FAST detector

Fast concentration and sample injection are considered with the use of a theory of vibrational relaxation. A possibility to reduce a detection limit for trinitrotoluene to 10 g/cnf in less than 1 min is shown. Such a detection limit can by obtained using selective ionization combined with ion drift spectrometry. The time of detection in this case is 1- 3 s. A detection technique based on fluorescent reinforcing polymers, when the target molecules strongly quench fluorescence, holds much promise for developing fast detectors. 

A.D Amico and G. Fortunato, Ambient Sensors Hiroshi Kukimoto, Amorphous Light-Emitting Devices Robert J. Phelan, Jr., Fast Detectors and Modulators Jacques I. Pankove, Hybrid Structures... 

An example of a fast, well-executed separation is shown in Figure 8. A 2-mm i.d. 3 cm 3.5- J,m column was used in a rapid, 1-min gradient. In order to maximize the peak capacity, a high flow rate was used 2mL/min. To reduce the column backpressure, the separation was carried out at 60°C. A fast detector sampling rate was employed to keep up with the high speed of the separation. The injection was coordinated with the arrival of the gradient at the top of the column in order to eliminate the... 

In most cases the time constant of the detector is due to slowness of the electronics this is especially true for optical detectoHi- There would be no technical problem to reduce the time constant tb 20-50 msec, although the noise level is expected to increase somewhan With such fast detectors computer data acquisition becomes necessary, as recorders with a time constant less than O.S sec are rare and expen ve. Since they are difficult to maintain, they are impractical. 

P. G. LeComber and W. E. Spear, The Development of the a-Si H Field-Effect Transistor and Its Possible Applications D. G. Ast, a-Si H FET-Addressed LCD Panel S. Kaneko, Solid-State Image Sensor M. Matsumura, Charge-Coupled Devices M. A. Bosch, Optical Recording A. D Amico and G. Fortmato, Ambient Sensors H. Kukimoto, Amorphous Light-Emitting Devices R. J. Phelan, Jr., Fast Detectors and Modulators J. I. Pankove, Hybrid Structures... 

Most of the traditional HPLC detectors can be applied to LCxLC analyses the choice of the detectors used in comprehensive HPLC setup depends above all on the nature of the analyzed compounds and the LC mode used. Usually, only one detector is installed after the second-dimension column, while monitoring of the first-dimension separation can be performed during the optimization of the method. Detectors for microHPLC can be necessary if microbore columns are used. Operating the second dimension in fast mode results in narrow peaks, which require fast detectors that permit a high data acquisition rate to ensure a proper reconstruction of the second-dimension chromatograms. 

E.g. tryptophane residues of proteins excite at 290-295 mn but they emit photons somewhere between 310 and 350 mn. The missing energy is deposited in the tryptophane molecular enviromuent in the form of vibrational states. While the excitation process is complete in pico-seconds, the relaxation back to the initial state may take nano-seconds. While this period may appear very short, it is actually an extremely relevant time scale for proteins. Due to the inherent thermal energy, proteins move in their (aqueous) solution, they display both translational and rotational diffusion, and for both of these the characteristic time scale is nano-seconds for normal proteins. Thus we may excite the protein at time 0 and recollect some photons some nano seconds later. With the invention of lasers, as well as of very fast detectors, it is completely feasible to follow the protein relax back to its ground state with sub-nano second resolution. The relaxation process may be a simple exponential decay, although tryptophane of reasons we will not dwell on here display a multi-exponential decay. 

Many experiments (see Section I.B) require the energy analysis and detection of two or more particles with time correlation in other words, coincidence counting techniques must be used. Coincidence methods have long been used in nuclear physics because of the convenient fast detectors that have long been available. The more recent availability of fast, high-gain electron multipliers has created the possibility of coincidence measurements in electron spectroscopy. Various aspects of coincidence measurements have been discussed elsewhere.100 102... 

Fig. 28 Schematic view of the Zeiss Plate Vision instrument which is state-of-the art for ultra-high throughput screening (uHTS) for drug discovery. The instrument resembles a 96-well parallel microscope the light of a excitation source (Xe-lamp or pulsed laser) is expanded to illuminate a microtiter plate. The excitation is structured into 96 channels by a mini-lens array (MLA) and focused into the well with a detection volume of < 100 nL. All 96 channels are read simultaneously by a gated, intensifed CCD. With this fast detector and the pulsed laser excitation, the instrument can be used to carry out miniaturized, 96 parallel lifetime measurements in microtiter plate format with nanosecond time resolution or time-gated detection [190]...

While an intensity profile at the detector as a function of retardation may be acquired in a step-scan mode, two major drawbacks affect this method of interferogram acquisition. First, the mirror(s) requires stabilization times with mirror inertia and time constants of the control loop determining this parameter in achieving a given optical retardation. Second, additional hardware and control mechanisms need to be incorporated into the spectrometer, thus increasing instrument cost and complexity. In certain cases, however, the utility of a step-scan instrument justifies this additional expense. Historically, the step-scan approach was favored with slow detectors. With the advent of fast detectors and electronics, step-scan interferometry became... 

Fluoride crystals are also well suited for fast detectors for high-energy radiation. Scintillators based on the Ce3+ emission have been particularly investigated. The discovery of the very fast cross-luminescence of BaF2 has led to the investigation of the luminescence of fluorides containing K, Rb, Cs and Ba under excitation by ionizing radiation. 

The ability to quickly ramp column temperature is an excellent way to increase analysis speed, given appropriate carrier gas flow rates and fast detector sampling rates. Along with column dimensions and operation above... 

Time-resolved fluorometry fahs into one of two categories, depending on how the fluorescence emission response is measured (1) pulse fluorometry, in which the sample is illuminated with an intense brief pulse of light and the intensity of the resulting fluorescence emission is measured as a function of time with a fast detector system, or (2) phase fluorometry, in which a continuous-wave laser illuminates the sample, and the fluorescence emission response is monitored for impulse and frequency response. ... 

Photodiodes are used as detectors in many automated systems either as individual components or in multiples as an array. Photomultiplier tubes are required in many immunoassay systems to provide adequate sensitivity and fast detector response times for fluorescent and chemiluminescent measurements. Several approaches have been used for the electrooptical integration and packaging in different analyzers. A logarithmic amplifier or microprocessor and/or computer software converts transmittance to absorbance. Low-cost analog-to-digital converters with conversion times... 

The main factor in beam analysis that affects the reliability of the analytical information is the reproducibility of the surfaces. When using scanning electron microscopy (SEM), the apparati are connected to the computer, which makes it possible to obtain quite a bit of information about the sample, especially by X-ray and AES. However, the apparati cannot assure the same length for beam penetration on the surface, which means that the analytical information can be uncertain. Because the beam analysis is rapid, it requires very fast detectors, e.g., Ge/Li or Si/Li. The LA can be successfully used in surface analysis. An automated system has been constructed, laser-induced breakdown spectrometry (LIBS).213 This is an alternative to other surface techniques — secondary ion mas spectroscopy (SIMS), SEM, X-ray photoelectron spectroscopy (XPS) — and it increases the lateral and depth resolution. 

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