Time delay, sample preparation

Stock solutions-alreadypreparedby central logistic centres - have the advantage of standard start conditions, which are also similar to conditions found in biological assays. They allow a high throughput because the time delaying sample preparation is already done. 

Solid-state NMR spectroscopy was also used to examine the post reaction behavior of pTrMPTrA samples prepared in bulk as thin films, as described in the experimental. All of the spectra in this aging study required a minimum of 720 scans on approximately 50 mg of sample with a 100 s pulse delay to achieve adequate signal/noise. Under these conditions, reliable peak areas could be obtained from the curve fits of the carbonyl region. Figure 3 depicts the evolution of the solid state spectrum of the sample stored under N2 over time and upon heating. The area of the peak at 174 ppm for the carbonyl adjacent to the reacted double bond increases as the peak at 166 ppm for pendant unsaturation decreases. The results of the aging study are given in Table I. 

Cycle time consists of several individual components. One is the separation time of a sample. Another component is instrument overhead time that may be subdivided into conditioning, sample preparation, and post-separation phases. The final component is system overhead time that covers delays caused outside the LC modules (Figure 3.9). These times do not necessarily have to follow the fixed order shown in the figure. In particular, the position of the instrument conditioning may vary and the tasks do not have to be arranged linearly. Cycle times in early chromatographic systems... 

The expense of an analytical procedure depends upon much more than the cost of the final analysis. Much of the expense of an assay is related to sample preparation, and for many applications immunoassays have tremendously reduced the time needed for sample preparation. Another consideration is the amount of time needed for the development of an assay. The additional expertise which must be developed in an analytical laboratory before immunoassays can be used with confidence may seem formidable, and waiting for an animal to develop antibodies may lead to unacceptable delays in assay development. On the other hand, once a usable antibody titer is obtained, the development of a workable assay is usually straightforward. It is also likely, if immunoassays become accepted for some aspects of pesticide analysis, immunoassay kits or at least critical reagents will become commercially available. Such kits already exist for many pharmaceutical products and hormones, and numerous companies will supply antibodies to a user supplied hapten on a contract basis (83). 

If delayed extraction increases the mass resolution without degradation of sensitivity compared with continuous extraction, it also has limitations. Indeed, delayed extraction complicates the mass calibration procedure. It can only be optimized for part of the mass range at a time and is less effective at high mass. Delayed extraction partially decouples ion production from the flight time analysis, thus improving the pulsed beam definition. However, calibration, resolution and mass accuracy are still affected by conditions in the source. For instance, in the usual axial MALDI-TOF experiments, optimum focusing conditions depend on laser pulse width and fluence, the type of sample matrix, the sample preparation method, and even the location of the laser spot on the sample. 

Additional experimental considerations for PCS include sample preparation (dilution and filtration), choosing the delay time range and spacing among cor-... 

Spin-lattice relaxation times, nTj, for different phases of various nylon samples are listed in Table 6. The a crystal form of both nylon-6 and nylon-11 exhibit a single exponential decay function in a plot of signal intensity vs delay x, with corresponding nTt values in the 103 s range. The sample prepared in situ has the shortest Tj relaxation time which indicates more rapid motions due either to plasticization by residual caprolactam or differences in the crystalline regions. 

Further performance improvements in analysing nucleic acids could be achieved by the introduction of 3-hydroxypicolinic add as matrix [8] and the introduction of delayed extraction in a linear time-of-flight mass spectrometer [9]. If, for MALDI Fourier transform mass spectrometry, the molecular weight range in analysing nucleic add fragments could be extended further this type of MALDI MS would become of significant value due to the extraordinary resolution possible [10, 11]. In order to reach the sensitivity level necessary for MALDI-TOF MS analysis an amplification step has to be incorporated into the sample preparation process for... 

Solid state CP/MAS NMR spectra were recorded with a 75 MHz Chemagnetics spectrometer. The standard pulse sequence for cross polarization with bilevel dipolar decoupling was employed with a contact time and recycle delay of 1 ms and 3 s, respectively. Chemical shifts were referenced to hexamethylbenzene at 17.4 ppm. Additional details concerning sample preparation and NMR studies can be found in a forthcoming paper. ... 

The coupling of sensors with flow injection analysis (FIA) is already a very popular option. The flow regime offers important advantages over discrete manual measurements that include (1) Sample preparation processes such as reagent mixing, selectivity enhancement (e.g., removal of large molecular mass interferents such as protein by dialysis in clinical assays), and solvent extraction can all be carried out online. The improved sample preparation and more reproducible sample delivery result in improved measurement precision and accuracy. Drift is less of a problem as measurements are made of peak heights relative to a baseline. (2) Improved sensor lifetime in flow analysis, the sensor may be exposed to the sample for only a short period of time, and maintained in a friendlier matrix between measurements that can help counteract or delay the deleterious effects of the sample. (3) Automation the entire analysis can be... 

The spectroscopic tool to be considered here is femtosecond pump/probe spectroscopy. This experimental technique uses two ultrashort laser pulses which are time-delayed with respect to each other. They are sent into a molecular sample and a signal is recorded as a function of the delay-time between the pulses. To be more specific, we assume the molecule to be in an inital state 0o) O). Here o) denotes the wave function for the nuclear motion and 0) the wave function of the electrons (the adiabatic separation of nuclear and electronic motion is assumed throughout). The pump pulse induces a transition and the resulting wave function which describes the molecule after the interaction with the electric field may be assigned as 0i l). We treat electronic excitation so that the molecule is prepared in another electronic state 1). After the pump pulse passed the sample, the molecule evolves unperturbed until the probe pulse starts interacting. This interaction results in a second excitation to (in our case) a final electronic state 2) with the respective nuclear wave function 1 2) The scheme just described is depicted in Figure 1 and illustrates the idea of many pump/probe experiments. 

Recently, monitoring techniques have been greatly improved by the combination of spectroscopic methods and fiber optics technology, which allow for the in-situ and in-line acquisition of process data, allowing for reduction of time delays normally involved with sample preparation. 

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