 

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