Photodiode array detector, output

An intensified photodiode array (IPDA) detector for onedimensional spatial imaging in the EUV is shown in Figure 2. This type of detector was originally described by Riegler and Moore (14) It consists of a microchannel plate whose output is optically coupled to a self scanning photodiode array. An incident photon produces a photoelectron which is subsequently amplified by the MCP. The exiting electrons are proximity... 

Figure 15 illustrates the schematic of the microfluidic compactor for parallel scan-like test of odd rows/columns in a 16 x 16 microfluidic array. The electrodes represent the last row/column where the pseudo-sinks are located. The compactor consists of three layers of microfluidic 2-input AND gates. The output of the AND gate in the third layer is connected to the photodiode detector located in the sink reservoir of the microfluidic array. 

A diode array consist of a series of photodiode detectors arranged side-by-side on a silicon crystal. The diode array typically has a photosensitive area of a few square millimetres. Each diode is dedicated to measuring a finite but narrow band of the spectrum and all diodes are connected to a common output line. By measuring the variation in fight intensity over the entire wavelength range, the absorption spectrum is measured. 

Figure 26 LC-APCI-MS of KS 176. (a) Diode array detector output (b) total ion current trace (c) APCI (-I-) spectrum (d) UV spectra obtained from an online photodiode array detector sampling at the peak apex. The formula of KS 176 is given in Figure 25. The interpretation of fragmentation seen in the mass spectrum shown is the same as that observed in MSI of Figure 25. Data courtesy Dr. J. Lepore, Waters.

A clever way to make a universal LC method more reliable for identification of surfactants in shampoos and hair conditioners was described by Kadano et al. (20). Two detectors were used, refractive index and UV. The ratio of the two responses was recorded versus retention time, giving a more specific signal than the output of either detector alone. Of course, calibration with the proper standards is all-important. Modern photodiode array UV detectors permit using a similar approach detection at two or more wavelengths, with automatic calculation of the ratio of the absorbance at different wavelengths. 

Another kind of linear solid state position sensitive detectors are the Photo-Diode-Arrays (PDA s), which are different from CCD s. A PDA consists of an array of separate photodiodes, each with an associated capacitance and a multiplexing read-out system (see Fig. 21). The charges collected in each cell are simply switched to the output, one by one. Unlike in the case of CCD s, the photosensitive elements are separated completely from the transfer circuity. 

Complete MCP s can be stacked to provide even higher gains. For response in the vacuum ultra-violet spectral region (50-200 nm) a SSANACON, self-scanned anode array with microchannel plate electron multiplier, has been used (36). This involves photoelectron multiplication through two MOP S, collection of the electrons directly on aluminum anodes and readout with standard diode array circuitry. In cases where analyte concentrations are well above conventional detection limits, multi-element analysis with multi-channel detectors by atomic emission has been demonstrated to be quite feasible (37). Spectral source profiling has also been done with photodiode arrays (27.29.31). In molecular spectrometry, imaging type detectors have been used in spectrophotometry, spectrofluometry and chemiluminescence (23.24.26.33). These detectors are often employed to monitor the output from an HPLC or GC (13.38.39.40). 

Fig. 6 SPR sensor in angular configuration with three parallel channels (A side view, B top view), a High output light emitting diode, b lenses, c sensor chip, d microfluidic cartridge, e coupling prism, / polarizer, g photodiode array detector. Reprinted from [11], copyright 1991, with permission from American Chemical Society...

Either a photodiode array or a charge-coupled device (CCD) array, placed at the output plane of the spectrometer, is used as the detector. This discussion concentrates on the use of the diode array, with some comments on the use of a... 

Many newer Raman instruments have replaced the single-wavelength output monochromator with a spectrograph and an array detector. The photodiode array was the first array detector to be used. It allows the simultaneous collection of entire Rantan spectra. Photodiode arrays are typically used in conjunction with an image intensifter to amplify the weak Raman signal. 

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