Consecutive scans over

When the samples are spiked with [2H9]-TMA instead of isopropylamine, the head-space gas can also be injected directly into the gas sample injection port of a mass spectrometer for TMA quantification [27]. Electron impact mass spectra are collected over the mass range m/z 10-500 at a scanning rate of once per 3 s. The ion intensities of 20 consecutive scans are averaged and the ratio of the ions at m/z 59 and 68 is determined for TMA [27]. 

In contrast, the presence of ions at m/z 29 (CH3 - CH2+ or +HC = O) and m/z 15 (CH3+) is very common. They are observed on a multitude of mass spectra as soon as ion scanning over a certain m/z ratio range allows their detection. It is therefore rare for the observation of these ions to supply pertinent information about the structure of an unknown compound. Ions with low m/z ratios are often issued from consecutive fragmentations of ions of high internal energy (see Chapter 3) that do not represent statistically the global population of formed molecular ions. 

Fig. 12. Transient photoabsorption spectriun acquisition at ISIR, Osaka University, (a) Two consecutive femtosecond pulses of white light continuiun collected by single scan of CCD camera, (b) Transient absorption spectrum of 100 mM biphenyl in Ar-bubbled tetrahydrofuran solution at 200 ps after the end of pulse. The peaks are attributed to biphenyl radical anion. Each point in near-UV region (ca. from 400 to 500 nm) and visible-NIR region (ca. from 500 to 900 nm) was measured by averaging over 10 and 2 beam-probe shots, respectively. The inset is a magnification in 400-500 nm.

Figure30.3 (a) Atypicalimageofthetotalfluorescenceintensilyofa couple of Anabaena cells with dark treatment. The scale bar on the right represents 2 lm. (b) Fluorescence spectra averaged over the 3D space ofthe left cell in (a), (c) Fluorescence spectra averaged over the 3D space of the right cell in (a). The spectra in (b) and (c) were generated from two consecutive 3D scans.

Hum bars Horizontal black and white bars that extend over the entire TV picture and usually drift slowly through it. Hum bars are caused by an interfering power line frequency or one of its harmonics. Interlaced A shortened version of interlaced scanning (also called line interlace). Interlaced scanning is a system of video scanning whereby the odd- and even numbered lines of a picture are transmitted consecutively as two separate interleaved fields. 

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