Scan speed

The system was installed and certified by TUV and the local authorities. Trials conducted on site after installation proved that the system allowed efficient inspection with scan speeds in excess of 100 mm/s, which is faster than initially required. Implementation of the system has resulted in savings enabling pay back of the full system in less than one year. 

These authors also analysed marine diesel fuel with GC X GC, connected to a quadrupole mass spectrometer for identification purposes, although the scan speed of the spectrometer was not quite suited for the fast second-dimension peaks... 

The fact that scanning speed can affect polarisation behaviour has already been mentioned. In the case of stainless steel a plot of critical potential E, vs. rate shows how becomes more positive with potential change rate (Fig. 19.43) . When a specimen was held at a fixed passive potential while aggressive ions (Cl ) were added to determine the concentration required... 

For the detection of weak Raman lines, high laser power, high signal amplification, long pen period, and very slow scanning speed should be... 

If the film is nonconductive, the ion must diffuse to the electrode surface before it can be oxidized or reduced, or electrons must diffuse (hop) through the film by self-exchange, as in regular ionomer-modified electrodes.9 Cyclic voltammograms have the characteristic shape for diffusion control, and peak currents are proportional to the square root of the scan speed, as seen for species in solution. This is illustrated in Fig. 21 (A) for [Fe(CN)6]3 /4 in polypyrrole with a pyridinium substituent at the 1-position.243 This N-substituted polypyrrole does not become conductive until potentials significantly above the formal potential of the [Fe(CN)6]3"/4 couple. In contrast, a similar polymer with a pyridinium substituent at the 3-position is conductive at this potential. The polymer can therefore mediate electron transport to and from the immobilized ions, and their voltammetry becomes characteristic of thin-layer electrochemistry [Fig. 21(B)], with sharp symmetrical peaks that increase linearly with increasing scan speed. 

The number of cycles that is attainable is also a function of the chromatographic peak width - the narrower the peak, then the faster the cycle rate required to define that peak accurately. The peak widths encountered in HPLC, which are relatively wide compared to GC, are such that a compromise between scan speed and sensitivity is less likely to be required. 

The molecular mass of the protein was redetermined by infusing a 5-10 pmolp.l solution of the protein in 50% aqueous acetonitrile containing 0.2% formic acid at a flow rate of 6 p,lmin into an electrospray source. The scan rate employed on the mass spectrometer was from m/z 60 to m/z 1800 in 12 s. This is a relatively slow scan speed which will lead to a more precise molecular weight determination. Scan speeds of this order may be, and indeed should be, utilized for infusion experiments if sufficient sample is available but it is unlikely to be feasible when chromatographic separations, particularly those involving capillary columns, are employed because of the restriction imposed by the chromatographic peak width (see Section 3.5.2.1 above). 

Physical properties of the prepared catalysts were measured by an adsorption analyzer [Quantachrome Co., Autosorb-lC]. The structure of prepared catalysts were investigated by XRD [Simmazdu Co., XRD-6000] with a Cu-Ka radiation source (X = 1.54056 A), voltage of 40.0 kV, ciurent of 30.0 mA and scan speed of 5.0 deg/min. Also, temperature-programmed reduction (TPR) profiles of the samples were investigated by a sorption analyzer [Micromeritics Co., Autochem II] and obtained by heating the samples from room temperature to 1100°C at a rate of lOTl/min in a 5 % H2/Ar gas flow (50 ml/min). 

A remarkable splitting of the two signals in the F-spectra of P2O3F4 is observed, when traces of difluorophosphoric acid are carefully excluded and the spectrum is scanned at very slow speed (777). The doublet is split into two triplets symmetrical to each other with the intensity ratio 1 2 5, which is in accordance with the AA XX A" a" expectation spectrum (777). The F-spectra of F2P(S)- 0—P(S)p2 can be interpreted in the same way the normally appearing doublet of lines splits into two symmetrical nonets at very slow scan speeds (777). 

FIG. 14 Constant height mode gray-scale image of a 5/xm-diameter pore in a polycarbonate membrane obtained with a 3 fim pipette tip. The filling DCE solution contained 10 mM TBATPBCl. The aqueous phase contained 0.4mM TEACl + lOmM LiCl. The scale bar corresponds to 10/xm. The tip scan speed was 10/xm/s. (Reprinted with permission from Ref. 30. Copyright 1998 American Chemical Society.)... 

Different options are available for LC-MS instruments. The vacuum system of a mass spectrometer typically will accept liquid flows in the range of 10-20 p,L min-1. For higher flow-rates it is necessary to modify the vacuum system (TSP interface), to remove the solvent before entry into the ion source (MB interface) or to split the effluent of the column (DLI interface). In the latter case only a small fraction (10-20 iLrnin ) of the total effluent is introduced into the ion source, where the mobile phase provides for chemical ionisation of the sample. The currently available commercial LC-MS systems (Table 7.48) differ widely in characteristics mass spectrometer (QMS, QQQ, QITMS, ToF-MS, B, B-QITMS, QToF-MS), mass range m/z 25000), resolution (up to 5000), mass accuracy (at best <5ppm), scan speed (up to 13000Das-1), interface (usually ESP/ISP and APCI, nanospray, PB, CF-FAB). There is no single LC-MS interface and ionisation mode that is readily suitable for all compounds... 

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