Stationary sampling

The efficiency of the "D is partly a consequence of the zone refocusing mechanism, as depicted in Figure 8.7. Each time the solvent front traverses the stationary sample in multiple development it compresses the zone in the direction of development. The compression occurs because the mobile phase first contacts the bottom edge of the zone, where the sample molecules start to move forward before those... 

Tokunaga R, Takahata S, Onoda M, Ishi-i T, Sato K (1974) Evaluation of the exposure to organic solvent mixture. Comparative studies on detection tube and gas-liquid chromatographic methods, personal and stationary sampling, and urinary metabolite determination. Internationales Archiv Arbeitsmedizin 33 257-267. 

FIGURE 11.7 An illustration of how two mixture components separate, by the movement of an extracting solvent across a stationary sample solvent, due to the differing solubilities of the components in the two phases. 

B) Stationary sample of ZnTPP (0.2n ) in CH2Cil2 in a NMR tube, excited at 135 with 476.5nm Ar+ laser beam (250mW, focussed) the sample was cooled in a cold N2 stream. The spectrum is the sum of five scans, each of a fresh sample from which O2 was removed by freeze-pumping. (C) As in B, but the NMR tube was spun, and the laser power was lowered to 30mW seven scans were added. (Reproduced from Ref. 7. Copyright 1986 American Chemical Society.)... 

Figure 5. V4 Raman peaks for a stationary sample of NiTPP (0.2n ) in pyridine, with 406.7nm excitation. Arrows indicate the decreasing (1346cm ) and increasing (1369cm"l) relative band intensities at increasing laser power levels (1.5, 5, 10,...

The estimates of the sample size obtained in this way are valid for one-dimensional objects, e.g. output of factories, rivers, sampling lines in lakes, stationary sampling points for air monitoring, etc. A sample of papers that are devoted to the application of autocorrelation in sampling schemes is e.g. 

The stationary sampling train consisted of a sample cassette containing the filters as described, a midget impinger containing 10 mL of concentrated HNO3 to trap any breakthrough or volatile... 

The first 27A1 MAS NMR study of zeolites was carried out by Freude and Behrens (151). They measured, first, chemical shifts and half-widths of signals from stationary samples of zeolites Na-A, Tl-A, Na-Y, and Tl-Y at 16 MHz. For MAS frequencies of vR such that vR > Vq/vl the central line of the 27A1 resonance is reduced to about j of its original value. Freude and Behrens next calculated the quadrupole frequencies vQ and shifts of the center of gravity of each line due to the quadrupole interaction, i.e., vQ = (v - vL)/vL at 70 MHz. Then, apparent line positions and line widths, S and <5v 2MAS, were measured experimentally using MAS at 70 MHz. The corrected chemical shift value at 70 MHz was then calculated from the relationship <5, = 5ex — <5q. They were several ppm different from the apparent values (see Table XII). 

Calculation of the Corrected Value of the 11 Al Chemical Shift in Various Zeolites from the Spectra of Stationary Samples at 16 MHz and of Rotating Samples at 70 MHz -1 ... 

Bosa5ek et al. (168) used wide-line 27A1 NMR measurements of stationary samples to measure the EFG at the nuclear site in decationated zeolites. In zeolite Na-Y they measured a line half-width of Sv1/2 = 61 kHz (for vL = 16 MHz) which led, via theoretical considerations (173) to vD = 840 kHz the calculated field gradient was 2.9 V/A2. In hydrated samples this gradient was partially averaged by random reorientation of water molecules, giving <5v,/2 = 5.7 kHz and vQ = 256 kHz. 

Harvey s and McGee s method both include abrading a stationary sample with a rotating grinding wheel. Its principle is similar to that of the above variations of Bohme s method. 

Increments must be spaced systematically. Stationary sampling employs a grid system, which may be a simple left front-middle center-right rear grid for samples from a railroad car or a surveyed grid system to take samples from a storage pile. 

Systematic spacing of increments collected from a stopped belt is accepted universally as the reference method of sampling that is intrinsically bias-free. Stationary sampling, that is, sampling coal at rest in piles, or in transit in trucks, railcars, barges, and ships, suffers decreased reliability to an indeterminate degree. 

It was also found that the hybridization kinetics were found to be faster in a moving sample, as compared to a stationary sample [939]. In another report, active acoustic mixing was used to achieve a five-fold faster DNA hybridization rate. Hybridization was detected electrochemically (by AC voltammetry) based on the ferrocene redox chemistry [62],... 

One-dimensional images of toluic acid were obtained with a stationary sample. For two-dimensional images, the 4-bromobenzoic acid crystal was rotated about an axis orthogonal to the gradient direction in constant increments of either 3° or 6° over a range of 180° to collect sets of 60 or 30 one-dimensional projections, respectively. The two-dimensional images were calculated with the filtered back-projection reconstruction algorithm (36). 

Fig. 3. H NMR spectra of a hexapeptide bound to tentagel resin, (a) Schematic diagram of the peptide-resin complex (b) stationary sample of the complex swollen in DMSO-4 (c) the same sample recorded with magic-angle spinning at 5 kHz. (Reproduced from Jelinek et al. with permission.)...

The molecular structures of the surface vanadium oxide species on the different supports were examined with Raman spectroscopy. The Raman spectrometer system possessed a Spectra-Physics Ar+ laser (model 2020-05) tuned to the exciting line at 514.5 nm. The radiation intensity at the samples was varied from 10 to 70 mW. The scattered radiation was passed through a Spex Triplemate spectrometer (Model 1877) coupled to a Princeton Applied Research OMA III optical multichannel analyzer (Model 1463) with an intensified photo diode array cooled to 233 K. Slit widths ranged from 60 to 550 m. The overall resolution was better than 2 cm l. For the in situ Raman spectra of dehydrated samples, a pressed wafer was placed into a stationary sample holder that was installed in an in situ cell. Spectra were recorded in flowing oxygen at room temperature after the samples were dehydrated in flowing oxygen at 573 K. 

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