Linearity emission spectrometers

Spectrometers on several spacecraft have provided information on the mineralogy of the martian surface, but only one set of spectral data is sufficiently quantitative to be recast into geochemistry. The thermal emission spectrometer (TES) on Mars Global Surveyor and the thermal emission spectrometer imaging system (THEMIS) on Mars Odyssey have provided global mineral mapping, and linear deconvolution allows the... 

Linearity. A common source of error for picosecond time-resolved emission spectrometers is a non-linear response of the detector to emission intensity. Streak camera temporal dispersors, for example, exhibit a limited dynamic range, which, in unfavorable cases, can lead to severe experimental artifacts (20-21). 

PMTs and linear photodiode array detectors are discussed in detail in Chapter 5. This section will cover the 2D array detectors used in arc/spark and plasma emission spectrometers. In order to take advantage of the 2D dispersion of wavelengths from an Echelle spectrometer, a 2D detector is required. The detector should consist of multiple... 

Due to the separation between excitation and emission in a fluorescence spectrometer, concentrations can be detected down to picomolar, with a wide linear range over up to five orders of magnitude. As a consequence of,e.g.,vibra-tional relaxation, the amount of energy which is released as fluorescence (quantum yield) is strongly dependent on solvent and temperature. 

CCD detector consists of 224 linear photodetector arrays on a silicon chip with a surface area of 13 x 18 mm (Fig. 4.16). The array segments detect three or four analytical lines of high analytical sensitivity and large dynamic range and which are free from spectral interferences. Each subarray is comprised of pixels. The pixels are photosensitive areas of silicon and are positioned on the detector atx -y locations that correspond to the locations of the desired emission lines generated by an echelle spectrometer. The emission lines are detected by means of their location on the chip and more than one line may be measured simultaneously. The detector can then be electronically wiped clean and the next sample analysed. The advantages of such detectors are that they make available as many as ten lines per element, so lines which suffer from interferences can be identified and eliminated from the analysis. Compared with many PMTs, a CCD detector offers an improvement in quantum efficiency and a lower dark current. 

Fluorescence and affinity measurements - Peptide in 25 mM Tris, 100 mM KCl and 1 mM CaCl2 at pH 7.5 and 30 C was titrated with a stock solution of calmodulin in UV transmitting plastic cuvettes since the peptides appear to bind to glass. Fluorescence titration spectra were recorded using a SPEX FluoroMax fluorescence spectrometer with excitation at 280 nm and emission scanned from 310 to 390 nm. The value of fluorescence intensity at 330nm was plotted as a function of calmodulin concentration and fitted using standard non-linear least squares methods (6) to obtain optimal values of the dissociation constant (Kj) and the maximum fluorescence enhancement (F/F ). The detection limit under our experimental conditions was 50 nM peptide and all quoted Kj values are the average of at least 3 independent determinations. 

Cho et al. [280] compared dc and rf gas jet-boosted GD-AES for the analysis of steel in terms of the voltage-current relationship they studied the effects of the gas flow-rate (0-800 ml/min) and pressure (3-5 torr) on the dc bias potential, sample weight loss and emission intensity. The use of a simultaneous spectrometer for the rf mode proved dispensable by virtue of the high stability (variations less than 0.3%) for both matrix and trace elements. Both the rf and the dc mode provided calibration graphs that were linear over two or three decades (or even more if the analytical signal was normalized to the signal of a matrix component) however, the limits of detection obtained in the rf mode for many trace elements in steel were at the level of tens of ppb, which was an order of magnitude better than in the dc mode. 

The major disadvantage of arc/spark emission spectroscopy is the instability of the excitation source. This problem can be virtually eliminated by the use of a plasma torch. The most common commercially available method uses an inductively coupled plasma (ICP), which is also called RF plasma, to excite the sample (13-19). The resulting spectrometers (Fig. 4) can simultaneously measure up to 60 elements with high sensitivity and an extraordinarily wide linear dynamic range. 

Another detector selected for its compactness and its orthogonality with respect to GC and MS, is spectro-chemical or optical emission as generated, e.g., by micro discharge detectors (MDD). Figure 9.3.6 presents photos of such emission for both in CO2 and in He (at left) and a cross section on an envisioned MDD structure, coupled into a linear-filter-based micro-spectrometer, which is compact but not efficient. 

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